Study On Preparation And Corrosion Resistance Properties Of Anodic Films On Mg-Li Alloys

A kind of white anodic film on magnesium-lithium alloy was prepared in a environmental friendly alkaline solution. Different kinds of additives were used to investigate the influence of additive concentration on the properties of the film.Organic coating and electroless plating were used to sealing the anodic film. And the optimum technological routes for sealing were determined.In this paper, the anodic films were prepared in a solution of NaOH 50g·L-1,C6H5Na3O7-2H2O 40g·L-1,Na2B4O7·10H2O 30g·L-1, Na2SiO3·9H2O 40g·L-1. The effects on the property of the anodic film of different current density and anodizing time were researched. The surface morphology was characterized, and the corrosion behaviors of the coating was investigate. The investigation showed that the optimumcurrent density was 10 mA·cm-2 and the optimum anodizing time was 20 min. The film prepared in this condition was uniform, smooth, less cracks and better corrosion resistance. The corrosion current density reached 2.189×10-7 A·cm-2 , and the corrosion potential was -0.346V.The effects of potassium biphthalate and triethanolamine on the morphologies,crystal structure, chemical composition and corrosion resistance of the anodic films were investigated. The results showed that the film became smoother and the corrosion resistance of anodic film was greatly enhanced by. When the addition of potassium biphthalate was 6g/L or the addition of triethanolamine was 15g/L, the films has the best corrosion resistance.The sealing treatment was conducted by organic coating and electroless plating,respectively. The effects of curing time and curing temperature on the sealing quality was investigated. The optimum sealing condition were 130?, 30min.A corrosion resistant film was prepared on the anodic film by electroless Ni plating method in a solution of NiSO4·6H2O 15 g·L-1,Na2H2PO2·H2O 14 g·L-1,NaC2H3O2 13 g·L-1, HF(40% V/V) 12 ml·L-1,NH3HF 28 g·L-1. The optimum pH value was 6. The morphology and composition of the surface and the cross section of the samples were characterized. And the film forming mechanism is analyzed.