Formation mechanism of black spot defects on surface of Al-Si alloy during anodic oxidation
Investigating the formation mechanism of black spot defects on the surface of anodized Al-Si alloy can provide a theoretical foundation and insights for the regulation of anodic oxidation process of Al-Si alloy.Utilizing scanning electronic microscopy,optical microscopy,energy disperse spectroscopy and x-ray diffraction,this study analyzes the black spot defects that occur during the anodizing process of Al-Si alloy workpieces.The results reveal that compared to the normal region,the microstructure morphology,phase distribution and volume fraction of the black spot defect area of Al-Si alloy workpieces change obviously.The needle-like compounds in the normal area and the fishbone compounds in the defect primarily consist of binary Fe-Al compounds.The eutectic transformation of the Fe-rich phase in the black spot defect area contributes to its complex morphology.It is evident that the black spot defect,generated by phase transition,is linked to the electrochemical processes during the anodic oxidation.
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