Abstract
The recently developed production method metal screw extrusion (MSE), has shown to be a viable method for producing nano-composite filler wires (FWs). AA1370 FW containing TiC nanoparticles (NPs) supported by titanium (Ti) powder has been produced via MSE. These have been used to arc-weld sheets of AA1050-H14. During previous work this has shown to strongly grain refine the weld metal (WM). During this work, site specific focused ion beam (FIB) transmission electron microscope (TEM) lamellas were produced. These were characterized using different transmission electron microscopy techniques, with a special focus on nucleation mechanism and TiC NP distribution, in addition to their effect on grain refinement. \bigskip The TiC NPs were found to generally be distributed along grain boundaries (GBs) and the α-Al grains had nucleated on large TiAl3 particles found in the centers of grains. The large TiAl3 particles are thought to have formed on smaller TiAl3 particles precipitated in the melt and grown supported by the high concentration of solute Ti at the solidifying front. The grain refining effect can be attributed to a combination of the segregating effect of Ti, precipitation of TiAl3 particles in the melt creating ideal nucleation sites for α-Al, and the growth restricting effect of the TiC NPs.