Effect of pulsed electron beam treatment on microstructure and functional properties of Al-5.4Si-1.3Cu alloy

https://doi.org/10.1016/j.nimb.2020.12.004Get rights and content

Highlights

  • The irradiation of the alloy by an electron beam results in the enhancement of its functional properties.

  • Electron beam processing brings about a 197% increase of wear resistance.

  • Microhardness rises by 83% for a beam energy density of 50 J/cm2.

  • The advancement of functional properties is possible due to the dissolution of intermetallic compounds.

  • Nano-dimensional particles to evolve on cell boundaries reinforce the material.

Abstract

The effect of pulsed electron beam treatment (density of energy 10, 30, and 50 J/cm2 and pulse times 50 and 200 µs) on the microstructure and functional properties of the Al-5.4Si-1.3Cu alloy is traced via exploring its microhardness, wear resistance and microstructure. The research pointed out the wear resistance of the alloy irradiated with pulsed electron beam to be 197% higher than the same characteristic of the untreated material. A maximal microhardness increase was recorded for following electron beam treatment parameters: 30 J/cm2, 200 µs and 50 J/cm2, 50 µs; the values of microhardness were as high as 860 MPa and 950 MPa, respectively. Key factors responsible for better wear resistance and higher microhardness in the samples treated with a pulsed electron beam were suggested to be silicon and intermetallic compounds, dissolving in the molten surface, a cellular nano-dimensional structure, resulting from rapid solidification, and nano-dimensional particles of silicon and multi-element compounds.

Introduction

Aluminum, to be more precise, an alloy on its base was synthesized by a Danish physicist Hans Christian Ersted in 1825; but its factory production and use were first mentioned in 1886. To date, aluminum alloys represent the next broadly used metallic constructional materials after iron and steel. These alloys are applied in aircraft, space, motor vehicle, navy and gun industries due to their unique properties, such as low density, high specific strength and sufficient corrosion resistance [1], [2], [3], [4], [5]. Each aluminum-based alloy irrespectively to its grade is distinguished with a quite broad application scope. In particular, the Al-5.4Si-1.3Cu alloy under study is a material used in machine elements and mechanisms of civil aircraft and motor vehicle engineering, supports and fixtures of furniture production and in the manufacture of various components for household appliances, etc. [6], [7].

Recently, machine parts are manufactured of aluminum using traditional techniques, e.g. casting, forging, stamping, and powder metallurgy [8], [9]. Despite a broad use, the manufacture and consumption of these goods have been experiencing certain problems. For instance, a low speed of cooling in casting is the reason for rough microstructure and numerous defects, e.g. displacement damages, shrinkage porosity, slag inclusions and segregation of elements in cast alloys, as a consequence mechanical properties of machine parts degrade [10], [11], [12], [13], [14]. Industrial conglomerates introducing stronger standards for the structure and operation characteristics of machine parts made of aluminum and its alloys make the situation even more difficult. To illustrate, materials with a lattice or cell structure, the production of which represents a complex and science intensive issue, are needed to satisfy technical requirements for high heat conductivity, a light weight, and high specific strength of heat protection systems in airspace vehicle engines. In the integrated manufacturing process of complex structure elements it is possible to reduce a time and a number of tools while producing and assembling small and middle-sized components, to decrease their weight, make less concentrated stresses arising in welding or mounting machine parts [15], [16], [17], [18], [19]. The principal aim of future research and development is suggested to be the advancement of technologies to produce alloys with specified properties. Nevertheless certain attempts have been already made to modify materials through surface treatment with concentrated energy flows [20], [21], [22], [23]. Laser and electron beam treatment are important surface processing methods. Laser processing has a positive effect on Al and its alloys, slows down a propagation rate of the fatigue crack growth [22], enhances corrosion resistance [24], changes the surface morphology; furthermore, microstructural transformations improve the welding of aluminum products [25] and their mechanical properties [26], [27].

