Shibaura Institute Researchers Develop Conductive, Corrosion-Resistant Coating for Lightweight Magnesium Alloys

Researchers at Japan's Shibaura Institute of Technology (SIT) have engineered a low-temperature chemical coating technique that makes lightweight magnesium alloys both highly corrosion-resistant and electrically conductive. Led by Professor Takahiro Ishizaki, the team developed a two-step steam-assisted solvothermal (SAS) process designed to unlock magnesium's potential in advanced energy conversion and storage applications, as first reported by TechXplore.

Magnesium alloys feature the highest strength-to-weight ratio among structural metals, making them ideal candidates to lighten hardware components in clean-technology systems. However, their industrial deployment in acidic operational environments—such as polymer electrolyte fuel cells (PEFCs)—has historically been stymied by severe susceptibility to corrosion. Furthermore, standard protective coatings and natural magnesium oxides are electrically insulating, creating a persistent engineering tradeoff between conductivity and material protection.

To bypass this conflict, the SIT research team created a synthesis route operating at significantly lower thermal thresholds than traditional ceramic coating techniques. Conventional ceramic synthesis typically demands processing temperatures surpassing 1,300 K, which inflicts severe thermal damage on magnesium substrates. The new SAS process achieves chemical conversion at just 453 K, preserving the structural integrity of the underlying metal while building a durable ceramic layer.

The SAS methodology begins with a steam treatment step that generates a dense magnesium hydroxide precursor layer across the alloy surface. Next, solvothermal growth converts this precursor into a magnesium ferrite layer via a controlled dissolution-precipitation mechanism, where dissolving magnesium ions combine with iron species. A final calcination phase at 773 K enhances the coating's crystal structure, fusing particles and fortifying grain connections to form a dense, ordered ceramic network.

Testing on AZ91D magnesium alloy samples yielded significant performance improvements over untreated metal and traditional double hydroxide coatings. Under electrochemical evaluation in a pH 3 sulfuric acid solution, the 453 K SAS coating achieved an ultralow corrosion current density of approximately 2.42 × 10⁻⁸ A cm⁻². Additionally, the continuous ceramic structure produced a sheet resistance of 4.40 × 10⁶ Ω/sq., establishing electrical pathways across the surface. During long-term testing, the treated material maintained chemical stability and suppressed iron ion release over 200 hours of acidic immersion.

"Our objective was to overcome the long-standing conflict between corrosion resistance and electrical conductivity on magnesium alloys without exposing the substrate to damaging high temperatures," said Ishizaki, a professor at SIT's College of Engineering. "By combining steam conversion with solvothermal growth, we created a highly crystalline spinel coating through controlled interfacial reactions at temperatures compatible with lightweight magnesium."

The researchers published their findings in the journal Surface and Coatings Technology alongside lead author Yuki Atsuumi. The team anticipates that the coating could allow lightweight magnesium components to replace heavier stainless steel, titanium, or carbon composite bipolar plates and interconnects in PEFCs. Beyond fuel cells, the surface engineering approach holds potential utility for hydrogen-fueled automobiles, aerospace structures, and industrial machinery operating in corrosive processing settings.

"Our innovation holds significant potential for next-generation energy conversion and storage systems in the automotive and aerospace sectors and offers a protective and conductive ceramic coating for various magnesium components exposed to aggressive acidic industrial processing environments," Ishizaki noted. The research team plans to focus future optimization work on improving coating adhesion and pore sealing to maximize practical operational lifespan.