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 (Al(3)Ni(2) > Al(7)Cu(4)Ni > Al(2)Cu) up to 350 degrees 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 Al(2)Cu phase. The Ni containing phases (Al(3)Ni(2) and Al(7)Cu(4)Ni) have a good high temperature stability up to 200 degrees C; however, they drop significantly at 350 degrees C due to the fact that the frequent jumps of Cu and Ni atoms cause disordered structures. The Si and alpha-AlFeMnSi phases have good mechanical properties up to 350 degrees C corresponding to their good creep resistance. Al(5)Cu(2)Mg(8)Si(6) with a lower hardness and elastic modulus exhibits the most stable phase at elevated temperatures, which is correlated with its good creep resistance. (C) 2009 Elsevier Ltd. All rights reserved.