Papers by Author: Heinz Hackl

Abstract: Recently a new welding technique, the so-called ‘Cold Metal Transfer’ (CMT) technique was introduced, which due to integrated wire feeding leads to lower heat input and higher productivity compared to other gas metal arc (GMA) techniques. Here microstructure formation and residual stress state in dissimilar steel to aluminum CMT welds are investigated. The intermetallic phase seam between the filler and the steel is only a few micrometers thick. Residual stress analyses reveal the formation of the typical residual stress state of a weld without phase transformation. Both in longitudinal and in transversal direction compressive residual stresses exist in the steel plate parent material, tensile residual stresses are present in the heat affected zone of the steel and the aluminum alloy. The area containing tensile residual stresses is larger in the aluminum alloy due to its higher heat conductivity than in the steel. Due to the symmetry in the patented voestalpine welding geometry and the welding from bottom and face side of the weld, the residual stress distributions at the top and at the bottom side of the weld are very similar.

Abstract: Distribution of Zn and interfacial microstructure of braze-welding CMT joints between aluminium and galvanized steel sheets were researched. The results showed, except the gas porosity contains a little Zn, the other areas of fusion zone almost have no Zn. Temperature plays a decisive role in the distribution of Zn. The content of Zn is higher in the dendritic crystal than the intergranular part. The Zn coat adjacent to the joint is almost evaporated entirely. The Zn coat of steel sheet in the heat-affected zone around the joint is badly destroyed, and the corrosion resistance of the joint will decline. There are FeAl3 intermetallics and Al-Fe-Zn triphase solid solution formed at the interface.

Abstract: Recently a new welding technique, the so-called ‘Cold Metal Transfer’ (CMT) technique was introduced, which due to integrated wire feeding leads to lower heat input and higher productivity compared to other gas metal arc (GMA) technique. Here microstructure formation and residual stress state in aluminum CMT welds are characterized and compared to those produced by pulsed MIG- and Laser-hybrid techniques. The results show a small heat affected zone (HAZ) in the MIG weld, the HAZ in the CMT and the laser hybrid welds was not visible by optical and scanning electron microscopy. Compared to the MIG welding the CMT process appears to introduce slightly smaller maximum tensile residual stresses into the weld.