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

• Published in: JOM (1989) 2023-04, Vol.75 (4), p.1345-1356
• Main Authors: Liu, Fei, Zheng, Huiting, Jiang, Yuanhang, Zhao, Haidong
• Format: Article
• Language: English
• Subjects: Aging; Alloys; Aluminum base alloys; Chemistry/Food Science; Copper; Corrosion resistance; Crack initiation; Die casting; Earth Sciences; Elongation; Engineering; Environment; Foundry practice; Grain boundaries; Heat treatment; Magnesium compounds; Mechanical properties; Metal silicides; Microstructure; Morphology; Phases; Physics; Silicon; Technical Article; Tensile strength; Transmission electron microscopy; Ultimate tensile strength
• ISSN: 1047-4838; 1543-1851
• DOI: 10.1007/s11837-022-05651-z

AlSiMgMn- x Cu ( 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 α-Al, eutectic Si, β-Mg 2 Si, Q-Al 5 Cu 2 Mg 8 Si 6 , and θ-Al 2 Cu 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 β′′ phase. As the Cu content increases to 0.3 wt.% and 0.6 wt.%, the β′′ and Q′ phases were co-precipitated in the α-Al matrix. As the Cu content further increases to 0.8 wt.%, the θ′ and Q′ phases were co-precipitated in the α-Al matrix and the predominant precipitate was the θ′ 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 β′′, Q′, and θ′ phases.