## 2 Materials and Methods
The objective of the experiments was to gain information about filler metal mixing behaviour in laser-arc hybrid and laser cold-wire welding of thick sections by comparing the effects of wire feeding orientation and groove cross-section. The welding tests included the following parameter combinations (A and B):  
(A)  
(B)  
(A)  
(Table 3). Figure 3b,d show the defocusing configurations with focal point position set to 20 mm above the test piece surface for the laser-arc hybrid and laser cold-wire welding experiments, respectively. The welds produced were cut transversally into specimens for metallographic examination. The cutting locations were in the middle area of the 300 mm long welds in order to ensure that the analysed weld cross-section is from a location where the welding process has already stabilized. During the metallographic preparation, the specimens were ground, polished and electrolytically etched (10% aqueous oxalic acid, 30V/2A/40s) to reveal the macroscopic weld cross-section appearance and weld microstructures. A light microscope was used for metallographic observation of the cross-sectional weld specimens. In addition, EDS analysis of selected weld cross-sections was done using a Hitachi SU3500 scanning electron microscope and a Thermo Scientific Ultradry DSS EDS-detector. Chromium  
Figure 3: Set-up of laser beam and filler wire feeding arrangements used in laser-arc hybrid welding (upper row; **a,b**) and laser cold-wire welding (lower row; **c,d**). A1 = leading wire feeding. A2 = trailing wire feeding. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Studied Parameter** & **Laser-Arc Hybrid Weld** & **Laser Cold-Wire Weld** \\
**Combinations** & **Identification** & **Identification** \\ \hline A1 + B1 & - & LCW1 \\ A2 + B1 & - & LCW2 \\ A1 + B2 & LAH1 & LCW3 \\ A2 + B2 & LAH2 & LCW3 \\ A1 + B3 & LAH3 & LCW5 \\ A2 + B3 & LAH4 & LCW6 \\ A1 + B4 & LAH5 & LCW7 \\ A2 + B4 & LAH6 & LCW8 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Welding parameter combinations in laser-arc hybrid and laser cold wire welding tests and weld identification designation. Abbreviations (A1, A2 and B1–B4) are explained in page 3. (Cr) was selected as a trace element and its distribution and quantity within the test weld cross-sections were identified using a transverse stepwise characterization and mapping technique. Weld metal Cr-values acquired from the EDS stepwise characterization were compared to known Cr-values of the base metal (17.6 weight-%) and filler metal (22.9 weight-%) to determine the filler metal mixing of each selected test weld (see Equation (1)). For example, if the detected chromium content of a measured point in the weld metal were 17.6 or 22.9 weight-%, the filler metal mixing would be 0 or 100%, respectively. The above relationship is shown in Figure 4, which illustrates how specific chromium weight-% content in the weld metal corresponds to filler metal mixing percent value. \[\text{\emph{Filler metal mixing}}\ \%=\frac{(\text{\emph{veld metal Cr content}})\ -\ (\text{\emph{base metal Cr content}})}{(\text{\emph{ filler metal Cr content}})\ -\ (\text{\emph{base metal Cr content}})}\ \times\ 100 \tag{1}\]  
In the EDS stepwise characterization, an acceleration voltage of 20 kV and sampling time of 90 s were used. As the aim was to study weld metal mixing and homogeneity at a macroscopic scale, the measurement \"spot\" size and step interval within the measurement line were chosen accordingly. Thus, measurement spot size of 40 \(\upmu\)m \(\times\) 60 \(\upmu\)m and step interval of 100 \(\upmu\)m (distance between individual spots) were used to ensure that an individual measurement spot gave data over several dendrites/dendrite spacing at every step. EDS measurements included four horizontal line segments from each studied weld cross-section sample running transversally across the weld fusion zone.