Effect of Ni-Ti filler on brazed W-Cu/18-8 joints J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-04-11 Chunzhi Xia, Weiwei Sun, Yi Zhou, Meng Zhao
W-Cu composite and 18-8 stainless steel were vacuum brazed with an improved Ni-based filler metal, with varying Ti content. The microstructure, element distribution, phase composition, and fracture mechanism of the brazed joints were investigated. The improved NiCrSiBFe-Ti quench filler metal showed good wettability on the W-Cu composite and 18-8 stainless steel. Enhanced diffusion and metallurgical reactions between the filler metal and base metal were observed. The addition of Ti not only optimized the structure, but also reduced the formation of brittle intermetallic compounds, which is important for significantly improving the brazed-joint strength. The highest brazed-joint shear strength (381 MPa) was observed when the Ti content was 1.6％.
A Quantitative Description of Machining Effects to Mechanical Behavior of Sintered Powder Metals J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-04-11 Long ZHANG, Huang YUAN
Sintered powder metals play increasingly important role in industry. The most remarkable mechanical characteristics of the sintered material is the high porosity, which characterizes deformations and failure of the material. It is confirmed additionally that manufacturing process affects mechanical behavior and fatigue performance of the material. In the present work a continuum damage mechanics model is used to describe the damage evolution in machined sintered iron. It is confirmed that machining effects are localized in the sub-surface layer of the mechanical part, and the damage can be quantitatively described by the damage model. The experimental results from the fabricated specimen have to be separated into mechanical behavior of the sub-surface layer and the specimen core. The damage model provides an effective way to describe mechanical performance of a machined part of the sintered iron.
Simulation of weld morphology during friction stir welding of aluminum- stainless steel joint J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-04-10 Behzad Sadeghian, Aboozar Taherizadeh, Masoud Atapour
In order to predict dissimilar materials’ flow behavior during friction stir welding, a morphological simulation of the weldment was performed using Level Set (LS) method. Thermal and computational fluid dynamics (CFD) simulations were conducted to calculate the temperature distribution and material flow velocity during the welding process. Level set model was created to predict the weld morphology based on CFD results. Weld morphologies in different tool rotational speeds, offsets position and height levels of the specimen were simulated. In order to validate the simulations, temperature measurements, optical microscopy (OM) of the weldment and scanning electron microscopy (SEM) of the stirred zone (SZ) were carried out. It was seen that the main cause of defects in the weld zone were steel particles detached in aluminum matrix. The simulation results revealed that increasing rotational speed and offset through the steel side could generate more steel particles. Also, the particles were more in the top height level of the weld section than in the middle and bottom levels.
Flash butt Weldability of Inconel718 Alloy J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-04-10 Xueru Zhu, Pingwei Xu, Yilong Liang, Zhijian Wei, Yu Liang
Following fast upsetting deformation, the welding seam (WS) is formed at the surface of flash butt welded Inconel718 joint due to dynamic recrystallisation. The dissolution of γ″ and γ′ phases during temporary flashing is mainly responsible for the ~30% hardness decrease in the heat-affected zone (HAZ). A wider zone with lowered hardness indicates a broader HAZ created with a gentler temperature gradient. The increased temperature in the whole HAZ leads to more serious formation of carbides and liquation at the grain boundaries. Such unsuitable microstructure accounts for a 50-70% loss of ductility, while only ~10% of ductility is lost in another welding joint with suitable temperature gradient.
Experiment and simulation to rolled profile strip with variable thicknesses in lateral direction J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-04-07 X.G. Wang, X.H. Liu, S. Wang, Y. Zhi
Tailored blanks are widespread and gaining increasing use in the market with a competitive edge due to their load adaption, cost reduction through the efficient use of materials, and their lightweight design. In order to meet market demands and efficiently produce lightweight products, a new method is now developed to obtain strips with different thicknesses in the lateral direction, i.e., Rolled Profile Strips (RPS), by cold rolling. The new method includes bending-spreading rolling (BSR) and flattening rolling (FR). Experiments were performed to obtain RPS samples with a thickness ratio of 1:1.3. Then the deformation, metal flow, and stress-strain field in the BSR processes were simulated by FEM with ABAQUS software. The results indicate that the desired strips are obtained, whereby the thick areas undergo compressive deformation while the curved deformation area (thin area and transition areas) undergoes both tensile and compressive deformations. These findings will lay a foundation for the industrial application of RPSs.
Experimental study on fabricating spirals microelectrode and micro-cutting tools by low speed wire electrical discharge turning J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-04-07 Yao Sun, Yadong Gong
This study is focused on the fabrication of spirals microelectrode and spirals micro-cutting tools by using low speed wire electrical discharge turning (LS-WEDT). Firstly, the concept, movement relationship and machining principle of LS-WEDT process are analyzed, respectively. Then, the effects of new parameter of rotating speed on surface roughness, surface microstructure, elements change and material removal rate in LS-WEDT are evaluated in detail. Experimental results demonstrate that LS-WEDTed surface is significantly improved, micro-voids become more and smaller but foreign element contents increase with the increasing of rotating speed. More importantly, the space flexibility, negligible electrode wear and multiple cutting strategy of the LS-WEDT make it competent in fabricating micro tools with complex structure and high accuracy. Consequently, spirals microelectrode with high accuracy can be obtained for spiral pitch standard deviation of 2.57 and thread angle standard deviation of 0.96, and pitch length and thread numbers can be flexibly controlled in LS-WEDT. Additionally, the three spirals taper micro-cutting tool is fabricated by LS- WEDT based on the shape and cutting edge trajectory simulation results. Furthermore, the three spirals micro-cutting tool with average diameter of 175.77 μm and length of 1300 μm is firstly and successfully manufactured by LS-WEDT method.
Distortion control in a wire-fed electron-beam thin-walled Ti-6Al-4V freeform J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-04-06 Zhao Chen, Hong Ye, Haiying Xu
The solid-state phase change (SSPC) temperature is important in the accurate thermal-mechanical simulation of a wire-fed electron-beam freeform. The SSPC temperature of the Ti-6Al-4V material was determined to be 850 °C by variable temperature XRD measurements. The forming process of a typical thin-walled TC4 piece was modeled, and the most accurate predictions were achieved with an SSPC temperature of 850 °C. The thin-walled piece could be formed if the electron beam operated at a scan current between 100 and 150 mA and a speed below 100 mm/s. The distributions of the residual stress were consistent in the reciprocating and unidirectional scan modes; however, the former produced less distortion. In the reciprocating mode, shrinkage distortion dominated and increased with the scan current. The maximum distortion along the x-axis increased from 0.18 to 0.32 mm when the current increased from 100 to 150 mA. A dynamic current scheme reduced the maximum distortion along the x-axis to 0.12 mm, and a constant temperature constraint at the bottom of the substrate reduced the distortions along the x- and z-axes to approximately zero.
