Semi-Solid Slurry Preparation Process, Microstructure and Mechanical Properties of Mg–7Al–1Ca–1Sb Alloy

In order to promote the application of magnesium (Mg) alloy semi-solid die casting (SSDC) technology, the semi-solid Mg–7Al–1Ca–1Sb alloy slurry with high solid fraction was prepared by the slurry enthalpy equilibrium device method, and vacuum die casting was used to prepare SSDC test rods. The optimum semi-solid slurry process parameters for the alloy were determined using the orthogonal test method. The effects of SSDC and heat treatment on the microstructure and mechanical properties of Mg–7Al–1Ca–1Sb alloy were investigated using optical microscopy, scanning electron microscopy, X-ray diffractometry, transmission electron microscopy, and tensile tests. The experimental results showed that the optimal slurry preparation parameter for Mg–7Al–1Ca–1Sb alloy was a pouring temperature of 680 °C, rotation speed of 190 rpm, and crucible temperature of 300 °C. The average grain size and shape factor of the slurry prepared under this condition was 69.66 μm and 0.739. After T6 heat treatment, a large number of Mg₁₇Al₁₂ and (Mg, Al)₂Ca phases were dispersed at the grain boundaries in the form of fine particles, which can effectively hinder the movement of dislocations and further improved the mechanical properties of the alloy. The ultimate tensile strength, yield strength and elongation of Mg–7Al–1Ca–1Sb–T6 alloy were 271 MPa, 172 MPa and 12.2%. Compared to SSDC alloy, the improvements were 25%, 53% and 56%, respectively. The improved mechanical properties of the alloy after T6 heat treatment were attributed dispersion strengthening of second-phase particles.