Effects of Sr and Sb modifiers on the sliding wear behavior of A357 alloy under varying pressure and speed conditions

The sliding wear behavior of unmodified, Sb-modified and Sr-modified A357 aluminum alloys under T6 heat treatment was investigated using a block-on-ring wear machine. The studies involved the effects of applied pressure and sliding speed on wear rate and mechanisms during dry sliding. The microstructural characterization and worn surfaces were examined using optical microscopy and scanning electron microscopy (SEM), the latter attached with an X-ray mapping system. The wear behavior of A357 alloys was influenced by the morphology of silicon particles and the stability of the mechanically mixed layer (MML). Sliding wear tests revealed that the addition of both Sr and Sb modifiers improves the wear resistance of the alloy. This beneficial effect of enhanced wear resistance was more apparent in the Sr-modified alloy than the Sb-modified one. This was attributed to the lower cracking tendency of the Sr-modified alloy owing to the near-spherical nature of silicon particles. Moreover, addition of both Sr and Sb modifiers in the alloy also enhanced the degree of spheroidization and refinement of silicon particles. Furthermore, the silicon particles in the Sr-modified alloy were finer and more spherical than those in the Sb-modified one. Additionally, the decreased wear rate was also substantiated through the formation of a stable MML on the worn surface. Observations of worn surfaces showed more stable MML on the worn surface of Sr-modified alloy than for the unmodified and Sb-modified alloys.