Squeeze-cast A356 alloy was fusion-welded by the gas tungsten arc welding (GTAW) process. The effects of T6 heat treatment, filler metals, and shielding gas flow rates on the qualities of the weld with or without an anodic coating were fully investigated. The fusion zone of squeeze-cast A356 alloys illustrated a greater amount of porosity and pore volume than that after T6 heat treatment. Using filler metal of Al-5Mg (ER5356 or 5556) significantly decreased the pore numbers and pore volume comparing with the results when using Al-5Si filler. For specimen of as-cast A356 welded after T6 heat treatment, the fusion zone was wider than that for specimen of as-cast A356 alloys. Increasing the shielding gas flow rate up to 20l/min during welding could reduce the pore numbers, the pore volume and the loss of magnesium content in the fusion zone, which in turn improved the mechanical properties of the weld.