Comparative effects of trace Ce or Y addition on microstructure and corrosion resistance of as-extruded Mg-1Sn-0.5Ca alloy: Role of secondary phase and oxide film

This study systematically examines the effects of 0.3 wt% Ce and Y additions on the microstructure and corrosion behavior of as-extruded Mg-1Sn-0.5Ca (TX10) alloys. Experimental results reveal that alloying (Ce or Y element) can induce grain refinement, with average grain size decreasing from 15.21 μm in the base alloy to 11.19 μm (Y-containing alloy) and 9.20 μm (Ce-containing alloy). As for the variation of secondary phase after Y or Ce alloying, in terms of secondary phase species: All three alloys are dominated by CaMgSn, while Ce, Y elements are mostly present in solid solution.in the secondary phase distribution: Compared with the TX10 alloy, the addition of Ce results in an increase in the CaMgSn phase with a more uniform distribution. However, the addition of Y causes local aggregation of the CaMgSn phase. Regarding corrosion performance, Ce addition significantly enhances corrosion resistance by reducing the corrosion rate from 2.90 mm·y⁻¹ to 1.28 mm·y⁻¹. This improvement primarily originates from three mechanisms: 1) homogenized distribution of CaMgSn phases, 2) suppression of porous Mg(OH)₂ formation, and 3) development of a dense CeO₂ protective layer that effectively impedes Cl^⁻ penetration. Conversely, Y addition increases the corrosion rate to 5.22 mm·y⁻¹ due to localized clustering of CaMgSn phases and formation of porous corrosion products, which accelerate the transition from uniform micro-galvanic corrosion to severe localized attack.