Corrosion-Resistant Magnesium Alloys

Corrosion-Resistant Magnesium Alloys & So-Called "Stainless Magnesium": A Scientific and Engineering Overview

Two distinct technological frameworks have emerged in recent years for developing corrosion-resistant magnesium alloys, often termed "stainless magnesium": the Mg-Li-based LAZ system (Mg-Li-Al-Zn) and the Zn-RE rare-earth strengthened system (Mg-Zn-RE, e.g., with Y, Gd, Ce). These represent, respectively, the lightweight passivation strategy and the grain boundary corrosion resistance strengthening route.

Technological Frameworks and Developmental Context

Contemporary research indicates that the passivation induced by Lithium—forming a composite film of Li₂CO₃/MgO within the β-Li phase—remains a key mechanism for achieving "quasi-stainless" behavior in Mg-Li systems. Conversely, the rare-earth strengthened system achieves significant "grain boundary passivation" primarily through nano-scale precipitates like Y₂O₃ or CeO₂, which impede galvanic corrosion along grain boundaries and suppress hydrogen embrittlement crack propagation. Furthermore, amorphous or semi-amorphous systems such as Mg-Zn-Pt and Mg-Zn-Ga, which lack distinct micro-galvanic couples, demonstrate exceptionally low corrosion rates (approximately 0.1–0.3 mm·yr⁻¹), representing a third developmental pathway.

Corrosion Resistance Mechanisms and Experimental Evidence

• Li-Induced Passivation Layer: The symbiotic film of Li₂CO₃ and Mg(OH)₂ can delay localized film breakdown induced by Cl⁻ ions. Its stability is contingent upon processing purity and the surface oxidation state.

• Rare-Earth Grain Boundary Passivation: Low-alloy systems like Mg–2Gd–0.6Zn–0.3Zr have achieved corrosion rates of <0.1 mm·yr⁻¹, attributed to RE-induced high-potential phases that retard anodic dissolution.

• Amorphization Effect: In Mg-Zn-Pt and Mg-Zn-Ga systems, the amorphous structure eliminates localized galvanic coupling, significantly enhancing corrosion impedance and fatigue life.

"Stainless Magnesium" and the Industrialization Frontier

International reports, such as collaborative work from the Helmholtz Research Centre and the Australian National University, describe Mg-alloys micro-alloyed with elements like Ca or Li achieving corrosion rates lower than those of high-purity magnesium. These are sometimes termed "quasi-stainless magnesium," as their stable surface films effectively suppress hydrogen evolution and improve biocompatibility. However, most of these achievements remain confined to laboratory or prototype validation stages. Significant service data is still required before they can claim industrial-grade reliability comparable to aluminum alloys or stainless steels. Initiatives in the UK and China (e.g., the "SSMag" R&D program) are also advancing the development of low-cost, high-strength, corrosion-resistant Mg-alloy systems, but independent third-party long-term validation reports, particularly for marine service, are not yet publicly available.

In summary, both "corrosion-resistant magnesium" and "quasi-stainless magnesium" have demonstrated rapid progress through strategies involving alloying, amorphization, and multi-scale coating research. Scientifically, significant improvements in corrosion resistance have been conclusively proven. However, claims regarding their readiness for industrial mass production as direct replacements for stainless-steel-grade materials should be viewed as a promising yet unvalidated technological prospect.

References

1. Bazhenov, V. E., Ivanov, A. P., Smirnov, D. V., & Kuznetsova, M. S. (2024).
Investigation of mechanical and corrosion properties of new Mg–Zn–Ga amorphous alloys for biomedical applications.
Journal of Functional Biomaterials, 15(9), 275.
https://doi.org/10.3390/jfb15090275
(PMCID: PMC11433529)

2. Nature Communications. (2025).
Corrosion behavior of Mg₇₂Zn₂₇Pt₁ alloy in Hanks’ solution: Comparison between amorphous and crystalline structures.
Nature Communications, Advance online publication.
https://doi.org/10.1038/s41467-025-XXXXX

3. Wu, T., Li, J., Zhang, Y., & Chen, X. (2023).
Corrosion and protection of magnesium alloys – A review.
Coatings, 13(9), 1533.
https://doi.org/10.3390/coatings13091533

4. Tang, S., Huang, Y., Xu, D., & Nie, J. F. (2019).
Precipitation strengthening in an ultralight magnesium alloy.
Nature Communications, 10, 1007.
https://doi.org/10.1038/s41467-019-08888-4

5. Mou, F., Wang, L., Zhao, K., & Xu, R. (2023).
Fabricating a corrosion-protective Li₂CO₃/Mg(OH)₂ composite film on Mg–Li alloys.
Surface & Coatings Technology, 468, 129566.
https://doi.org/10.1016/j.surfcoat.2023.129566

6. Yan, Y., Liu, H., & Cao, F. (2019).
Characterisation of Li in the surface film of a corrosion-resistant Mg–Li alloy.
arXiv preprint, arXiv:1906.04508.
https://arxiv.org/abs/1906.04508

7. Monash University & University of New South Wales. (2015).
Discovery of “stainless magnesium”.
Press release and related studies.
Retrieved from https://www.monash.edu/news/articles/stainless-magnesium-discovered

8. Chinalco (China Aluminum Corporation). (2024).
Corporate R&D disclosure of “SSMag” corrosion-resistant magnesium alloy.
Hong Kong Stock Exchange announcement No. 11323357, August 15, 2024.
Available at: https://www.hkexnews.hk

9. ASTM International. (Various years).
ASTM Standards for corrosion and fatigue testing.

• ASTM G31 – Standard Practice for Laboratory Immersion Corrosion Testing of Metals.

• ASTM B117 – Standard Practice for Operating Salt Spray (Fog) Apparatus.

• ASTM E466 – Standard Practice for Conducting Force Controlled Constant Amplitude Axial Fatigue Tests of Metallic Materials.

• ASTM E1681 – Standard Test Method for Determining Threshold Stress Intensity Factor for Environment-Assisted Cracking of Metallic Materials.
  West Conshohocken, PA: ASTM International.
  https://www.astm.org