Microstructure And Low-cycle Fatigue Behavior Of Permanent-Mold Cast Al-Si-Cu-Nd Alloys

Cast aluminum alloys have gotten the wide application because of their excellent properties. The Al-Si-Cu series alloys, with such comprehensive advantages as good casting performances of Al-Si series alloys and high mechanical properties of Al-Cu series alloys, have received more and more attention. At present, the study on the fatigue behavior of cast aluminum alloys is still limited to the regular cognition. As for the specific influence of rare earth elements and heat treatments on low-cycle fatigue behavior of cast aluminum alloys and the corresponding microcosmic mechanism, the systematical understanding still lacks. Obviously, the investigation on the microstructures and fatigue behavior of Al-Si-Cu series cast aluminum alloys can not only provide the reference for the development of new type cast aluminum alloys, but also the reliable theoretical foundation for the safety design and reasonable use of cast aluminum alloy components. Therefore, the rare earth element Nd was selected as the micro-alloying element on the basis of Al-Si-Cu alloy, and the effect of rare earth element Nd and solid solution plus aging treatment on the microstructures and low-cycle fatigue behavior of the permanent-mold cast Al-Si-Cu series alloy was investigated.The observation and analysis results on microstructure show that the microstructure of the permanent-mold cast Al-7%Si-3.5%Cu alloy can be effectively refined with the addition of rare earth element Nd. In addition, the microstructure of the permanent-mold cast Al-7%Si-3.5%Cu-x%Nd alloys can be further refined after solid solution plus aging treatment.The results of low-cycle fatigue tests show that under total strain controlled fatigue loading condition, the cyclic stress response behavior of the permanent-mold cast Al-7%Si- 3.5%Cu-x%Nd alloys with both as-cast and solid solution plus aging treated states exhibits the cyclic strain hardening and cyclic stability, which is mainly related to the applied total strain amplitude and heat treatment state. In addition, the relationship between the plastic and elastic strain amplitudes as well as reversals to failure for the permanent-mold cast Al-7%Si-3.5%Cu-x%Nd alloys with both as-cast and solid solution plus aging treated states obeys the Coffin-Manson and Basquin equations, respectively.The observation and analysis results on fatigue fracture surfaces reveal that under the low-cycle fatigue loading condition, the fatigue cracks initiate at the surface of fatigue samples in a transgranular mode, and propagate transgranularly for the permanent-mold casting Al-7%Si-3.5%Cu-x%Nd alloys with both as-cast and solid solution plus aging treated states.