The novel strategy for enhancing mechanical properties and corrosion resistance via regulating multi-scale microstructure characteristics in Al-Si-Cu-Mg-Zr cast alloy

High strength and low corrosion resistance are always the contradiction in Al-Si-Cu-Mg cast alloy due to introducing high Cu and Mg levels. In this work, the new strategy was achieved for enhancing corrosion resistance and mechanical properties by regulating multi-scale microstructure characteristics in Al-9Si-4.2Cu-0.25Mg-Zr alloy. Electrochemical and corrosion morphology results indicate that the addition of Zr significantly enhances the corrosion resistance of the alloy. The grain refinement inhibits the charge transfer process between cathode phases and the matrix is the main reason at the Zr level of less than 0.15%. When the Zr level is up to 0.3%, the multi-scale synergistic effect of grain refinement and passive film enhancement significantly inhibits the corrosion process. Moreover, 0.3%Zr addition increases the yield strength to 419 MPa, tensile strength to 490 MPa, and the acceptable fracture elongation to 3.8%. The strengthening of mechanical and corrosion properties originates from the nano-Al3Zr precipitates after T6 treatment. This study provides a novel micro-mechanism and design strategy for simultaneously improving corrosion resistance and enhancing the mechanical properties of Al-Si-Cu-Mg cast alloy.