252 Prakt. Met. Sonderband 38 (2006) 
However, the texture observed for the CMT weld is clearly weaker than the texture is 
obtained for aluminum welds produced by laser welding [10], where the cooling rate is Th 
significantly higher. by 
Residual Stresses. Residual stress analysis % the 
(Fig.12) shows mostly compressive stresses in the (a) 60 res 
weld seam with balancing tensile stresses in the FT 4 in 
AIMg3-parent material next to the fusion zone. 2 2 CM 
The maximum tensile stress within the parent 1 3 
material is less than 80MPa in all welds a Ac 
investigated. Longitudinal compression in welds is -60 J — 
atypical for materials, which do not undergo phase = 80 Mn Th 
transformations during rapid cooling. As a result of HH un 
thermal contraction of the weld pool at the end of ty enter men eu Int 
the cooling process, tensile residual stresses are La: 
generally observed in welds produced by fusion (b) % Wr 
welding techniques [11]. However, the butt-joints F aw . . 
investigated were clamped in order to avoid EE) 
distortion. Mechanical clamping introduces tensile "9 5, 
stresses into the AIMg3-rolled sheets to be joined. = 
These are released by de-clamping after the 60 a MG Transvorse [1] 
welding process and, therefore, compressive g 80 mR Te 
residual stresses remain in the weld seam [12]. A [21 
The residual stress profile of the CMT weld in both OS rr arty [31 
weld directions is symmetric with respect to the ee [41 
weld centerline (Fig.12a). The residual stresses in (c) 80 J. 
both the weld seam and the parent material are = i [5) 
higher in the longitudinal than in the transverse © Cy [6] 
direction of the weld. In case of the MIG weld, the * of ‘ Hv 
residual stresses are very similar to those of the ‚20 [71 
CMT weld (Fig.12a,b). The magnitude of the > Ta An 
tensile residual stresses in longitudinal direction of ; Fa thre Longitucing [8] 
the weld is also slightly higher than in the * 406 [91 
transverse direction. In the laser hybrid weld 108.64. 2.0.2.4. 680 (+ 
(Fig.12c) the stresses in the longitudinal direction Distance to the weld center [mm] MC 
follow the same pattern as in the CMT and MIG Fig.12: Residual stresses across the top 
welds. However, the transverse stresses in the side of the welds (20 
laser-hybrid weld are significantly lower. In I! 
addition, due to the asymmetry of the laser hybrid weld geometry the stress profile is not ' 
symmetric with respect to the weld center. 
4. Conclusions 
The microstructure of AIMg3 butt-joints produced by the new CMT technique is compared 
to those of MIG and laser hybrid welding. The porosity of the CMT weld is lower than in 
the pulsed MIG weld. All three joining processes lead to similar dendritic microstructures. 
The MIG weld shows a larger heat affected zone compared to the CMT and the laser- 
hybrid welds. In the fusion zone the AISi5-filler increases the volume fraction of 
segregations and precipitates. Thus, the microhardness and the strength of the fusion 
zone are higher than in the parent material. Crystallographic texture in the CMT weld seam