A Study of Mg and Ti + Sr Additions to Strengthen Commercial A380 High-Pressure Die Cast Alloy

The effect of Mg and Ti + Sr on the microstructure and mechanical properties of commercial HPDC (high-pressure die cast) A380 aluminum alloy was investigated. The results show that Mg and Ti + Sr improved the hardness and yield strength up to 69 HRB and 201 MPa, respectively, while maintaining the elongation at the same level of 1.4–1.6% as the alloy without Mg and Ti + Sr additions. The Transmission Electron Microscopy (TEM) study of the microstructure shows that Sr is primarily precipitated in the eutectic Si phase with a trace amount in solid solution with Al matrix. In contrast, Ti is detected in a solid solution with aluminum throughout the α-Al grains. The presence of Sr and Ti forced Mg, Cu, and other elements out of the matrix to form intermetallic compounds in the grain boundaries at the last stage of solidification. The TEM results suggest that the combined addition of Mg and Ti + Sr improves the yield strength and hardness through the refinement of eutectic Si by Sr and solid solution hardening by Ti. Additionally, Mg contributed to improved strength and hardness by forming intermetallic compounds with Si and Cu.