Stannate and permanganate conversion coatings on AZ31 magnesium alloy

Surface modification of magnesium alloy AZ31 by hydrofluoric acid treatment and its effect on the corrosion behaviour

“…At low frequencies it is obvious that there is a decrease in the impedance, followed by an increase. This impedance decrease stands for the corrosion of the metal, and the subsequent increase indicates the deposition of corrosion products on the metal surface [8][9][10]. For all treated samples the Bode plots also show impedance at least one order of magnitude higher than that of an untreated sample.…”

“…Chemical species with a nobler potential can form a galvanic couple in which magnesium acts as an anode, and therefore its corrosion rate increases. This is one of the reasons why corrosion protection methods like plasma electrolytic oxidation [5][6][7], conversion coatings [8][9][10], polymeric coatings [11][12] and others are preceded by a cleaning procedure that may consist of a simple grinding and polishing process, blasting, or of chemical processes such as acid pickling.…”

Effective and Environmentally Friendly Nickel Coating on the Magnesium Alloy

“…However, some of methods include harmful chemicals such as chromate [2], fluoride [11], and vanadium [12], which is contrary to the environmental protection regulative [13]. In addition, conversion coatings based on stanate [14,15], rare elements [16], and ionic liquids [17], at this point, are not applicable for practical use. Also, a pretreatment including phosphate/phosphate-manganate [18], molten salt [19], and stearic acid [20] were reported.…”

“…Therefore, the tendency in the industry is to eliminate hexavalent chromium from the pretreatment procedures and replacement it with nontoxic and environmentally friendly compounds [8]. An environmentally friendly chemical deposition process is considered to be the one in which hydrofluoric acid is not used (or only a small amount is used) and chromate is replaced by stannates [15,23], phosphates permanganate [22,24], or molybdates [25].…”

A Blade-Abrading Method for Surface Pretreatment of Mg Alloys

“…However, since Mg alloys are electrochemically too active to be used without surface treatment in corrosive environments, their practical applications have been limited. Thus, many scientists have tried to develop surface treatment methods to improve corrosion resistance of Mg alloys [1][2][3][4][5][6][7][8][9] . For the surface treatment of Mg alloys, one of the most important and difficult steps is a pretreatment process by which clean and well-defined surface should be obtained.…”