中文摘要：

采用双电偶热分析技术和SEM表征了Mg-6Al-xZn合金（简称AZ6x合金，x=0，2，4，6，质量分数，％）在砂型铸造过程中的凝固行为和显微组织；采用背散射电子衍射（EBSD）分析对合金的晶粒尺寸进行定量表征．利用Pandat热力学软件计算了合金的平衡截面相图、非平衡Scheil模型凝固过程，以及枝晶生长抑制因子（growthrestrictionfactor,或称为Q值）．结果表明，在AZ6x合金的砂型铸造凝固过程中，AZ60合金中只有非平衡凝固的产Mg17Al12，而AZ62-AZ66合金的铸态组织中除了γ-Mg17Al12相，还出现了Ф-Mg21（Al，Zn）17相，并且随着zn含量的增加，γ-Mg17Al12相减少而Ф-Mg21（Al，Zn）17相增多．热力学计算结果表明，AZ60～AZ64合金中γ-Mg17Al12相和Ф-Mg21（Al，Zn）17相在一定温度下能够完全固溶到a-Mg中，而AZ66合金中的Ф-Mg21（Al，Zn）17相在任何温度下都不可能完全固溶．研究结果还表明，Zn含量高的合金具有高的Q值、小的晶粒尺寸及低的枝晶相干点固相分数；并讨论了p值、晶粒尺寸与矿。的关系．

英文摘要：

The solidification behavior and microstructure evolution of sand cast Mg-6Al-xZn alloy （named as AZ6x alloys, x=0, 2, 4, 6, mass fraction, %） were characterized by two-thermocouple thermal analysis technology and SEM. The grain sizes of the alloys were quantitatively determined by EBSD technology. Thermodynamic cal- culations were applied in Pandat soRware for phase diagram calculation, Scheil model solidification simulation and growth restriction factor values （GRF or Q values）. The results show that solidification of AZ6x alloys follows non-equilibrium solidification paths. Besides the γ-Mg17Al12 phase, which is the only secondary phase in AZ60 al- loy, another Ф-Mg21（Al,Zn）17 phase appears in the as-cast microstructure of AZ62 to AZ66 alloys. With the in- crease of the Zn content, the amount of γ-Mg17Al12 phase decreases and while increase the amount of Ф-Mg21（Al,Zn）17 Tphase. Calculated equilibrium phase diagram shows that in the AZ60-AZ64 alloys both γ-Mg17Al12 phase and Ф-Mg21（Al,Zn）17 phase can be dissolved into a-Mg under proper heat treatment conditions. However, Ф-Mg21（Al,Zn）17 phase in AZ66 alloy can not be completely dissolved into a-Mg for any temperature. The results also indicate that higher Zn content alloys have higher Q values and smaller grain size, and lower solid fraction at dendrite co- herency point fsDCP）. The relationship of Q values, grain size and fsDCP has been also discussed.