What effect does aluminum alloy hard oxidation have？

Hard anodizing is the full name of hard anodizing. The thickness of hard anodic oxide film is generally required to be 25-150um. The thickness of most hard anodic oxide films is 50-80um. The thickness of hard anodic oxide film with film thickness less than 25um is used for parts used in tooth keys, spirals and other occasions. The thickness of anodic oxide film for wear resistance or insulation is about 50um. Under some special process conditions, it is required to produce hard anodic oxide film with thickness of more than 125um, However, it must be noted that the thicker the anodic oxide film, the lower the microhardness of the outer layer and the increase of the surface roughness of the film. The bath solution for hard anodizing is generally sulfuric acid solution and sulfuric acid added organic acids, such as oxalic acid, aminosulfonic acid, etc. In addition, the hard anodizing treatment can be realized by reducing the anodizing temperature or reducing the sulfuric acid concentration. For deformed aluminum alloys with copper content greater than 5% or silicon content greater than 8%, or die-casting aluminum alloys with high silicon, some special measures of anodizing may also be considered. For example, for 2XXX series aluminum alloy, 385g / L sulfuric acid and 15g / L oxalic acid can be used as electrolytic cell solution to avoid burning of aluminum alloy during anodizing, and the current density should also be increased to more than 2.5a/dm.

Surface finish

After hard anodizing, the surface finish of parts is changed. For rough surfaces, it can appear smoother than the original after this treatment. For parts with high original finish, after this treatment, the displayed surface finish brightness is reduced by about 1 ~ 2 levels.

Dimensional allowance

Due to the high thickness of hard oxide film, if aluminum parts need to be further processed or parts need to be assembled later, a certain machining allowance and designated clamping parts shall be reserved in advance.

Due to the change of part size during hard anodizing, it is necessary to predict the possible thickness and dimensional tolerance of oxide film in advance during machining, and then determine the actual size of parts before anodizing, so as to meet the specified tolerance range after treatment.

Generally speaking, the increased size of parts is about half of the thickness of oxide film [3].

Specifically, hard anodizing is mainly used in aluminum alloy parts with high wear resistance, heat resistance and good insulation. Such as all kinds of inner wall of cylinder, piston, steam plug, cylinder, bearing, floor of aircraft cargo compartment, roller and guide rail, hydraulic equipment, steam impeller, leveling machine, gear and buffer pad.