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Keyhole is a defect which seriously restrains the industrial application of friction stir welding (FSW) technique. In this study, a new technique of non-keyhole friction stir welding (N-KFSW) was proposed, which could eliminate the keyhole during the in-situ welding process. Experiments were performed using a 6 mm thick 6061-T6 aluminum alloy plate under different rotating velocities. Due to the unexpected consumption of rotating sleeve during N-KFSW, the N-KFSW tool was simplified to a system consisting of a hollow sleeve and a clamping ring based on the working principle of N-KFSW. Compared with the solid sleeve, this hollow sleeve promoted the material flow below the sleeve. Therefore, the depth of the sleeve-stirring zone (SSZ) was equal to the thickness of the plate when the plunging depth was only 4.2 mm. The SSZ was divided into the sleeve directly affected zone (SDAZ) and the sleeve indirectly affected zone (SIAZ). The material in the SIAZ was transferred by the indirectly stirring effect of hollow sleeve, so the butt interface in the SIAZ was distributed as the S-shape line at the bottom of the SIAZ. The maximum tensile strength of 217.3 MPa was obtained at 1200 rpm, which was 71.5% of that of the base material. The height of the S-shape line shrunk with the rotating velocity increasing, and then governed that the fracture position of the joint transferred to the HAZ from the SSZ. The fracture surface morphology exhibited typical ductile fracture.

A novel non-keyhole friction stir welding technique was proposed to weld the butt joint of 6061-T6 aluminum alloy with the thickness of 6 mm. A sound joint was obtained by this technique, simultaneously eliminating the flash, shoulder mark and keyhole defects. The sleeve directly affected zone (SDAZ) and the sleeve indirectly affected zone (SIAZ) were divided into the joint according to the plunging position of the hollow sleeve. The lack of root penetration defect was avoided when the plunging depth of the hollow sleeve was only 4.2 mm, because the hollow part inside the sleeve improved the material flow below the sleeve. An S-shaped line was left at the SIAZ, and the height of it had the minimum value of 1.47 mm at 20 mm/min. Whether the failure location of the joint was in SIAZ/SDAZ or the heat-affected zone (HAZ) depended on the height and bonding strength of the S-shaped line. The joint fracture location changed from the SIAZ/SDAZ at 35 mm/min to the HAZ at 20 and 30 mm/min. The maximum tensile strength of 224.3 MPa was obtained at 30 mm/min which was 73.7% of that of the base material. The fracture surface morphology exhibited the typical ductile fracture.

Friction stir lap welding (FSLW) is expected to join the hybrid structure of aluminum alloy and steel. In this study, the Al-Mg-Si aluminum alloy and 301L stainless steel were diffusion bonded by FSLDW with the addition of 0.1 mm thick pure Zn interlayer, when the tool pin did not penetrate the upper aluminum sheet. The characteristics of lap interface and mechanical properties of the joint were analyzed. Under the addition of Zn interlayer, the diffusion layer structure at lap interface changed from continuous to uneven and segmented. The components of the diffusion layer were more complex, including Fe-Al intermetallic compounds (IMCs), Fe-Zn IMCs and Al-Zn eutectic. The largely changed composition and thickness of uneven and segmented diffusion layer at the lap interface played a significant role in the joint strength. The tensile shear load of Zn-added joint was 6.26 kN, increasing by 41.3% than that of Zn-not-added joint. These two joints exhibited interfacial shear fracture, while the Zn interlayer enhanced the strength of diffusion bonding by extending the propagation path of cracks.

Plasma-MIG hybrid welding and MIG welding of 5083 marine aluminum alloy was carried out. The influences of parameters of welding process on the weldments morphology were investigated in order to optimize the welding process parameters. The macrostructure, microstructure, tensile and bending properties of the optimized joint were studied. The results show that Plasma-MIG hybrid welding not only has a synergistic effect of Plasma and MIG welding but also has a high welding efficiency. Welding speed, Plasma current and MIG current have a significant effect on welding penetration and welding morphology. Meanwhile, the ductility and strength property of weld joint was qualified though the bending test and tensile test. The average tensile strength of weld joint is about 285MPa at room temperature, about 86% of the base metal.

