Investigation of mechanical properties of intermetallic phases in multi-component Al–Si alloys using hot-stage nanoindentation

Multi-component Al–Si alloys are important for the engineering applications such as automotive pistons. The presence of additional elements in the Al–Si alloy system allows many complex intermetallic phases to form. The mechanical properties of different intermetallic phases have been investigated as a function of temperature using hot-stage nanoindentation. In particular, the hardness and modulus of a number of phases have been established for a range of alloy compositions. In this study, the results show that both hardness and reduced modulus increase as the Ni ratio (Ni/(Ni + Cu)) of the AlCuNi phases increases (Al3Ni2 > Al7Cu4Ni > Al2Cu) up to 350 °C. The creep effect of the intermetallic phases has also been investigated with a heating stage and indicated that the hardness strongly depends on the creep rate of the phase, particularly in the Al2Cu phase. The Ni containing phases (Al3Ni2 and Al7Cu4Ni) have a good high temperature stability up to 200 °C; however, they drop significantly at 350 °C due to the fact that the frequent jumps of Cu and Ni atoms cause disordered structures. The Si and α-AlFeMnSi phases have good mechanical properties up to 350 °C corresponding to their good creep resistance. Al5Cu2Mg8Si6 with a lower hardness and elastic modulus exhibits the most stable phase at elevated temperatures, which is correlated with its good creep resistance.