Size effect affected mechanical properties and formability in micro plane strain deformation process of pure nickel J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-04-05 Chuanjie Wang, Haiyang Wang, Shaoxi Xue, Gang Chen, Yibin Wang, Shuting Wang, Peng Zhang
Effect of heat treatment on bonding strength of aluminum/steel bimetal produced by a compound casting J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-04-05 Wenming Jiang, Guangyu Li, Yao Wu, Xinwang Liu, Zitian Fan
A compound casting process combined with hot-dip galvanizing was used to produce an aluminum/steel bimetal, obtaining a superior metallurgical interface that mainly consisted of τ6-Al4.5FeSi, Al-Zn eutectic and Si phases. Under as-cast condition, the aluminum/steel bimetal had a relatively low bonding strength, resulting from the poor morphology and size of the τ6-Al4.5FeSi phase and the Si particles. An appropriate heat treatment procedure greatly improved the interfacial microstructure and bonding strength of the aluminum/steel bimetal, and the phase compositions in the interface were nearly similar to that of the as-cast condition. The excessive heat treatment promoted the excessive growth and cracks of the interface layer, sharply weakening the bonding strength of the aluminum/steel bimetal. With a solution temperature of 500 °C for 2 h, the shear strength of the aluminum/steel bimetal significantly increased by 39% in comparison with that of the as-cast sample, which was mainly attributed to the improvements of the morphology and size of the τ6-Al4.5FeSi phase and the Si particles. No excessive growth of the interface layer and the absent of the crack defect were also responsible for the improvement of the shear strength of the aluminum/steel bimetal.
Influence of the application of a PN+Cr/CrN hybrid layer on the improvement of the lifetime of hot forging tools J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-04-05 Hawryluk Marek, Gronostajski Zbigniew, Widomski Paweł, Kaszuba Marcin, Ziemba Jacek, Smolik Jerzy
This article presents the results of field tests performed on forging tools in a selected lid hot forging process. The aim of the studies was to increase the durability of hot forging tools. Different coating types dedicated to hot forging tools were proposed and first tested in laboratory conditions. Based on the laboratory test results, the PN+Cr/CrN hybrid layer was selected to improve tool durability. Tools (upper punches used in second forging operation) with a PN+Cr/CrN layer applied on them were tested in comparison with gas-nitrided tools. The hybrid layer was produced on a plasma-nitrided substrate, onto which a PVD Cr/CrN coating was deposited. All the analyzed tools were tested in industrial conditions through the manufacturing of specific quantities of forgings. Next, the wear of each tool was analyzed by surface scanning and then compared to the CAD model. All the tools were checked for changes in the surface layer under an optical and a scanning electron microscope, as well as by way of a microhardness measurement. The results obtained in industrial conditions confirmed the effect of improvement of the forging tool lifetime owed to the application of the PN+Cr/CrN hybrid layer.
Stretch-Flangeability of Twinning-Induced Plasticity Steel-Cored Three-Layer Steel Sheet J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-04-05 Jung Gi Kim, Jae Ik Yoon, Seung Mi Baek, Min Hong Seo, Kwang-Geun Chin, Sunghak Lee, Hyoung Seop Kim
In this study, the stretch-flangeability of twinning-induced plasticity (TWIP)-cored three-layer steel (TWCLS) sheet was evaluated. Although the mechanical properties of TWCLS sheet follow the force-based rule-of-mixtures (ROM), the experimental hole expansion ratio (HER) is less than the predicted HER values. The poor HER in TWCLS sheet originates from crack initiation at the fracture zone of the TWIP steel-core. The fracture initiation energy vs. HER in TWCLS sheet reveals that the layered material follows the behavior of the monolithic material when the sound interface is conserved. If the initial defects are removed by a reaming process in the hole, the HER of TWCLS sheet follows the force-based ROM. This result shows that the stretch-flangeability of the layered material can be controlled by managing the volume fraction of parent materials when the sources of extrinsic damage (i.e, interface delamination and defects) are removed.
Laser Shock Micro Clinching of Al/Cu J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-04-04 Xiao Wang, Xinding Li, Cong Li, Zongbao Shen, Youjuan Ma, Huixia Liu
The influences of ablative layer, soft punch, die depth, and laser energy on novel micro clinching of Al/Cu were investigated. Ablative layer thickness notably influenced metal flow including neck and interlock; the relationship between reasonable ablative layer thickness and certain laser energy range was summarized. Soft punch with 100 μm was more suitable than with other thickness for the process. In the joinable laser energy range, with increase of laser energy, interlock thickness gradually increased, whereas the neck and bottom thicknesses gradually decreased. The process window of Al/Cu combination was acquired, and a certain thickness difference which was at least 40 μm inevitably existed between the upper and lower metal foils. For every joinable combination, matching function of optimum die depth are derived based on Al and Cu foil thickness when the thickness of each metal foil was less than 200 μm. The single lap shearing test showed that the tensile strength and failure model of the joint both depended on neck and interlock thicknesses; only the joint that simultaneously formed a large interlock and large neck can attain a high joining strength.
Effect of macro- and micro-segregation on hot cracking of Inconel 718 superalloy argon-arc multilayer cladding J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-04-04 Xin Ye, Peilei Zhang, Jian Zhao, Pan Ma
The hot cracking sensitivity dramatically increases because of the longitudinal macro-segregation of craters and the transverse macro-segregation of welding center in pre-layers. Statistical analysis of the total area, average size and Nb concentration of interdendritic low-melting point Laves phase, the Nb concentration of the γ phase in the dendritic core, and the arm spacing of different sub-regions was used to explore the effects of macro- and micro-segregation of Nb. Solidus and liquidus curves were used to determine the temperature at which solid and liquid phases coexist in different sub-regions, which were combined with Scheil equation curves to identify Nb sources and interlayer transfer, so as to develop a model for the molten pool of subsequent layers. This model explains the effect of transversal and longitudinal macro-segregation in the pre-layer on the Nb concentration of the melt pool of subsequent layers, the dynamic balance of the solidification interface and the relative area of Laves phase in the macro-segregated sub-region of the solidified metal.
High surface quality welding of aluminum using adjustable ring-mode fiber laser J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-04-03 Martin Ruthandi Maina, Yasuhiro Okamoto, Akira Okada, Matti Närhi, Jarno Kangastupa, Jorma Vihinen
A method to improve penetration and stabilize the welding phenomenon at a high welding speed has been described through experimental and numerical investigations. Using a high power laser beam consisting of a center and a ring part, influences of shielding gas direction and flow rate, laser power density, and welding mode defined by variable intensity distribution have been clarified. The weld bead was evaluated in terms of width, height, shape and roughness. Dual-mode laser irradiation of center and ring power made it possible to stabilize the welding process. The center power helps to achieve sufficient deep penetration, while ring power ensures good temperature distribution. Good surface quality and deep penetration welding could be achieved with dual-mode welding, using low flow rate of shielding gas supplied from the backside direction.
