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The friction stir welding (FSW) butt joint of 2mm 6061-T6 aluminum alloy was tested. The effects of welding speed and lower shoulder pressure on the microstructure and mechanical properties of the joint were analyzed, and the possible problems in the welding process of thin plate were analyzed in depth. The results show that the yield strength of the welded joint of 6061-T6 aluminum alloy increases with the increase of welding speed, and the mechanical properties of the joint are not sensitive to the change of the pressure under the shoulder. The core area of the welded joint is the weakest area due to the softening of the welded joint and the insufficient amount of plastic metal transfer.

Vision sensor systems with an auxiliary light source such as structured light–based vision sensor have been widely used for weld seam detection. However, the main drawback of this method is the preview distance between the welding position and the sensing position, which can generate unavoidable detecting errors. Laser welding of the small workpiece or narrow butt joint is especially vulnerable to detection error caused by preview distance. Meanwhile, only one point of the weld seam can be measured each time, which makes the corresponding image processing very sensitive to light noise. Consequently, a seam measurement method based on a passive vision sensor for narrow gap butt joint is proposed in this article. The weld pool is observed directly by this vision sensor so that there is no preview distance. An adequately adjusted telecentric lens is used to increase the contrast between the seam feature and the background welding noise. By this manner, a long and noticeable weld seam feature, as well as the weld pool, can be obtained in the captured images. A corresponding image processing algorithm based on particle filter is designed to extract the captured long weld seam. The particle filter is used to track the slope and intercept of the weld seam, which combines the advantage of both particle filter and Hough transform. As the particle filter algorithm could generate the result by evaluating both the previous and the current measurement results, the corresponding image processing can be robust even when a few images are of poor quality. Finally, laser welding experiments were carried out, and the results revealed that the proposed method could achieve detection accuracy of 0.08 mm when welding 0.1 mm width narrow butt joint at 2000 mm/min welding speed.

The double-pass butt welding process was carried out on 9-mm-thick 2014-T4 aluminum alloy T-joints by stationary tool shoulder friction stir welding (STS-FSW). Microstructure changes were analyzed by grain and EBSD, combined with the evolution of the precipitation phase, to explore the influence of regulations of different process parameters on T-joints’ mechanical properties. Defect-free T-butt joints were obtained within the rotational speed range of 400–500 rpm and the welding speed range of 100–140 mm/min. Due to severe dynamic recrystallization, the weld nugget zone exhibits fine equiaxed grain characteristics, with a grain size of approximately 10 μm. The degree of recrystallization and deformation in the weld nugget overlapped zone (WNOZ) did not significantly change, and the grain size of WNOZ was approximately 4 μm. T-joints’ hardness has an uneven distribution, and the hardness is greatest in the weld nugget zone at 110–125 HV. The T-butt joints have the weakest hardness at the skin and stringer in the TMAZ, approximately 70–80 HV. The ultimate tensile strength of the skin and stringer in the T-butt joints is equivalent to 85% and 59.6% of the base material. According to the fitting of a quadratic polynomial with multiple variables, it is found that the maximum tensile strength of the skin and stringer can only be achieved when the thermal input is within a reasonable range. The fracture is a ductile fracture with numerous dimples visible on the fracture surface. The tensile fracture of the specimen is analyzed by the finite element method. T-butt joints exhibit lower stress concentrations during the tensile test than T-fillet joints.

