Morphology of Corrosion Pits on the Surface of Friction Stir Welded Joint of AA7075 Aluminum Alloy in Salt Water Environment

Based on the different zones and microstructures of 7075 aluminum alloy joints surface by friction stir welding, the 3D morphology of corrosion pit within in 3.5% NaCl solution, over a period of time, have been observed and discussed by ultra-depth 3D microscopy system(UDM) during a certain period of time. Further, the laws of distribution and 3D morphology about corrosion pit have been analyzed. The results show that there is a positive correlation between the corrosion degree in different zone on the joints surface and grain sizes. After 360 h immersion test, the average depth and maximum depth of corrosion pit in heat affected zone (HAZ) which the average depth reached 120 μm is the most serious. The corrosion degree of shoulder affected zone(SAZ) which the average depth reached 50 μm is the least serious.