Effect Of Silver Blush Plating Pretreatment Techonology On The Properties Of Silver Coating On Aluminum Alloy

Aluminum and aluminum alloys were widely used in industrial production due to their advantages such as small specific gravity,easy die casting,good electrical conductivity and thermal conductivity.With the development of science and technology,and the improvement of people’s living standard,the demand for aluminum alloy was increasing day by day,whether the lightweight material in the aerospace field,or the lightweight technology of the automobile.But the aluminum and aluminum alloy were prone to intergranular corrosion,low surface hardness,wear-resisting.It was very necessary to improve the surface performance by anodized aluminium.Silver plating on aluminum was an important way of surface modification,electroplating and brush plating were common method for some special aluminum alloy workpiece.The aluminum surface easily reacted with oxygen to produce a natural oxide film in the air,and the interface property between metal and substrate was poor.At present,there were a lot of pretreatment methods to obtain the appropriate silver-plate layer for plating silver on aluminum alloy.With the extensive application of aluminum alloy,it was found that binding capacity between aluminum alloy brush silver coating and substrate was poor under high temperature.The purpose of this project was aluminum alloy brush-plate silver layer could resist high temperature of 500 ℃.The effect of zinc dipping pretreatment and anodic oxidation pretreatment on cyanide silver-plate layer of the brush system was studied during the experiment.The effects of different pretreatment process and process parameters on discoloration,microstructure,corrosion resistance and thermal shock resistance were also researched.Anodic oxidation time 4min and oxidation voltage 13 V were selected to treat aluminum alloy surface,The comprehensive performance of silver coating which prepared by preplate silver with cyanide first,brush-plate silver second and preplate silver without cyanide first,brush-plate silver second were compared.The experimental results found that the brush silver layers made by four kinds of zinc dipping process were not resistant to thermal shock of 500℃,dip zinc and preplated copper were mixed between coating and aluminum alloy substrate in the pretreatment process,which spread by coating gap to the coating surface at high temperature.The brush-plate silver layer which process parameters were oxidation time 4min,oxidation voltage 13 V or oxidation time 10 min,oxidation voltage 13 V could resist 500℃ thermal shock.Combined with the actual production,it was necessary to reduce the cost of time and the oxidation time 4min and oxidation voltage 13 V were selected as parameters of anodizing parameters.Based on this parameter,the system of brush-plate silver layer with cyanide was made and the corrosion current density in 0.1mmol/L Na2 S and 0.1mol/L K2SO4 solution were 1.898×10-6A/cm2,9.43×10-6A/cm2 respectively.When the oxidation time 4min,oxidation voltage 13 V,no matter what methods(preplate with cyanide or without cyanide)were used,the corrosion resistance of silver coating which prepared by preplate silver with cyanide first,brush-plate silver second was better than that of preplate silver without cyanide first,brush-plate silver second.But two kinds of thermal shock resistance of brush silver layer were poor.