Development of novel Al-Si-Ce filler wires to enable high contrast in X-ray imaging of fusion welded aluminum alloy joints

One challenge in using X-ray imaging for post-process inspection of aluminum alloys fusion welded with conventional filler wires (e.g., 4xxx, 5xxx) is the negligible contrast between the fusion zone and base metal, which hinders measurement of important weld characteristics such as weld penetration. The current study outlines the development of novel filler wires that are based on commercial 4xxx (Al-Si) wires, but include additions of Ce to create grayscale contrast in X-ray imaging. Four custom Al-Si-Ce filler wires were fabricated by casting and extrusion, and were used for fusion welding of AA6061 plates. X-ray computed tomography of the lap joints with the Al-Si-Ce filler wires showed enhanced contrast between the fusion zone and the base metal enabling superior quantitative inspection. Microstructure analysis revealed that the increased X-ray contrast was due to Ce-containing precipitate particles within the fusion zone, which were identified to be τ1-Ce(AlxSi1-x)2 and τ4-Al2CeSi2. Hardness and other mechanical tests indicate a slight increase in mechanical properties with increasing Si and Ce content in the filler wire. It is concluded that the addition of relatively small amounts of Ce to conventional Al-Si filler wires is an effective method for creating the needed fusion zone contrast for measurement of weld penetration by X-ray imaging.