Effect of heat treatment on microstructure and hardness of as-cast Al-Mg2Si-Eu alloy

To further improve the comprehensive performance of Al-15Mg2Si-0.1Eu alloy, T6 heat treatment was performed for as-cast Al-15Mg2Si-0.1Eu alloy. The influence mechanism of solid solution treatment on Mg2Si phase was revealed. The optimal heat treatment process for Al-15Mg2Si-0.1Eu alloy is solution treatment at 530 °C for 6 h and subsequently aging treatment at 175 °C for 8 h. A short solid solution time or a low solid solution temperature leads to insufficient dissolution of Mg2Si. Conversely, when the solid solution time is greater than 6 h or the solid solution temperature is higher than 530 °C, the microstructure exhibits coarsening. With an increase in aging time, GP zone, β″ phase, and β′ phase form within the matrix, corresponding to the under-aged, peak-aged, and over-aged stages respectively. The Al-15Mg2Si-0.1Eu alloy reaches its peak-aged state after aging treatment at 175 °C for 8 h, during which a large amount of fine dispersed β″ phase precipitates within the matrix. Following this 8 h aging treatment, the alloy reaches its maximum hardness of 106 HV.