Influence of minor La additions and melt purification on the corrosion behavior and mechanical properties of Zn–7Al–3 Mg alloy
摘要
This study aimed to clarify the synergistic effects of minor La addition, Al–Ti–B grain refinement, and melt purification on the solidification microstructure, corrosion behavior, and mechanical properties of Zn–7Al–3 Mg alloy. Zn–7Al–3 Mg alloys containing 0–0.20 wt.% La were prepared by casting with Al–Ti–B grain refinement. The 0.15 wt.% La alloy underwent additional argon degassing and slag removal (melt purification). Microstructure, phase constitution, corrosion behavior, corrosion-product evolution, and compressive properties were characterized by OM, SEM/EDS, XRD, electrochemical testing, immersion weight-loss testing, XPS, and room-temperature compression testing. La addition refined the dendritic structure and promoted a more uniform distribution of secondary phases, with the most pronounced refinement at 0.15 wt.% La. Melt purification further reduced porosity and increased the fraction of equiaxed grains. Electrochemical testing showed that the melt-purified 0.15 wt.% La alloy achieved an Ecorr of − 1.088 V and an Icorr of 1.26 × 10⁻5 A cm⁻2, lowering the 42-day corrosion rate to 0.0873 g m⁻2 h⁻1. Compression tests indicated the highest strength of 730 MPa and yield strength of 620 MPa for the same alloy. The improved corrosion resistance and mechanical properties were attributed to the synergistic effects of La-induced microstructural regulation, Al–Ti–B-assisted grain refinement, and melt purification-induced defect reduction. These effects refined the solidification structure, homogenized the secondary phases, and promoted the formation of a denser and more stable corrosion-product film. The combined use of 0.15 wt.% La and melt purification provides an effective strategy for improving the comprehensive performance of Zn–Al–Mg alloys.
Graphical abstract