Effect of Al-Ti Master Alloy on the Grain Refinement and Hot Tearing of AZ91 Mg Alloys

The AZ91D magnesium (Mg) alloy is a widely used aluminum (Al)-bearing commercial alloy. However, due to the presence of low-melting temperature phases, the alloy remains highly susceptible to hot tearing. In many Al and Mg alloys, grain refinement was seen to reduce the hot tearing severity, but an effective refiner for Al-bearing Mg alloys has been elusive. In the present work, a novel titanium (Ti)-based master alloy was developed using a spark plasma sintering (SPS) powder metallurgy route. Its effect on hot tearing was quantitatively studied in-situ using a mold with a load cell. In addition to a significant grain refinement, the master alloy eliminated hot tearing in casting conditions where untreated AZ91D Mg alloy readily nucleated hot tears.