Enhancing the bake-hardening responses of a pre-aged Al-Mg-Si alloy by trace Sn additions

Abstract Effects of additions of trace Sn on the bake-hardening responses of a pre-aged Al-0.85Mg-0.85Si (in wt%) alloy were investigated through mechanical tests, differential scanning calorimetry, electrical resistivity and transmission electron microscopy. Results indicate that trace Sn additions reduced the number density of pre-aging clusters by inhibiting the formation of unstable counterpart during pre-aging treatment, leading to low strength and high supersaturation of solute atoms. In a subsequent paint-bake treatment, the presence of highly supersaturated solute atoms and high concentrated free vacancies moderated the activation energy barrier of βʺ phase and thus kinetically accelerated the formation of βʺ. Consequently, the trace Sn additions enhanced the bake-hardening responses of the pre-aged alloys significantly. The Sn-containing pre-aged Al-Mg-Si alloys with low strength and great bake-hardening responses hold promising potential for automotive body skin applications.