Additive manufacturing (AM) presents a wide range of benefits for structural applications, but many high strength aluminum alloys and nickel-based alloys for high temperature service are susceptible to solidification cracking. Alloy 6061, a precipitation hardenable aluminum alloy, is generally considered un-processable using fusion-based welding and AM, and Haynes 230, a solid solution and carbide precipitate strengthened nickel alloy, frequently exhibits cracking in laser powder bed fusion. The addition of inoculants for nucleation sites and/or increased constitutional undercooling to promote grain refinement is an effective strategy to reduce solidification cracking during AM in both alloys, but they are impacted by inoculation to different degrees. In this work, Sigmajig weldability testing using autogenous laser welding was conducted on standard and inoculated versions of gas metal arc directed energy deposition processed 6061 and laser powder bed fusion processed Haynes 230. In both alloys, solidification cracking was eliminated in the inoculated AM built base metal conditions when compared to non-inoculated counterparts. However, differences in the weldability response using Sigmajig were observed in the two alloys based on the addition of inoculation. A model was presented that shows the combined effects of grain size refinement from inoculation as well as modification of terminal solidification reactions when inoculant particles dissolve. Overall, these findings suggest that simple modifications to traditionally non-weldable alloys can improve weldability and add to the library of usable materials where the benefits of additive manufacturing can be fully realized.