The effects of the characteristic microstructure developed in extruded 6005A alloys on tensile properties, fatigue strength, and liquation cracking in the heat affected zone of weldments were investigated. An in-situ observation of the grain growth occurring in the sample was made with an optical microscope with a hot stage to determine the temperature of the excessive grain growth during extrusion. The extruded samples were heat treated under various conditions and welded using a gas metal are welding process. The results indicated that liquation occurred mainly at coarse grain boundaries and significantly influencing the mechanical properties of the joint.