Study On The Process Of Phosphate Conversion Treatment On Magnesium Alloys

Magnesium is abundant on earth, and has some special properties. It is known as "the 21 century green metal". Magnesium alloys have a number of desirable features, low density, high strength-to-weight ratio included, and excellent process feature. So it is widely used in automobile,electronics,aerospace,etc. but because of low chemical potential of magnesium alloys, it can be vulnerable to corrode in many media environment, and it hinders the application and development of magnesium alloys, So domestic and foreign experts search for many methods of surface treatment to improve corrosion resistance of magnesium alloys. The ways of chemical conversion treatment are widely used owing to low cost. Traditional ways of chemical conversion treatment have some problems, which is difficult to comply with or meet the actual needs of the project.The study is based on the method of phosphate conversion treatment. The special technology method of conversion treatment for magnesium alloy is drawn up by studying and analyzing the effect between the phosphate and magnesium alloy. Applying orthogonal design to optimize the components of treatment solution for magnesium alloys, and a good proportion of the component of the treatment solution is found. And in this proportional component we search for the technology method of conversion treatment to improve the corrosion resistance of magnesium alloys in contrast to magnetic field acting on the process of conversion treatment.The surface morphology, structure and corrosion resistance of conversion coating are studied by SEM, AFM, XRD and Electrochemistry workstation. The results show the order that the process composition has an effect on conversion resistance of AZ31 magnesium alloy is H3PO4, MnCO3, K2HPO4, Zn(NO3)2. The conversion coatings of AZ31 magnesium alloy can be further formed when the direction of magnetic field is vertical to the surface of magnesium alloy. Conversion coatings are mainly made up of crystal Zn3(PO4)2·4H2O and AlPO4 and non-crystal Mn compounds. We obtain the dense conversion coatings by applying magnetic fields in the phosphate process.