The most common harmful impurity in aluminum is iron, in the production process of building aluminum profiles, when the iron content is greater than 0.25%, it can not get a very normal tone, with the increase of iron content, gloss decreases, the color is green, light gray is very ugly. When the silicon content of gold is low, the effect of iron is more obvious, and the harmful effect of iron can be reduced to a certain extent when the silicon is high. At this time, iron and silicon form AlFeSi intermetallic compounds, and part of the excess silicon is also consumed.
The main reason for the influence of iron on coloring is that iron and aluminum form a pointed or rod-like structure, ranging from a few microns to tens of microns, and its electrode potential is different from aluminum, which affects the uniformity and continuity of oxidation coloring, and also reduces the luster and transparency of the oxide film, affecting the coloring effect.
A small amount of copper is beneficial to the mechanical properties and surface brightness of the profiles without reducing the corrosion resistance. However, when the copper content is long, the oxide film is black, which can be seen by the naked eye.
A small amount of manganese will to some extent eliminate the harmful effects of AlFeSi tissue and reduce the production of extrusion lines. However, when the content of manganese is high, the oxide film tends to be yellow, and the coloring effect is worse with the increase of manganese content.
When the zinc content is high, the extrusion difficulty is increased, the grain size of the profile is coarse, the mold loss is also large, the oxide film is opaceous color, and leads to the accumulation of zinc ions in the alkali etching solution, and the zinc inversion on the profile, resulting in shiny pear skin spots.
When the titanium content is greater than 0.1%, it has a greater impact on the hue and color difference of the profile coloring, which is caused by the non-uniformity of titanium. Therefore, in order to ensure the surface quality of the profile, the iron content should be controlled below 0.25%, and the content of other impurities should be less than 0.1%.