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Description
The resistance spot welding is widely employed by automotive manufacturers because of its low cost and fast process. However, when the galvanized TRIP steel plates are joined by resistance spot welding, cracks are generated by liquid metal embrittlement (LME) because the substrate gets exposed to liquid zinc. These cracks deteriorate mechanical reliability of welds and limit the application of TRIP steel.
The present study investigated the microstructural evolution and LME sensitivity of differently Zn-coated TRIP steels. Three Zn-coated TRIP steel sheets were prepared by applying different coating process: (i) continuous galvanizing, (ii) galvannealing, and (iii) electrogalvanizing. Hot tensile testing and microstructural analysis exhibits that the coating method influences Fe-Zn reaction which controls the contact between steel substrate and liquid Zn alloy at the high temperature. The electrogalvanized TRIP steel exhibits the highest resistance to LME, while the galvanized one shows the lowest resistance.
Keywords
Liquid metal embrilttlement, Hot tensile testing, Resistance spot welding, Fe-Zn intermetallic compounds, Galvanized TRIP steel