Effect of Magnesium Addition by Thixoforming Process on Wear Properties of A319 Alloy

Abstract

The effect of Mg addition (0.5–2.0%) on the as-cast and thixoformed microstructures, hardness and the tribological properties of A319 aluminium alloy was investigated. The investigations highlight the dry sliding wear test behaviour using a pin-on-disk tester configuration under the applied pressures of three loads of 10, 50 and 100 N at a constant sliding speed of 1 m/s and a sliding distance of 9 km. Detailed microstructural morphology studied for these alloys is correlated with the wear properties obtained. Results in the as-cast A319 alloy revealed that Mg addition transformed the Al2Cu phase and Si particle to form the Al5Cu2Mg3Si5 and Mg2Si intermetallic phases during the solidification. Moreover, the platelet-like morphology of β-Al5FeSi intermetallic completely converted to Chinese script-like morphology, π-Al8Mg3FeSi6 phase with the addition of Mg up to 1.5 wt.%. By adding Mg and performing thixoforming, the microstructure of the α-Al phase shows a fine globular primary phase surrounded by uniformly distributed Si and refined fragmented of intermetallic phases formed. The morphology of Mg2Si particles was modified from large, polygonal particles into relatively smaller and more globular, whereas the Chinese script-like morphology π-Al8Mg3FeSi6 changes to a compact shape. Adding Mg up to 2 wt.% increased the hardness at 100 Hv. The increase in Mg content enhances the wear resistance, friction coefficient and volume loss of thixoformed A319 alloy. A combination of abrasion and adhesion for alloys of low Mg dominates the wear mechanism. In contrast, excessive subsurface fracturing and delamination with minor abrasion are mainly observed for alloys of high Mg.