Ho添加对Al-Zn-Mg-Cu合金均匀化热处理过程中微观组织和性能演变的影响

Microstructure and Property Evolution of Al-Zn-Mg-Cu Alloy with Ho Addition During Homogenization

通过SEM、OM和DSC,研究添加Ho的Al-Zn-Mg-Cu合金均匀化热处理制度,测试不同均匀化热处理过程中合金的电导率和硬度变化。结果表明,铸态合金中存在4种第二相:T(AlZnMgCu),Al7Cu2Fe,Al8Cu4Ho及S (Al2CuMg),第二相导致合金元素分布存在严重微观偏析。合金在475℃均匀化热处理20 h后,T相完全回溶基体且未观察到S相,仅剩余Al7Cu2Fe和Al8Cu4Ho。硬度和电导率随T相的回溶而变化,T相的回溶使得合金硬度升高,电导率降低。同时,在475℃均匀化热处理5~20 h过程中,Al3Ho相析出,这一现象引起硬度和电导率的升高。结合均匀化动力学分析,确定合金适宜的均匀化热处理制度为470~475℃/20~25 h。

Homogenization treatment for Al-Zn-Mg-Cu alloy with Ho addition was investigated by scanning electron microscope(SEM), optical microscope(OM), and differential scanning calorimeter(DSC). Electrical conductivity and micro-hardness were tested during different homogenization processes. The results show that there are four kinds of second phases in as-cast alloy: T(AlZnMgCu), Al7Cu2Fe, Al8Cu4Ho and S(Al2CuMg), which cause severe micro-segregation in microstructure. After homogenization treatment at 475 ℃ for 20 h, T phase is completely dissolved back into matrix and no S phase is observed, with Al7Cu2Fe and Al8Cu4 Ho remaining. Micro-hardness and electrical conductivity are associated with vibration of T phase, dissolution of which can increase micro-hardness and decrease electrical conductivity. Besides, precipitation of Al3 Ho also contributes to the increase in both micro-hardness and electrical conductivity during homogenization at 475 ℃ for 5~20 h. Finally, through homogenization kinetic analysis, the appropriate homogenization parameter is determined as 470~475 ℃/20~25 h.