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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(growth restriction factor,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g-Mg17Al12,而AZ62~AZ66合金的铸态组织中除了g-Mg17Al12相,还出现了F-Mg21(Al,Zn)17相,并且随着Zn含量的增加,g-Mg17Al12相减少而F-Mg21(Al,Zn)17相增多.热力学计算结果表明,AZ60~AZ64合金中g-Mg17Al12相和F-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F-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fs DCP;并讨论了Q值、晶粒尺寸与fs DCP的关系.
The solidification behavior and microstructure of Mg-6Al-xZn alloy (AZ6x alloy, x = 0, 2, 4, 6, mass fraction,%) during sand casting were characterized by galvanic analysis and SEM. The grain size of the alloy was quantitatively characterized by backscattered electron diffraction (EBSD) analysis.Pandat thermodynamic software was used to calculate the phase cross section of the alloy, the solidification process of the non-equilibrium Scheil model, and the growth restriction factor Or Q.) The results show that during the solidification of the AZ6x alloy, only non-equilibrium solidified g-Mg17Al12 exists in AZ60 alloy, and the as-cast microstructure of AZ62 ~ AZ66 alloy except for g-Mg17Al12 phase also appears (Al, Zn) 17phase, and with the increase of Zn content, the content of g-Mg17Al12 phase decreased and the content of F-Mg21 (Al, Zn) 17phase increased.The results of thermodynamic calculation show that the g- The Mg17Al12 phase and the F-Mg21 (Al, Zn) 17 phase are completely dissolved in a-Mg at a certain temperature, whereas the F-Mg21 (Al, Zn) 17 phase in the AZ66 alloy can not be completely formed at any temperature The results show that the alloy with high Zn content has high Q value, small grain size and low dendrite coherent solid phase Number fs DCP; and discusses the relationship Q value, the grain size fs DCP.