Replacement for Hexavalent Chromium Conversion Coatings for Magnesium and Zinc-Nickel

The European Union''s RoHS and WEE Directives mandated the elimination of the carcinogenic, hexavalent chromium coatings for metals, including magnesium and zinc-nickel plated substrates.  The purpose of this project is to find chemistry that will meet requirements of industry performance specifications and of the mandate.  METALAST intends to explore trivalent chromium in conjunction with two other components to build a corrosion resistant, adhesive, environmentally-friendly coating for Zn-Ni plated steel and magnesium substrates.  METALAST is planning to utilize various techniques for quantitative and qualitative observation of corrosion, surface energy, and other properties that the solutions impart to the substrates. The trivalent chemistry is expected to impart similar anti-corrosion characteristics as the proven, hexavalent chromium technology.  The other two components are for increasing the coating thickness and improving thermal stability.  Methodology for testing will include EIS, SEM/EDX, OCP, dyne analysis, and chemical dissolution, salt spray, and potentiodynamic polarization testing.  In doing so, the objectives for performing the research are to determine which components of the intended formula are most influential to corrosion and adhesive behavior, and at which operating parameters, as well as determine whether the formulas, will meet common specifications of the industry the METALAST intends to pursue upon commercialization. BENEFIT: Military, aerospace, aviation and commercial industries requiring hexavalent chromium on Zinc-Nickel and magnesium alloys would most likely change or alter their respective specifications and require a trivalent chromium product. Most manufacturers who require chromate conversion on their parts will opt for trivalent chromium for compliance purposes.