铸态AZ91镁合金加热至液固相温度区间内等温热处理后演变成半固态金属,对淬火组织形态分析的试验表明:在高固相体积分数条件下,网状分布的共晶组织首先熔化,二次枝晶臂消失或熔断脱落并重新沉淀在枝晶主干上,在Gibbs-Thomson效应下,发生Ostwald熟化,固相颗粒由枝晶逐渐演变成球形颗粒,并随着热处理时间的延长发生合并现象,而且热处理温度越高晶粒间合并现象越严重。同时在界面能降低的驱使下,晶粒内部包裹的液滴以两种方式形成:晶粒内富Al、Zn的质点经过熔化、扩散、合并、或者脱落的二次枝晶臂沉淀后搭桥生长形成。 The as-cast AZ91 magnesium alloy was heated to the liquid-solid temperature range and was then isothermally heat-treated to form a semi-solid metal. Experiments on the morphology of the as-quenched microstructure showed that at high solid volume fraction, the networked eutectic first Melted, the secondary dendrite arm disappears or melts and falls off and re-precipitates on the dendrite trunk. Ostwald ripening occurs under the Gibbs-Thomson effect. The solid phase particles gradually dendrite into spherical particles and occur as the heat treatment time prolongs Merger phenomenon, and the higher the temperature of the heat treatment, the more serious the phenomenon of intergranular merger. At the same time, the interface can be reduced under the impetus of the crystal grain droplets formed in two ways: the grain of Al, Zn particles after melting, diffusion, merging, or falling secondary dendrite arm deposition after bypass growth form.