Fabrication of Al/Mg/Al laminate by a porthole die co-extrusion process J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-03-30 Liang Chen, Jianwei Tang, Guoqun Zhao, Cunsheng Zhang, Xingrong Chu
Micro-voids quantification for damage prediction in warm forging of biocompatible alloys using 3D X-ray CT and RVE approach J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-03-28 X.Z. Lu, L.C. Chan
Effect of chemical oxidizer on material removal rate in electrochemical oxidation assisted machining J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-03-28 Eunseok Nam, Hyunho Jo, Jaehong Min, Sang Jo Lee, Byung-Kwon Min
Mechanical machining of brittle material is difficult due to generation of fracture or cracks on machined surfaces. Glassy carbon (GC) is a brittle carbon material having outstanding mechanical and chemical characteristics making it suitable for use in glass molds. However, brittleness of GC makes its machining complicated and difficult. In order to fabricate GC surfaces with minimum cracks, hybrid machining processes utilizing electrochemical oxidation have been proposed. In the present study, a new, mixed acidic electrolyte incorporating a chemical oxidizer was utilized to improve the material removal rate of electrochemical oxidation assisted machining. Machining experiments were conducted to evaluate and to confirm the effect of the oxidizer-mixed electrolyte on material removal.
Ultrasonic dynamic impact effect on deformation of aluminum during micro-compression tests J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-03-28 Jun Hu, Tetsuhide Shimizu, Tomoaki Yoshino, Tomomi Shiratori, Ming Yang
An experimental and numerical study on laser shock clinching for joining copper foil and perforated stainless steel sheet J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-03-27 Xiangying Wang, Zhong Ji, Jianfeng Wang, Shuxin You, Chao Zheng, Ren Liu
This paper presents an experimental and numerical study on laser shock clinching (LSC) for joining copper foil and perforated stainless steel sheet. The deformation evolution of an interlock was discussed by analyzing the cross sections and thickness distribution of the specimens. Failure modes and failure mechanism in the joining process were discussed to obtain a better understanding of the process. Fracture of copper foil commonly takes place at the hole edge and the base of clinch, meanwhile, the region with large strain concentration was more likely to generate fracture. The effect of main process parameters on the joining conditions has been investigated and process windows have been made based on a series of experiments. The results show that good joining can only be obtained under the combination of moderate laser energy and forming height. Clinched joints produced in the LSC process can absorb both radial and axial force, while shearing strength was far larger than peeling strength of the clinched joints produced under the same experimental parameters. What’s more, the LSC process has then been simulated by finite element method (FEM). FEM results agree well with the experimental results, which implies that numerical simulation can be effectively used to analyze the deformation and the failure mechanism in the LSC process.
Dendritic Coarsening Model for Rapid Solidification of Ni-superalloy via Electrospark Deposition J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-03-27 Pablo D. Enrique, Zhen Jiao, Norman Y. Zhou, Ehsan Toyserkani
Control of splat thickness in an electrospark deposition (ESD) process can be used to improve the mechanical properties of deposited Inconel 718. The lower cooling rates of thicker deposition splats obtained through higher energy ESD parameters result in greater subgrain coarsening and lower microhardness. A subgrain growth model and Hall-Petch relationship are used to quantify the extent of subgrain coarsening and the influence of splat thickness on hardness, with a 4.5 times reduction in splat thickness achieving a 20% increase in microhardness.
The effects of forced interpass cooling on the material properties of wire arc additively manufactured Ti6Al4V alloy J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-03-27 Bintao Wu, Zengxi Pan, Donghong Ding, Dominic Cuiuri, Huijun Li, Zhenyu Fei
To achieve improved microstructure and mechanical properties, an innovative wire arc additive manufacturing (WAAM) process with forced interpass cooling using compressed CO2 was employed in this study to fabricate Ti6Al4V thin-walled structures. The effects of various interpass temperatures and rapid forced cooling on deposition geometry, surface oxidation, microstructural evolution, and mechanical properties of the fabricated part were investigated by laser profilometry, optical microscopy (OM), scanning electron microscopy (SEM), hardness testing and mechanical tensile testing. Results show that the microstructural evolution and mechanical properties of the deposited metal are not greatly affected by an increasing interpass temperature, however, the deposited wall tends to be widened, flattened and exhibit increased surface oxidation through visible coloration. When rapid forced cooling using CO2 is used between deposited layers, slightly higher hardness values and increased strength can be obtained. This is mainly attributed to the combined effects of less surface oxide and high density dislocation caused by the generation of large amounts of fine-grained acicular α within the microstructure. Furthermore, forced interpass cooling not only improves deposition properties, but also promotes geometrical repeatability and also improved manufacturing efficiency through the reduction of dwell time between deposited layers.
Porosity reduction through a Ti particle based gap-paste in arc welding of zinc coated steel J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-03-26 Dong-Hyuck Kam, Tae Hyun Lee, Jedo Kim
Gap-paste is used to create gaps, for zinc vapor release, between the zinc coated steel sheets during the arc welding process. In-depth morphology analysis of the gap after the welding is presented which shows zinc oxide formation patterns are consistent with zinc vapor release through the formed gaps. Porosity analysis for four different mask configuration shows that the porosity of the sample, with 120 μm gaps created by the paste, is reduced from ~15 % to a near zero value. The tensile shear stress test reveals that the strength of the welded samples increased by ~30 % compared to that of the samples with no gaps. High-speed camera images are also presented showing the changes in the zinc vapor release mechanism when the paste is applied, and the various stages of zinc vapor release during the welding process are discussed.
Modeling and simulation of machining distortion of pre-bent aluminum alloy plate J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-03-26 Weidong Li, Lixia Ma, Min Wan, Jingwen Peng, Bao Meng
Microstructure and mechanical properties of ultrasonic pulse frequency tungsten inert gas welded Ti-22Al-25Nb (at.%) alloy butt joint J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-03-23 Ling Shao, Sujun Wu, Amit Datye, Haitao Zhao, Miles Petterson, Wenya Peng
Controlling surface strain distribution in copper using plane strain wedge sliding J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-03-23 Yang Guo, Anirban Mahato, Narayan K. Sundaram
Utilizing plastic strain to modify surface attributes is a common way to improve the functional performance of engineering components. The ability to control the strain distribution in the surface layer is critical for controlling the microstructures and properties of the processed surface. This paper explores the possibility of controlling the surface / subsurface strain distribution in copper by using a wedge-shaped sliding tool of large negative rake angle (≤ -60°). The surface flow and deformation at various sliding conditions are characterized in situ using high speed imaging and image analysis techniques. Deformation fields like flow velocity, strain rate and strain are quantified. It shows the sliding can result in two modes of surface deformation: (1) steady prow deformation with laminar flow and (2) unsteady prow deformation with sinuous flow and surface folding. The former creates a uniformly strained subsurface layer while the latter creates surface defects and inhomogeneous strain field. Utilizing the steady prow deformation and multi-pass sliding technique, the subsurface strain in copper can be controlled in a large strain range (>10). Strategies to control both the strain magnitude and distribution in the subsurface region are discussed. The results indicate the wedge sliding process is a promising method for imposing controllable surface plastic deformation.
