(1. 兰州理工大学 甘肃省有色金属新材料省部共建国家重点实验室，兰州 730050；
2. 兰州理工大学 有色金属合金反加工教育部重点实验室，兰州 730050)
摘 要: AZ91D镁合金经重熔加入0.3%(质量分数)SiC细化后浇注成不同尺寸(直径)的锭料。研究SiC对不同尺寸AZ91D镁合金坯料半固态等温热处理组织的影响。结果表明：未经SiC细化处理AZ91D镁合金的半固态组织存在明显的尺寸效应，从心部到边缘，固相颗粒尺寸由大逐渐变小，如d 70 mm试样内的固相颗粒尺寸从心部的150 μm变为边缘的110 μm，并趋于圆整，液相逐渐增多；随着坯料尺寸的增加，由心部到边缘的组织差异进一步加大。SiC细化的AZ91D镁合金坯料经半固态等温热处理后，其组织中的固相颗粒尺寸整体变得细小，d 70 mm试样内的固相颗粒均不大于80 μm，边缘和心部的固相颗粒尺寸变得很相近，在70 μm与80 μm之间，球化圆整且分布均匀；经SiC处理的半固态压铸件中，气孔等缺陷明显减少。
关键字: 镁合金；SiC颗粒；半固态等温热处理；尺寸效应；晶粒细化
（1. State Key Laboratory of Gansu Advanced Non-ferrous Metal Materials,
Lanzhou University of Technology, Lanzhou 730050, China;
2. Key Laboratory of Non-ferrous Metal Alloys and Processing, Ministry of Education,
Lanzhou University of Technology, Lanzhou 730050, China）
Abstract:AZ91D magnesium alloy was remelted; then, 0.3%(mass fraction) SiC particles as grain refiner were introduced into the melt; and finally, the melt was poured into cavities with different diameters to form ingots. Those ingots were cut into some billets with determined diameters, and heated to semisolid temperature. The effect of SiC addition on microstructure of mutative-size AZ91D initial billet during semisolid isothermal heat treatment was studied. The results show that there is an obvious dimensional effect on microstructure for semi-solid AZ91D alloy without SiC. In other words, the microstructures from center to edge for the AZ91D billet are different. The size of solid particles gradually changes from large to small. For example, the size of solid particles of the billet with d70 mm changes from 150 μm to 110 μm, and the particles tend to be gradually spheroid and more liquid. With increasing diameter of the billet, the difference of microstructures from center to edge for the billet further increases. For AZ91D alloy with SiC addition, the average size of solid particles becomes smaller than that without SiC addition after isothermal treatment. The size of solid particles of the billet with d 70 mm is not larger than 80 μm. And the solid particle sizes of the billet with SiC from edge and center areas are almost of identical dimension, between 70 μm and 80 μm and in spheroid shape with homogeneous distribution. Casting defects for AZ91D alloy with SiC addition, such as porosity, decrease significantly after SiC semisolid die-casting.
Key words: magnesium alloy; SiC particle; semisolid isothermal heat treatment; dimensional effect; grain refinement
