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Industrial aluminum anodic oxidation surface corrosion spots?
discussion of spot corrosion after anodic oxidation surface as the research object, analyzed the nature and causes of spot corrosion spots of corrosion of the key factors. Due process and alloy composition is not appropriate, 6063 aluminum can appear after anodic oxidation or surface forms of corrosion defects, the spot corrosion is common in production. 6063 aluminum after anodic oxidation, has good corrosion resistance and decorative performance, in recent years, with the development of national economy, the use of industrial aluminum is more and more popular, but many of the aluminum alloy in use after a period of time, surface forms of corrosion defects, the spot corrosion is common, serious impact on the use of aluminum performance and decorative effect. Reasonable in order to improve the quality of the surface of the aluminum, achieve the goal of control surface spot corrosion, small make up for the spot defects made in-depth understanding. First of all, we analyze the essence of spot corrosion. Look from the surface corrosion of aluminum, spots of corrosion pit is there are a large number of residues. Using SEM share corrosion residue composition, excess Si not only can form free of Si phase, also with the matrix form of alpha phase ( Al12 Fe2Si) And beta phase ( Al9Fe3Si2) , alpha and beta alloy has great influence on the corrosion performance of relatively, especially the beta phase can reduce the corrosion of the alloy. Spots residue composition is mainly free Si and AlFeSi phase, also found that there have also been adsorption chlorine residue in place, aluminum which showed that the Cl - Participated in the corrosion process. Zinc content in the corrosion area is much higher than matrix, the above showed that the impurity element zinc alloy is also involved in the corrosion process. So-called advantage and disadvantages, in order to ensure that the Mg element fully formed strengthening phase Mg2Si, generally in the preparation of alloy element of human make a moderate amount of surplus Si element. Because with the increase of Si content, grain size of alloy and heat treatment effect is good. But on the other hand, the excess of Si is having a negative effect, reduce the plastic alloy, the corrosion resistance worse. Anodic oxidation process, the anode is alloy phase Mg2Si pitting source. Priority in the anodic oxidation alkaline cleaning, Mg2Si particles dissolve and corrosion pit formation, including magnesium dissolved in solution and silicon in aluminium alloy on the left, when the corrosion pit converged on the grain will make the dark grain color. Silicon in the sulfuric acid neutralization process is not easy to remove, the spot corrosion erosion bottom silicon content is higher than other regions. By the well-known research surface, 6063 in the aluminum spot corrosion was due to the aluminum alloy anode phase Mg2Si caused the segregation and coarsening, and the impurity elements in the alloy of zinc and Cl - in the solution And pH accelerated the occurrence and development of spot corrosion. So effective solutions for the following, adjust mass ratio of powder and magnesium alloy of silicon is unfavorable make high silicon content, and reasonable arrangement of limitation system in order to prevent the Mg2Si particle partial poly, lest affect corrosion properties of aluminum; Trace elements zinc, and control the alloy during the processing of solution of Cl - Concentration and pH value, reduce the negative impact of active elements.