Effects of the Quenching Rate on the Microstructure, Mechanical Properties and Paint Bake-Hardening Response of Al-Mg-Si Automotive Sheets

The quenching rate of Al-Mg-Si alloys during solution treatment is an important parameter for the automotive industry. In this work, the effect of the different quenching rates on the microstructures, mechanical properties, and paint bake-hardening response of Al-Mg-Si sheets was studied. Large dimples form on the fracture surface of a sample at a quenching rate of 0.01 degrees C/s. When the quenching rate increased to 58.9 degrees C/s, the dimples became smaller. The recrystallized grains and textures were slightly affected by quenching rates beyond 1.9 degrees C/s. Thus, higher r values of the samples were achieved with slower quenching rates. Furthermore, only the Al(FeMn)SiCr insoluble phases were observed in samples with a rapid quenching rate. Sufficient solute atoms and vacancies resulted in the improvement of the precipitation kinetics and paint bake-hardening capacity for Al-Mg-Si sheets at rapid rates. With a decrease in the quenching rate, the formation of the rod-like coarse beta' phases consumed many solute atoms and vacancies, leading to the deterioration of the paint bake-hardening capacity. This study provides a critical reference on quenching rates for industrial practices, so that good mechanical properties can be achieved using precision control of the quenching process.