Absorbing Ca-P composites by Zr element in the alloy: A new method to improve the corrosion resistance of biodegradable Mg alloy

• Stable Ca-P corrosion layer with a thickness of 10.5 μm was formed by adding trace Zr. • Enhancing the long-term corrosion resistance of Mg alloys by the absorption of Ca-P layer. • The primary absorption mechanism of Ca-P layer is complexation reaction. • The nano-sized ZrO 2 transform from Zr-rich phase has strong adsorption of phosphate. Traditional alloying strategies for enhancing the corrosion resistance of biodegradable Mg alloys often face challenges in achieving a balance between biocompatibility and corrosion control. This study exploited the adsorption of ZrO₂ onto the calcium phosphate (Ca-P) layer to enhance the long-term corrosion resistance of a Mg alloy. The addition of trace Zr facilitated the thickening of the Ca-P salts adsorption layer formed during degradation. The results showed that Mg-Zn-Nd-Zr alloy with diffusely distributed nano Zr-rich phase presented higher corrosion rate in the short-term immersion due to the galvanic corrosion between the Zr-rich phases and the ɑ-Mg substrate. However, enhanced long-term corrosion resistance was observed, which is attributed to the presence of Zr. Nano Zr-rich phase facilitated the adsorption and deposition of Ca-P compounds, resulting in the formation of a more homogenous protective layer. And the Ca:P (atom ratio) is 1.54, close to that of hydroxyapatite structure. This study proposed and verified a new method to enhance the long-term corrosion resistance of biomedical Mg alloys, promising for future application.