Al/Ti dissimilar alloy plates with a thickness of 6 mm were butt joined using the direct laser fusion-brazing method. A systematic comparison of laser fusion brazing of four groups of AA5083 to TA31 plates with different groove angles ranging from 60 to 90° was performed by laser beam offsetting to the aluminum alloy side. The related weld appearance, microstructures in the weld and at the joint interface, defects formation mechanism, and fracture resistance were analyzed and compared in detail. A preferable joint appearance characterized by wetting the top and bottom sides of the titanium alloy with molten aluminum alloy can be obtained except for the joints with 60° groove angle. The uniformity of intermetallic compound (IMC) morphology and thickness distribution at the interface was improved as the groove angle decreases, accompanied by a decrease in the diffusion distance of main elements at the same location. Severe interfacial crack and intergranular hot crack defects were formed in the joints with 90 and 60° groove angles, respectively. The interfacial cracks are induced by the difference in hardness and elastic modulus between TiAl3 phases and titanium base metal or aluminum weld. The hot crack defects are mainly caused by microstructure mismatch including grain size and texture orientation mismatch between the fine grain zone near the interface and the coarse grain zone inside the aluminum alloy weld. The crack-free joints with groove angles of 70° show the highest tensile strength of 268.76 MPa due to the relatively uniformly distributed and fine interfacial IMCs. This study reveals the possibility to realize efficient joining of medium-thick titanium alloy and aluminum alloy plates by using the laser fusion-brazing method without other auxiliary equipment.

The development of high-strength advanced additively manufactured (AM) aluminum alloys is driven by the need for weight reduction in complex-shaped structural applications. In this context, heat-treatable aluminum-scandium alloy, known commercially as Scalmalloy®, offers high strength and lightness, also at high temperatures, due to solution strengthening Al 3 (Sc, Zr) particles. A widespread diffusion of such AM alloy is also related to welding technologies that could preserve its engineered microstructure. This study investigates the microstructural and mechanical properties of butt friction stir welding (FSW) joints of LPBF Scalmalloy® plates under different welding settings. Joint performance was evaluated under quasi-static and cyclic loading conditions. Porosity in Scalmalloy® and welds was assessed using 3D X-ray computed tomography. An aging heat treatment assessed the extent of precipitation hardening in the FSW joints. Results show that metal stirring during FSW notably reduced the intrinsic porosity of Scalmalloy®, decreasing the equivalent pore diameter from about 200 μm to 60 μm in the welded joints. Under quasi-static loading, welded specimens failed at the interface between the thermo-mechanically affected and the stir zones on the advancing side. The aging heat treatment improved the mechanical strength of Scalmalloy® from approximately 400 to 480 MPa, albeit at the expense of ductility (elongation at fracture decreased from 16 to 4%). The higher heat input and stirring developed at a low welding speed reduced lazy S defects but limited the effectiveness of subsequent aging. In fatigue testing, welded joints consistently failed within the aged base material due to the intrinsic porosity of Scalmalloy®.

Friction stir welding of aluminum alloys is today an essential joining technic for various industrial sectors. However, making a quality joint is relatively expensive compared to the electric arc welding processes. The aim of this work is to maximize the ultimate tensile strength (UTS) of AA3004-H32 aluminum alloy butt joint and minimize its production cost. The welding parameters are rotational speed, welding speed, and pin shape of the tool. Then, a test campaign is carried out according to the Box-Behnken design of experiments. Mathematical models of power consumption and ultimate tensile strength were developed by multiple linear regression. The analysis of variance (ANOVA) of the experimental data revealed the preponderant effect of the tool rotational speed and the pin profile on the studied responses. The bi-objective optimization problem was solved using the genetic algorithm and optimal welding parameters were presented. In terms of joint quality and electrical energy consumption, the results showed that the tool rotational speed plays a key role, and that the threaded cylindrical profile of the pin is the most preferred compared to other studied shapes. The welding speed is the most significant parameter in reducing welding costs. The approach proposed in this study can be used as a guide and recommendation to reduce FSW costs and at the same time ensure the quality of the AA3004-H32 alloy joint.

