中文摘要：

采用近液相线半连续铸造技术制备了6061铝合金半固态坯料，在610℃下对其进行二次加热部分重熔；采用光学显微镜及图像分析仪分析了加热不同时间合金的显微组织及尺寸特征，研究了二次加热过程中的液相形成、组织演变及晶粒长大过程。结果表明：随着保温时间延长，在相变及扩散作用下，液相体积分数不断增加并达到平衡，蔷薇状非枝晶组织特征逐渐弱化，并向近球状组织演变；随着保温时间继续延长，晶粒长大且尺寸分布不均匀；保温480S左右时晶粒圆整、尺寸分布均匀，适合触变成型。

英文摘要：

The 6061 semi-solid aluminium alloy feedstock was prepared by nearby-liquidus semi-continuous casting technology. The feedstock was re-heated and partially remelted at 610℃. The microstructure and size characteristics of the alloy heated for different times were analyzed by optical microscopy and image analyzer. The liquid formation, microstructure evolution and growth of grains during holding time were observed and analyzed. It is found that the volume fraction of liquid phase increased first and reached equilibrium then with the prolongation of holding time due to the effects of phase transition and diffusion. The rosette-like non-dendritic structure characteristic was gradually weakened and the microstructure transformed to near-spherical structure. The grains grew and the size distributed heterogeneously with the increase of the holding time. The grains were round and the size distributed homogeneously after holding for 480 s, which was suitable for thixocasting.