Effect of Low Cu Content and Heat Treatment on the Microstructure and Mechanical Properties of High-Vacuum Die-Cast AlSiMgMn Alloys

摘要

AlSiMgMn-xCu (x = 0.1wt.%, 0.3wt.%, 0.6wt.%, 0.8wt.%) alloys were produced by a high-vacuum die-casting (HVDC) process, and the effect of varying Cu contents on the microstructure evolution and mechanical properties under as-cast and T6 heat-treatment conditions have been systemically investigated. The results indicated that the microstructure under the as-cast state consists of alpha-Al, eutectic Si, beta-Mg2Si, Q-Al5Cu2Mg8Si6, and theta-Al2Cu phases. Increasing the Cu content brought about an apparent change in the main precipitate of the alloys after T6 heat treatment. When the Cu content is 0.1 wt.%, the precipitate is only beta '' phase. As the Cu content increases to 0.3 wt.% and 0.6 wt.%, the beta '' and Q ' phases were co-precipitated in the alpha-Al matrix. As the Cu content further increases to 0.8 wt.%, the theta ' and Q ' phases were co-precipitated in the alpha-Al matrix and the predominant precipitate was the theta ' phase. As the content of Cu increases from 0.1 wt.% to 0.8 wt.%, the yield strength and ultimate tensile strength after T6 heat treatment increase to 241 MPa and 366 MPa, respectively. Meanwhile, the elongation increases to 8.2%. The improved mechanical properties are mainly attributed to the co-precipitation of the beta '', Q ', and theta ' phases.

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