*3.7. Vickers Hardness*

To characterize the strength of the of the joint via cross-sections, maps of the Vickers hardness values are reported here. Figure 12 shows the hardness map of the completed joint for standard GMAW and CW-GMAW specimens.

One can see that the Vickers hardness in the weld for the CW-GMAW is higher, which indicates that the cooling rate of the weld metal in CW-GMAW was faster than the standard GMAW. For some conditions, the melting efficiency of CW-GMAW was higher than in conventional GMAW. The melting efficiency is the amount of heat that actually transfers to the melting pool over the welding total power, and the difference in this value might explain slower cooling rates.

Figure 13 shows the hardness map of the root pass in cross-section extracted from the middle of the joint. Regarding the root pass, one can see that the values are similar in standard GMAW and CW-GMAW. However, comparing Figures 12 and 13, one can see that the bottom of the CW-GMA welds is harder than the bottom of conventional GMAW. Given that the hardness patterns of the roots were similar, one has to consider that the cooling rate near the root was faster in CW-GMAW. However, the exact mechanism behind this fact is still unclear, but may be due to a faster heat transfer due to a

larger contact area (the area of contact between the weld metal and the base metal) as well as a higher gradient between the weld and base metals in CW-GMA welds.

**Figure 12.** Hardness map of the cross-sections: (**a**) standard GMAW; and (**b**) CW-GMAW, with weld interface marked by dashed lines.

**Figure 13.** Hardness map of the root pass, middle cross-section: (**a**) standard GMAW; and (**b**) CW-GMAW, with weld interface marked by dashed lines.
