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The refinement of microstructure in aluminum cast ingots can provide important advantages, for example: less porosity, enhanced mechanical properties such as strength and ductility and a higher resistance to the formation of solidification cracks. Grain refinement is usually achieved by inoculation with aluminum master alloys containing selected amounts of titanium and boron.
The principle of grain refinement by inoculation can also be used in arc and laser welds through additions of Ti and B to the filler metal. In this way it is possible to enhance the mechanical properties of the weld metal and weldability of the alloy. The basic effect of this addition on the weld metal grain structure was analyzed in this study using different aluminum alloys and welding processes. To accomplish this, a filler metal consisting of the base metal and different amounts of the master alloy AlTi5B1 was produced. The filler metal was then deposited in the base metal and fused using either a gas tungsten arc (GTAW) or laser beam welding process (LBW).
Experiments have shown how the grain refiner addition level influences the weld metal mean grain size and shape. Additions of titanium and boron have refined the microstructure considerably. Both changes in grain size and shape depended strongly on the welding and solidification conditions. Furthermore, the observed grain refinement depended on the chemical composition of the base metal. Different alloys showed, for comparable welding conditions and addition levels, a different weld metal grain structure.