Given the limited build volumes for most current additive manufacturing (AM) machines, a method for taking advantage of the unique capabilities offered by AM while combining it with traditional manufacturing methods is needed. Welding of AM produced components is a solution to this challenge. The objective of this study was to determine the feasibility of using FSW to join powder-bed-fusion laser melted (PBF-L) AlSi10Mg and examine the effects of post weld heat treatment and hot isostatic pressing (HIP) on the overall joint quality and mechanical performance. Samples were examined using optical microscopy, scanning electron microscopy (SEM), hardness testing, and tensile testing. Examination of the samples which underwent a post-weld annealing heat treatment revealed cracking along the stir zone and thermo-mechanically affected zone (TMAZ) boundary. Examination of the crack revealed evidence of liquation near single-phase Si precipitates in the TMAZ, despite the annealing temperature being 27°C (49°F) below the solidus temperature of the material according to the material specification. Using a calculated pseudo-binary phase diagram of AlSi10Mg, the annealing heat treatment was determined to be in the partial liquation regime for AlSi10Mg. The voids and crack formation mechanisms were determined to be caused by constitutional liquation coupled with the unique TMAZ microstructure and stress state. The as-welded and HIP coupons were void free and defect free, and FSW was determined to be a feasible method of joining PBF-L printed aluminum alloys with minimal knock-down in tensile strength.