Influence of surface chemistry on the formation of crystalline hydroxide coatings on Mg alloys in liquid water and steam systems

•A steam treatment was employed to provide protective coatings to Mg-alloys.•The steam treatment was conducted in stainless steel autoclaves at 150 °C for 3 h.•The formation mechanism of the steam coatings on various Mg-alloys was explored.•Steam is more favourable than liquid water regarding to coating properties.•Alloying elements also influence coatings properties.