Grain refinement in MSG welding of aluminum alloys by surface-coated additives for initial solidification crack reduction

Funding: DFG
Duration: October 2019 to September 2022

Abstract
the research project aims to transfer the known grain-refining effect of certain elements during the solidification of aluminum alloys to the weld metal during fusion welding. By coating the filler wires with grain-forming elements, such as titanium, these elements are to be introduced into the weld metal, thereby contributing to grain refinement. The formation of fine grains in the weld metal is expected to significantly reduce solidification cracks. Furthermore, the study aims to investigate whether grain refinement can be applied to hardenable alloy types that are extremely susceptible to hot cracking. In addition, hardening of the weld metal will be implemented to achieve a positive effect on strength properties and to partially compensate for the strength loss in the heat-affected zone through the supporting effect of the now stiffer weld. The metal-glass technique will 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 visualize the distribution of solidification nuclei in a scanning electron microscope using energy-dispersive X-ray spectroscopy. This technique is intended to expand our understanding of weld metal formation during MSG welding of aluminum materials, as it allows for the visualization not only of the coating elements but also of other solidification nuclei generated by the welding process. A further objective is therefore to derive laws governing the formation of the microstructure in the weld metal due to the layer of grain-refining elements on the modified filler materials. In doing so, general relationships between grain size, mechanical properties, coating thickness, and/or composition are to be established. Through high-speed imaging and the functional relationship between current and voltage values, the influence of the wire electrode coating on the welding process can be determined. This includes the influence on arc length, droplet transfer, and penetration behavior. Here, too, the goal is to derive general principles.