Microstructure and Aging Behavior of Nonflammable AZ91D Mg Alloy

Phase equilibria of AZ91D Mg alloys for nonflammable use, containing Ca and Y, were carried out by using FactSage® and FTLite database, which revealed that solid solution treatment could be performed at temperatures from 400 to 450C. Solid solution treatment of AZ91D Mg alloy without Ca and Y was successfully conducted at 420C and supersaturated microstructure with all beta phase resolved into matrix was obtained. In the case of AZ91D Mg alloy with some Ca and Y; however, a little amount of intermetallic particles were observed after solid solution treatment. After solid solution treatment, each alloy was annealed at temperatures of 180 and 200C for time intervals from 1 min to 48 hrs and hardness of each condition was measured by micro-Vickers method. Peak aging conditions were deduced as at the temperature of 200C for 10 hrs. Keywords—Mg alloy, AZ91D, nonflammable alloy, phase equilibrium, peak aging.