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以Al-9.2Zn-2.0Mg-1.8Cu合金为基础合金,共设计了3种化学成分的合金,采用金相显微镜(OM)、扫描电镜(SEM)、X射线衍射(XRD)、差热分析(DSC)等手段,同时结合Pandat热力学计算,研究了Zn和Mg元素对半连续铸造高Zn含量Al-Zn-Mg-Cu合金铸态和均匀化组织的影响。结果表明:合金铸态组织中第二相主要包括非平衡共晶(AlZnMgCu)四元相、大量细小的短棒状MgZn_2相以及很少量的富Cu相;提高Zn和Mg元素的含量均会导致合金铸态组织中非平衡共晶相数量及非平衡共晶相厚度的增加,且在高Zn含量Al-Zn-Mg-Cu系合金中Mg元素影响更大,这与热力学计算结果基本一致。各合金经过470℃/24 h均匀化处理后,Al-9.2Zn-2.0Mg-1.8Cu合金回溶完全,Mg和Zn元素含量更高的合金回溶不充分,组织中仍存在一定数量的(AlZnMgCu)四元相,其中,在高Zn含量Al-Zn-Mg-Cu合金中Mg元素的增加尤其不利于均匀化的进行。
Al-9.2Zn-2.0Mg-1.8Cu alloy as the base alloy, a total of three kinds of chemical composition of the alloy designed, the use of OM, SEM, XRD and DTA (DSC) and Pandat thermodynamic calculations, the effects of Zn and Mg on the as-cast and homogenized microstructures of Al-Zn-Mg-Cu alloys with high Zn content were investigated. The results show that the second phase in the as-cast alloy mainly includes the unbalanced eutectic (AlZnMgCu) quaternary phase, a large number of small short rod-shaped MgZn 2 phases and a small amount of Cu-rich phase. Increasing the content of Zn and Mg elements will lead to The amount of non-equilibrium eutectic phase and the thickness of non-equilibrium eutectic phase in the as-cast alloy increase more, and the influence of Mg element in Al-Zn-Mg-Cu alloy with higher Zn content is larger, which is consistent with the thermodynamic calculation. After all the alloys were homogenized at 470 ℃ for 24 h, the Al-9.2Zn-2.0Mg-1.8Cu alloy was completely dissolved back and the alloy with higher Mg and Zn contents was not well-dissolved. There was still a certain amount of AlZnMgCu) ternary phase. Among them, the increase of Mg element in Al-Zn-Mg-Cu alloy with high Zn content is not conducive to the homogenization.