## 4 Conclusions  
Laser-arc hybrid and laser cold-wire welding tests were conducted on 10 mm thick butt-welded joints of AISI 316L austenitic stainless steel base metal using an overmatching type 2205 duplex stainless steel filler metal. The objective of the work was to study filler metal mixing behaviour in laser-arc hybrid welding and laser cold-wire welding. The following variables and their effect on mixing behaviour were of interest: leading and trailing filler wire feeding and butt-joint preparation, namely I-groove and V-groove type welds. The following conclusions can be drawn from the results of the laser-arc hybrid welding tests:  
1. Open square preparation (I-groove) with a 0.4 mm root gap in a 10 mm thick butt joint showed a clear difference in filler metal mixing between the upper half and lower half of the weld cross-section. Average filler metal mixing values in percent were within the range \(\sim\)31-38% in the upper half of the weld cross-section but only \(\sim\)25-28% in the lower half of the weld. 2. Increasing the cross-sectional groove area by using a root gap of 0.8 mm in a square butt weld (I-groove) enhanced filler metal mixing across the whole weld cross-section. This change was particularly evident in the root portion of the test welds, where average mixing values in percent were between \(\sim\)40-46%. 3. With laser-arc hybrid welding, V-groove type welds with trailing and leading wire feeding had the highest filler metal mixing values (averages from 41% to 56%) but the homogeneity of the mixing was not as good as I-groove welds with 0.8 mm wide root gap. 4. In all test welds, trailing filler wire feeding produced stronger filler metal mixing in the root portion than leading filler wire feeding. 5. Near the weld surface, the average filler metal mixing-% values were smaller when using trailing wire feeding (i.e. trailing torch) than leading wire feeding (i.e. leading torch). This result was probably caused by larger local base metal dilution near the weld surface when a trailing torch configuration was used. Following conclusions can be drawn from the results of the laser cold-wire welding tests:  
1. In closed square (zero root gap) welds, filler metal mixing behaviour was observed to be remarkably inhomogeneous with both leading and trailing wire feeding compared to the welds with wider gaps. Large local spikes in mixing profiles were found and the difference between the high and low mixing values could be almost 45%-units. Acute local changes in the chemical composition of the weld metal induced changes in the weld solidification mode, which had separate islands of both primary austenite and primary ferrite solidification microstructures. 2. A clear difference was noticed in filler metal mixing between the upper half and lower half of the weld cross-sections in the case of the I-groove weld with 0.4 mm root gap for both leading and trailing filler wire feeding. When the root gap was widened to 0.8 mm, leading wire feeding still showed a noticeable difference in mixing between the upper and lower half of the weld cross-section. Corresponding results with trailing wire feeding, however, showed enhanced mixing behaviour across the whole weld cross-section with greater homogeneity and higher mixing values. Average filler metal mixing values in percent were in the range \(\sim\)39-47% for the entire weld cross-section. 3. Utilization of V-groove preparation with trailing wire feeding gave the best filler metal mixing in terms of both homogeneity and high mixing values. Average filler metal mixing values in percent were in the range \(\sim\)60-67% for the entire weld cross-section. Overall, the results of the mixing studies indicate that both welding processes benefit from the use of a larger groove cross-section. The use of trailing wire feeding showed more robust mixing behaviour with V-groove preparation for the laser cold-wire process and with I-groove preparation with a 0.8 mm root gap for the laser-arc hybrid process. Methodology, M.K. ; Investigation, M.K.