Al-4.5Cu-3.5Zn-0.5Mg铸造铝合金的均匀化工艺及组织演变

Homogenization process and microstructure evolution of Al-4.5Cu-3.5Zn-0.5Mg as-cast alloy

对Al-4. 5Cu-3. 5Zn-0. 5Mg铸态合金进行不同双级均匀化处理,采用扫描电镜、电子探针显微分析仪、差示扫描量热仪和光学显微镜等,研究了该合金的铸态组织及其在均匀化过程中的组织演变。结果表明:铸态组织主要由α-Al、粗大Al2Cu相以及少量AlZnMgCu、Al7Cu2Fe相组成,合金元素枝晶偏析严重。经470℃×12 h均匀化处理后,AlZnMgCu相已基本回溶至基体;第二级均匀化温度由490℃逐渐升高到520℃或者延长保温时间,Al2Cu相逐渐回溶至基体,合金元素分布趋于均匀。合金过烧温度为520℃,最佳双级均匀化制度为470℃×12 h+510℃×32 h,该制度与均匀化动力学计算结果基本一致。

The microstructure of an as-cast Al-4. 5Cu-3. 5Zn-0. 5Mg alloy and its evolution during different two-step homogenization treatments were studied by means of scanning electron microscope( SEM),electron probe micro-analyzer( EPMA),differential scanning calorimeter( DSC) and optical microscope( OM). The results show that the as-cast microstructure is mainly composed of α-Al and coarse Al2Cu phase with a small amount of AlZnMgCu and Al7Cu2Fe phases,and severe dendritic segregation of alloying elements exists in the alloy ingot. After homogenized at 470 ℃ for 12 h,the AlZnMgCu phase is mainly dissolved into the matrix. The Al2Cu phase is gradually dissolved into the matrix by increasing the second-step homogenization temperature from 490 ℃ to 520 ℃ or prolonging the holding time,and all the alloying elements tend to be homogenized. The over burnt temperature of the alloy is 520 ℃,and the proper homogenization process is 470 ℃ × 12 h + 510 ℃ × 32 h,which agrees well with the kinetic calculation results of homogenization.