Black Lines Analysis of Al–Zn–Mg Alloy After Anodic Oxidation.

A 3C production uses Al–Zn–Mg alloy as the material of its housings which appeared with black lines on the surface after anodic oxidation treatment. Through appearance observation, 3D outline scanning, SEM section observation, EDS composition test, inclusion analysis, and chemical composition, the cause of the black lines and the solution was brought forward. The results show that the black lines were induced by particles rich in Ti and B in the anodic oxidation film along the extrusion direction. The particles were TiB2 which came from the grain refiner Al–Ti–B during the Al–Zn–Mg alloy manufacture. [ABSTRACT FROM AUTHOR]