Arc welding of dissimilar aluminum alloys is in high demand in industry but often challenging in practice. Dissonant material properties between the base metals often lead to solidification cracking in the weld metal upon cooling. Here, we report a nano-treatment approach that infuses TiC nanoparticles into filler material mimicking commercial ER5183 to successfully join dissimilar systems of AA2024 + AA5083 and AA2024 + AA7075 with the gas-tungsten arc welding process. Welded specimens were free of hot cracking, and microstructural studies revealed globular, refined grains smaller than 20 µm in the weld metals of both systems. Mechanical properties of both systems were examined with microhardness and tensile testing, and they showed sound behavior in their as-welded conditions. Nano-treatment therefore presents a new way to reliably weld dissimilar systems that are traditionally considered unweldable.