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为了研究触变注射成形AZ91D合金中固相颗粒的形貌演变和液相的凝固行为,对该合金的组织和凝固行为进行了试验观察和理论分析。典型触变注射成形AZ91D合金由α-Mg和β-Mg17Al12两相构成,α-Mg相又可分为未熔固相和初生固相。未熔固相主要有形貌较为接近球状的固相、形貌不规则的固相、内部含有小液池的固相以及包裹液相的固相4种形貌。形貌不规则的固相被认为是球状固相和包裹液相的固相的中间发展形貌,内部含有小液池的固相可能是包裹液相的固相的初级形貌,包裹液相的固相则可能发生破裂形成不规则固相,最终发展成球状固相。球状固相被认为是最理想的也是最终的固相形貌。初生固相在液相合金中形核并长大,直至有不稳定长大行为发生为止,较为细小、圆整,主要受冷却速率的影响。Mg-Al合金二元相图的分析结果与试验观察到的组织相吻合。
In order to study the morphology evolution and the solidification behavior of solid particles in the thixo-injection-molded AZ91D alloy, the microstructure and solidification behavior of the alloy were experimentally observed and theoretically analyzed. The typical thixo-injection AZ91D alloy consists of two phases, α-Mg and β-Mg17Al12. The α-Mg phase can be divided into unmelted solid phase and primary solid phase. The unmelted solid phase mainly has a spherical shape, a solid phase with irregular morphology, a solid phase containing a small liquid pool and four kinds of solid phase inclusions in the liquid phase. The irregular morphology of the solid phase is considered as an intermediate development of the solid phase in the form of a spherical solid phase and a solid phase containing the liquid phase. The solid phase containing a small liquid pool inside may be the primary morphology of the solid phase entrapping the liquid phase, Of the solid phase rupture may occur to form an irregular solid phase, eventually evolving into a spherical solid phase. Spherical solid phase is considered the most ideal and final solid phase morphology. The primary solid phase nucleates and grows in the liquid phase alloy, until the instability grows up until the behavior is relatively small and round, which is mainly affected by the cooling rate. The results of the binary phase diagram of Mg-Al alloy coincide with those observed in the experiment.