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

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 C for 20 h, T phase is completely dissolved back into matrix and no S phase is observed, with Al7Cu2Fe and Al8Cu4Ho 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 Al3Ho also contributes to the increase in both micro -hardness and electrical conductivity during homogenization at 475 degrees C for 5 similar to 20 h. Finally, through homogenization kinetic analysis, the appropriate homogenization parameter is determined as 470 similar to 475 degrees C120 similar to 25 h.