中文摘要：

利用消失模铸造振动凝固技术,得到Al-Si7-Mg合金的近等轴晶组织。在此基础上研究了580℃不同时间保温半固态等温热处理（SSIT）组织中α-Al晶体的形貌与尺寸变化。结果表明：合金580℃保温1h,得到α晶粒的等积圆直径在50-150μm的分布比例达85%,α晶粒圆度均值1.41。通过凝固动力学和热力学分析,得出半固态热处理过程中,低熔点的三元共晶和二元共晶相首先熔化,并随着溶质元素扩散速度的增加,液相不断增多,α晶体形状大小不断改变；当液相率达到平衡之后,α晶粒在界面张力的作用下，不断圆整球化，合并长大。半固态热处理α枝晶演变形式明显不同于等轴晶演变过程。

英文摘要：

Near equiaxed grains of Al-Si7-Mg alloy were fabricated by vibration solidification in lost foam casting（LFC）.Then the morphology and size of α-phase fabricated by semi-solid isothermal heat treatment（SSIT） process at 580 ℃ with different holding time were studied.The results show that the fraction of α-Al grain diameters between 50 μm and 150 μm is up to 85%,and the average roundness of α-Al grain is 1.41 when the alloy is obtained at 580 ℃ holding for 1 h.According to the analysis of solidification kinetics and thermodynamic,ternary eutectic and binary eutectic with low melting point are melted at first in SSIT process,and the liquid fraction increases when the solute diffuses adequately,and the shape and size of α-phase are changed.After the liquid fraction ratio reaches balance,α-phase is keeping spheroidization under the boundary tension dominates and combines to grow up.Evolution of α dendrite in SSIT process is obviously different from the evolution of equiaxed grains.