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 degrees C and 420 degrees 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 degrees 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 degrees C is higher than that formed at 350 degrees C. Both room temperature (RT) and 350 degrees C tensile strengths, as well as the high cycle fatigue life of the alloy after being re-aged at 420 degrees C are higher than those of re-aged at 350 degrees C due to the notable precipitation strengthening effect of nano particles Al11Cu5Mn3.