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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. [ABSTRACT FROM AUTHOR]

The use of soldering based on metallurgical bonding, as opposed to conventional rubber sealing, is capable of achieving the firm sealing of stainless-steel subway car bodies, though the corrosion resistance of such joints has rarely been investigated. In this study, two typical solders were selected and applied to the soldering of stainless steel, and their properties were investigated. As indicated by the experimental results, the two types of solder exhibited favorable wetting and spreading properties on stainless-steel plates, and successfully achieved sealing connections between the stainless-steel sheets. In comparison with the Sn-Zn9 solder, the Sn-Sb8-Cu4 solder exhibited lower solidus–liquidus, such that it can be more suitably applied to low-temperature sealing brazing. The sealing strength of the two solders reached over 35 MPa, notably higher than that of the sealant currently used (the sealing strength is lower than 10 MPa). In comparison with the Sn-Sb8-Cu4 solder, the Sn-Zn9 solder exhibited a higher corrosion tendency and a higher degree of corrosion during the corrosion process. [ABSTRACT FROM AUTHOR]

• Hybrid laser heat source was selected for repairing of hybrid laser welded A7N01 alloy. • Defects in original joints were effectively eliminated by hybrid laser heat source. • HCF property with a little increase can be obtained compared with original joints. As one of the key concerns in the health maintenance system for modern railway equipment, defect repair plays an important role in enhancing the running safety reliability and economic benefits. In this study, welding defects of A7N01 alloy commonly used in high-speed trains were repaired by hybrid laser welding. The surface integrity of the welded zone before and after repairing was evaluated by various characterization methods in terms of the microstructures, tensile and fatigue properties. The results show that the original incomplete penetration defects would be eliminated by welding repair, giving rise to some microstructural changes such as the grain refinement and the widening of fine grain zone in the original welded joints. The heat input during welding repairing induced significantly reduction of the hardness and tensile strength from 105 HV to 75 HV and from 358 MPa to 338 MPa, respectively. Nevertheless, the fatigue properties of hybrid welded A7N01 alloy with the hybrid welding repairing were improved by 33.8%, probably because of reduced defects. [ABSTRACT FROM AUTHOR]