Elevated re-aging of a piston aluminium alloy and effect on the microstructure and mechanical properties

T6 heat treated piston aluminium alloy (Al-13Si-4Cu-2Ni-1Mg-0.25Mn) were further aged at 350 °C and 420 °C, respectively, for various time (0-1000 h). The microstructures of the re-aged alloy were analyzed using optical microscope (OM, Nicon300) and transmission electron microscope (TEM, JEM-2010). The tensile strengths at room and 350 °C, as well as high cycle bending fatigue of the alloy were tested. The results show that the Al11Cu5Mn3 nanoparticles will precipitate during the elevated re-aging process. The volume fraction formed during re-aging at 420 °C is higher than that formed at 350 °C. Both room temperature (RT) and 350 °C tensile strengths, as well as the high cycle fatigue life of the alloy after being re-aged at 420 °C are higher than those of re-aged at 350 °C due to the notable precipitation strengthening effect of nano particles Al11Cu5Mn3.