Reasons for affecting the quality of anodized aluminum sheets

1. Current density: Within a certain limit, the current density increases, the film growth rate increases, the oxidation time is shortened, the pores of the film are formed, the color is easy to be colored, and the hardness and wear resistance are increased; the current density is too high, The influence of Joule heat causes the surface of the part to overheat and the temperature of the local solution to rise, the dissolution rate of the film increases, and there is a possibility of burning the parts; if the current density is too low, the film growth rate is slow, but the formed film is dense, hardness and Reduced wear resistance.
Aluminum oxidation, used for protection, decoration and pure decorative processing, the upper limit of the allowable concentration is used, that is, 20% sulfuric acid is used as the electrolyte.

2.Oxidation time: The choice of oxidation time depends on the electrolyte concentration, temperature, anode current density and the required film thickness. Under the same conditions, when the current density is constant, the growth rate of the film is proportional to the oxidation time; but when the film grows to a certain thickness, the film resistance increases, affecting the conductivity, and the dissolution rate of the film increases due to the temperature rise. Therefore, the growth rate of the film will gradually decrease and will not increase until the end.
3.sulfuric acid concentration: usually 15% – 20%. When the concentration increases, the dissolution rate of the membrane increases, the growth rate of the membrane decreases, the porosity of the membrane is high, the adsorption force is strong, the elasticity is strong, the dyeability is good (easy to dye dark), but the hardness and wear resistance are slightly poor; When the concentration of sulfuric acid is lowered, the growth rate of the oxide film is increased, the pores of the film are small, the hardness is high, and the wear resistance is good.

4.electrolyte temperature: The electrolyte temperature has a great influence on the quality of the oxide film. As the temperature increases, the dissolution rate of the film increases and the film thickness decreases. When the temperature is 22-30 ° C, the obtained film is soft, the adsorption capacity is good, but the abrasion resistance is rather poor; when the temperature is greater than 30 ° C, the film becomes loose and uneven, sometimes even discontinuous, The hardness is low, and thus the use value is lost; when the temperature is between 10 and 20 ° C, the generated oxide film is porous, has strong adsorption capacity, is elastic, and is suitable for dyeing, but the film has low hardness and poor wear resistance; When the temperature is lower than 10 ° C, the thickness of the oxide film is increased, the hardness is high, the wear resistance is good, but the porosity is low. Therefore, the temperature of the electrolyte must be strictly controlled during production. To produce a thick and hard oxide film, the operating temperature must be lowered. During the oxidation process, compressed air is used for agitation and a relatively low temperature is usually performed, and hard oxidation is usually performed at about zero degrees.
5.Stirring and moving: It can promote the convection of the electrolyte, strengthen the cooling effect, ensure the uniformity of the temperature of the solution, and will not cause the quality of the oxide film to decrease due to local heating of the metal.

6.Impurities in the electrolyte: The impurities which may be present in the electrolyte used for the anodization of aluminum are Clˉ, Fˉ, NO3ˉ, Cu2+, Al3+, Fe2+ and the like.The Cl ˉ F, NO3 ˉ increase the porosity of membrane, the surface is rough and loose. If its content is more than limit value, and even make the parts occur corrosion perforation (Cl ˉ should be less than 0.05 g/L, F ˉ should be less than 0.01 g/L); When the content of Al3+ in the electrolyte exceeds a certain value, white spots or specular white blocks often appear on the surface of the workpiece, and the adsorption property of the membrane decreases, making dyeing difficult (Al3+ should be less than 20g/L). When the content of Cu2+ reaches 0.02g/L, dark streaks or black spots appear on the oxidation film. Si2+ is often suspended in the electrolyte, making the electrolyte slightly cloudy and adsorbed on the membrane with brown powdery substance.
7.aluminum alloy composition: In general, other elements in the aluminum metal reduce the quality of the film, and the obtained oxide film is not thicker than that obtained on pure aluminum, and the hardness is also low, and the aluminum alloy of different compositions is subjected to anodizing treatment. Be careful not to work with the slot.