Plasticine Modeling of Material Mixing in Friction Stir Welding J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-03-21 Vinayak Malik, Satish V. Kailas
Plasticine of primary colours was utilized and the hue attribute of generated secondary colour was tracked. The degree of mixing was indicated by the intensity of secondary colour. Hue component was obtained from digital images of joined plasticine cross-section by converting RGB colour-maps to HSV colour-maps. Effect of tool pin profile that included circular, hexagonal, square and triangular was examined in this context. As the number of faces on the tool pin reduces, up-till pin with four faces (square) the pin induced mixing increases and results in the elimination of joint line remnant. Material adjacent to the face was transported in lumps and experienced spinning/whirling movement. During mixing phenomenon flow velocities of constituents undergoing it tends to fluctuate. The fluctuation is significantly large for higher levels of mixing and the same was noticed for a square profile from the results of finite element simulations. The results obtained from plasticine and finite element simulations are validated using aluminium weld.
Densification behavior of pure Zn metal parts produced by selective laser melting for manufacturing biodegradable implants J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-03-20 Peng Wen, Lucas Jauer, Maximilian Voshage, Yanzhe Chen, Reinhart Poprawe, Johannes Henrich Schleifenbaum
Behavior of M23C6 phase in Inconel 617B superalloy during welding J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-03-20 Shanlin LI, Kejian LI, Zhipeng CAI, Jiluan PAN
The room/high temperature mechanical property of the Inconel 617B joined by multi-layer narrow gap tungsten arc welding technology (NG-TIG) is investigated, and thermal simulation is utilized to reveal the behavior of M23C6 phase in Inconel 617B superalloy during welding. Eutectic microstructures and micro fissures resulting from constitutional liquation due to thermal exposure in welding occur in the heat affected zone (HAZ), which leads to slight softening in the HAZ after welding. Room/high temperature tensile tests show that little adverse effects on the mechanical strength of joint has been caused by the welding process. It is shown by the thermal simulation that constitutional liquation of this micro-scale M23C6 carbides would occur when the peak temperature (Tp) reached 1300 ℃. The behavior of the micro-sized M23C6 in multi-layer welding cycle could be described as: M23C6+ (γ-Ni) → liquid →M23C6+γ-Ni →M23C6+γ-Ni + econdary M23C6.
Self-Cleaning Mechanisms in Ultrasonic Bonding of Al Wire J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-03-20 Yangyang Long, Folke Dencker, Andreas Isaak, Jörg Hermsdorf, Marc Wurz, Jens Twiefel
In the present work, the self-cleaning mechanisms of ultrasonic aluminum wire bonding were revealed by real-time observing the changes of the artificially increased oxide layer during the bonding process. After the normal force loading, cracks occurred in the Al2O3 layer at the peripheral region of the wire/substrate interface and were perpendicular to the wire direction. As the US vibration started, the oxides started to detach from the pure metal surface and moved towards the middle of the contact area. With further vibration cycles, these detached oxides were milled from flakes into small particles. Due to three mechanisms including penetration, oxide flow and pushing, the small oxide particles were transported to the peripheral contact region or the outside of the contact area. When a metal splash existed, the flowing out of large amounts of oxides was facilitated. Pre-deformation originates cracks; vibration plays a significant role in detachment, milling, penetration and oxide flow; while the plastic deformation induced material flow is more critical on removing the oxides from the substrate by pushing. The shear tests showed that a 50 nm oxide coating could significantly enhance the Al-glass bonding strength by 2~3 times.
Liquid-phase alloy as a microfluidic electrode for micro-electro-discharge patterning J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-03-20 Ruining Huang, Ying Yi, Wenbin Yu, Kenichi Takahata
This study reports on the first patterning method based on micro-electro-discharge machining (μEDM) that uses microfluidic electrodes in a liquid form. This novel method is developed to address a variety of problems associated with electrode wear, which is one of the most fundamental issues with µEDM technology. During the machining process, a liquid electrode is continuously supplied to a metallic micro capillary nozzle to eliminate the impact of its “wear” or liquid consumption on the removal process. Experiments show that Galinstan, a non-toxic liquid alloy, can be used as the electrode material to create discharge pulses and perform microscale removal on the samples. Controlled discharge generation and scanning-mode arbitrary patterning are experimentally demonstrated using the microfluidic Galinstan electrodes. The process is evaluated with varying discharge conditions to reveal the dependence of the patterned geometry on the parameters. It is also shown that a Parylene C coating is effective for protecting the nozzle from discharging. The elemental analysis of the processed samples indicates that the process does not cause detectable Galinstan contamination on the patterned surfaces.
Fabrication of semi-circular micro-groove on titanium alloy surface by through-mask electrochemical micromachining J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-03-19 G.Q. Wang, D. Zhu, H.S. Li
Titanium/silicon-carbide-fibre composites offer an excellent combination of weight-specific properties that make them ideal for many components in aeroengines. However, potential industrial applications are hampered by the need to fabricate semi-circular micro-grooves on the titanium alloy foils. Through-mask electrochemical micromachining (EMM) has been developed to fabricate micro-grooves on the surface of titanium alloy. The distribution of current density affects the micro-groove profile, and different mask aspect ratios can form different distributions of current density in through-mask EMM. Therefore, micro-grooves with semi-circular profiles can be fabricated by controlling the aspect ratio of the mask groove. In this paper, the effect of mask aspect ratio on the micro-groove profile during through-mask EMM is investigated by electric field simulation. From simulation results obtained in a series of experiments, the appropriate mask aspect ratio is found for fabricating semi-circular micro-grooves. Ultimately, a group of micro-grooves is fabricated successfully with the required accuracy by through-mask EMM.
