Prakt. Met. Sonderband 38 (2006) 247 
that the MICROSTRUCTURE FORMATION IN CMT-, MIG- AND LASER- 
oe HYBRID ALUMINUM WELDS 
> of the H. Pinto’, J. Bruckner”, H. Hackl”, A. Pyzalla’ 
* Max-Planck Institute for Iron Research, Max-Planck Str. 1, 40237 Diisseldorf 
** Fronius GmbH, BuxbaumstraBe 2, 4600 Wels, Austria 
ABSTRACT 
eatment 
Slice of The microstructure of AIMg3 butt-joints produced by the new ‘Cold Metal Transfer’ (CMT) 
hoice of technique is compared to those of butt joints produced by traditional pulsed MIG- and 
J Laser-hybrid techniques. The results reveal the formation of similar dendritic 
ain; sre microstructures in all three welds investigated. A small heat affected zone (HAZ) is visible 
only for the MIG weld. In the weld seam the AISi5 filler increases the volume fraction of 
segregations and precipitates and, thus, an increase in microhardness is observed. 
Crystallographic texture formation in the CMT-weld is only moderate and driven by the 
system, direction of heat flow. Compared to MIG welding process, the CMT process introduces 
slightly smaller tensile residual stresses into the weld 
can be 
1. INTRODUCTION 
Due to the increasing demand for welding technologies in CMT 
industrial applications, Fronius International GmbH, Wels, 
) 2144 — Austria, has developed in the last 6 years a nearly spatter 
free welding technique, the so-called ‘Cold Metal Transfer 
5 7.256. (CMT) [1,2,3], with excellent reproducibility, applicability in 
diverse welding positions and high gap bridging ability. The 
CMT process is based on the dip-transfer arc with a 
- systematic discontinuity of this arc. Once a short circuit 
ı Mat. 13 occurs, the digital process-control interrupts the power pulsed Mi 
supply and controls the retraction of the wire. This for- and 
backward wire motion takes place at a frequency of up to 90 
) 4281 — Hz and assists droplet detachment during the short circuit. 
This results in a reduced heat input in comparison to other 
conventional ‘Gas Metal Arc’ (GMA) processes. Thus, the 
work pieces to be joined remain considerably ‘colder’ and wy 
y (2006), welds with low distortion and higher precision are obtained. 
Recently, the microstructure [4], the residual stresses [5] and ~~ -aser- "hr 
02) 345. the mechanical properties [6] of both similar and dissimilar 
CMT welds have been characterized. 
The present investigations aim at comparing the 
6) 360 — microstructure in aluminium butt-joints welded with the 
pulsed metal arc welding (MIG), the laser-hybrid and the 
02) 51 — CMT process. For comparability reasons, the welds were 
produced with the same parent material (AIMg3), the same , . 
filler (AISi5), the same sheet thickness, and -as far as Fig.1: Cross-sections of the 
possible- similar welding speed and similar weld geometry. oye pulsed WIC and 
aser hybrid welds