Investigation On The Pretreatment Process Of Electroplating On AZ91D Magnesium Alloy

Magnesium alloys have many excellent properties such as low density,high specific rigidity,high specific strength,good castability and so on.It has so many advantages of abundant reserves in the earth and recyclable use,so that magnesium alloy is studied by more and more researchers nowadays,but the poor corrosion resistance of magnesium limits its wide application in industry greatly.Therefore,the treatment of surface on magnesium alloy is very important.Plating is one of the most important treatments on the surface of magnesium alloy.It does not like other metal plating process,the influence of factors about pretreatment process of magnesium alloy plating is rather complex,so the research of pretreatment process of magnesium alloy electroplating has a very important significance.The paper uses contrast,orthogonal design experiments to research the best oil removal and the best activation process,and AZ91D magnesium alloy was used as the research object;using scanning electronic microscope and the method of spectrum analysis to study the surface of magnesium alloy specimen;using the polarization technique,weight addition method to study the effect of factors on zinc dipping process of AZ91D Mg alloy.When take appropriate pretreatment process,we can obtain qualified copper coating on AZ91D magnesium alloy surface successfully.The research draws the following important conclusions of research work:1.The samples of magnesium alloy are disposed by the two different degreasing techniques in degreasing process:the first one is chemical degreasing,and the another one is the electrolytic degreasing.After the chemical degreasing process,the effects of oil removing are very poor on surface of magnesium alloy.Therefore,the paper takes the second electrolytic degreasing technique.The best chemical degreasing:Na₂CO₃12g/L,Na₃PO₄ 20g/L,emulsifier A 1.0g/L,using phosphoric acid changing the pH value to 10,time 5min,temperature 65?.The best electrolytic degreasing:Na₃PO₄20 g/L,Na₂CO₃ 12g/L,temperature 60?,density of current 7 A/dm²,time 40 s,pH13¹4.2.Two times of activation technology are adopted in activation process of the paper:once inorganic acid activation and second alkali activation techniques.Because the oxide film on the surface of magnesium alloy is difficult to be cleaned up after once activation.Therefore,the paper takes the second alkali activation technique.The best acid activation formula:H₃PO₄ 200mL/L,mineral A 5g/L,NH₄HF₂ 90g/L,room temperature,pH 1,time 5min.The best second alkali activation formula:Na₄P₂O₇ 120g/L,Na₂CO₃ 48 g/L,KF 11 g/L,temperature 70±5?,the soaking time:5 min,pH 11.3.The paper adopts two zinc dip processes.The density of zinc layer on the surface of magnesium alloy is poor after once zinc immersion process,and there is a little leakage places.So the paper takes two zinc dip processes to increase the zinc layer density.The best once zinc dipping formula:ZnSO₄ 30g/L,mineral B 120g/L,NaF 3g/L,Na₂CO₃ 6g/L,temperature 75?,soaking time:10min,pH 11.The best second zinc dipping formula:Zn SO₄ 30 g/L,mineral B 120 g/L,NaF 3g/L,Na₂CO₃ 6g/L,temperature 75?,soaking time:8 min,pH 11.4.Copper electroplating is used to verify the effect of zinc immersion on pretreatment process of magnesium alloy in order to the verify the advanced pretreatment process of magnesium alloy.Copper coating player is proved to meet the electroplating process requirements of surface smoothness and combined with the binding force test after pretreatment process of magnesium alloy,it also can be further applied in industrial production after amplification.