【作者】 姜锋；

【导师】 张喜燕；

【作者基本信息】 西南交通大学 ， 材料学， 2004， 硕士

【摘要】 通过拉伸试验并采用SEM、XRD、TEM等方法对基于ZM5合金的两种Mg-9Al-xZn合金（ZM5和ZM5y，后者含有较多的Zn和少量Ag）的性能和显微组织进行了研究，分析了合金的成分、组织和性能之间的变化规律，探讨了合金在凝固、固溶处理以及人工时效处理过程中的相变（组织演变），并讨论了Mg-9Al-xZn合金中的合金强化。研究发现，Zn和Ag在Mg-9Al-xZn合金中可以起到明显的固溶强化效果。Zn促进了Mg-9Al-xZn合金中珠光体型二次γ(Mg₁₇Al₁₂)相的析出，较多的Zn的添加还使得合金中出现了新相MgZn。Ag对Mg-9Al-xZn合金的组织没有明显影响，也没有因此而增加新相，但在时效状态下Ag会在基体晶界出现偏聚现象，而不利于合金的耐腐蚀性能。固溶处理可提高Mg-9Al-xZn合金的抗拉强度和延伸率；而其后的人工时效处理能明显提高合金的屈服强度和屈强比，但也明显降低了延伸率。人工时效处理对固溶处理的ZM5合金的抗拉强度几乎没有影响，但小幅降低了ZM5y合金的抗拉强度，这是Zn元素和人工时效共同作用的结果。固溶处理和人工时效处理可以明显改变γ相的形貌。研究还发现，片层状二次γ相对Mg-9Al-xZn合金的力学性能有重要影响：随着片层状二次γ相的数量逐渐增多、尺寸逐渐增大（形态也趋于复杂），合金的延伸率逐渐降低，而屈服强度和屈强比逐渐升高：但过于粗大的片层状二次γ相对抗拉强度不利。分析认为，初次γ相的形成是由于非平衡凝固过程中的晶内偏析造成的，是一种离异共晶现象，Zn对初次γ相的形成也有促进作用；无论是铸态、固溶状态，还是人工时效状态，界面都是片层状二次γ相的有利形核部位；在铸态下，初次γ相和邻近基体晶粒的界面比其它晶界更有利于冷却过程中片层状二次γ相的形核，但晶内偏析不利于其生长。本研究的结果，可以对Mg-9Al-xZn合金的热处理起到一定的指导作用。通过合理控制化学成分，采用适宜的工艺参数，可以期望获得令人满意的性能，满足使用的需要。更多还原

【Abstract】 By tensile test and using methods such as SEM, XRD and TEM, the tensile properties and microstructures of two kinds of Mg-9Al-xZn alloys (ZM5 and ZM5y, the latter has more Zn and a little Ag) are investigated, and the relations among the chemical composition, microstructure, and properties are analyzed, and the phase transformation (microstructure evolution) and alloying strengthening are discussed. It is indicated that Zn and Ag can well strengthen Mg-9Al-xZn alloy through solid solution (s.s.). Zn facilitates the precipitation of peralite-like secondary (Mg17Al12) in Mg-9Al-xZn alloy, and a new phase MgZn appears due to more addition of Zn. Ag has little effect on the microstructure of Mg-9Al-xZn alloy and no new phase related appears, but it segregates near the boundaries through artificial ageing and thus the corrosion resistance of the alloy is deteriorated. UTS (ultimate tensile strength) and elongation of Mg-9Al-xZn alloy increase through S.S., and YS (yield strength) and the value of YS/UTS increase through the followed artificial ageing with obvious loss of elongation. Artificial ageing has little effect on UTS of ZM5, but slightly decreased that of ZM5y due to the joint effects of more addition of Zn and artificial ageing. The morphology of Y phase can be obviously changed through s.s. and artificial ageing. It is also showed that the peralite-like secondary Y phase has remarkable effect on the mechanical properties of Mg-9Al-xZn alloy: with the increase of the amount and size of the secondary Y phase (its morphology also becomes more complicated), the elongation decreases while YS and the value of YS/UTS increase, but too large peralite-like secondary Y phase deteriorates UTS. It is deemed that the primary Y phase is resulted from composition segregation during un-equilibrium solidification, which is also partly facilitated by Zn. Boundaries are good sites for nuclear formation of the pearlite-like secondary Y phase under the condition of either as-cast or solid soluted or artificial aged. When as-cast, the boundary between the primary Y phase and the matrix grain is more preferential than other boundaries for nuclear formation of pearlite-like secondary Y phase, but composition segregation is not good for Y phase slices to grow up. The results in this paper can be useful to the heat treatment of Mg-9Al-xZn alloys. With reasonable control of thechemical composition and using appropriate process parameters, satisfactory properties can be got to meet the requirements in practice.更多还原