Bake Precipitation Behavior in AA5182 Sheet for Can End Stock

Abstract

By means of Vickers hardness tester, optical microscope (OM), scanning electron microscope (SEM), X-ray diffraction (XRD) and high resolution transmitted electron microscope (HRTEM), the bake softening and precipitation behaviors of AA5182 H19 sheet for can end stock at 205°C and 249°C were investigated. All specimens at both temperatures showed recovery and bake softening phenomenon, which meaning the dislocation density and HV decreased. However, the specimens baked at 205°C showed higher recovery impediment, because the bake softening curve departed from the dynamic laws when it had less amount of recovery than the specimens baked at 249°C. The hardness was higher for the specimen baked at 205°C compared with the specimen baked at 249°C, even both specimens had the same dislocation density measured by XRD. Further observations revealed that the precipitated particles in the specimens baked at 205°C distributed along the shear bands. The precipitates were needle shape with the length of 5-15 nm and the width of 5-10 atom layers, which occurred mostly in the area with higher dislocation density. These precipitates were guessed to be Al-Mg binary phases, which could contribute to the higher hardness of the specimens baked at 205°C.