(1.甘肃工业大学 材料科学与工程学院， 兰州 730050;
2.西安交通大学 金属材料强度国家重点实验室，西安 710049;
3.西安电子科技大学 机电工程学院， 西安 710043)
摘 要: 用SEM和TEM对金属型铸造并经18个月自然时效的Z A27合金的微观组织进行了观察。结果表明：ZA27合金凝固的初生相为富Al的树枝状α ′相，随后在α′相周围形成一层富Zn的包晶β相，最后剩余液体发生共晶反应，共晶β优先依附于包晶β相形核、长大，而共晶η则在包晶β相间形成一层薄膜，在有些区域则形成棒状共晶组织；在随后的冷却及时效过程中，β发生胞状分解形成规则的共析α+η层片组织或不规则的复杂形状组织，共析胞以共晶η相为基形核，并向枝晶中心生长，使α′相也分解为层片α+η组织，当其生长被α′中心的连续分解所阻挡时，致使其芯部形成细小的α+η颗粒组织；富Cu的ε相存在于所有η相中。
关键字: ZA27合金；金属型铸造；自然时效；微观组织
ZA27 alloy
（1.School of Materials Science and Engineering，
Gansu University of Technology，Lanzhou 730050，China;
2.State Key Laboratory of Mechanical Behavior for
Materials， Xi′an Jiaotong University，
Xi′an 710049，China;
3.School of Mechanical and Electronic Engineering，
Xi′an University of Electronic Science and Technology，
Xi′an 710043, China）
Abstract:The microstructure of permanent mold casting ZA27 alloy was examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) after natural aging for 18 months. The solidification begins with the formation of aluminum-rich α′ dendrites，followed by the peritectic reaction wherebya zinc-rich β phase forms around the edges of the primary phase. Finally，the solidification is completed by formation of eutectic β and η phases，the β phase joining the peritectic β phase and the η phase remaining as thin film in the inter dendritic regions. In some regions，the eutectics form in the form of fibrous β within η phase. The morphologies of the eutectics are determined by the size of the eutectic pools. On cooling after casting and on aging， both of the β phases decompose into well-formed eutectoid α+η lamellae or irregularly complex structures through cellular reaction. These cell colonies nucleate on the eutectic η phase and grow into the low-aluminum α′ phase cores of the dendrites to make the α′ phases form lamella structures. But the growth of these lamellae is always retarded by the continuous decomposition of the α′ phase in the dendritic cores and they decompose into mixture of fine zinc-rich η phase in a n aluminum matrix. The Cu-rich ε phase particles form in all η phases.
Key words: ZA27 alloy；permanent mold casting；natural aging； microstructure
