Preparation of submicrocrystal Al-Ti-B master alloy and its influence on microstructure and properties of AZ91D

To improve the mechanical properties of AZ91D magnesium alloy, the submicrocrystal Al-Ti-B master alloy was prepared with copper mold inject casting method, and the influence of submicrocrystal Al-Ti-B master alloy on the microstructure and mechanical properties of AZ91D was investigated. Results show that, the distribution of TiB₂ phase in submicrocrystal Al-Ti-B alloy is even and disperse, and the average size of TiAl₃ phase is reduced from 10-30 pm to ~1 µm. The properties of AZ91D refined with submicrocrystal Al-Ti-B master alloy are better than that with coarse-grained Al-Ti-B master alloy without copper mold inject casting. The tensile strength, elongation and Brinell hardness of AZ91D are increased by 10.6%, 25% and 18.1%, respectively. Therefore, refinement of AZ91D with submicrocrystal Al-Ti-B that is obtained by copper mold inject casting is an effective method to improve its mechanical properties.