Effects of Pb and Cu additives on microstructure and wear corrosion resistance behaviour of PM Al–Si alloys

Abstract

The wear and wear corrosion resistance of Al–20Si–XPb–YCu (X=0–10 wt-%, Y=0–3 wt-%) alloys fabricated using powder metallurgy technique and subsequent heat treatments were evaluated using a block on ring tribotest. The microstructures of all aluminium alloys were observed using an optical microscope, a scanning electron microscope and an X-ray energy dispersive spectroscope. The evaluation studied the effects of applied potential and environments of dry air and 3·5 wt-%NaCl aqueous solution. The microstructural analysis showed that Pb was bimodally distributed in Pb containing alloys, and Cu particles formed the intermetallic phase CuAl₂. Additionally, the hardness of both Pb and Cu containing alloys increased significantly. The wear and corrosion results showed that the addition of both lead (Pb) and copper (Cu) increased the wear resistance and the corrosion rate, while heat treatments reduced the corrosion rate of most alloys except the Al–Si alloy. Furthermore, comparison of all alloys following heat treatment shows that the wear corrosion resistance of Al–Si alloy is inferior to that of the other alloys. Therefore, addition of Pb and Cu further improved the wear corrosion resistance. Additionally, at anodic potential, the wear corrosion rate and current density of both Al–Si and Al–Si–Cu alloys containing particle Pb were significantly lower than those of alloys containing no Pb, because the layer produced by corrosion comprised Al, O and Pb elements.