The most familiar harmful substance in aluminum is iron. In the production of aluminum for picture frames , if the iron content is greater than 0.25%, the conventional color cannot be obtained, because the increase in the iron content reduces the gloss  the color is greenish. It's very ugly. When the silicon content in gold is low, the influence of iron is more prominent. When the silicon is high, the influence of harmful substances in iron can be reduced to a certain extent. At this time, iron  silicon cause intermetallic compounds  consume some of them. The remaining silicon.

      The key reason that iron affects coloring is that iron  aluminum cause sharp  rod-shaped structures, ranging  a few microns to tens of microns. Its electrode potential is different  aluminum, so it affects the uniformity  continuity of oxidation coloring,  also makes oxidation Film gloss  transparency are reduced, affecting the coloring effect. 

      A small amount of copper contributes to the mechanical properties  surface gloss of the frame aluminum, but it is  easy to reduce the corrosion resistance. However, when the copper content is large, the oxide film becomes black, which can be seen by the naked eye. A small amount of manganese will remove the harmful effects of the tissue to a certain extent  reduce the cause of squeeze lines. However, when the composition of manganese is high, the oxide film becomes yellow. As the increase of manganese composition slowly develops into yellow-brown, the coloring effect is even worse.  

When the zinc content is high, the extrusion difficulty is increased, the profile grains are coarse, the mold wear is also large, the oxide film is opacified,  it causes the accumulation of zinc ions in the alkaline etching solution. Like spots. When the titanium component is greater than 0.1%, the color  color difference of the aluminum frame frame are greatly affected, which is caused by the unevenness of titanium. Therefore,  the perspective of ensuring the surface quality of the aluminum frame, the iron composition should be controlled below 0.25%,  the rest of the material composition should be below 0.1%.