Wear behavior of secondary processed spray formed Al-28Si-5Cu-4Mg alloy

In the present study Al-28Si-5Cu-4Mg alloy has been spray formed and hot pressed
for densification. Hot pressing refined the microstructure and reduced the porosity in the
spray formed alloy from 10 to 1%. The microstructure of spray formed and hot pressed alloy
exhibited equiaxed grain morphology with fine and uniform distribution of both primary and
eutectic Si with fine needles of Q-Al 12 Si 7 Mg 4 Fe intermetallics and Chinese script like θ-
Al 2 Cu precipitates in α-Al matrix. The size of Si particles ranged from 3–10 µm. In contrast
the microstructure of as-cast alloy consisted of coarse primary and eutectic Si, long needles
of Q-Al-Si-Mg-Cu-Fe phase and bright grey θ-Al 2 Cu phase in the α-Al matrix. The size of
primary Si varied from 30–250 µm. The spray formed and hot pressed alloy exhibited a
higher hardness compared to the as-cast alloy. The wear behavior of both the alloys, under
dry sliding conditions, showed an increase in the wear rate with an increase in the load.
However, the spray formed and hot pressed alloy exhibited maximum wear resistance and
minimum coefficient of friction, while as-cast alloy exhibited minimum wear resistance and
maximum coefficient of friction over the entire range of applied load. The high wear
resistance and high hardness of spray formed and hot pressed alloy are explained in the light
of its microstructural modifications induced during spray forming and subsequent hot
pressing and also the topographical features of worn surfaces and morphology of debris
particles.