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 percent , a normal color tone cannot be obtained. As the iron content increases, the glossiness decreases, and the color tone tends to be blue, with a light gray and light gray that is difficult to look at.

When the silicon content in gold is low, the influence of iron is more significant. When the silicon content is high, the harmful effects of iron can be alleviated to a certain extent. At this time, iron and silicon form AlFeSi intermetallic compounds, while also consuming some excess silicon. The main reason why iron affects coloring is the formation of pointed or rod-shaped structures between iron and aluminum, ranging from a few micrometers to tens of micrometers. Its electrode potential is different from that of 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.

When the titanium content is greater than {{0}}.1 percent , it has a significant impact on the color tone 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 percent , and the content of other impurities should be less than 0.1 percent .