Evolution of surface roughness of a cast Al-Si-Cu piston alloy during thermal exposure

In the present work, samples of Al-Si-Cu piston alloy after T6 heat treatment were exposed for 2 h at temperatures ranging from 400 to 550 degrees C. The evolution of surface roughness and microstructure of the alloy during thermal exposure was studied by combination methods of roughness profiles, optical and scanning electron microscopy as well as XRD analysis. It is found that the roughness and mass of the alloy increase with the raise of the thermal exposure temperature, and the increasing rates of them are slow as the exposure temperature is below 500 degrees C, but accelerates abruptly when the temperature is higher than 500 degrees C. The variation of surface roughness of the alloy is closely related to phase transformation and oxidation during the thermal exposure.