自動車部材アーク溶接部の腐食挙動と耐食性向上

Reducing auto body weight by use of high strength steel is an important issue. Although it is necessary to increase the strength of steel sheets for underbody parts, use of high strength steel sheets has not progressed sufficiently due to the problems of fatigue and corrosion. Corrosion of underbody parts mainly occurs in arc welded joints, but the detailed corrosion mechanism had not yet been clarified.The author investigated the corrosion behavior in arc weld by laboratory corrosion tests using Ar-20%CO2 gas shielded arc weld, and clarified the corrosion mechanism. Based on that work, Ar-5%CO2 gas shielded arc weld was applied as an approach to improve corrosion resistance. The corrosion behavior of arc welded joints was classified into three phases. In the 1st phase, rust occurred at the slag portion as a paint defect on the weld bead and toe. In the 2nd phase, under-film corrosion occurred from the weld toe. In the 3rd phase, perforation corrosion progressed at the film peeling portion near the weld toe. When Ar-5%CO2 gas shielded arc weld was applied as an improvement technique, slag generation was suppressed and as a result, corrosion resistance was improved.