Bi对AZ91镁合金时效析出动力学过程的影响

实验合金中Bi的加入量为0.5％～2％，合金在SF61％/CO

Influence of Bismuth on the Aging Kinetics of AZg1 Magnesium Alloy

The bismuth additive contents cover a range of 0.5％～2％. A mixture of CO2/1％ SF6 is used as a protective gas during melting process. The melt is homogenized with argon bubbling before pouring. The test sample plates (230 mm×40 mm×20 mm) are cast at the pouring temperature of 720℃ in a permanent mold preheating to about 250℃. All the specimens are heated at 420℃ for 12 h followed by quenching, then aged at 200℃ for different times. The results show that the bismuth addition to AZ91 retards the aging process, suppresses the discontinuous precipitation and accelerates the formation of continuous precipitates. EDAX and TEM study indicates that the continuous precipitate in the Bi-bearing magnesium alloys has a stoichiometric composition of Mg17 (Al, Bi)12, which has semicoherent orientation relationship with matrix and increases the thermal stability of the precipitates. Accordingly, the heat resistance of magnesium alloy at elevated temperature could be increased by addition of bismuth.