Large allowance electrochemical turning of revolving parts using a universal cylindrical electrode J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-03-19 YongCheng Ge, Zengwei Zhu, Zhou Ma, Dengyong Wang
There are many large-scale revolving parts in aerospace engines, which usually require relatively large machining allowances to ensure production of the necessary shapes and sizes. Efficient removal of the machining allowances from such large-scale revolving parts, especially for hard-to-cut materials, represents a challenge for traditional mechanical processing. In this research, electrochemical turning with a universal cylindrical electrode is proposed as an efficient method to remove the large machining allowance of revolving parts. Lateral flow and internal flow patterns are exploited to ensure timely removal of electrolysis products and Joule heat. The electric field distribution shows that the current in the machining area increases significantly for the method. The flow field distribution shows that a more uniform flow velocity distribution can be obtained using an internal flow pattern. Experiments were performed to verify the proposed method. The results show that the internal flow pattern allows for faster feed rates and more stable processing, and the material removal rate may be improved significantly through use of an optimized flow pattern, especially for work-pieces with a large machining allowance. To demonstrate application, three differently shaped revolving structures were machined successfully with a radial removal allowance of 10 mm.
Sensitivity of Ti-6Al-4V components to oxidation during out of chamber Wire + Arc Additive Manufacturing J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-03-19 M.J. Bermingham, J. Thomson-Larkins, D.H. St. John, M.S. Dargusch
Reactive metals including titanium readily oxidise and should be protected from the atmosphere during Additive Manufacturing processes. This work explores the sensitivity of Ti-6Al-4V components to oxidation contamination during out of chamber Wire + Arc Additive Manufacturing when using inert gas trailing shields. Five Ti-6Al-4V components were produced with varying argon trailing shield configurations that range from ideal inert gas shielding (resulting in no surface contamination) through to very poor inert gas shielding that results in substantial surface oxidation. Despite significant changes in the degree of surface oxide contamination between each component, the overall increase in oxygen concentration in the bulk alloys was minimal and had negligible influence on the tensile strength and ductility.
Effect of beam profile on heat and mass transfer in filler powder laser welding J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-03-19 Jiazhu Wu, Haiying Wei, Fengbo Yuan, Penghui Zhao, Yi Zhang
A three-dimensional transient heat and mass transfer model for laser-powder coupling is created based on the lumped parameter method. A super-Gaussian beam model that is closer to the fiber laser beam profile for welding is employed instead of a frequently-used Gaussian beam. A beam characteristic parameter identification method is proposed to identify the beam characteristic parameters such as the focal spot radius and Rayleigh length. The spatial distribution of the beam power density is reconstructed. The super-Gaussian beam model has a better goodness-of-fit index than the Gaussian beam model. Finite difference method is used to solve the heat and mass transfer model developed. Some powder particles, under the action of three types of laser beams, have evaporated before falling into the laser-induced pool. The average heating rate for the super-Gaussian beam and non-ideal Gaussian beam is lower than that of the ideal Gaussian beam. Although the heated powder distribution zone and the melted powder distribution zone on the workpiece surface for the super-Gaussian beam are larger, the maximum powder mass loss by evaporation is the smallest. The effect of the identified super-Gaussian beam and non-ideal Gaussian beam on the heat and mass transfer zone and evaporation-induced mass loss is not significantly different, except for the ideal GB.
Effect of Si content on the interfacial reactions in laser welded-brazed Al/steel dissimilar butted joint J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-03-17 Hongbo Xia, Xiaoye Zhao, Caiwang Tan, Bo Chen, Xiaoguo Song, Liqun Li
Geometric design of the rolling tool for gear roll-forming process with axial-infeed J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-03-13 Ziyong Ma, Yuanxin Luo, Yongqin Wang, Jian Mao
Roll-forming process is an innovative manufacturing technology for the near-net-shape production of high-performance gears. Outstanding surface quality, high material utilization rate and short process chain are the essential merits of this process. The geometry of rolling tool has a significant impact on its lifetime and the quality of formed gears. In this paper, analytical models with consideration of geometric parameters of rolling tools (cone angle, tooth depth and addendum modification coefficients) were proposed to investigate the forming force, root stress of rolling tool, rabbit ear defect and scratches on tooth flank. Then, an example was studied by using the proposed models, Finite Element Method (FEM) simulation and experiments. The results show that the optimized geometric design of rolling tool will not only reduce the deflection and root stress of rolling tool’s teeth, but also eliminates the scratches on tooth flank of the formed gear. Moreover, the positive addendum modification design of rolling tools also contributes to reduce the height of rabbit ear in the roll-forming process with axial-infeed.
Influence of Cu micro/nano-particles mixture and surface roughness on the shear strength of Cu-Cu joints J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-03-10 Yang Zuo, Jun Shen, Jiacheng Xie, Lu Xiang
With the optimal mass ratio (9/1) of 100 nm to 1 µm particles, the bonding layer showed a highly dense sintering structure and was thinner than that of only 100 nm particles, the shear strength of the Cu-Cu joint was over 20 MPa even at relatively low temperature 250 °C and pressure of 4 MPa. The sawtooth structure formed between the bonding layer and the copper substrates can increase the bonding area and further promote the shear strength of joint, the optimal surface roughness of copper substrate for maximum enhanced effect was Ra = 189.9 ± 5.4 nm.
Microstructure and properties of Cu/Ti laser welded joints J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-03-08 Yong Zhao, Weiyu Wang, Keng Yan, Chuan Liu, Jiasheng Zou
Microstructure and properties of Cu/Ti laser welded joints. The optical microscopy, SEM, EDS, XRD and TEM were applied to assess the microstructure and bonding mechanism of Cu/Ti joints. When the laser beam was used to irradiate the copper side with an offset value of 0.45 mm, the welded metal and fusion line of Cu side were mainly consisted of the Cu solid solution. The intermetallic layer was formed at the titanium-welded metal interface. The thickness of IMCs was about 25µm and consisted of the Cu solid solution, intermetallic compounds such as TiCu, TiCu2, Ti2Cu and Ti3Cu4. The tensile strength of butt joints could reach 151 MPa, i.e. 61 % of the tensile strength of the copper base metal. The quasi-cleavage fracture occurred at the IMCs.
Joining of aluminum alloy and polymer via friction stir lap welding J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-03-06 Yongxian Huang, Xiangchen Meng, Yuhua Wang, Yuming Xie, Li Zhou
Development, characterization and test of an ultrasonic vibration-assisted ball burnishing tool J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-03-06 Ramon Jerez-Mesa, Jose Antonio Travieso-Rodriguez, Giovanni Gomez-Gras, Jordi Lluma-Fuentes
This paper presents the design and characterization of an ultrasonic vibration-assisted ball burnishing (VABB) tool on Ti-6Al-4V. This process is based on the modification of conventional ball burnishing, by means of the addition of a 40-kHz vibratory force to the burnishing preload exerted by the spring inside the tool. For the purposes of successfully executing the process, a new tool is designed through the assembly of different modules responsible for the various aspects involved in it. That design is hereby presented. Then, a methodology comprising acoustic emission and high frequency sampling is proposed to characterize the functioning of a prototype manufactured according to the previously presented design. The set of techniques deployed to measure the performance of the VABB prototype is presented as a feasible means of characterizing this sort of advanced manufacturing tools, especially like this one which is governed by ultrasonic frequencies. Last of all, the prototype is tested on a Ti-6Al-4V surface to validate it. The superior results of VABB, compared to the non-assisted version of the process, is shown in terms of average and total surface roughness, as well as surface hardness. The highest improvement is achieved by applying the VABB process with 300 N and 5 passes. The effectiveness of the designed prototype is confirmed, and places this kind of VABB tools as inexpensive systems to successfully execute an innovative finishing process for industrial components.
