To achieve weight reduction of vehicles, multi-material body structures—combining conventional steel with other materials such as Al and Mg alloys—are increasingly being adopted. Consequently, there is a demand to establish integrated corrosion protection technologies for multi-material automotive body structures. Layered double hydroxides (LDH) are attracting attention as corrosion-resistant coating materials because they can intercalate metallic corrosion inhibitors at their interlayers and are expected to release these inhibitors through ion exchange with external chloride or carbonate ions. However, methods for LDH coating and inhibitor loading have not yet been established, and it remains unclear whether the release of inhibitors via ion exchange occurs under corrosive environments.
Our research addresses these challenges by preparing LDH loaded with corrosion inhibitors and developing an electrophoretic co-deposition (electrodeposition) technique for coating metal surfaces. Compared to conventional methods, which load inhibitors via ion exchange after LDH deposition, our approach allows for broader inhibitor selection and is expected to facilitate coating on multi-material structures. We have demonstrated that LDH coatings loaded with inhibitors on Mg alloy surfaces exhibit higher corrosion resistance than non-inhibitor LDH coatings. Furthermore, through Raman spectroscopic measurements before and after corrosion testing of Al alloys coated with nitrate-type LDH, we have, for the first time, shown that anion exchange occurs in LDH and releases the loaded inhibitors under corrosive conditions.

Mg alloys are promising biodegradable metallic materials that gradually dissolve and are resorbed in the body as the affected area heals, making them candidates for applications such as bone fixation plates and screws and vascular stents. However, Mg alloys are susceptible to rapid corrosion during the initial implantation period, which can cause strength degradation and gas accumulation and potentially affect the healing process. To suppress initial corrosion and promote integration with surrounding bone, we are developing coatings of hydroxyapatite (HAp) and carbonate apatite (CAp), which have similar compositions to the main constituents of bone. Whereas HAp remains stable in vivo for extended periods, CAp is gradually resorbed by osteoclasts and replaced by bone tissue. We have conducted animal implantation studies with Mg alloys coated with HAp/CAp and demonstrated that these coatings suppress corrosion and enhance new bone formation. In the case of CAp coatings, gradual resorption of the coating within the bone was observed. Furthermore, we have clarified that the corrosion resistance and bone resorbability of CAp coatings are dependent on their carbonate content.