Analysis of the nature of spot corrosion of LED aluminum profiles

It can be seen from the composition of the 6063 LED aluminum profile used that in order to ensure that the Mg element fully forms the strengthening phase Mg2Si, an appropriate amount of Si element is generally artificially excessive when formulating the alloy composition. Because as the Si content increases, the grains of the alloy(LED aluminum profile) become finer and the heat treatment effect is better. But on the other hand, excess Si also has negative effects, reducing the plasticity of the alloy(LED aluminum profile) and deteriorating the corrosion resistance. Research shows that excess Si can not only form free Si phase, but also form α phase (Al12Fe2Si) and β phase (Al9Fe3Si2) with the matrix. In this way, there are free Si phase, α phase (Al12Fe2Si), β phase ( Al9Fe3Si2) and other cathode phase particles and anode phase Mg2Si particles. The α phase and β phase have a great influence on the corrosion properties of the alloy, especially the β phase can significantly reduce the corrosion properties of the alloy. The components of the residue at the spots are mainly free Si phase and AlFeSi phase. It is also found that chlorine element is also adsorbed on the residue, which shows that Cl- is involved in the corrosion process. The zinc element content in the corrosion zone is much higher than that in the matrix, indicating that the impurity element zinc in the alloy also participates in the corrosion process.

In the anodizing process, the anodic phase Mg2Si is the pitting corrosion source of the alloy. During anodic oxidation alkali cleaning, Mg2Si particles are preferentially dissolved to form corrosion pits, in which magnesium is dissolved in the solution and silicon remains on the aluminum alloy and LED aluminum profile. When corrosion pits gather on the grains, the color of the grains will become dark. Silicon is not easily removed during the sulfuric acid neutralization process, so the silicon content at the bottom of the spot corrosion pits is higher than in other areas.

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