Corrosion protection of magnesium and its alloys by metal phosphate conversion coatings

This work describes a group of metal phosphate films, including calcium, manganese and strontium phosphate conversion coatings, for corrosion protection of magnesium alloys. These films have been developed by a process that is simple for implementation, chemically stable and non-toxic. The preparation and characterisation of these coatings, along with evaluation of their corrosion performance in 0·1M NaCl, are systematically described. Phase diagram of calcium phosphate was produced to elucidate the coating formation mechanism, which depends upon the chemistry of coating solution, in particular pH and ion concentration. A discussion of the advantages and disadvantages of the coatings is presented, along with perspectives for industrial applications.