Sn–Sc microalloying-induced property improvement and micromechanisms of an Al–Mg–Si alloy

Microalloying is of great importance for the property modulation of lightweight high-strength aluminum alloys. Little is known, however, about the properties and micromechanisms of Al-Mg-Si alloys microalloyed with Sn and Sc. In this work, the property changes of Al-0.5Mg-0.4Si (wt%) alloys induced by 0.1Sn and 0.1Sn-0.1Sc (wt%) additions and underlying alloying mechanisms are revealed by atomic-scale transmission electron microscopy and first-principles calculations. The results show that the Sn-Sc coaddition results in a decreased diameter and an increased number density of the Sc-containing constituent particles of Mg2Si and Mg2(Si,Sn), as compared to the sole Sn addition. The featured Si-site columns in β'', B' and β' structures can be occupied by Sn and Sc. Substantial peak-aging β'' needles with confined cross-sectional coarsening are observed for the Sn-Sc containing alloy compared to the Sn containing alloy. The modified constituent particles and precipitates improve the plasticity and strength of peak-aging Al-Mg-Si-Sn-Sc alloy. The elevated peak-aging corrosion resistance and over-aging thermal stability of Al-Mg-Si-Sn-Sc alloy are associated with the sparse Sc-containing Mg2(Si,Sn) grain boundary precipitates and low strain filed of Al matrix around the β' containing Sn/Sc, respectively. The obtained results are hoped to guide the design of high-performance Al alloys.