KCl, KNO₃, and Annealing for Modifying the Morphology and Properties of Ca-P Layers on Mg Alloy

The aim of the work was to obtain a dense and uniform calcium phosphate (Ca-P) coating on the studied magnesium (Mg) alloy using simple methods that are easy to implement on an industrial scale. In this work, Ca-P layers were prepared on the surface of a Mg alloy. The simple wet chemical method based on immersion in an aqueous solution was used to prepare the Ca-P layer on the Mg alloy (AM60) surface. The effect of chemical modification by potassium chloride (KCl) and potassium nitrate (KNO₃), as well as annealing on the morphology of the phosphate layers on the AM60 alloy, was determined, as well as the impact of this layer on the evolution of hydrogen in Ringer’s solution. The addition of KCl and KNO₃ to the phosphating bath caused coagulation and agglomeration of the elements of the Ca-P coating. Consequently, the flake structure of the Ca-P coating changes into two types of structures: chrysanthemum and rhombohedral. Annealing at 150 °C for 3 h allows one to obtain a dense and uniform Ca-P coating on the studied Mg alloy. The Ca-P coating obtained by annealing at 150 °C can greatly decrease the hydrogen evolution rate of AM60 alloy in Ringer’s solution to 0.02 ml/cm²/day, which is similar to the safe amount of hydrogen for the human body (H₂ ≈ 0.01 ml/cm²/day).