Effect of RE addition on solidification process and high-temperature strength of Al−12%Si−4%Cu−1.6%Mn heat-resistant alloy

The effect of RE addition on solidification process and high-temperature strength of Al−12%Si−4%Cu−1.6%Mn (in wt.%) heat-resistant alloy was investigated by microstructure observation and tensile test. A great number of fine needle-like RE-rich phases are observed in the alloys with RE addition. Solutionizing treatment does not change their morphologies and sizes, indicating that they have good thermal stability. The addition of RE totally alters the solidification process of eutectic CuAl2 phase, from network-like phase in the form of segregation at the final eutectic grain boundaries to discretely blocky phase growing on the hair-filamentous RE-rich needles. In the alloys with Ce addition, blocky CuAl2, particulate Al15Mn3Si2 and needle-like RE-rich needle phases grow together, but they did not occur in the alloy with only La addition. The addition of RE does not considerably improve the strength of the alloy at high temperatures. The formation of RE-rich phases also does not significantly alter the originating and propagating of micro-cracks in the alloy during tensile test.