On the Improved Mechanical Properties and Corrosion Resistance in LM6 Alloy Through Eutectic Modification

Abstract

The present study investigates the effect of microstructure modification on the mechanical properties and corrosion resistance of the near-eutectic LM6 Al-Si alloy. The addition of 130 ppm of Sr significantly modifies the microstructure, transforming the flake-like morphology of eutectic Si into a fine fibrous form, promoting the formation of equiaxial dendrites of α-Al and reducing the size of the flake-like β-phase. These changes result in improved mechanical properties, including an increase in yield strength (106–113 MPa), ultimate tensile strength (155–174 MPa), and elongation (2.6–3.2%). Fractography analysis reveals that the LM6-Sr alloy exhibits a ductile fracture mode, whereas the unmodified LM6 alloy fails in a brittle manner. Despite a slight increase in porosity from 2.8% to 4.7%, the morphological modifications dominate the negative impact of porosity, resulting in an overall increase in mechanical properties. Additionally, the corrosion resistance of the LM6-Sr alloy was significantly improved, with a reduction in corrosion rate from 0.0593 mm/year to 0.0266 mm/year. Electrochemical impedance spectroscopy studies further confirmed enhanced corrosion resistance, showing higher charge transfer resistance (R_ct), oxide resistance (R_ox), and total impedance (Z_mod) for the LM6-Sr alloy.