Abstract
Recently developed fabrication methods have made it possible to produce nanocomposite Al-TiC filler wires (FWs) for Al weld metal (WM) inoculation, which reduces the notorious hot-cracking susceptibility of heat-treatable Al alloys in traditional arc-welding. This study examined whether an alternative solid-state process route involving metal screw extrusion (MSE) could be viable for producing composite FWs. Four composite AA1370 FWs were successfully produced with a combination of the following dispersed particles: Ti (<150 μm), TiB2 (0.5 μm), and TiC (40-60 nm). Commercially pure Al was chosen as base alloy in order to reduce complexity. The composition of each FW was (wt%): (1) 1.1Ti, (2) 1.1Ti-0.18TiB2, (3) 1.5TiC, (4) 1.1Ti-1.5TiC. A reference FW (no additions) was also produced as benchmark. All five FWs were welded with GMAW (gas metal arc-weld) and GTAW (gas tungsten arc-weld), and the resulting WMs were characterized by light microscopy (LM), scanning electron microscopy (SEM), and Vickers hardness. The 1.1Ti FW resulted in a 70% reduction in WM mean grain size relative to both GMAW and GTAW reference. However, the extra addition of 0.18TiB2 did not seem to have any grain refining effect. The 1.5TiC FW reduced the mean grain size by 75% and 80% relative to the GTAW and GMAW reference respectively; while the 1.1Ti-1.5TiC FW reduced the mean grain size further to 80% and 90% respectively. No GTA-welded FWs resulted in a fully equiaxed WM grain structure; however, the GMA-welded 1.1Ti, 1.5TiC, and 1.1Ti-1.5TiC FWs resulted in completely equiaxed grain structures. No significant increase in WM hardness relative to reference was found for any FW, however, the 1.1Ti-1.5TiC GMA-WM was slightly harder (15%). Overall, the WM porosity increased with increasing particle additions, and porosity was found to be significantly higher with GMAW compared to GTAW. The porosity is believed to stem from the adsorption of moisture on particle surfaces due to air exposure at supplier and/or during MSE. The results in this study indicate that MSE could be a viable method to produce nanocomposite Al-TiC FWs in the future. However, the issue of porosity must be resolved, and the study should be expanded to more relevant Al base alloys (i.e, 2xxx, 6xxx, or 7xxx).