Liquation cracking in the partially melted zone (PMZ) of aluminum welds was studied. The PMZ is the region immediately outside the fusion zone where the material is heated above the eutectic temperature. Highly crack-susceptible alloys 2024 and 7075 were welded using gas-metal arc welding (GMAW) with filler metals 1100 and 4043, respectively. Circular-patch welds were made on 3.2 mm thick workpiece with full penetration, and single-pass welds were made on 9.5 mm thick workpiece with partial penetration. Liquation cracking was observed in all welds. Dualpass welds were also made on 9.5 mm thick workpiece, with overlapping between the penetration tips of the two partial-penetration passes made on the opposite sides of the workpiece. Liquation cracking was found in the first pass but not in the second pass. The results were explained using TfS (temperature vs. fraction solid) curves of the weld metal (WM) and the PMZ based on the following criterion proposed recently: liquation cracking can occur if WM fS > PMZ fS during PMZ solidification.