| Abstract |
| An expulsion phenomenon occurred during resistance spot welding of advanced high-strength steel sheets, and the effects of the Cr and Si contents on the expulsion limit current (CExp) were investigated. The correlation between CExp and the steel properties (e.g., resistivity, melting point, coefficient of thermal expansion, high-temperature yield-strength and viscosity), were evaluated, as were the qualities of the alloying elements. The CExp decreased with increasing Si contents. This resulted in a narrow range of acceptable welding current, as well as poor suitability for spot welding. On the other hand, the effects of Cr-contents on the CExp, and on the acceptable range of welding current were minimal (with content of 3 wt%). Thus, the suitability for spot welding was not affected by the Cr-Contents (at the experimental concentration). As Si-Contents increased, resistivity also increased and the melting point decreased. This resulted in easy melting of the base metal at a low welding current (low heat input) and in the rapid increase of the pressure due to the increased coefficient of expansion. However, the high-temperature yield-strength of the corona bond, which blocked the expulsion of the molten melt, also decreased. Consequently, the CExp of steel containing additional Si was lower than that containing Cr. |
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| Key Words |
| metals, welding, microstructure, optical microscopy, expulsion |
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