Synergistically enhancing corrosion resistance and formability potential in low-alloyed Mg alloys by regulating existence state of Ca

The inherently poor corrosion resistance and low formability of magnesium (Mg) alloys fundamentally constrain their wider application, particularly the challenge of simultaneous enhancement. In this work, we fabricate a low-alloyed Mg-1Sm-0.8Mn-0.5Ca-0.4Zn extruded alloy and specifically focus on the influence of the existing states of Ca in the microstructure. By developing a simple heat treatment to effectively tailor Ca into grain boundary segregation, we propose a novel strategy that synergistically enhances both corrosion resistance and formability potential — achieving an exceptional combination of low corrosion rate (0.35 mm y -1 ), high elongation (46%), and large yield-to-tensile strength difference (91 MPa). The results demonstrate that the transition of Ca from Mg 2 Ca phase to grain boundary segregation substantially suppresses micro-galvanic corrosion, nearly doubling the corrosion resistance. Furthermore, studies reveal that Ca-segregated grain boundaries effectively activate pyramidal slip at one side of the grains with low m ' value, contributing to the enhanced ductility. This study provides important insights for the development of Mg alloys with high corrosion resistance and high formability.