Crystals (May 2022)
Microstructural, Mechanical and Wear Properties of Al–1.3%Si Alloy as Compared to Hypo/Hyper–Eutectic Compositions in Al–Si Alloy System
Abstract
The microstructure, mechanical properties, and wear behavior of three Al–Si alloys, namely: Al–1.3%Si, Al–1.5%Si and Al–13.5%Si were investigated. The specimens were examined by using an optical microscope to investigate the microstructural features of pin materials. Microhardness numbers and mechanical behavior parameters were determined by using a microhardness indenter and compression test, respectively. The dry sliding wear test was carried out using a pin-on-disc apparatus by varying the rotational speed (250, 350, and 450 rpm), normal load (5, 10 and 20 N) and test time (5, 10 and 15 min) at a constant sliding diameter of 300 mm. The surface roughness index (Ra) of the worn surfaces was determined by using a profilometer. The microstructure of Al–1.3%Si alloy was described as a fine eutectic colonizing in the FCC-Al phase matrix. Coarse eutectic dendrites surrounding the primary FCC-Al grains were observed in Al–1.5%Si alloy. The microstructure of Al–13.5%Si alloy showed a uniform layered structure of FCC-Al + Diamond Si eutectic. The average microhardness number was directly proportional to the Si concentration. Al–13.5%Si alloy with a high microhardness number (47.16 HV) showed excellent resistance to wear and exhibited a smoother surface at the end-of-wear test. The improved wear resistance in this case could be due to the presence of Diamond-Si hard phase in large quantities compared with other compositions. On the other hand, Al–1.5%Si alloy showed poorer resistance to wear because the mass loss action was dominated by a particle detachment mechanism. The response surfaces of the mass loss vs. speed, normal load and time showed increased mass loss when the three controlled parameters were increased. However, Pareto charts of the main effects of parametric interactions showed that the normal load was the main factor that must be considered when studying the tribological properties of Al–Si alloys.
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