Scaling laws for the additive manufacturing J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-03-05 Alexander M. Rubenchik, Wayne E. King, Sheldon Wu
The evaluation of simple thermal model of selective laser melting (SLM) process shows that the temperature distribution in the sample is characterized by two dimensionless parameters: normalized enthalpy and the ratio of dwell time to the thermal diffusion time. We demonstrated that the melt depth data taken for different machines for different materials collapsed in one curve, making possible to rescale the optimal processing parameters between the different materials and machines. The melt pool depth, width and the length are the universal function of these two parameters. Within the operational range of parameters for SLM these functions can be interpolated by the simple algebraic expressions given the possibility to reduce the calculation of the melt pool characteristic to spread sheet model.
Ultrasonic vibration-strengthened adhesive bonding of CFRP-to-aluminum joints J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-03-05 Hui Wang, Xufei Hao, Kui Yan, Huamin Zhou, Lin Hua
The strengthening mechanism of an ultrasonic vibration-strengthened adhesive bonding method was studied via experimental and numerical analyses. This processing method was found to enhance the bonding strength and stability of CFRP-to-aluminum joints by 40% and 60%, respectively. Ultrasonic vibration could promote the flow of adhesive to fill the bonding gap through the vibration conversion and transmission in the CFRP laminate. The high-frequency vibration of the adhesive caused large bubbles in the adhesive layer to stretch, deform towards the nearby flow front and burst on account of the asymmetric resistance offered by the bubbles to the vibration-induced flow. Ultrasonic vibration made it easier for the adhesive to permeate into the fine structure of the surface, because the permeation was driven by the hydraulic pressure difference produced by the prompted flow of the adhesive. The processing method improves the adhesion strength and bonding stability by utilizing external energy to effectively facilitate the adhesive bonding process; hence, it is an active enhancement method.
Role of hybrid tool pin profile on enhancing welding speed and mechanical properties of AA2219-T6 friction stir welds J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-03-05 P. Mastanaiah, Abhay Sharma, G. Madhusudhan Reddy
The friction stir welds of thick precipitation-hardenable aluminum alloys suffer from reduced joint strength due to dissolution/coarsening of the strengthening precipitates. The article portray hybrid pin profiled tool that enables sound welds at speeds 7-times faster than a conventional tool (a conical threaded tool), without pin breakage. The conical threaded and triangular cross-section in the upper and lower pin half-lengths of the hybrid tool facilitate material flow in a downward direction and shear deformation at a faster rate, respectively. The paper brings out the process mechanism responsible for the enhanced welding speed and mechanical properties obtainable with the hybrid tool through a case of 13-mm thick aluminum alloy AA2219-T6. The hybrid tool facilitates a 26% improvement in weld strength by reducing TMAZ softening, as evidenced by the microhardness and mechanical properties and supported by microstructural investigation and fractography.
Effect of upper-die temperature on the formability of AZ31B magnesium alloy sheet in stamping J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-03-05 Zimin Wang, Ruiying Gu, Shichao Chen, Wurong Wang, Xicheng Wei
To ensure the temperature and formability of magnesium sheet metal transferring from a continuous oven, stamping of magnesium alloy sheet normally requires a setting of stationary heating oven in which lower-punch and binder are heated simultaneously. This paper studied the effect of unheated or extra heated upper-die with different temperatures on AZ31B magnesium sheet metal's formability in stamping. Forming limit curves (FLC) under different temperature upper-die were generated to analyze the temperature effect, which shows that the formability decrease significantly as upper-die temperature drops. Moreover, temperature fields simulated through thermo-mechanical coupling FEM simulation and microstructure of different specimen region indicate inhomogeneous mechanical properties due to temperature gradient, which results in different modes of crack initiation and propagation. Finally, FLC result was verified through a tryout stamping of automobile hinge cover.
Investigation on evolution mechanisms of site-specific grain structures during metal additive manufacturing J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-02-27 P.W. Liu, Y.Z. Ji, Z. Wang, C.L. Qiu, A.A. Antonysamy, L.-Q. Chen, X.Y. Cui, L. Chen
A modeling study of stress and strain formation induced during melting process in powder-bed electron beam melting for Ni superalloy J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-02-27 Satoshi Tadano, Takehisa Hino, Yuujiro Nakatani
In order to decrease deformation and stress in powder-bed electron beam melting, clarification of the characteristics of strain and stress formation during the melting process would be of great benefit. We developed an FE-based 3D thermal elastoplastic model with a Gaussian heat flux distribution profile in raster scanning pattern for Ni superalloy “René 80”. It was confirmed that strain variation in simulation showed good agreement with values calculated by a proposed mechanical model and proved to be quantitatively valid. The stress distribution during the melting process showed anisotropy in that the stresses in the beam scanning direction were higher than those in the other directions. The anisotropy formation mechanism was explicable by plastic strain anisotropy dominated by the restraint condition in that orthogonal direction was free boundary and lengthwise direction was subjected to restraint.
Process Parameters for Hot Stamping of AA7075 and D-7xxx to Achieve High Performance Aged Products J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-02-27 Kaab Omer, Atekeh Abolhasani, Samuel Kim, Tirdad Nikdejad, Clifford Butcher, Mary Wells, Shahrzad Esmaeili, Michael Worswick
This work examines the necessary process parameters for die quenching (DQ) during hot stamping and subsequent age hardening and paint bake cycle (PBC) response for two alloys: AA7075 and a developmental 7xxx alloy (referred to as AA7xxx), with a lower Chromium content, higher Zirconium content and higher Zinc-to-Magnesium ratio in comparison to AA7075. For both alloys, a minimum solutionizing time of 8 minutes was found to be required, along with a minimum quench rate of 56°C/s and 27°C/s for AA7075 and AA7xxx, respectively. Two-step aging treatments, leveraging a paint bake cycle (PBC) of 177°C for 30 minutes as the second step, were considered after die quenching and were devised to achieve T6- or T76-level strengths. For AA7075, an aging treatment of 120°C for 8 hours, followed by the paint bake cycle (PBC) produced strength levels similar to a T6 temper. DSC experiments showed that the microstructure from this heat treatment was similar to a peak-aged T6 temper. For AA7xxx, a treatment of 100°C for 4 hours and followed by the paint bake produced a strength similar to a T76 temper, while 120°C for 3 hours followed by the paint bake yielded T6 strength levels. The properties of the custom aging treatments were validated through tensile tests. The resulting stress-strain curves show that it is possible to achieve T6 or T76 properties using a custom aging treatment incorporating the PBC that is 65-83% shorter than standard T6 or T76 treatments.
