Az31 Magnesium Alloy Direct Electroless Nickel-phosphorus Alloy

Magnesium is the sixth most rich metal on the surface of the earth。With high conductivity, magnetic interference, die-casting workpieces and easily recycled etc, magnesium alloy is the third metal engineering materials after steel and aluminum alloy in the world, known as"the 21st century green engineering material". With limited corrosion resistance and high chemical and electrochemical activity, developing tendency and application of magnesium alloys were greatly restricted. Corrosion resistance of magnesium alloy surface can be improved by electroless plating, but magnesium belongs to the matrix, direct electroless plating of which is very difficult,and pre-processing of electroless plating will directly influence the effect of corrosion resistance of the chemical coating. In addition,the scientific allocation of solution of electroless plating would lead to the best effection.This paper studies the following contents:(1) The research of effect of electroless plating by pre-processing, Which finds that the effection of grinded specimen would reach to a certain degree, not too coarse,because roughness Less than 0.6 can effectively reduce the porosity of the electroless plating. Including Na3PO4 and NaOH and Na2CO3, orthogonal allocation of solution taked in the alkaline cleaning technology, which explore the factors of alkaline cleaning process. Acid pickling and activation of pre-processing have a corresponding influence factors. through researching the relationship of several factors and testing standards of plating , the best formula of the pre-treatment was found.(2) Based on the orthogonal experiment of electroless plating ,I researched the influencing regularities of chemical composition and objective conditions, such as temperature, PH value of the stability of the solution of time, the coating corrosion resistance and coating hardness, etc. Polarization curves of the plating taked by autolab,which show the corrosivity of the plating in the solution of 3.5% NaCl. Through detecting hole of the plating by magneson,analysing chemical composition of the plating by EDS,and most importantly analysing the test data of the orthogonal experiment, the best compositions of solution of electroless plating was found.According to the compositions ,the content of phosphor of the plating is 9% ~ 11%.By X-ray diffraction analysing the plating is shown "mantou" shape curve, typical diffraction pattern of amorphous alloys,which shows amorphous structure of the plating.(3) On the basis of the existing solution, by adding different amounts of complexing agent, the thickness of Ni-P coating would not be added conspicuously by optimizing compound of complexing agent. At the same time , comparing to electroless pating with single complexing agent ,Both corrosion resistance and hardness of electroless pating with multiple complexing agent are found improved.