Investigation On High-voltage Anodic Oxidation With Direct Electroless Nickel Plating Of Aluminum Alloy 6063 At Middle Temperature

Aluminum alloys are regarded as the light metal structure materials, which have a number of desirable features and prosperous applications in many fields such as aerospace, automobile, mechanical and electronic components etc. However, aluminum is easily oxidized form aluminum oxide in the dry air due to its active chemical properties, and its hardness is very poor, lacking for wearability. In order to overcome shortcomings of surface properties of aluminium alloy, surface treatment technology is an important means to solve three aspects of the problem such as preventive, decorative and functional. This thesis mainly studies high-voltage anodic oxidation and direct electroless nickel plating that commonly used in surface technology of aluminum alloys.In this thesis, the voltage selection of high voltage anodic oxidation of aluminum alloy 6063 is 180～380 V. In order to compare the effects of oxygen acid salt in electrolytes on the film thickness and the oxidation time in the process of high voltage anodic oxidation of aluminum alloy 6063, the oxidation films were prepared by anodic oxidation of the aluminum alloy in the three electrolyte systems of Na2SiO3, Na2HPO4, NaAlO2.The results show that oxidation time was prolonged and the hardness of the film was increased after adding sodium hexametaphosphate in the three electrolytes. But at the same time it also can make membrane layer become coarse, stomatal was bulky, acidoresistant decline. Appropriate concentrations of Na2WO4 can improve thickness, hardness, wear resistance and acidity of membrane layer. High levels of Na2WO4 will make electrolyte turn turbidity, and the electrolyte system is unstable. When the applied current density was 3 A·dm-2, the electrolyte suitable for high voltage anodic oxidation is the Na2SiO3 system. Specific formula are:KOH 2 g·dm-3, Na2SiO3 15 g·dm-3, and C4H4O6Na2 moderate.5 g·dm-3(NaPO3) 6 and Na2WO4 were added as additives respectively. This electrolyte can produce compact oxidation coating with high corrosion resistance.During the process of direct electroless nickel plating, to achieve direct electroless nickel plating on 6063 aluminum alloy in temperature (70℃), joined activator (fluoride compoundsand) and the main complexing agent was adjusted in the chemical plating bath. Experimental results show that:appropriate concentrations of activator can accelerate the speed of induced chemical nickel sedimentary, and make it possible to direct electroless nickel plating on 6063 aluminum alloy in medium temperature. It also can accelerate the deposition rate and improve the comprehensive performance of coatings. The aminoacetic as the main complexing agent, can obviously improve the corrosion resistance of coating, rise the corrosion potential and reduce corrosion current in the corrosive medium. And the resistance of color degeneration also showed some improvement. When the activator was contrllled to 2 g·dm-3 and aminoacetic was 8 g·dm-3, the resulting Ni-P coating had a better comprehensive performance.