Effect of Solution Heat Treatment on Microstructure and some Properties of Al-Cu-Mg Alloy

This research paper examines the effect of different solution heat-treatment parameters (quenching media and aging time) on microstructure, mechanical and corrosion properties of Al-Cu-Mg alloy. Scanning electron microscopy and X-ray diffraction analysis results have shown that a precipitate phase [S phase (Al2CuMg)] gets formed in as-cast conditions, but undergoes dissolution during solution heat-treatment process. Water quenching after solution heat treatment does not allow the precipitates to get reformed because of the faster cooling rate. However, air cooling enables some precipitate phases to get formed due to its slow cooling rate. It has been observed that water-quenched samples exhibit higher hardness (100.6 +/- 0.6 HV1) than as-cast (93.3 +/- 0.5 HV1) and air-cooled (84.9 +/- 0.7 HV1) samples. Increase in aging time is observed to reduce Vickers hardness from 74.4 +/- 1 HV1 (for 2 h aging) to 67.1 +/- 0.5 HV1 (for 7 h aging) in case of solution heat-treated samples. Corrosion resistance is observed to improve after the solution heat treatment due to the dissolution of precipitate phase forms an almost single phase solid solution. A combination of solution heat treatment and water quenching is found to increase compressive stress (484.6 MPa to 508.4 MPa) and decrease strain (40.4% to 31.0%) as compared to the as-cast alloy. It is due to the formation of solid solution by the atoms constituting the precipitate phase (S phase (Al2CuMg)) as it undergoes dissolution during solution heat treatment. After aging (at 170 degrees C for 2 h), compressive stress reduces to 456.8 MPa and strain increases to 36.3% as compared to solution heat-treated samples.