中文摘要：

采用气泡搅拌法制备AZ91D镁合金半固态浆料,研究工艺参数变化,包括气体流量、冷却速率和搅拌结束温度,对AZ91D镁合金半固态浆料显微组织的影响规律。结果表明：随着气体流量从0升高至5L/min,α-Mg初生相平均颗粒尺寸从119.1μm降至77.2μm,而平均形状因子从0.1升高至0.596,气泡搅拌中非枝晶初生相来自于枝晶破碎和熔体形核;随着冷却速率从3.6℃/min升高至14.6℃/min,α-Mg初生相平均颗粒尺寸从105.0μm降至68.1μm,而平均形状因子在冷却速率为9.1℃/min时达到最高,过高或过低的冷却速率都会导致初生相的枝晶生长;搅拌结束温度从590℃升至595℃对最终的AZ91D镁合金半固态浆料显微组织无明显影响,这是因为半固态浆料中已经形成了足够数量的初生相。

英文摘要：

The semi-solid slurry of AZ91 D magnesium alloy was prepared by gas bubbling process.The effect of processing parameters,including gas flow rate,cooling rate and stirring end temperature,on microstructure of AZ91 D semi-solid slurry was investigated.With increasing the gas flow rate from 0 to 5 L/min,the average size of primary α-Mg particles decreases from 119.1 to77.2μm and the average shape factor increases continuously from 0.1 to 0.596.The formation of non-dendritic primary α-Mg particles during gas bubbling is the result of combined effects of dendrite fragmentation and copious nucleation.With increasing the cooling rate from 3.6 to 14.6℃/min,the average particle size of primary α-Mg phase decreases from 105.0 to 68.1μm while the average shape factor peaks at 9.1℃/min.Both high and low cooling rates can induce dendritic growth of primary α-Mg particles.Changing the stirring end temperature from 590 to 595℃ has little effect on the average size and shape factor of primary α-Mg particles in AZ91 D semi-solid slurry.The insensitivity of semi-solid microstructures to the stirring end temperature is attributed to the sufficient quantity of primary particles formed in the melt.