Chemical conversion coatings have attracted significant interest in the study because of their potential to improve the corrosion resistance of alloys. Chemical conversion coatings are the most widely applied coating method due to their economic aspects with low cost and the promised results of the produced protective coatings. Previously, chromate compounds were widely used for producing conversion coatings to protect most metallic surfaces such as aluminum, steel and magnesium alloys. In spite of its toxicity hexavalent chromate (IV) has remain an essential ingredient in the metal finishing industry for corrosion control. But combining the economic impact of corrosion damage, the environmental and health problems caused by hexavalent
chromate (IV), and the increasing the regulatory restrictions, scientists have a huge incentive to develop a new generation of environmentally friendly protective coating systems. This research focuses on a two-layer coating system, including a non-chromate conversion coating layer and a commercially available, self-priming top coating containing nontoxic corrosion inhibiting materials for AZ91D magnesium alloys. The objective of this research are to develop Sodium metavanadate (NaV03) conversion treatments for AZ91D Magnesium alloy in manufacturing application by using conversion coating method. Then, to investigate the microstructure of oxide film that formed on magnesium substrate and finally to study the corrosion behavior and
corrosion protection of AZ91 D magnesium alloy so that it can be applied in manufacturing application. Sodium metavanadate (NaV03) is used as a corrosion inhibitor in this research. When used non-chromate conversion coating, an environmentally friendly anti-corrosion coating system would be obtained. Coatings that result from these processes are composed mostly of vanadium oxide phases. The operating parameters and conditions used to deposit the coating significantly influence the quality and performance of the deposited film . Four critical steps in producing the vanadium oxide conversion coatings are surface preparation, vanadia coating concentration, treatment time and pH values. Three types of base solution whereas lanthanum nitrate, magnesium nitrate and lanthanum with magnesium nitrate were prepared on AZ91 D magnesium alloy in electrolytes containing various concentration of NaV03 ranging from lg/1 to 7gll. The morphologies, chemical compositions and corrosion resistance of the vanadia coating were characterized by Scanning Electron Microscope (SEM) with Energy Dispersive X-Ray (EDX) capability. The effects of vanadia solution on the corrosion protection performance of magnesium substrate were investigated by Potentiodynamic polarization test in 3.5% Sodium Chloride (NaCI). These results with use of magnesium nitrate solution for 5 gil NaV03 as an additive in 30 minutes of treatment time with pH 8.5 demonstrated that the conversion of vanadia
coating is capable to be used in manufacturing application.