Experimental study on fracture mechanism transformation in chip segmentation of Ti-6Al-4V alloys during high-speed machining J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-02-27 Hongguang Liu, Jun Zhang, Xiang Xu, Wanhua Zhao
Ti6Al4V alloy is one of the typically difficult-to-machine materials which is widely used in aerospace industry. During the machining process of Ti6Al4V alloys, serrated chips are easily formed and would influence cutting forces significantly. In this study, the variation of cutting forces of Ti-6Al-4V alloys during high-speed milling from 50–500 m/min is investigated, and the fracture mechanisms and microstructure evolution of chips are analyzed by optical microscope (OM), scan electron microscope (SEM) and transmission electron microscope (TEM). The results show that cutting forces and serrated degree of chips both increase first and then decrease with the increase of cutting speeds, especially when adiabatic shear bands appear. The microstructure evolution inside adiabatic shear bands also show a significant difference with different chip morphology at different cutting speeds, which finally cause the variation of cutting forces due to the change of fracture mechanisms between chip segmentations. As a result, the evolution of adiabatic shear bands is analyzed, and replica method by polydimethylsiloxane (PDMS) is used to reveal the relationship between cutting forces variation and fracture mechanism transformation in chip segmentation. It shows the relationship between cutting forces and microstructure evolution in adiabatic shear bands, and the transformation of fracture mechanism between type-I and type-II would occur around the gap between chip segmentations, where cutting forces are higher under type-I fracture.
Surface Texturing by Indirect Laser Shock Surface Patterning for Manipulated Friction Coefficient J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-02-26 Bo Mao, Arpith Siddaiah, Pradeep L. Menezes, Yiliang Liao
Various surface engineering techniques have been developed to improve the tribological performance at tribo-contacts. In particular, research efforts have been put on either enhancing the wear resistance through surface strengthening processes or manipulating the coefficient of friction (COF) through surface patterning processes. A new material process integrating both strengthening and patterning effects might lead to broader impacts in tribology research and applications. In this study, a novel laser-based surface processing technique, named indirect-laser shock surface patterning (indirect-LSSP), is developed. This process utilizes the laser-induced shockwave loadings to introduce the surface strengthening and patterning effects simultaneously, leading to the fabrication of anti-skew surfaces with arrays of micro-indentations for the enhanced wear resistance and manipulated friction values. Indirect-LSSP experiments were carried out on AISI 1045 steels. The 3D surface profiles after LSSP were characterized. The hardness of surface patterns prepared by laser processing was measured. The friction values as affected by laser processing parameters were measured by sliding tests. The relationships among laser processing parameters, micro-feature characteristics, and COF were discussed.
Effect of support structures on Ti-6Al-4V overhang parts fabricated by powder bed fusion electron beam additive manufacturing J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-02-25 Xiaoqing Wang, Kevin Chou
Fundamental study of exit burr formation mechanisms during orthogonal cutting of AlSi aluminium alloy J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-02-24 Tristan Régnier, Guillaume Fromentin, Bertrand Marcon, José Outeiro, Alain D’Acunto, Arnaud Crolet, Timothée Grunder
Burr formation during machining is an important issue in industry. It causes an additional deburring operation, which is time consuming and has a negative economic impact. This study aims to analyse burr formation mechanisms and its accumulation in successive passes during orthogonal cutting of a cast aluminium alloy. A customized experimental setup was developed, which includes a high speed imaging system and a laser profilometer. A design of experiments using the setup mentioned previously is carried out and a methodology for geometric burr characterization is developed and applied. Furthermore, statistical representation of the obtained results is performed, which allows the understanding of the geometric heterogeneity influence associated to burr formation mechanisms and to work material microstructure. Based on the exit burr analysis, new geometrical criteria are proposed for the characterisation and the definition of two main burr formation mechanisms. The influence of cutting parameters on burr morphology along the workpiece exit edge is investigated in depth. The results show that two types of burrs can be produced simultaneously along the workpiece exit edge due to the work material microstructure heterogeneity. The results present as well the influence of low uncut chip thickness that leads to a higher proportion of burrs without chamfer. This type of burr is higher and more propice to burr accumulation. After performing several cutting passes, these burrs may be eliminated and replaced by a burr with chamfer.
Material characterization for plane and curved sheets using the in-plane torsion test – an overview J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-02-24 Heinrich Traphöner, Till Clausmeyer, A. Erman Tekkaya
The in-plane torsion test offers a broad range of applications for the characterization of mechanical properties of sheet metal materials and components. True plastic strains beyond 1.0 can be achieved. Such data can be used for the numerical analysis without extrapolation of the flow curve. The stress and strain state correspond to truely ideal simple shear during the entire process. The full-field strain and stress analysis of the test area makes it possible to determine an almost arbitrary number of cyclic flow curves with only one single specimen. By using a grooved specimen, the ideal simple shear state can be obtained until fracture of the material without loosing the shear state. New investigations show that the in-plane torsion test is also suitable for the determination of flow curves of sheets with curved surfaces. Investigations on curved rotationally symmetrical as well as a tubular shape sheets were performed. Finally, first results for the determination of the local strength at arbitrary positions of a sheet component are presented.
The deformation mechanism of circular hole flanging by magnetic pulse forming J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-02-24 Haiping Yu, Qiuli Zheng, Shoulong Wang, Yu Wang
Fabrication of Ni-Aluminides Long-Fiber Reinforced Ni Matrix Composite by a Reaction at Narrow Holes Method J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-02-24 Yoshimi Watanabe, Shingo Gonda, Hisashi Sato, Seiji Miura
A novel method (reaction at narrow holes method, RANH method) to fabricate an intermetallic compound fiber / metal matrix composite is proposed. Narrow holes are drilled in the metal matrix A, and then metal fibers B are inserted into these holes. The assembly is heated to elevated temperatures to obtain molten metal B in the holes. Then the reaction between A and B should cause within the narrow holes. During the reaction, intermetallic compound of AmBn replaces the metal B keeping its fiber shape embedded in the metal matrix A. In this study, a Ni-aluminides fiber / Ni composite is fabricated by the novel method. Microstructure and mechanical property of these specimens were investigated. To evaluate the reaction during the RANH method, in-situ observation by laser scanning microscope and differential thermal analysis (DTA) were also carried out. From obtained results, effects of swaging treatment and heating condition on these microstructure and mechanical properties were discussed.
