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

Abstract

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.

In-situ grown super- or hydrophobic Mg-Al layered double hydroxides films on the anodized magnesium alloy to improve corrosion properties

“…However, the protection against general corrosion and galvanic corrosion remains a great challenge by simple alloy development. Therefore, the other effective way is surface treatments for forming the uniform, adherent, pore-free or even self-repairing films to effectively protect underlying Mg substrates from the galvanic corrosion [8].Various techniques, including anodizing [9,10], chemical conversion films [11,12], superhydrophobic films [13,14], electro-or electroless metal plating [15,16] anions [18,19].…”

Formation Process of an LDHs Coating on Magnesium Alloy by a CO2 Pressurization Method

“…Although chromate chemical conversion treatment has a high-performing corrosion resistance for magnesium alloys, hexavalent chromium (Cr 6+ ) has been gradually banned, since it is toxic and harmful for the environment; hence the development of new ways towards chromium-free chemical conversion treatments [20][21][22]. Chromium-free acid salt treatment includes: phosphate conversion coating [23,24], phosphate-permanganate conversion coating [25][26][27], stannate conversion coating [28,29], vanadate conversion coating [30,31], cerium conversion coating [32,33], lanthanide conversion coating [34], hydrotalcite surface coating, and so forth [35,36]. Hydrotalcite coating has attracted much attention, due to its unique intercalation structure and its environmentally friendly properties [37][38][39][40][41][42][43][44][45][46][47][48][49][50].…”

Anticorrosion Performance of LDH Coating Prepared by CO2 Pressurization Method

“…However, chromate is toxic to the environment and hazardous to human beings, leading to it being banned in recent years. Lately, focus has turned to conversion coating that contains no chromium [12,19,20], such as phosphate [21,22], phosphate-permanganate [23][24][25], stannate [26,27], vanadate [28,29], cerate [27,30], lanthanite [31], and LDHs surface coatings [32][33][34][35][36]. Of these, LDH surface coating, as an environmentally friendly coating, has attracted more attention as it brings no pollution to the environment.…”