Effect of surface grinding on the microstructure and corrosion of Al-Mg-Si-Cu alloys

Abstract

Surface treatment has shown strong effects on the corrosion resistance of Al-Mg-Si-Cu alloys. To elucidate the surface grinding effects, a set of the peak-aged Al-Mg-Si-Cu samples are ground using SiC papers with different grits, and the ground surface microstructure and corrosion performance are investigated. The results show that grinding generates a deformed near-surface layer. The deformed layer is characterized by nanocrystalline and the alloying element Cu segregates at nano-grained boundaries. The Cu segregation bands increase the available cathode area and the potential difference between the grain boundary and grain interior, which enhances the microgalvanic corrosion effect between the phase α-AlFeSi (Mn, Cu) and the adjacent matrix. As the SiC paper grit number decreased from 1200 to 80, the Cu segregation bands of the deformed layers increases from 600 to 1600 nm, the corresponding corrosion current density increases from 1.0 ± 0.1 to 22.8 ± 0.7 μA.cm−2, and the corrosion potential decreases from −742 ± 13.1 to −791 ± 15.0 mV (versus SCE).