Study On Welding Technology And Joint Mechanical Properties Of Friction Stir Welding Of 7N01 Aluminium Alloy

Weight reduction and high-performance materials have always been hot issues of research in the transportation industry.7N01 aluminum alloy has been widely used as structural materials of railway car bodies,for its light weight, high strength, excellent welding performance, et al. This paper have studied the selection of the stirring heads, the welding technology of FSW and the mechanical properties of the welded joints by combining with the properties of 7N01 aluminum alloy. Also the application to the pillow beam structure in FSW has been investigated, which will provide the experimental basis and theoretical support for the further study on welding equipment welding technology of aluminum alloy in FSW, and material performance.Result shows that properties of aluminum alloy are almost the same to that of the parent material, such as the bending property, micro-hardness and the stress corrosion resistance; the tensile strength is improved up to 80% of that for the parent material and the impact toughness reaches the level of 1.5～2.5 times. The microstructure of the 7N01 aluminum alloy welded joint is fine equiaxed grain in the size of 2-10 microns which is much finer than that of the parent material. The fine equiaxed grain results that the weld microstructure is uniform without any defect and the mechanical property of the alloy is excellent.Comparing with the flat butt joint, the mechanical properties of the pillow beam structure is quite different. For the wall of 15 mm, the tensile strength is reduced by 5.9%, the yield strength is improved by 14.7% and the ductility is reduced by 31.2%. On the other hand, for the wall of 6 mm, the tensile strength is improved by 1.8%, the yield strength is improved by 2.1% and the ductility is improved by 12.5% as well. Also the impact toughness value is reduced by 40%. However, both the bending property and the stress corrosion resistance are almost the same. What’s more, the fatigue characteristic value for the wall of 15mm is 119.03MPa which is reduced by 8%, whereas for the wall of 6 mm, that is improved by 34% as 115.16MPa. It is also found that the fatigue source is easily appearing on the uneven surface of the specimen.Through welding experiment of alloy and sleeper beem structure,7N01-T5 should be placed in the advancing side in FSW; the parameter welding speed ranges from 100 to 200 mm/min,while rotate speed ranges from 300 to 700 mm/s; it’s better to use Type I(SF-D26-S15-I) stir welding head in FSW of 15mm 7N01 aluminium alloy plate,and Type A (SF-D15-6-A) in FSW of 6mm alloy plate as well.