Post-heat treatment of laser powder bed fusion Al-Mn-Sc alloy: synergetic enhancement of mechanical property and corrosion resistance

Conventional isothermal aging (IA) for Al-Mn-Sc alloy processed by laser powder bed fusion (LPBF) can significantly improve mechanical properties but will reduce the corrosion resistance of the alloy. In this work, a novel heat treatment of non-isothermal aging (NIA) was applied to Al-Mn-Sc alloy to simultaneously enhance strength and corrosion resistance, and a comparative analysis was conducted between NIA specimens and IA samples. After NIA, the yield strength of the LPBF Al-Mn-Sc alloy increased from 460 MPa to 586 MPa, approaching the yield strength of 582 MPa observed during IA. However, the elongation of the NIA sample (14.8%) closing to as-built sample was higher than that of IA sample (10.7%). The intergranular corrosion results indicate that the maximum corrosion depth of the NIA sample (20 µm) is slightly smaller than that of the as-built sample (39 µm), but significantly smaller than that of the IA sample (175 µm). The corrosion and strengthening mechanisms of the three types of samples were revealed by analyzing the bonding zone and the interior of the melt pools. The rational regulation of grain boundary precipitates in the melt pool and bonding zone of NIA sample is critical to achieving excellent mechanical properties and corrosion resistance.