The paper describes the influence of the friction stir welding travel speed on the mechanical properties of the butt joints of copper plates. The results of static and fatigue tests of the base material (Cu-ETP R220) and welded specimens produced at various travel speeds were compared, considering a loading applied both parallel and perpendicularly to the rolling direction of the plates. The mechanical properties of the FSW joints were evaluated with respect to parameters of plates’ material in the delivery state and after recrystallisation annealing. The strength parameters of friction stir welding joints were compared with the data on tungsten inert gas welded joints of copper plates available in the literature. The results of microhardness tests and fractographic analysis of tested joints are also presented. Based on the above test results, it was shown that although in the whole range of considered traverse speeds (from 40 to 80 mm/min), comparable properties were obtained for FSW copper joints in terms of their visual and microstructural evaluation, their static and especially fatigue parameters were different, most apparent in the nine-fold greater observed average fatigue life. The fatigue tests turned out to be more sensitive criteria for evaluation of the FSW joints’ qualities.

To solve the shortage of austenite phase precipitation caused by nitrogen loss in the welding process of UNS S2205 duplex stainless steel (DSS), shielding gas nitriding was investigated by adding different N2 contents in Ar shielding gas during the welding process. A good thin-walled pipe butt joint was formed using the pulsed tungsten inert gas (P-TIG) welding method with Ar-N2 shielding gas. High cycle fatigue tests of the weld joints were conducted to study the effect of shielding gas nitriding on the fatigue properties. Fatigue tests at three stress levels of 225 MPa, 270 MPa, and 360 MPa were carried out on the weld joints with different N2 contents, and the fatigue samples were all fractured in the high temperature heat-affected zone (H-HAZ). Within the current process parameters, the fatigue life of the 4 vol.% N2 welded joints was optimal. Fatigue striations appeared in the fatigue crack propagation zone, and the transient fracture zone was similar to the tensile fracture. Under the low-stress level, the area of the crack propagation zone under 4 vol.% N2 was the highest, the tear ridges all expanded around the crack source area, and the fatigue crack propagation zone presented a radial distribution. The proliferation and expansion of dislocations were mainly carried out in the austenite grains, and the dislocation density of the fatigue specimens under 4 vol.% N2 was smaller than that of the Ar specimens. Shielding gas nitriding effectively improved the balance of the two-phase ratio and the hardness of austenite phase, optimized the internal slip system, inhibited the proliferation of dislocations in the austenite phase, and improved the fatigue life of weld joints.

Riveting is widely used in aircraft manufacturing. The strap butt joint is often used in the aircraft’s main bearing area such as the aircraft docking area. The connection quality affects the reliability and safety of the aircraft directly. To study the effect of the rivet position on the connection quality of the strap butt joints, this paper analyzed the distribution of stress around the rivet hole at different positions by the finite element method, and then further analyzed the influence of the different rivet layouts on the connection quality of the strap butt joints by experiments. The static load tensile failure test of the joints was carried out, and the obtained tensile strength and failure mode of the strap butt joints showed that the main static tensile failure form of the single strap butt joint is that the whole rivets is sheared and the connecting sheets are separated. By changing the layout of different rivets, the connection strength can be maximized by reducing the outer row spacing (ORSD) of rivets. The results can be used for reference in the design of the riveting structure of aircraft panels.

In this research, the temperature field characteristics and melt flow behaviors of 5A06/6061 aluminum alloy lock-butt joint during the electron beam welding (EBW) process are investigated by numerical simulation involving heat transfer and flow of fluid. The calculated mesh model of the lock-butt joint is established with the computational domain divided into three phases. The rotating Gauss heat source is applied to simulate the electron beam energy loaded on the base metal during the welding process. Immediately, not only the temperature filed distributions on the surface and different sections of the molten pool are analyzed carefully, but the flow behaviors of the liquid metal in the molten pool are studied in detail. The results demonstrate that the asymmetric distribution of the temperature field, keyhole, and molten pool morphology exist constantly during the welding process. Besides, there are asymmetric metal flows on both sides of the molten pool and obvious vortex metal flows near the rear and the surface of the molten pool. The melt flow on the keyhole wall represents diversity including the surrounding, downstream, and upstream flow. Moreover, the corresponding experiment is conducted to verify the accuracy of the established model and the simulation results are in good agreement with the experimental results in this work.