Advanced Materials Research Vols. 941-944

Abstract: 7A52 aluminum alloy was welded by using 5356 welding wire added Sc, Zr and Er. Microstructure of the welding joint was observed by using optical microscope (OM). Bending property was tested by bending tester. The results demonstrated that, compared to employ traditional 5356 welding wire, the grains in welding zone (WZ) were much finer; The grains in fused zone (FZ) nucleated and grew from the matrix; The grain size along heat affected zone (HAZ) dercearsed gradually.The welding joint prepared by using 5356 welding wire added single 0.3%Sc possessed maxium face bending strength. The welding joint fabricated by using 5356 welding wire added compond 0.1%Sc+0.2% Er possessed maxium rear bending strength. The fine isometric crystal and isometric dendrite generated at the welding zone when the new type 5356 wire added gingle Sc or compound Sc+Er was employed, which make the welding joint represent excellent bending property, respectively.

Abstract: An incremental and thermal electro-mechanical coupled finite element model has been presented in this study for predicting spot nugget size, gap between workpieces, and thermal expansion displacement during spot welding process. Approximate temperature dependent material properties, including physical and mechanical properties, have been considered. The spot nugget shape and the thermal expansion displacement were obtained by simulation. The solutions showed that the displacement of workpieces was directly related to the quality of solder joints and can be as a monitoring parameter of spot weld quality. These calculations provide a theoretical reference for nugget quality monitoring and forecasting by electrode expansion displacements.

Abstract: Traditional welding methods are difficult to adapt to the development of welding technology of aluminum alloys. Laser welding plays an important role in this field increasingly for its advantages. In this investigation, LF21 plate with a thickness of 2mm was welded utilizing the pulsed laser welding and the mechanical properties of the laser welded joints are analyzed. The tensile strength of welded joint is in the range of 196 Mpa to 232 Mpa. The maximum tensile strength is obtained at the working current of 250 A, pulse width of 6 ms and pulse frequency of 2 Hz. The maximum tensile strength can reach 87% of base material. The intensity factor of welded joint is in the range of 74% to 87%. The welded joint can meet the requirements of users.

Abstract: Longitudinal hot tearing, popularly called as end cracking, frequently takes place in the end portions of large steel panels’ butt joints, using one-sided, submerged-arc welding with flux copper backing welding process (FCB welding). The study was to look for the possibility to improve and/or prevent the end cracking issue during FCB welding, center blind-hole drilling technique was used to measure the welding residual stress for five different cases, considering hot tearing mechanism, its influence factors and the relevant reported prevention measures. Unpredictable result was observed subsequently that transverse compressive stress is found on the shallow surface of weld seams, which could give supplementary information to the common assumption for conventional low heat input welding method that cracks initiation is caused by tensile stresses across the welded joints. The study concluded that FCB welding end cracking issue is caused by the comprehensive function of different stresses, and also properly use tack welding practice, suitable elastic run-off plate and relatively low heat input energy which will reduce the end cracking susceptibility for the tested materials.

Abstract: The wire material and the workpiece was fused together by the transient arc heat from disconnect impulse, to achieve metallurgical bonding. The process of arc striking and the arc was very short in disconnect impulse arc welding. The image signals of disconnect impulse arc and droplet transfer were acquired using speed camera systems. Then, the arc and the droplet transfer characteristics in repairing the metal defects process were discussed. The results showed that the process of arc striking was only 0.5-1ms in disconnect impulse arc welding. The maintain arc time must be matched with the arc current, the longer maintain arc time the less the arc current was likely to be.

Abstract: The microhardness and microstructure of Ti-24Al-15Nb-1.5Mo/TC11 dual alloy joining interface processed by different heat treatment regimes were investigated. The results show that the microhardness of the weld zone and Ti-24Al-15Nb-1.5Mo alloy side of the dual alloy processed by gradient heat treatment are higher than that of the specimen processed by balance heat treatment. Moreover, the microstructure differences between the specimens processed by gradient heat treatment and balance heat treatment are very obvious, particularly in the interface between the TC11 alloy and the weld zone. While the joining interface is processed by gradient heat treatment, the microstructure change homogeneously, and the demarcation lines are ambiguous. However, for the joining interface processed by balance heat treatment, the demarcation lines are very obvious, and the microstructure of the TC11 alloy side is bi-morphic, the lath is short and coarse. Therefore, the interface integrity of the dual alloy processed by gradient heat treatment is better, which is an adoptable method to improve the properties of the dissimilar alloy joining interface.

Abstract: Mg/Al dissimilar materials were welded successfully by GTAW with SAlSi welding wire of Al-Si system. The nice surface forming and free defects of joints are formed. Mg/Al welded joint were tested and analyzed by means of optical microscope, scanning electron microscope, microhardness tester. The test results show that in the fusion zone of Mg side, it shows the intense columnar crystalline structure and little intergranular precipitates, and has more dendritic intergranular precipitates. However, the weld zone shows the typical columnar structure zone. There is no high hardness brittle phase in fusion zone of Mg side. The hardness of weld zone is slightly higher than one of Mg substrate, and far less than the Al substrate.

Abstract: The corrosion resistance layers can be surfaced in the valve casted by carbon steel, to enhance the corrosion resistance performance. By the 3D solid model, the weight and internal area of valve body was obtained. The surfacing process was designed and the welding rods theory amount was calculated. And the actual amount was close to the theory one. The surfacing and cutting process was designed for the fit surfaces and the dimension chain was calculated to meet the fit accuracy and the corrosion resistance layer thickness. The results show that it has the engineering significance by using 3D solid model to estimate the producing costs; the fit accuracy and the corrosion resistance layer thickness can be obtained together based on the surfacing and cutting process; in this way, the cost can be cut down more than 30%, compared the whole stainless steel valve.

Abstract: Based on the friction stir welding rig,the temperature field model was established by COMSOL Multiphysics under the coupling effect of joule-heat and friction heat. The coupled temperature field distribution and variation rule of the analysis model were simulated and analyzed under current-carrying or without current. The results show that the maximum temperature mainly distributes the contact area of the pin tool and work piece. The distribution of the temperature and isothermal layer with current is basically same with non current. The temperature distribution area of shoulder with current gets larger than without current condition. Under the constant welding velocity,axial force,rotation velocity and displacement,the maximum temperature produced by coupling function of joule-heat and friction heat is much higher than the one,which engendered by friction heat.

Abstract: AZ31B magnesium alloy and T2 Cu metal plates with the thickness of 2mm were bonded by argon tungsten arc welding (TIG) under the conditions that the welding current is 100A and the welding speed is 150 mm/min. The microstructure, phase composition and properties of welded joint were studied by scanning electron microscopy (SEM), X-ray diffraction (XRD), micro-hardness test. The results show that AZ31B magnesium alloy and T2 Cu combined well with no cracks, porosities, incomplete penetration and other metallurgical defects. A transition zone composed of equiaxed and columnar crystals of α-Cu exists between the weld metal and base metal Cu, its width is about 80μm. The central area of the weld is made up of α-Mg matrix and Mg-Cu eutectic. The joint consists of α-Cu, α-Mg, Cu₂Mg, Mg₂Cu and little MgO, CuO phase. The micro-hardness of weld zone is significantly higher than that of the base metals, and its heat affected zone appears softening phenomenon.