Characterization of the Aging Precipitates of Al-12Si-4Cu-2Ni-0.8Mg-0.2Gd Piston Alloy
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The aging precipitates of cast-T6 Al-12Si-4Cu-2Ni-0.8Mg-0.2Gd piston alloy were investigated. Microstructure observations indicate that the thermally unstable θ-Al2Cu precipitates disappeared inside the grains and the thermally stable Al3CuGd precipitates were formed at the grain boundary. The Al3CuGd precipitates were formed more easily than Al2Cu phases according to the ab initio calculations. Owing to the combined strengthening effect of precipitates, the Al-Si-Cu-Ni-Mg-Gd alloy has a higher tensile strength than the Al-Si-Cu-Ni-Mg alloy. The disappearance of the unstable θ-Al2Cu precipitates and the formation of Al3CuGd at the grain boundary facilitate the increase in the elevated-temperature strength of the Al-Si-Cu-Ni-Mg-Gd alloy.
This work was supported by the China Postdoctoral Science Foundation (Grant Numbers 2017M623319XB, 2018T110999) and Yunnan Provincial Department of Education Science Research Fund Project (No. 2018JS033).