RESEARCH THE INFLUENCE OF La, Ce ON THE MICROSTRUCTURE AND PHASE HARDNESS OF Al-5Zn-3.5Mg-1.2Cu ALLOY WHEN THERMAL- MECHANICAL

Abstract

The article presents about influence of aging temperature on the microstructure and hardness of Al-5Zn-3.5Mg-1.2Cu alloy after modification by Vietnam’s rare-earth, containing elements La, Ce. By analytical results of structure such as optical microscopy; XRD and SEM, the microstructure have identified. After modification by 0,21%La + 0,16%Ce, the grain size of this alloy is 48µm compare than the non-modification alloy. The experiment result shows that the heat treatment process of this alloy was annealing, quenching and aging, the aging process was determined at temperature 120^oC in 6 hours. After that, the grains size of modified alloy and aging treatment was ≈ 41,5μm meanwhile this value of the sample after quenching  ≈ 38,7 μm. In addition, after aging process the microstructure of alloy has intermetallic phases of Zn, Mg, Cu elements such as η(MgZn₂) và S(Al₂CuMg) phases distributed in the α-Al matrix. The hardness of α phase and intermetallic phase are 126 and 150HV.