Effect of Sn on microstructure and corrosion behaviors of Al-Mg-Si alloys

Abstract x wt% (x = 0, 0.03, 0.40) Sn addition in Al-Mg-Si alloys were prepared to investigate the effect of Sn on the performance of Al-Mg-Si alloys. Optical microscope (OM), scanning (SEM) and transmission electron microscope (TEM) were applied to observe the microstructure of these alloys. X-ray diffraction (XRD) was used to investigate the phase component among different alloys. Electrochemical polarization measurements and intergranular corrosion test were used to investigate the corrosion behaviors of these alloys. The experimental data shows that 0.03 wt% Sn can slightly enhance mechanical properties and corrosion resistance of Al-Mg-Si alloys because of the smaller precipitate free zones (PFZ) area and grain boundary refinement. Higher Sn addition (0.4 wt%) may cause detrimental effect on both mechanical properties and corrosion resistance of Al-Mg-Si alloys. Excess Sn tends to replace part of Si in Mg2Si phase and forms Mg2(Si,Sn) phase which is thought to be an anodic phase compared to Al matrix. Electrochemical measurements may not comprehensively reveal the overall corrosion processes, such as de-alloying process of Mg2(Si, Sn) phase and thus enrichment of Sn which leads to much faster dissolution of Al.