Role of grain boundary on the growth behavior of anodic film on spark plasma sintered AA6061

To explore the influence of grain boundary on the growth behavior of anodic film, the grain boundary density of aluminum alloy is adjusted by spark plasma sintering (SPS) with different grain sizes and investigated by techniques including SEM, TEM, and SKP. The results indicated that a suitable grain boundary density effectively uniforms the anodizing current distribution and improves the thickness of the anodic film. In 30 min sulfuric-adipic acid anodizing, the growth rate of the film on the sintering AA6061 reaches 0.47 μm min⁻¹, which is much higher than that of commercial AA6061 under the same conditions. However, excessive grain refinement results in the formation of fine-crystal clusters and a surge of grain boundary density. It enhances field-assistant dissolution in initial anodizing and has a direct weaken effect on the final anodic film thickness.