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Abstract
Dual phase 980 MPa grade (DP980) steel sheets were resistance spot welded using a pulsed current, and the effects of the pulsed current on the strength properties of the joints were investigated. The pulsed current improved the mechanical properties of the joints in cross tensile tests. In situ observations during tear tests revealed that the ductility of the nugget was improved and that the propagation of cracks into the nugget was inhibited when the pulsed current was used. Microstructural observations and electron probe microanalysis (EPMA) of the nugget showed that the segregation of phosphorus at the nugget was reduced in the joint welded using the pulsed current, suggesting that the pulsed current improved the ductility of the nugget by altering their microstructures.
The authors are grateful to Mr K. Ohmitsu of Osaka University for performing the EPMA. Part of this work was supported by Priority Assistance for the Formation of Worldwide Renowned Centers of Research—The Global COE Program (Project: Center of Excellence for Advanced Structural and Functional Materials Design) from the Ministry of Education, Culture, Sports, Science, and Technology (MEXT) and by a Grant-in-Aid for Young Scientists (B) no. 24760599, Japan.