Corrosion resistance and hydrogen generation performance of Mg-Li-Al-Zn alloys: Role of second phase and grain size

This study systematically compares the corrosion resistance and hydrogen generation performance of Mg‑1Li‑9Al‑1Zn (A2) and Mg‑1Li‑1Zn (A1) alloys by integrating microstructure analysis, hydrogen evolution tests, and electrochemical measurements. Results indicate that the A2 alloy exhibits a significantly poorer corrosion resistance, together with enhanced hydrogen generation performance relative to the A1 alloy. This improvement stems from its refined grain structure and the presence of the Mg₁₇Al₁₂ phase, both of which accelerate corrosion and promote hydrogen release. Within the A2 alloy, micro‑galvanic couples are established, where grain boundaries act as anodes, and the Mg₁₇Al₁₂ phase serves as the cathode. These microstructural features also facilitate the formation of a surface corrosion product layer. However, this layer is discontinuous and contains numerous micro‑cracks, which severely compromise its protective ability. Instead of resisting chloride ion (Cl⁻) attack, these cracks provide direct pathways for Cl⁻ to penetrate the alloy matrix. Consequently, the A2 alloy demonstrates inferior corrosion resistance but improved hydrogen generation performance.