Why anodize?
By anodizing aluminum, we can achieve three effects.
We increase the surface hardness and give increased wear protection. In addition, the surface is more weather-resistant, which improves the corrosion behavior. Lastly, there is the possibility to color the anodized surface, which gives us an optical effect.
The anodizing of aluminum
The process of anodizing is an electrolytic process in which the surface is converted by the application of direct or alternating current in a specific electrolyte. This transformation process transforms the surface of the aluminum workpiece from its elementary form AL3 + into the oxide form Al2O3 (alumina). The aluminum oxide consists of a honeycomb structure with a centrally located pore. Due to the significantly higher hardness of the aluminum oxide and its high resistance to weathering, we get a wear-resistant and corrosion-resistant surface.
A distinction is made between:
· GS (DC method in sulfuric acid electrolyte)
· WS (AC process in sulfuric acid electrolyte)
· GX (direct current oxalic acid method)
· WX (AC-oxalic acid method)
Which is the procedure we use at Rieger Metallveredlung?
At Rieger Metallveredlung, the direct current process in sulfuric acid (GS) and the direct current process in oxalic acid (GX) are used.
The electrolyte consists of H2SO4 (sulfuric acid) and H2O (water) in the direct current process with sulfuric acid (GS). In the direct current process with oxalic acid (GX), the electrolyte consists of H2O (water), H2SO4 (sulfuric acid) and C2H2O4 (oxalic acid).
First of all, the workpieces are pretreated, including the degreasing of the workpieces as well as the decaping. In this way, we achieve a clean surface of our workpiece.
With this electrolyte we produce layer thicknesses up to 25 μm.
After the anodization, the workpiece must be watered so that the sulfuric acids are released from the pores. Now, the surface is prepared to be e.g. colored.
Gray, bronze, olive brown, deep black and black are the colors we can produce.
Finally the workpiece is dipped in hot water which is also called hot sealing.
The pores are closed (Al2O3 x 1H2O).
Application areas
Not only in the automotive industry is anodized but also in the electrical industry, mechanical engineering, lighting industry, fitting industry and medical technology.
Written by
Thomas Frik (trainee)
