中文摘要：

使用基于金属型的微精密铸造工艺成形了微米尺度的三维复杂的Zn-4Al合金微齿轮铸件,观察了微铸件显微组织的演变规律.结果表明,与常规铸件相比,微铸件表现出典型的快冷非平衡凝固特征,晶粒显著细化,最小的晶粒尺寸仅为常规铸件的1/20左右;而且共晶组织的形态发生转变,由平衡凝固时的层片状转变为棒状,初生相β-Zn的比例提高,其主要原因是微铸件尺寸引起的冷却速度的提高.

英文摘要：

Three-dimension complicated microgear castings in micron size for Zn-4Al alloys were produced by the micro-precision-casting technology based on metal mold. The evolutive regularity of microstructure of microgear castings were observed by optical microscope and scanning electron microscope （SEM）. The results show that microcastings demonstrate typical nonequilibrium rapid solidification characteristics comparing with conventional castings. Its grain size decrease significantly, i.e. minimal castings is only about one to twentieth of conventional castings, and its eutectic structure transform from lamellar morphology for equilibrium solidification to rod eutectic. And the ratio of primary phaseβ-Zn is increased. This kind of microstructure may help to promote mechanical properties of microcasting. The increase of cooling rate resulted from the change of microcastings size is the main factor in the change of microstructure.