Besides laser processing, electron beam treatment represents one of the promising surface treatment techniques intended to advance physical and technical characteristics of a product and form a unique structure of metals and alloys [28], [29], [30]. Electron beam melting technologies are known to be a surface processing method of Al-Si alloys and a self-sufficient production process of these alloys [31]. The study demonstrated an ultrafine grained structure with better functional properties to evolve in electron beam melting. The electron beam treatment of Al-Si alloys led to the surface remelting and changed the element and phase composition as a consequence. Several works [32], [33], [34] reported on close to the total dissolution of primary Si crystals in the modified layer in electron beam melting and disclosed transformations of the Al crystal lattice parameter for the oversaturated solid solution of aluminum was formed in the molten layer. Tribological tests made it possible to claim the wear resistance of processed alloys to be considerably better than this characteristic of untreated Al-Si compounds [31], [32], [33], [34], [35], [36], [37]. A number of works have examined the effect of various treatment processes on the structuring and behavior of mechanical properties in Al-5Si alloys. Several studies paid particular attention to the role of laser in surface processing or for the total remelting of Al-5Si alloys [38], [39]. The researchers argued that laser processing improves the functional properties, refines the microstructure and changes the element and phase composition. The explorations we present in this paper are unique for the alloy with the given chemical composition. This study aimed to analyze the behavior of functional properties (wear resistance and microhardness) of Al-5.4Si-1.3Cu alloy surface irradiated with a pulsed electron beam in different modes and reveal why they changed. The outcomes of the research may be of crucial importance to the machine building industry as a post-processing procedure to advance technical characteristics.

Section snippets

Material and methods of research

For the purpose of research, we used the Al-5.4Si-1.3Cu alloy; its chemical composition determined relying on the X-ray analysis data is given in Fig. 1a. When manufacturing, the alloy was poured into moulds in liquid form under the gravitation force and made solidify at an ambient temperature. Prepared samples were squares (dimensions – 15 × 15 × 5 mm3) (Fig. 1b).

The irradiation of samples with an intensive electron beam was performed using the “SOLO” laboratory unit [40]. It encompasses a

Results

Fig. 2 displays the tribological test findings and data on microhardness of Al-5.4Si-1.3Cu alloy samples irradiated with an intensive electron beam (red and blue bars). From the data it is apparent the wear parameter drops given the electron beam energy density increases when irradiating with a pulse time of 200 µs and demonstrates a trend to saturation (Fig. 2, red bars). Once the pulse time of electron beam processing is 50 µs (Fig. 2, blue bars), the wear resistance of the alloy is more

Discussion

To sum up, the outcomes of the investigation show that there are two behavior types of hardness and wear resistance, which depend on the electron beam pulse time.

Hardness and wear resistance tend to increase for a relatively short (50 µs) time of electron beam impact. This phenomenon may result from the incomplete dissolution of micron inclusions (needle-shaped inclusions are observed to dissolve partially), which are found in the untreated material and cause its over-brittleness under friction

Conclusion

To summarize, the irradiation of the Al-5.4Si-1.3Cu alloy with an intensive pulsed electron beam in various modes improved its tribological properties; that is, the wear parameter (a reciprocal of wear resistance) decreased. The wear resistance of the Al-5.4Si-1.3Cu alloy (the irradiation parameters 50 J/cm2, 200 µs) was detected to be 197% higher than that of the untreated material. A maximal increase in microhardness was 83% as compared with the as delivered alloy and observed for the

CRediT authorship contribution statement

Dmitrii Zaguliaev: Conceptualization, Writing - original draft, Writing - review & editing, Formal analysis. Yurii Ivanov: Investigation, Writing - original draft, Writing - review & editing. Sergey Konovalov: Conceptualization, Writing - original draft, Writing - review & editing. Vitalii Shlyarov: Investigation. Damir Yakupov: Investigation. Andrey Leonov: Investigation, Writing - review & editing.

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.

Acknowledgement

The research was granted by Russian Science Foundation (RSF) (project №. 19-79-10059).

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