The Effects of Inoculation on the Weldability of 6061 Aluminum Processed with GMA-DED

The weldability of plain and inoculated 6061 aluminum processed with gas metal arc directed energy deposition (GMA-DED) was evaluated and compared to wrought 6061. Autogenous gas tungsten arc welds of varying heat inputs were made, and the degree of solidification cracking was evaluated. The degree of cracking in the inoculated 6061 material was lower than that of plain GMA-DED and wrought 6061. Microstructure characterization revealed that the welds on the inoculated 6061 produced fine, equiaxed grains, whereas the plain 6061 showed coarse, columnar grains. A combination of heat transfer and solidification models were employed to predict the solidification morphology of the 6061 welds, which closely matched the experimental results in all cases. A model was developed to understand the effect of grain morphology on solidification cracking, and it was found that equiaxed grains shifted the critical liquid film range for cracking to lower solid fractions where thermal stresses are the lowest. However, cracking can be caused if sufficient external stresses are applied when the critical liquid film thickness is present during solidification of the equiaxed grain structure. This work provides insight into the role grain size and morphology control can have in suppressing solidification cracking of other aluminum alloys.