The Preparation And Properties Of Ornamental Hard Anodic Oxidation Film For Aluminum Alloy

Aluminium and aluminium alloy anodic oxidation is the process that oxide film forms under impressed current, the process. generate in appropriate electrolyte, In this process, lead or pure aluminium is cathode material, workpiece of aluminium or aluminium alloy is anode.In general, anodic oxidation of aluminium and its alloy can be divided into decorative anodic oxidation and functional anodic oxidation by use. The film of decorative anodic oxidation is even and has consistent color, functional anodic oxide film is the film which has a variety of special properties. Hard anodic oxidation is part of functional anodic oxidation. After hard anodic oxidation, aluminium alloy could obtaina layer of oxide film which has high hardness, good abrasion performance, high-temperature resistant, excellent electrical insulation and superior corrosion resistance. But hard anodizing film commonly present dark grey or black, and has no decorative effect, which affect its uses.In this study, aluminium alloy was machine sandblasted and chemical polished.Indicator was thickness, microhardness, color and uniformity of oxidation film. Aluminium alloy hard-ornamental anodizing process was optimized with orthogonal experiments:current density of 1.5A-dm-2, sulfuric acid concentration of 150g/L, oxidation temperature of 4℃, oxidation time of 90min,The analysis of mean value and range shows that the hardness of oxide film was more than 310HV and the thickness was more than 18μm under optimal process conditions; all factors which influence thickness and microhardness of oxide film were current density, oxide time, sulfuric acid concentration, the oxide temperature.The optimal process was verified, the oxide film under this process was charcoal grey, uniformly, continuous,no aberration and defect-free.The thickness of oxide filmwas 19.3μm and the hardness was 328HV, which accord with technical requirements and analysis of even value. The hardness and thickness of the anodic oxide film is much better than conventional anodic oxide film and oxide film which generate in electrolyte without organic acid. Additives of organic acid can enhance the growth rate of oxide film, increase its thickness, improve the quality of film, which make it more uniformly and compactly.Different types of oxidation films were measured by polarization curve and CASS tests, which show basically similar results:corrosion-resistance of hard-ornamental anodic oxide film is excellent, which is superior to conventional anodic oxide film and aluminium alloy without anodic oxidation. Corrosion resistance of oxide film increased first and then decreased with time extending.Corrosion resistance decreases with increasing temperature.Anodic oxide films were analysed by SEM, hard-ornamental anodic oxide film was compact and uniform, whose pore was smaller than that of conventional anodic oxide film, and uniformity of conventional anodic oxide film are worse.With time extending, the pore of anodic oxide film was larger, the quantity of pores increased, corrosion action of solution weakened first and then increased. With the increasing of the electrolyte temperature, the pore of oxide film was larger, the quantity of pores increased, corrosion action of solution increased.The results of scratch test show that adhesive strength of hard-ornamental anodic oxide film was greater than that of conventional anodic oxide film.adhesive strength of oxide film was scarcely influenced by the length of time. With the increasing of the electrolyte temperature, adhesive strength of oxide film decreased.