导流器在AZ91D镁合金半固态组织形成中的作用

采用新型的自孕育法制备AZ91D镁合金半固态浆料,研究了导流器在半固态组织形成中的作用.结果表明,合金熔体加入孕育剂并经导流器浇注后,导流器吸收大量过热,使合金温度迅速降低至液相线附近；合金液在导流器表面流动时,导流器促进了熔体中非均质形核及游离晶粒的产生,使合金凝固时晶粒增殖.导流器表面凝固组织从上至下依次为树枝晶、细小树枝晶、等轴晶；倾斜角度影响合金流动方式及传热效果,角度过大和过小均不利于晶粒增殖,角度为45°时冷却效果和剪切作用最佳,此时合金有效形核数量最多,半固态浆料组织初生相细小且分布均匀.

Role of Fluid Director in Semi-solid Microstructure Formation of Magnesium Alloy AZ91D

The semi-solid slurry of AZ91D magnesium alloy was prepared by a novel self-inoculation method, and the role of fluid director in formation of non-dendritic microstructure in semi-solid slurry was described. The results show that temeprature of the alloy melt is decreased sharply to nearby liquidus as a result of absopting a lot of super-heat by fluid director after pouring alloy melt with inoculation tretament on fluid director. With melt flowing on the fluid driector, heterogeneous nucleation is promoted and a large amount of free grains are generated, resulting in a proliferation of grains density during solidification, so the microstructure of solid shell solidified on the fluid director surface is varied from developed dendritic to fine dendritic, and finally to equiaxed grain. The degree of slope angle has affected flow way and heat transfer effects. An excessively high or small angle is harmful to the proliferation of grain density, and the desirable cooling and shearing effect can be obtained with slope angle of 45°,where the number of efficient grains is the most and the microstructure of primary phase in semi-solid slurry presents small size and uniform distribution.