The Corrosion Modification Of EDTA-2Na On Vanadate Conversion Coating On Mg Alloy Surface

Magnesium alloys are used in the manufacture of military products,commercial cars and 3C products because of their low density,easy conductivity,good heat conductivity and casting properties.However,magnesium alloys are very easy to be corroded.In recent years,surface treatment technology has been used to improve the corrosion resistance of magnesium alloys.At present,one of the most commonly used methods is chromate conversion technology,which has the advantages of low cost and good corrosion resistance.However,chromate is harmful to human body and can cause cancer,which has been banned worldwide.Therefore,it is necessary to develop chromium-free conversion coating technology for magnesium alloys to replace chromium conversion coating.Previous research results of vanadate conversion coatings on magnesium alloys show that the corrosion resistance of magnesium alloys has been significantly improved after treatment with sodium metavanadate?NaVO₃?,sodium dodecylbenzene sulfonate?SDBS?and OP10 conversion solution.However,there are some problems in the system,such as fast consumption of SDBS,poor stability of conversion solution and less amount of magnesium alloy treatment.In order to solve this problem,the study of substituting sodium dodecylbenzenesulfonate?SDBS?with disodium ethylenediaminetetraacetate?EDTA-2Na?was carried out in this paper.The results show that:The conversion solution consisting of 2.2 g/l sodium metavanadate?NaVO₃?and 1.0 g/l disodium ethylenediaminetetraacetate?EDTA-2Na?was prepared on AZ31magnesium alloy surface at pH 2.5,reaction time 15 min and reaction temperature 40 C.Compared with the conversion liquid consisting of NaVO₃,SDBS and OP10,the amount of treated magnesium alloy increased five times and the conversion liquid was more stable.The morphology,structure and composition of the conversion film were analyzed by scanning electron microscopy?SEM?and energy dispersive spectroscopy?EDS?.The results showed that the addition of EDTA-2Na promoted the reaction between magnesium alloy and vanadate,and made the conversion film more uniform and dense,with better corrosion resistance and 140 h salt spray time.