Effect of Zn Addition on the Microstructural Heterogeneity and Mechanical Properties of Vacuum-Assisted High-Pressure Die Casting Al-Si-Mg-Cu alloys

Herein, Al-8Si-0.5Mn-0.5 Mg-0.2Cu-xZn alloys (x = 0, 1, 2, and 3 wt%) are produced by a vacuum-assisted high-pressure die casting process. The effects of Zn addition on the surface layer thickness and segregation band, the number density of externally solidified crystals (ESCs), and mechanical properties of the alloys are systemically investigated. As the Zn content increases, the size and number density of the ESCs increase. The morphology and size of the eutectic Si phase could be modified by the addition of Zn. In addition, the microstructural heterogeneity indicates that the thickness of the surface layer and segregation band zone increase with increasing Zn content. Proper Zn addition can effectively promote the improvement of strength and elongation in the as-cast state. When the Zn content is 2 wt%, the yield strength, ultimate tensile strength, and elongation of the alloy are 167, 311 MPa, and 10.8%, respectively.