In order to improve the quality of laser cutting of stainless steel porous, the investigation on cutting 0.12mm stainless steel plates was carried out by a50W-powerbridgefiber laser cutting machine.The influence of the auxiliary line angle, laser power, and the pulse width and gas pressure on the cutting quality was studied in this paper.The results show that fewer defects was found on the samples when the cutting angle of auxiliary line was 90°and few splash orburrswas found on the samplesby 40 Wlaser power, with 56 μs pulse width and 1.3MPa gas pressure.

In this paper we use the same idea as the complex analytic dynamics to study general Mandelbrot sets and Julia sets generated from the complex non-analytic iteration . The definition of the general critical point is given, which is of vital importance to the complex non-analytic dynamics. The general Mandelbrot set is proved to be bounded, axial symmetry by real axis, and have (m+1)-fold rotational symmetry. The stability condition of periodic orbits and the boundary curve of stability region of one-cycle are given. And the general Mandelbrot sets are constructed by the escape-time method and the periodic scanning algorithm, which present a better understanding of the structure of the Mandelbrot sets. The filled-in Julia sets Km,c have m-fold structures. Similar to the complex analytic dynamics, the general Mandelbrot sets are kinds of mathematical dictionary or atlas that map out the behavior of the filled-in Julia sets for different values of c.

The effect of strain hardening and strain softening behavior of flow stress changing with temperature on welding residual stress, plastic strain and welding distortion of A7N01-T4 aluminum alloy was studied by finite simulation method. The simulation results show that the weld seam undergoes strain hardening in the temperature range of 180–250 °C, however, it exhibits strain softening at temperature above 250 °C during welding heating and cooling process. As a result, the strain hardening and strain softening effects counteract each other, introducing slightly influence on the welding residual stress, residual plastic strain and distortion. The welding longitudinal residual stress was determined by ultrasonic stress measurement method for the flat plates of A7N01-T4 aluminum alloy. The simulation results are well accordant with test ones.

A new technique named rotating extrusion was proposed that uses rotating extrusion action to rectify residual distortion of aluminum alloy thin-plate weldments to improve mechanical properties of welded joints. The basic principle and device of rotating extrusion were introduced. The residual distortion and stresses in rotating extrusion weldments were compared with those in conventional weldments. The differences in microstructure and mechanical properties between conventional welded joints and rotating extrusion welded joints were investigated and analyzed in order to make clear the effect of rotating extrusion on the performance of aluminum alloy weldments. Experimental results show that rotating extrusion can enhance the hardness and tensile strength of aluminum alloy welded joints evidently. This method has also potential effect on extending the life of welded structures.

In this paper, a thermal elastic-plastic finite element method (FEM) is used to simulate the plasma welding process in order to predict the welding distortion of automobile stator iron core. Six spatial symmetrical welding torches are adopted in the welding process so as to make the iron core rings welded firmly and the distortion symmetric. The effect of rigid clamp on actual welding process is replaced by the contact function between rigid body and deformation element in the MSC software, MARC. The welding process restrained by clamp and deformation analysis after the removal of clamp was successfully simulated. The predictions show good agreement with the test results when the rigid clamps are taken into account in the welding simulation, which satisfies the design requirement for manufacture.

In this paper, the welding residual distortion of aluminum alloy thin plates is predicted using the elasticity-plasticity finite element method (FEM). The factors contributing to the welding buckling distortion of thin plates are studied by investigating the formation and evolution process of welding stresses. Results of experiments and numerical simulations show that the buckling appearance of thin-plate aluminum alloy weldments is asymmetrical in the welding length direction, and the maximum longitudinal deflection appears at the position a certain distance from the middle point of the side edge towards the arc-starting end. The angular deformation direction of thin-plate weldments is not fixed, and such case as the angular deformation value of the arc-starting end being higher than that of the arc-blowout end exists.

The numerical simulation calculation of longitudinal seam TIG welding of thin-wall aluminium cylinder was conducted by the FEM software, Marc. Based on the generating of analysis model, displacement field was quantitatively described. Circular profile of aluminium alloy cylinder after welding was predicted by the radial displacement. The simulation results showed that the post-weld deformation for the longitudinal seam of aluminium alloy cylinder was mainly destabilizing deformation.

The distribution and value of welding residual stress for 1Cr18Ni9 stainless steel stud welding joints was systemically simulated by ANSYS FE software. The mathematical estimating models of strength of the welded joints were established. Simulation results showed that the welding residual stress was tensile at the edge of the stud, while it was compressive stress at the position near axis center. The largest tensile stress did not exceed yield limit of material. The residual stress had more influence on the strength of welded joints.