The effect of quenching rates on microstructure and mechanical properties of an Al-Si-Cu-Mg alloy

The effect of quenching rates after solid solution treatment, i.e., water-quenching (WQ) and wind-cooling (WC) on the precipitation behavior during subsequent artificial aging and mechanical properties of aged Al-Si-Cu-Mg alloys at room temperature and 150 °C–300 °C have been investigated. Compared with the peak-aged WC alloy, the number density of precipitates in the peak-aged WQ alloy is higher. After further holding at 300 °C for 10 min, plenty of metastable Q', θ' and β'' phases have transformed into equilibrium phases (Q, θ and β), with some also dissolved. However, the number density of precipitates in the peak-aged WQ alloy with holding at 300 °C for 10 min is relatively higher. The results demonstrate that the age hardening response rate and peak hardness of the WQ alloy during aging are much higher. At room temperature, the peak-aged WQ alloy owns a higher yield strength (YS) of ∼324 MPa than that of the peak-aged WC alloy (∼301 MPa), which can be attributed to the enhanced precipitation of Q' and θ' phases. The ultimate tensile strength (UTS) and YS decrease as the tensile temperature increases. However, the strength of the water-quenched alloy is higher than that of the wind-cooled alloy, due to the retention of more precipitated phases.