Generation of a fine-grained microstructure in GMA-welded aluminium by modified filler materials for a reduction of solification cracks

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The aim of the research project is to transfer the known grain-refining effect of certain elements during the solidification of aluminum alloys onto the weld metal during GMA-welding. By the coating of the welding wires with nuclei-forming elements, such as titanium, they are transported into the weld metal and thus contribute to grain refinement. Due to the fine grain formation in the weld metal, it is possible to significantly reduce solidification cracks. Furthermore, it will be investigated whether the grain refinement can be transferred to the self-hardening and extremely hot-crack-sensitive alloy types. In addition, a hardening of the weld material is to be realized in order to achieve a positive effect on the mechanical strength of the weld metal and partly to compensate the strength drop in the heat-affected zone by a supporting effect of the now stronger weld metal.The metal-glass technology is to be used to investigate the nucleation mechanisms of the coating elements in the weld metal. This makes it possible to virtually freeze the state of the melt and to make the distribution of the solidification nuclei visible in the scanning electron microscope by means of energy-dispersive X-ray radiation. This technology is intended to extend the level of knowledge about the formation of the weld metal during the GMA-welding of aluminum materials. In addition to the coating elements, other solidification nuclei occurring as a result of the welding process can also be made visible as well. A further object is the derivation of functional relationships for the formation of the micro-structure in the weld metal by the layer of grain-refining elements on the modified filler materials. Here, general relationships between grain size, mechanical properties, coating thickness and / or composition are to be developed.As a by-product of the investigations, the influence of the coatings on the welding process can be determined. This includes the influence on the arc length, the droplet transition and the penetration behavior. Here, too, the derivation of general principles is striven for.