Corrosion behavior of arc welded joints of chassis parts and an approach to improve its corrosion resistance

Abstract

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 1^st phase, rust occurred at the slag portion as a paint defect on the weld bead and toe. In the 2^nd phase, under-film corrosion occurred from the weld toe. In the 3^rd 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.