If the requirement of oxidation film after oxidation is colorless and transparent, 5 and 6 series of aluminum alloys are better, and can also be oxidized after coloring.Most aluminum alloys can be oxidized if they are only required to be anodized to form a dense anodized film and there is no requirement for color.Before selecting the oxidation process, aluminum or aluminum alloy material should be understood, because the quality of the material quality, the composition of the different, will directly affect the quality of aluminum products after anodizing.For example, aluminum surface defects such as bubbles, scratches, peeling, rough, etc., after anodizing, all defects will still appear.The alloy composition has a direct influence on the surface appearance after anodizing.Aluminum alloy contains copper, silicon, iron and other impurities on the surface appearance of the oxidation film performance is as follows: copper will make the oxidation film red, destroy the quality of electrolyte, increase oxidation defects;Silicon grays the oxide film, especially when the content exceeds 4.5%.Iron has a characteristic black spot after anodizing.
In addition, there are other impurities in the alloy on the appearance of the oxide film: 1-2% manganese aluminum alloy, after oxidation is brown-blue, with the increase of manganese content in aluminum, oxidation surface color changes from brown-blue to dark brown.Aluminum alloys containing 0.6-1.5% silicon are gray after oxidation, and white gray when containing 3-6% silicon.The zinc ones are milky, the chrome ones are gold to gray, and the nickel ones are pale yellow.Generally speaking, only aluminum containing magnesium and titanium more than 5% contain gold, which can be oxidized to obtain a colorless, transparent, bright and clean appearance.
It should be noted that: the appearance of some aluminum profiles make different colors, these colors are not oxidized, but aluminum after anodizing, dyeing or electrolytic coloring formed.Dye basically any color, and electrolytic coloring is less, can be done, black, bronze, champagne, gold, imitation stainless steel color.
The common harmful impurity in aluminum is iron. In the production process of aluminum profiles in the construction industry, when the iron content is greater than 0.25%, the color tone is not very normal. With the increase of the iron content, the gloss decreases.When the content of silicon in gold is low, the influence of iron is more obvious. When the content of silicon is high, the harmful effect of iron can be reduced to some extent. At this time, iron and silicon form AlFeSi intermetallic compound, which also consumes some excess silicon.The main reason why iron affects the coloring is that iron and aluminum form a pointed or rod-shaped structure, ranging from a few microns to dozens of microns. Its electrode potential is different from aluminum, which affects the uniformity and continuity of oxidation coloring, and reduces the luster and transparency of oxidation film, affecting the coloring effect.
A small amount of copper is beneficial to the mechanical properties and surface brightness of aluminum profiles without reducing corrosion resistance.However, when copper content is high, the oxide film tends to be black, which can be seen by the naked eye.
A small amount of manganese will eliminate the harmful effects of AlFeSi formation to some extent and reduce the production of extrusion grain.However, when the content of manganese is high, the oxide film tends to yellow, and gradually develops to brown-yellow color with the increase of manganese content, and the coloring effect is worse.
High zinc content increases the difficulty of aluminum extrusion, profile grain size, mold loss is also large, oxidation film opacities, and lead to the accumulation of zinc ions in alkali corrosion solution, zinc inverted on the profile, produce shiny pear-like spots.
When the titanium content is more than 0.1%, it has a great influence on the color tone and color difference of aluminum profiles, which is caused by the unevenness of titanium.
Therefore, to ensure the surface quality of aluminum profiles, the iron content should be controlled at less than 0.25%, and other impurities should be less than 0.1%.