- freely available
Metals 2016, 6(12), 299; https://doi.org/10.3390/met6120299
2. Materials and Methods
3. Results and Discussion
3.1. Microstructure and Nugget Geometry of the Weldment
3.2. Tensile Shear Performance of Weldment
3.3. Hardness Measurement
- The microstructure of both weldments was decorated by the predominantly martensite phases in the weld nugget. Martensite, bainite, and retained austenitic phases were evaluated in the HAZ.
- It was found that the nugget diameter increased with increasing welding currents greater than 6 kA for all welding times (15, 20 and 25 cycles). Using a welding current greater than 6 kA causes more forging of soft zones and decreases the nugget height. The galvanized coating on the surface of the TRIP steel resulted in a smaller nugget diameter and a thicker nugget cross section.
- The HAZ of the galvanized TRIP800 weldment was found to be slightly larger due to the higher thermal conductivity of the galvanized steel.
- The tensile shear strength of both weldments improves by increasing the heat input associated with the welding current and the welding time, except 9 kA. The coating presents a negative effect on the strength and failure mode.
- A partial interfacial failure (PIF) mode was observed in the uncoated sample joined at 6 kA for all welding times due to insufficient heat input. Meanwhile, a PIF mode due to excessive heat input was also observed in the galvanized sample joined at 9 kA for all welding times.
- The welding current and welding time range, to obtain indented weld nugget geometry and a desired PF mode for the uncoated sample, should be higher. Increasing the heat input up to expulsion enables joining at a larger area, which provides an extended nugget size and a desired PF mode for both weldments.
- It was found that hardness increased in the fusion zone and the HAZ of both weldments due to martensitic transformation. In addition, the HAZ hardness of the galvanized weldment was found to be slightly higher. It is believed that coating leads to the conduction of heat faster, thus preventing the coarsening of the grains in the HAZ, so fine grains cause high hardness.
Conflicts of Interest
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|Welding Current (kA)||Electrode Force (kN)||Weld Time (Cycle)||Hold Time (Cycle)||Squeeze Time (Cycle)||Clamping Time (Cycle)||Electrode Type(F16)||Electrode Diameter (mm)|
|15||25||15||Spherical tip (Cu–Cr–Zr)||5.5|
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