Effect of Cr content and heat-treatment on the high temperature strength of eutectic Al-Si alloys

In this work, the effects of Cr content (0-0.67 wt%) and heat treatment on the microstructure evolution and high temperature (HT) tensile strength (350 degrees C) of the Fe-containing eutectic Al-Si alloy were studied. The results show the main intermetallics are similar in tested specimens at both different heat treatment states, including gamma-Al3CuNi, delta-Al7Cu4Ni, Al4Cu2Mg8Si7, and AlFeSi. The addition of Cr leads to the transformation from needle-like beta-AlFeSi phases to fishbone-like alpha-Al(Fe, Cr) Si phases. For the HT strengths (350 degrees C), the UTSs of Al-Si alloys at T5 state are higher than T6 state correspondingly, both of which are progressively decreased with the Cr contents. For the elongation, the Al-Si alloys at T6 state have better plasticity than T5 state correspondingly. Comparably, the elongations remain stable at T5 state, and keep increasing at T6 state with the addition of Cr. The variations of HT strengths and elongations dependent on the Cr content and heat treatment are accounted on the microstructural evolutions, including AlFeSi phase transformation and the Si spheroidization. (C) 2015 Elsevier B.V. All rights reserved.