Research On A Faster Anodizing Of Aluminum Alloys

A hard anodizing process on aluminum was researched at the high pulse current in this paper. The mechanical property, structure feature and morphology of the hard anodic oxidation film formed in electrolyte H₂SO₄ were investigated by eddy thickness gauge, micro-hardness tester, SEM and XRD.According to the enterprise's request for the property of the hard anodizing film on the top surface of piston, a set of equipment for hard anodizing at high pulse current was auto-designed by the laboratory. The H₂SO₄ concentration used widespread was 18% as the base electrolyte, a new process of faster forming film at high pulse current was developed by means of adding addition agent, ameliorating power and cooling equipments. The results obtained indicated that the optimization parameter of this process was as following: the base current Ii was 5A, pulse current I₂ was 7A, frequency f was 10Hz, the rising time and falling time of the trapezoidal pulse were 5s, pulse forms can be adjusted at random, current density was 5.5⁸A /dm2, electrolyte temperature was —5²0℃, oxidation time was 0⁶0min, using compound cooling conditions between inside and outside of the piston. The thickness of the hard anodizing film was 3⁴ times as others, the highest thickness was up to 107μm and the micro-hardness was 350 600 HV. The oxidation temperature was improved up to room temperature by adding addition agent. The current density was 2³ times as others and the growth rate of the oxidation film was improved greatly, at the same time, the phenomenon of "ablation" was avoided.The nano sealant was used in the sealing treatment;nano particle were penetrated into the porous layer and the contamination was hindered between the porous layer and the outer environment, the corrosion and the wearing resistances of the hard anodizing film were improved, the operating life of the piston was also improved. This new process compounding simple, operating conveniently, the oxidation film formed compaction, higher thickness and hardness, faster growth rate, and oxidized in the high current density, the faster forming film technique was come true.The morphology of the hard anodic oxidation film was studied using SEM and XRD, the results obtained indicated that the porous layer in this solution undergo two layers, the film and matrix combined tightly, there was no gap between them. The oxidation film was made of compact barrier layer and loose porous layer, and the porous layer had particular structure, it was made of pole "single cell" arranged regularly, the middle of every "single cell" had a round hole, and they arranged prismatic parallel each other and grew against the matrix.