Xiaoyong Yun1,, Yoshinobu Motohashi2, Tsutomu Ito2,, Toshiyuki Asano3 and Satoshi Hirano4
1Graduate School of Science and Engineering, Ibaraki University, Hitachi 316-8511
A cyclic neutral-salt spray test, CCT, has been applied to friction-stir-welded A7075 and A6N01 aluminum alloys and corrosion behavior in each region of stirred-zone (SZ), thermo-mechanically affected zone (TMAZ), heat affected zone (HAZ) and base metal (BM) in the joints are studied. Weight loss, appearance of corroded regions, depth of corrosion and so forth were examined by means of optical and scanning electron microscopies and violet laser color 3D profile microscope. Energy dispersive X ray spectroscopy, EDS, analysis was made on SZ, TMAZ, HAZ and BM regions of the joints. It was found that the region of the TMAZ/HAZ boundary and around it was most susceptible to corrosion among the four regions in both of the FSWed A7075-T6 and A7075-O alloys. The EDS result showed that Cu might be enriched in the TMAZ/HAZ region. It seemed that a main cause of the susceptibility to corrosion in the TMAZ/HAZ region was due to the formation of the second phase particles containing Cu in them in the region. We presumed that the Cu atoms migrated from SZ to TMAZ/HAZ during FSW process that brought about sharp temperature and internal stress gradient in the alloy, which would lead to the enrichment of Cu in the TMAZ/HAZ region. Meanwhile, the FSWed A6N01-T5 alloy showed excellent corrosion resistance under CCT for 1000 h.
A7075 and A6N01 aluminum alloys, friction-stir-welding, corrosion behavior, cyclic neutral-salt spray test
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