Synergistic enhancement of strength and corrosion resistance in LPBF Al-Mg-Sc-Zr-Si-Mn alloy by precipitation regulation

This study systematically investigated the effects of microalloying elements Si and Mn on the microstructure evolution and properties of Al-4.5Mg-0.62Sc-0.27Zr-0.47Si-0.47Mn (wt%) alloy formed by laser powder bed fusion (LPBF). The introduction of Si and Mn aimed to control the formation of Mg₂Si and Al₆Mn precipitates through heat treatment, thereby strengthening the matrix while regulating the corrosion path. The results showed that the tensile strength of the as-built (AB) state was 322 MPa, and the corrosion current density (icorr) was 0.309 μA/cm². The results indicated that compared with the as-built state, the low-temperature secondary aging (T6-1) significantly improved the alloy performance: its tensile strength reached 351 MPa, an increase of approximately 9% compared to the as-built state and 23% compared to the traditional T6 treatment. Meanwhile, the corrosion current density decreased to 0.209 μA/cm², a reduction of approximately 32% compared to the as-built baseline. This simultaneous improvement in performance was attributed to the microstructure evolution induced by the T6-1 treatment: it not only promoted the formation of high-density intragranular β'' strengthening phases but also transformed the originally continuous Al₆Mn/Mg₂Si grain boundary network into discrete particles through the Ostwald ripening mechanism. This microstructure evolution effectively blocked the corrosion path and reduced the potential difference between the matrix and the grain boundaries. This study revealed the optimization mechanism of breaking the “strength-corrosion resistance” trade-off relationship in aluminum alloys by synergistically regulating the morphology of precipitates through microalloying and multi-stage heat treatment.