Brief introduction of hard oxidation of aluminum
Hard anodizing is a thick film anodizing method and a special anodizing surface treatment process for aluminum and aluminum alloys. By this process, the maximum thickness of anodic oxide film can reach about 250 microns, and the microhardness oxide film of 1500kg/mm2 can be obtained on pure aluminum, while the microhardness oxide film of 400 ~ 600 kg/mm2 can be obtained on aluminum alloy.
The thermal conductivity of the oxide film is poor, the melting point is 2050℃, and the resistance coefficient is relatively high. The breakdown voltage can reach 2000V after sealing treatment (insulation or paraffin). It has high corrosion resistance and wear resistance in the atmosphere. It is also an ideal thermal insulation film, which has good insulation and strong binding force with base material, so it has been widely used in national defense industry and mechanical parts manufacturing industry.
There are many methods of hard anodic oxidation electrolysis, such as sulfuric acid, oxalic acid, propylene glycol, sulfosalicylic acid and other inorganic salts and organic acids. The power supply used can be divided into DC, AC and AC -DC superimposed power supply. At present, there are two kinds of hard anodic oxidation widely used.
(1) direct current method for hard anodic oxidation of sulfuric acid;
(2) AC-DC gravity separation by hard anodic oxidation of oxalic acid.
Among them, sulfuric acid method is a widely used hard oxidation method at present.
Influencing factors of aluminum hard oxidation
Influence of various factors on hardness and growth rate of oxide film. Whether a high-quality hard oxide film can be formed on the surface of aluminum and aluminum alloy mainly depends on the composition concentration, temperature, current density of electrolyte and the composition of raw materials.
Electrolyte concentration
When using sulfuric acid electrolyte for hard anodic oxidation, the concentration is generally in the range of 10% ~ 30%. When the concentration is low, the hardness of the oxide film is higher, especially for pure aluminum, except for aluminum alloy with high copper content (CY 12). Because aluminum alloy with high copper content is easy to produce CuAl2 compound, this compound dissolves quickly after oxidation, and it is easy to burn aluminum parts. Therefore, it is generally not suitable to use low-concentration sulfuric acid electrolyte, and it must be in high concentration (H2SO4 in? 300 ~ 400 g/l) or the method of superposition of alternating current and direct current.
Effect of temperature on film layer
The temperature of electrolyte has a great influence on the wear resistance of oxide film. Generally speaking, if the temperature decreases, the wear resistance of anodic oxide film of aluminum and aluminum alloy will increase, which is due to the decrease of dissolution rate of electrolyte to the film. So as to obtain an oxide film with higher hardness. The temperature of hard anodizing should be controlled within 2℃.
Mainly used for aluminum and aluminum alloy parts requiring high wear resistance, heat resistance and good insulation performance. Such as cylinder inner wall, piston, steam plug, cylinder, bearing, aircraft cargo floor, roller and guide rail, water conservancy equipment, steam impeller, leveler, gear, buffer pad, etc. Compared with hard chromium plating process, hard oxidation process has the advantages of low cost, firm membrane bonding and convenient treatment of plating solution and cleaning waste liquid. However, the disadvantage of the film obtained by this process is that the mechanical fatigue strength index of aluminum and aluminum alloys is affected when the film thickness is large.
The products after aluminum hard oxidation can be used in many places, for example, in machinery running with cylinders and pistons, the piston, cylinder, steam plug and other parts inside are aluminum or aluminum alloy parts after aluminum hard oxidation; It is also used in large aircraft, and the cargo hold in the aircraft uses this material with strong wear resistance and hardness as the floor; Compared with hard chromium plating, aluminum hard oxidation products have lower cost, stronger film bonding and easier plating process. The above is the hard oxidation of aluminum introduced by Bian Xiao.
Tubatu Online provides you with "every decoration quotation, 1-4 local decoration companies, 3 sets of decoration design schemes" and the decoration pit avoidance strategy for free! Click this link:/Zhu Ye /zxbj-cszy.php? to8to _ from = SEO _ zhidao _ m _ jiare & amp； Wb, you can get it for free ~