Dynamic force balance model considering tapering effect in gas metal arc welding J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-02-23 M.S. Kang, H. Chung
This paper proposes a metal transfer model describing the dynamic growth and detachment process of the molten drop at the electrode tip in gas metal arc welding under an Ar-rich shielding gas. The proposed model simulates the metal transfer including the growth of the molten drop as well as the formation and break-up of the liquid bridge between the electrode tip and the molten drop based on the forces exerted on the molten and the second order displacement equation. The tapering effect occurring at the side of the electrode tip is considered to enhance the prediction performance in the high-current region above the transition current. Simulation results are compared with experimental results reported in the available literatures and they show good agreement from the low to high current region.
Jet electrochemical machining of micro dimples with conductive mask J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-02-23 X.L. Chen, B.Y. Dong, C.Y. Zhang, M. Wu, Z.N. Guo
Micro dimples as a typical surface texture has been used in many fields for enhancing the functionality and performance. Electrochemical machining (ECM) is a promising approach for generating micro dimple. However, due to the isotropy of metal dissolution, the lateral undercutting of micro dimple is inevitable in ECM, which reduces the machining localization. This paper proposed a method of conductive mask jet electrochemical machining to reduce the undercutting of micro dimple and improve the machining localization. In this method, a conductive patterned mask instead of insulated patterned mask was covered on the workpiece directly during machining, which could decrease the undercutting of micro dimple by reducing the electric field intensity at the edge of micro dimple. In addition, a metallic nozzle (inner diameter of 2 mm) was employed to provide a stable columnar jet flow for enhancing the attachment between the mask and workpiece as well as the renewal of electrolyte in machining area, which was useful for generating deep micro dimple. Simulated results showed that the conductive mask could reduce the electric field identity at the edge of micro dimple effectively, and the undercutting of the profile was evidently reduced compared to that generated with insulated mask. Experimental results indicated that with conductive mask JEM, the undercutting of micro dimple was just 9 μm when the depth increased to 55 μm, the etch factor (EF) reached to 6.11, and it was four times greater than that with insulated mask. With the depth increased from 45 μm to 85 μm, the undercutting of micro dimple enlarged from 7 μm to 15 μm. The material removal rate in depth was evidently faster than that in diameter, which showed a low undercutting and high machining localization. In addition, compared with pulse current, direct current was more appropriate for generating deep micro dimple in conductive mask JEM.
Transition of failure mode in hot stamping of AA6082 tailor welded blanks J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-02-23 Jun Liu, Ailing Wang, Haoxiang Gao, Joao Gandra, Kathryn Beamish, Lihua Zhan, LiLiang Wang
A novel sheet metal forming process, by manufacturing parts in a single sheet with varying thickness, has been employed in this work. It combines hot forming and cold-die quenching, also known as HFQ®, and the use of aluminium tailor welded blanks (TWBs) into a hybrid process. A series of hot stamping tests on the AA6082 TWBs were performed to investigate the deformation behaviour and failure features. Two failure modes, i.e. circumferential necking and parallel weld necking have been observed in the formed parts depending on the forming speed and thickness ratio of the TWBs. An advanced forming limit prediction model has been developed and further integrated into finite element simulation via a cloud-based multi-objective platform1 to investigate the failure/necking features of AA6082 TWBs. The model incorporates the theories of Hosford yield function, the anisotropic nature of plastic deformation in sheet metals and the Marciniak-Kaczynski (M-K) theory. According to the theories, the incremental work per unit volume ratio ( d ε ¯ B ∙ σ ¯ B / d ε ¯ A ∙ σ ¯ A ) between Zone B (thickness imperfect zone) and Zone A (the remainder of the material) is a key parameter determining the formability, by which the complex failure features have been fundamentally studied. The transition of failure mode in a TWB was attributed to the joint effects of temperature, strain rate and loading path changes. Strain rate could accelerate the development of localised necking in the TWBs when the failure mode was in transition from the circumferential mode to parallel mode.
Similitude Analysis on Flow Characteristics of Water, A356 and AM50 alloys during LPC Process J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-02-23 Abhilash Viswanath, S. Savithri, U.T.S. Pillai
A Stir Casting System for Drawdown of Light Particles in Manufacturing of Metal Matrix Composites J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-02-23 Thanh Tinh Tran, Thanh Thinh Vo, Seung Chan Cho, Dong Hyun Lee, Wook Ryol Hwang
An extensive set of experiments was carried out to examine the effects of impeller types, impeller locations (submergence), solid volume fraction, and baffle configuration on the drawdown efficiency. Flow simulations in a turbulent regime were also performed to investigate the flow patterns, spatial homogeneity (using the mean age distribution), and particle drawdown mechanisms (using a particle level simulation with the discrete phase model). A combination of two casting impellers (a helical impeller near the top and a radial one near the bottom) with two half-baffles was determined to be the optimal configuration for complete drawdown with enhanced particle distribution, while avoiding air entrainment and lowering the impeller speed. Hydrodynamic mechanisms leading to superior drawdown and dispersion performance of the optimal design are discussed with the formation of free surface swirling, turbulence strength, roles of half baffles and helical/radial impellers on the flow and particle motions.
Enhancing workability in sheet production of high silicon content electrical steel through large shear deformation J. Mater. Process. Tech. (IF 3.147) Pub Date : 2018-02-21 Andrew B. Kustas, David R. Johnson, Kevin P. Trumble, Srinivasan Chandrasekar
Enhanced workability, as characterized by the magnitude and heterogeneity of accommodated plastic strains during sheet processing, is demonstrated in high Si content Fe-Si alloys containing 4 and 6.5 wt% Si using two single-step, simple-shear deformation techniques – peeling and large strain extrusion machining (LSEM). The model Fe-Si material system was selected for its intrinsically poor material workability, and well-known applications potential in next-generation electric machines. In a comparative study of the deformation characteristics of the shear processes with conventional rolling, two distinct manifestations of workability are observed. For rolling, the relatively diffuse and unconfined deformation zone geometry leads to cracking at low strains, with sheet structures characterized by extensive deformation twinning and banding. Workpiece pre-heating is required to improve the workability in rolling. In contrast, peeling and LSEM produce continuous sheet at large plastic strains without cracking, the result of more confined deformation geometries that enhances the workability. Peeling, however, results in heterogeneous, shear-banded microstructures, pointing to a second type of workability issue – flow localization – that limits sheet processing. This shear banding is to a large extent facilitated by unrestricted flow at the sheet surface, unavoidable in peeling. With additional confinement of this free surface deformation and appropriately designed deformation zone geometry, LSEM is shown to also suppress shear banding, resulting in continuous sheet with homogeneous microstructure. Thus LSEM is shown to produce the greatest enhancement in process workability for producing sheet. These workability findings are explained and discussed based on differences in process mechanics and deformation zone geometry.
Some contents have been Reproduced by permission of The Royal Society of Chemistry.
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