If the anodizing film is required to be transparent, then the 5xxx and 6xxx series aluminum alloys are all good for this good appearance, and they can also be dyed after anodizing. If only corrosion resistance is required to form a dense anodic oxide film, then most aluminum alloys can be chosen. Before the anodizing process, you should have an understanding of the aluminum alloy material. The quality of the alloy material and the difference in the metal content of the material will directly affect the quality of anodized aluminum products. The alloy composition directly affects the surface appearance after anodizing.
When the iron content is more than 0.25%, a very normal hue cannot be obtained. As the iron content increases, the gloss decreases and the hue becomes pale gray. The effect of iron is more pronounced when the silicon content in aluminum alloy is low, and the harmful effects of iron can be mitigated to a certain extent when silicon is high. From the perspective of ensuring the surface quality of aluminum profiles, the iron content should be controlled below 0.25%.
A small amount of copper is beneficial to the mechanical properties and surface brightness of aluminum profiles without reducing corrosion resistance. However, when the copper content is large, the anodizing film becomes black, which can be seen by eyes.
A small amount of manganese will eliminate the harmful effects of AlFeSi to a certain extent, and reduce the occurrence of extrusion lines. However, when the content of manganese is high, the anodizing film becomes yellow, and as the content of manganese increases, it gradually develops into brownish yellow, and the coloring effect is worse.
When the zinc content is high, the difficulty of aluminum extrusion is increased, the aluminium profile grains are coarse, the mold loss is also large, the oxide film is opacified, and zinc ions are accumulated in the alkaline etching solution, and zinc produces shiny spots on the profile.
When the titanium content is greater than 0.1%, the hue and color difference of aluminum profile coloring have a greater impact, which is caused by the unevenness of titanium.
The aluminum alloy containing copper, silicon, iron, etc, and these metal contents all will affect the appearance of the anodized surface on aluminium profiles. Copper can make the surface reddish and increase oxidation defects. Silicon can gray the anodizing film, especially when the content exceeds 4.5%. Due to its characteristics, iron will exist as black spots after anodizing.