Improving liquation cracks and mechanical properties of 6005A aluminum alloy MIG welded joints via a hybrid milling-friction stir processing tool

The 6005A aluminum alloy extrusion profiles are widely used in China Railway High-speed trains and mainly welded by metal-inert gas welding. The coarse-grain layer covering the profiles leads to the formation of liquation cracks and deteriorates the mechanical properties of the welded joints. In addition, the weld reinforcement has negative effects on the fatigue life. To improve the mechanical properties of the welded joints, a novel hybrid milling-friction stir processing (HMFSP) tool is developed. The surficial coarse grains and intergranular eutectic could be eliminated by the tool, which suppressed the formation of liquation cracks. Meanwhile, the weld reinforcement was removed simultaneously and the stress concentration near the weld toe was eliminated. The average grain size of the affected zone was refined to 5.7 μm and the tensile strength of the welded joints increased by 10% after HMFSP. Moreover, a 62.1% prolongation of the fatigue life was obtained.