Effect of Q-Al5Cu2Mg8Si6 phase on mechanical properties of Al-Si-Cu-Mg alloy at elevated temperature

The effect of Q-Al5Cu2Mg8Si6 phase on creep and tensile properties of Al-Si-Cu-Mg alloy at elevated temperatures was investigated. Microstructure observation clarifies that the Q-Al5Cu2Mg8Si6 phase is distributed in the Al matrix. The creep stress exponent is in the range of 4.20-4.67 and activation energy for creep varies from 218 to 226 kJ/mol with increasing the volume fraction of Q-Al5Cu2Mg8Si6 phase. The stress exponent and activation energy suggest that dislocation climb is the dominant creep mechanism. In addition, slight variation of the stress exponent and activation energy indicates that the creep mechanism do not change with the increase of Q-Al5Cu2Mg8Si6. The relation between the minimum creep rate and creep fracture life are fitted by Monkman-Grant equation, which indicates that the creep fracture life is increased with the increase of Q-Al5Cu2Mg8Si6 phase. The ultimate tensile strength at 250 °C increases from 157 MPa to 199 MPa with the volume fraction of Q-Al5Cu2Mg8Si6 phase varying from 3.2% to 6.4%. However, the ultimate tensile strength at 350 °C only increases 9 MPa with increasing the Q-Al5Cu2Mg8Si6 phase. The slight increase in ultimate tensile strength at 350 °C indicates that the Q-Al5Cu2Mg8Si6 phase is not effective in improving the ultimate tensile strength at 350 °C.