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Effect of Cu Additions on the Microstructure and Mechanical Properties of Spray Deposited Zn-30Al Alloy

Zn-30Al-xCu (x=0, 1, 2, 4) alloys were prepared by the spray atomization and deposition technique. The microstructures of the spray-deposited alloys were investigated by means of scanning electron microscope, transmission electron microscope, X-ray diffraction. The results indicate that the 1 wt. % Cu addition to spray-deposited Zn-30Al alloy does not make significant change in microstructure. However, with the 2, 4 wt. % Cu additions to the alloy, some ε-CuZn4 compounds with particle or irregular shapes were observed on the grain boundaries in the microstructures. Tensile test results confirmed that the 1 wt. % Cu addition displays superior tensile strengths, whereas the 2, 4 wt. % Cu additions led to the decreasing of the improvement effect of the tensile strengths. Introduction Zn-Al alloys have been found to be a promising energy and cost effective substitute to a certain extent plain bearings. Zn-Al alloys exhibit high specific strength, excellent wear resistance, good casting properties and lower coat compared to other nonferrous metals [1]. The addition of Cu to the eutectoid Zn-Al alloys improves its mechanical properties, creep resistance and corrosion behavior [2,3]. In order to improve the mechanical properties of Zn-Al alloys, various metallurgical processes, such as continuous casting, thermal evaporation and spray deposition etc. are developed[4,5]. It has been recognized generally that the spray deposited process is an innovative technique of rapid solidification. In this process, droplets are first atomized from a molten metal stream, quickly cooled by an inert gas, then deposited on a substrate, and finally built up to form a low-porosity deposit with the required shape[6,7]. In this work, one binary Zn-Al and three ternary Zn-Al-Cu alloys were produced by the spray atomization and deposition technique. The objective of this study is to investigate the microstructural evolution and mechanical properties of spray-deposited Zn-30Al-xCu (x=0, 1, 2, 4) alloys, and the effect of Cu addition on the microstructure and mechanical properties of spray-deposited Zn-Al alloy was analyzed. Experimental Procedures In Table 1 are listed the chemical compositions of the Zn-Al-Cu alloys. The spray deposition experiments were conducted in an environmental chamber. During spray-deposition process, the molten metal was atomized by N2 at 700 °C, the distance of atomizing deposition was kept constant at 500 mm. The preform, after being cut into cylindrical billets was extruded at a temperature of 250 °C with a reduction ratio of 10:1 and a ram speed of 5 mm/s. After extrusion, the materials were cooled in air. The microstructures of spray-deposited materials were characterized using scanning electron microscopy (SEM) attached with energy dispersive X-ray analyses (EDX), transmission electron microscopy (TEM) and X-ray diffraction. A S360 type scanning electron microscopy working at 15 kV was used to observe the microstructures. The scanning electron microscopy samples were prepared using standard metallographic techniques and were etched using Keller's reagent. The transmission electron microscopy studies were conducted on a H-800 type transmission 2nd Annual International Conference on Advanced Material Engineering (AME 2016) © 2016. The authors Published by Atlantis Press 361 electron microscope at an acceleration voltage of 200 kV. The X-ray diffraction experiments were performed on a Japan Rigaku diffractormeter using Cu-Kα radiation. The tensile tests were conducted with an Instron tensile testing machine at an initial strain rate of 0.5 s. Table 1 Chemical compositions of the alloys (mass%) Alloy Al Cu Zn A0 30 0 Bal. A1 30 1 Bal. A2 30 2 Bal. A4 30 4 Bal. Results and Discussion Microstructure Fig.1 (a) shows the typical SEM microstructure of the spray-deposited A0 alloy, which is composed of the α-Al matrix and the η-Zn phase mostly with a lamellar shapes. The coarse and fine lamellar α-Al + η-Zn eutectoid was primary phase in the microstructure. With the addition of 1 wt. % Cu to the spray-deposited A0 alloy, no obvious change was observed in the micrograph, in Fig.1 (b). Fig.1 (c) and (d) show the SEM micrographs of spray-deposited A2 and A4 alloys, it can be seen that 2, 4 wt. % Cu additions lead to the variation in the microstructures. Some compounds with particle or irregular shapes were observed on the grain boundaries, as labeled by arrows. Quantitative energy-dispersive spectroscopy analysis results indicate that the compounds mainly contain elements of Zn and Cu. Fig.1 SEM micrographs of the spray-deposited alloys, (a) A0; (b) A1; (c) A2; (d) A4 Fig. 2 shows the X-ray diffraction (XRD) patterns of the spray-deposited alloys. XRD was performed to identify the phases in the microstructures, and analysis of the diffraction patterns shows that the compound phases mainly are ε-CuZn4 in spray-deposited A2 and A4 alloys. No definitive evidence for the presence of ε-CuZn4 was found in the XRD result of spray-deposited A1 alloy, this 5 μm (a)