Microstructural evolutions and mechanical properties of 6082 aluminum alloy part produced by a solution-forging integrated process
Graphical Abstract
Introduction
Aluminum alloy forgings are widely applied and exhibit outstanding specific strength, recyclability, and fatigue resistance, especially for safety-critical structural components, as reviewed by Deng et al. (2018). The 6082 aluminum alloy is the most commonly used Al-Mg-Si alloy and is extensively utilized in vehicle chassis and steering forgings.
Conventionally, 6082 aluminum alloy forgings are manufactured using a series of operations that can be divided into two distinct stages: forging to acquire the desired shape and heat-treating to achieve the required mechanical properties. To guarantee proper plasticity, the raw extruded bars are preheated to the forging temperature and kept there for a short time until thoroughly heated. The preheated bars are then pressed between one or more sets of dies, depending on their pressability, to create specific geometric shapes. Lai et al. (2019) summarized that the superior properties of the heat-treatable Al-Mg-Si alloys are primarily attributable to the dispersed nano-sized precipitates resulting from the post-forging heat treatment. This is why the solutionizing, quenching, and aging treatments must be performed sequentially on the forged parts. Shao et al. (2020) demonstrated that solutionizing results in a uniform distribution of alloying elements, which is then quenched to form a supersaturated solid solution (SSSS). Mrówka-Nowotnik and Sieniawski (2005) concluded that the 6082 aluminum alloy is sensitive to cooling conditions and samples cooled in water have the highest hardness compared to samples cooled in oil or air. Therefore, water-based quenchants are extensively used in the heat treatment of aluminum alloy forgings. Finally, the SSSS is precipitated in an orderly manner by artificial aging to form precipitates, which play a crucial role in the final mechanical properties, as pointed out by Chen et al. (2020).
Conventionally processed forgings often suffer from an inhomogeneous grain structure caused by abnormal grain growth (AGG), also known as discontinuous grain growth or secondary recrystallization, in the surface layer of forgings after SHT. Birol (2015) elaborated that AGG defects occurred in a conventionally forged part after SHT, and these abnormally grown grains were observed to extend from the surface layer to the interior of the part to a certain depth. AGG phenomenon is not limited to forgings. Sun et al. (2019) investigated that secondary recrystallization also occurrs on extruded aluminum alloy due to post-forming SHT. On friction stir welds, Lezaack and Simar (2021) concluded that post-welding SHT is also the main reason leading to AGG, but it can be improved by optimizing process parameters. The coarse grains greatly affect the mechanical properties of forgings, such as tensile strength, elongation, fatigue behavior, and so on. For example, Chang et al. (2019) studied that the grain growth occurred after SHT reduces the elongation and tensile strengths of aluminum alloy forgings. Shou et al. (2016) discussed that the coarse grains have a negative effect on the fatigue crack propagation resistance. Therefore, automobile manufacturers limit the thickness of the coarse-grained layer on aluminum alloy parts to ensure service performance.
To reduce the high energy and equipment costs and to improve the quality of forgings, there has been great interests in designing novel forging processes. Jin et al. (2016) proposed a single-step hot stamping-forging process to produce pan-shaped shell aluminum alloy parts, which improved the production efficiency and reduces the cost compared to conventional manufacturing methods. He et al. (2020) introduced an improved thermomechanical treatment for aluminum forgings that comprises hot deformation, cold deformation, and a subsequent heat treatment to improve grain structure and mechanical properties. Manjunath et al. (2021) reviewed that multi-directional forging/multi-axial forging are adequate processes for obtaining fine equiaxed grains in aluminum alloys. Kumar et al. (2022) proposed a multi-axial forging process at liquid nitrogen temperature and investigated the grain refinement mechanism in 6082 aluminum alloy. Recently, Zhao et al. (2022) demonstrated an integrated forging process via uniaxial hot compression tests that combined SHT and hot forging into one operation followed by artificial aging. Notably, one of the characteristics of this integrated forging process is the preservation of the deformed grain structure by immediately quenching following forging. Güzel et al. (2012) concluded that post-forming quenching could be used to prevent static recrystallization and grain growth. Considering the post-forging SHT plays a key role in AGG defects during conventional forging, it is possible to avoid the AGG induced by the secondary recrystallization effect if the forgings are not treated with SHT after quenching. As a result, aluminum alloy forgings with a more homogeneous and uniform microstructure may be achievable. Therefore, it is worthwhile to investigate the utilization of the integrated forging process on an industrial scale that potentially combines the advantages of short processing and fine microstructure.
With regard to the application of the forging process of 6082 aluminum alloy, automobile chassis parts were produced on an industrial scale with a conventional forging process (forging, solution treatment, and artificial aging) and an integrated forging process (forging and artificial aging only) to investigate their influences on the microstructure and mechanical properties. The mechanical properties were evaluated by tensile tests. The microstructure and strengthening mechanisms were illustrated by optical microscopy (OM), scanning electron microscope (SEM), electron backscatter diffraction (EBSD), high-resolution transmission electron microscopy (HRTEM), and finite element method (FEM) simulations.
