Effect of Solution Temperature and Quench Delay on the Microstructure and Mechanical Properties of an Extruded Al-Mg-Si-Cu-Mn alloy

The effect of solution temperature and quench delay on the microstructure and mechanical properties of an extruded Al-Mg-Si-Cu-Mn alloy was investigated by employing differential scanning calorimetry, transmission electron microscopy, hardness test, and tensile test. The extruded specimens were held at 500 and 540 degrees C, respectively, for 80 min for solutionizing and then immediately quenched in water or exposed to air for 30 sec before water quenching. Each specimen was further heat treated at 180 degrees C for 6 hr for artificial aging. Quantitative analysis of the precipitates in the artificially aged specimens was performed using high -angle annular dark field -scanning transmission electron microscopy (HAADF-STEM) and fast Fourier transforms (FFT) analysis. Solution treatment at 540 degrees C led to higher number density of precipitates and higher strengths after artificial aging, compared with solution treatment at 500 degrees C. Quench delay resulted in a lower number density of precipitates and lower strengths after artificial aging. The specimen solution treated at 540 degrees C with no quench delay showed the largest peak area of precipitate formation in the differential scanning calorimetry, and concurrently exhibited the highest strengths after artificial aging. Strength reduction by quench delay was higher in the specimen solution treated at 500 degrees C than that treated at 540 degrees C; this was consistent with the results of higher reduction in the number density of precipitates.