Papers by Author: Keng Yan

Abstract: Microstructures and mechanical properties of pure copper weld joints are discussed under different parameters of friction stir welding. The results reveal that it is conducive to the formation of compact joint in friction stir welding by applying high speed steel tool with high anti-bonding temperature. The friction stir welding joint with compact and defect-free microstructure could be obtained when the tool rotation rate is 1250- 1650 r/min and the tool traverse speed is 20-50 mm/min. Intensively plastic deformation occurs in the soften materials of the weld nugget zone and numerous crystal particles are broken under the influence of tool stirring. The microstructure of weld nugget zone is composed of tiny isometric crystals, which is due to the dynamic recrystallization of broken crystal particles. The structure of thermo-mechanical affected zone on both sides is asymmetric. Obvious boundary of the thermo affected zone could be seen on the advancing side, and the plastic streamline is apparent.

Abstract: FBTIG(Flux Bounded TIG)welding experiments for aluminum alloy were made using five species of single-component activating fluxes, including SiO₂、TiO₂、CaF₂、MgO, and NaCl, which was carried out to investigate the effects of flux gap and activating fluxes on weld formation. The mechanism of increasing welding penetration was analyzed linked with the change of arc shape in FBTIG. The experimental results indicate that five species of single-component activating fluxes can increase weld penetration obviously. Specifically, SiO₂ can increase weld penetration remarkably. When flux gap is 4mm, the D/W (depth/width) ratio of weld for FBTIG welding reaches 0.59. The significant increase of weld penetration is the result of comprehensive effect by arc contraction and reversal of the surface tension gradient in the liquid metal.