Section snippets
Materials
In this work, 160-mm-long 6082 aluminum alloy extruded bars in fabricated state with a diameter of 110 mm were prepared for industrial scale forging experiments; the chemical composition was Al-0.65Mg-0.93Si-0.06Cu-0.17Fe-0.12Cr-0.03Ti-0.45Mn (wt %).
Forging procedure
Fig. 1 depicts the schematic diagrams of conventional and integrated forging processes under industrialized conditions. In the conventional forging process, the preheated 6082 aluminum alloy bar is sequentially forged, solutionized, quenched, and
Mechanical properties
The mechanical properties of the conventionally and integrally processed 6082 aluminum alloy automobile parts are listed in Table 2. It can be concluded that the internal mechanical properties of the parts processed by the conventional and integrated forging processes are comparable. However, significant sacrifice of tensile strength, yield strength, and elongation occurs in the conventionally processed parts’ surface layer compared to those of the interior. Specifically, the tensile strength
Effect of processing impact on the evolution of grain structure
To understand the grain evolution during pre-forging and final-forging of the 6082 aluminum alloy parts, the Zener-Hollomon parameter (Z), established by Zener and Hollomon (1944), is used to express the strong connection between the forming parameters and microstructure characterization. The Z is defined as follows:where is the strain rate (s−1), R represents the gas constant (8.314 J/K·mol), Q is the deformation activation energy that equals 173.54 kJ/mol as calculated by Li
Conclusions
This paper reports the microstructural evolution and mechanical properties of 6082 aluminum alloy parts produced using a novel forging process that integrates forging and SHT in one operation, along with comparisons to the conventionally processed parts. Based on the observations and analyses of representative identical areas in the parts via tensile tests, OM, SEM, EBSD, HRTEM, and FEM simulation, the following conclusions are proposed:
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The novel forging process is capable of producing 6082
CRediT authorship contribution statement
Ning Zhao: Investigation, Formal analysis, Visualization, Writing – original draft. Huijuan Ma: Formal analysis, Investigation. Qian Sun: Formal analysis, Investigation. Zhili Hu: Methodology, Writing – review & editing, Resources. Yang Yan: Validation, Investigation. Tianfu Chen: Validation. Lin Hua: Supervision, Resources.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This work was supported by the National Key Research and Development Program of China [grant number 2019YFB1704500]; the National Natural Science Foundation of China [grant numbers 52075400, 51805393]; the 111 Project [grant number B17034]; and the Key Research and Development Program of Hubei Province [grant number 2021BAA200].
References (41)
- et al.
Study of microstructure and tensile properties of infrared-heat-treated cast-forged 6082 aluminum alloy
J. Mater. Res. Technol.
(2019) - et al.
Atomic scale investigation of the crystal structure and interfaces of the B′ precipitate in Al-Mg-Si alloys
Acta Mater.
(2020) - et al.
A yield strength model for the Al-Mg-Si-Cu alloy AA6111
Acta Mater.
(2003) - et al.
A new method for determining dynamic grain structure evolution during hot aluminum extrusion
J. Mater. Process. Technol.
(2012) - et al.
Effects of thermomechanical treatment on grain refinement, second-phase particle dissolution, and mechanical properties of 2219 Al alloy
J. Mater. Process. Technol.
(2020) - et al.
A single-step hot stamping-forging process for aluminum alloy shell parts with nonuniform thickness
J. Mater. Process. Technol.
(2016) - et al.
Assessment of geometrically necessary dislocation levels derived by 3D EBSD
Acta Mater.
(2015) - et al.
Al 6082 alloy strengthening though low strain multi-axial forging
Mater. Charact.
(2019) - et al.
Grain refinement mechanism in 6082 Al alloy fabricated by cryo-multiaxial forging
Mater. Sci. Eng. A.
(2022) - et al.
Avoiding abnormal grain growth in thick 7XXX aluminium alloy friction stir welds during T6 post heat treatments
Mater. Sci. Eng. A.
(2021)
Hot deformation and dynamic recrystallization in Al-Mg-Si alloy
Mater. Charact.
Coupling of dislocations and precipitates: Impact on the mechanical behavior of ultrafine grained Al–Zn–Mg alloys
Acta Mater.
A review on effect of multi-directional forging/multi-axial forging on mechanical and microstructural properties of aluminum alloy
Mater. Today. Proc.
Modeling of rolling texture in aluminum
Mater. Sci. Eng. A
Dynamic recovery: sufficient mechanism in the hot deformation of Al (<99.99)
Mater. Sci. Eng. A
Comments on ‘a model of continuous dynamic recrystallization’ proposed for aluminum
Scr. Mater.
Influence of heat treatment on the microstructure and mechanical properties of 6005 and 6082 aluminium alloys
J. Mater. Process. Technol.
On the Hall-Petch relationship in a nanostructured Al-Cu alloy
Mater. Sci. Eng. A
A study of various heating effects on the microstructure and mechanical properties of AA6082 using EBSD and CPFE
J. Alloy. Compd.
A process model for age hardening of aluminium alloys-I. The model
Acta Mater.
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