Effects of Various Ageing Heat Treatments on Microstructural Features and Hardness of Piston Aluminum Alloy

Piston aluminum alloys have different intermetallic phases, such as Cu3Al, Mg2Si ,and AlNi phases. The morphology and the distribution of such phases have important roles on mechanical properties of the piston material. Therefore, in this research, various ageing heat treatments on the mentioned material were done and the microstructural feature and the hardness were studied. Obtained results showed that solutioning at 515 °C for 7 hours and ageing at 205 °C for 7 hours, was the superior heat treatment process, since such treatment led to increase the hardness value to its highest value (153 BHN) for the piston aluminum alloy. This heat treatment caused to increase the size of Si particles obviously and caused to precipitate other intermetallic phases of Al (Ni,Cu) and Ni-Si. Additionally, solutioning at 500 °C for 5 hours and ageing at 180 °C for 9 hours resulted in coarsening Si and Al-Ni participates in the longitudinal direction, which was caused to increase the hardness value to 137 BHN. Energy dispersive X-ray spectroscopy (EDS) results indicated that when the specimen aged at 230 °C for 5 hours, other intermetallic phases such as Al (Ni,Si) and Mg2Si appeared in the matrix.