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Aluminium alloy 6060 is typical of a family of Al-Mg-Si extrusion alloys, which are considered weldable only
when using an appropriate filler alloy such as 4043 (Al-5Si) or 5356 (Al-5Mg). This study concerns the
thermal analysis and solidification path determination of aluminium alloy 6060 diluted with variable amounts
of 4043. Casting of controlled mixtures of alloys 6060 and 4043 was used to simulate different weld dilutions
in order to facilitate thermal analysis. Thermal analysis and metallography were applied in order to reveal
solidification reactions and phases, and allow calculation of solid fraction versus temperature curves.
Although the liquidus temperature was little affected, different phases formed with increased 4043 dilution,
with a trend toward lower temperature reactions and a larger fraction interdendritic constituent.
Crack and fatigue resistance are relevant evaluation criteria for welded joints and are decreased by tensile residual
stresses resulting from the welding and cooling process, while compressive residual stresses can have a positive
influence on the characteristics mentioned. In order to generate compressive residual stresses, a set of post weld
treatment procedures is available, like shot peening, hammering, etc. These procedures have the disadvantage that
they are time and cost extensive and have to be applied after welding. As another point, such technologies can only
produce compressive stresses at the top surface, i.e. can only contribute to the reduction of the risk of cracks initiated
at the surface, like fatigue cracks. A chance to generate compressive stresses over the complete weld joint during the
welding procedure is offered by the so-called Low Transformation Temperature (LTT -) filler wires. Compared to
conventional wires, these materials show lower phase transformation temperatures, which can work against coolingrelated
tensile stresses, resulting from respective shrinkage restraint. In consequence, distinct compressive residual
stresses can be observed within the weld and adjacent areas. The strength of these fillers makes them potentially
applicable to high-strength steel welding. Welds produced with different LTT filler wires have shown different levels
and distributions of the resulting residual stresses depending on the specific transformation temperature. The
transformation temperatures are determined by temperature measurement. Classical X-ray diffraction as well as
diffraction methods using high energy synchrotron radiation have been used for residual stress analysis. By means of
high energy synchrotron diffraction in reflection mode residual stress depth gradients can be determined nondestructively.
The phase selective nature of the diffraction measurements enables the simultaneous determination of
the phase specific residual stresses of all contributing crystalline phases within one experiment. The application of
white beam diffraction implies recording of a multitude of diffraction lines within the energy range of the provided
energy spectrum of the white beam. By this means phase specific residual stress depth distributions up to distances of
150 ìm below the surface can be analysed for steel using the energy dispersive set-up of the HMI-beamline EDDI at
the Bessy site, Berlin, providing an energy range between 20-150 keV. As a side effect quantitative phase analysis can
be carried out using white energy dispersive diffraction e.g. the determination of the content of retained austenite in the
weld.
The results of a collaborative research project on laser beam weldability of carbon steels of high sheet thickness are presented. That includes single and multiple pass welding of 16 mm and 20 mm thick plates, as well as the investigation of acceptable tolerances i.e. gap bridgeability and edge misalignment. For the welding experiments fibre lasers with 8 kW, 20 kW laser power and different GMAW-techniques were used in various applications. With the 20 kW fibre laser 16 mm plates could be welded with a single pass, 20 mm required a seam preparation or alternatively preheating of the material. For multi pass welding with 8 kW laser power a joint preparation with a single V-butt joint with a broad root face (Y-groove) was applied. The root pass was always welded with a hybrid process, the filler passes with a hybrid process as well as a GMAW process which produced the best results.