•The combined laser bionic and ultrasonic impact were firstly treated welded joints.•Composite treatment had a compatibility effect and optimized the bionic structure.•Gradient heterogeneous ...structure was formed by composite treatment.•The fatigue strength of Mg alloy welded joint was increased by composite treatment.
The present work investigates the effect of combined laser bionic treatment (LBT) and ultrasonic impact treatment (UIT) on the fatigue properties of AZ31B magnesium alloy TIG welded joints. The fine grains with random orientation were obtained in weld seam after LBT, resulting microhardness increased, and the surface of welded joint formed a “soft-hard” alternating bionic structure. After the composite treatment, the maximum compressive residual stress was induced on the surface of welded joint, which was about −272 ± 30 MPa. In addition, obvious plastic deforming layer and nanocrystalline grains were formed. The grains with preferred orientation were obtained in the plastic deforming layer. The fatigue test showed that the fatigue strength of composite treated welded joint sample increased by 33% and 125% compared with LBT treated welded joint and untreated welded joint samples at 107 cycles, respectively. The composite treatment changed the nucleation position and fracture morphology of the crack, as well as induced a series of strengthening mechanisms.
Tungsten Inert Gas (TIG) welding is one of the most widely used welding procedures for joining aluminium alloys. However, welding efficiency is dependent on the welding circumstances and filler rods ...used. As a result, this study examined the effect of the ER5183 filler rod on the mechanical properties and metallurgical of the TIG welded AA5083 and AA5754. These two alloys combination joints are used in automobiles, shipbuilding, etc. A V-groove joint was attempted on 5 mm thick plates with a 2.4 mm diameter tungsten electrode. First, the microstructural characterization was carried out to observe grain structure in the weld sample. Mechanical properties were studied to determine the yield and ultimate tensile strength after TIG welding. Finally, a hardness study along a transverse direction of weldments was carried out at the different weld zones. The results showed that the maximum UTS of the weld joint was achieved as 169 MPa and hardness of 89 HV on the weld joint.
To study the influence of welding defects on welding quality and the detection effects of different nondestructive testing methods on welding defects in large cruise ships, tungsten inert gas welding ...tests were carried out on Q355 steel to prepare three types of welding specimens, including defect free, with porosity defects, and with slag inclusion. The microstructure, mechanical properties, and nondestructive testing of the three sample types were investigated. The results showed that weld zone microstructures of the three types were mostly formed of acicular ferrite, grain boundary ferrite, and pearlite, whereas heat-affected zone microstructures were primarily composed of martensite and bainite. Compared with weld without defects, the average Charpy impact toughness of welds with porosity defects in the weld and heat-affected zones decreased by 4.0 and 38.0%, respectively. The Charpy impact toughness of welds with slag defects in the weld zone was basically the same as those of welds without defects, while it increased by 5.6% in heat affected zones. The finer the grains in a weld were, the greater the microhardness. In terms of nondestructive testing, certain surface defects are related to internal defects, and they might be a symptom of internal problems in the weld.
•The microstructure of the welded joints was characterized using Scanning Electron Microscopy and Metallurgical Microscopy.•Tensile, bending, impact and hardness tests were used to compare the effects of welding defects on welded joint quality.•The effectiveness of common nondestructive testing methods for the detection of welding defects was compared.
This paper reports on a study aiming at comparing properties of the Ti6Al4V titanium alloy joints between pulsed Nd:YAG laser welding and traditional fusion welding. To achieve the research purpose, ...Ti6Al4V titanium alloy plates with a thickness of 0.8mm were welded using pulsed Nd:YAG laser beam welding (LBW) and gas tungsten arc welding (TIG), respectively. Residual distortions, weld geometry, microstructure and mechanical properties of the joints produced with LBW and TIG welding were compared. During the tensile test, with the aid of a high speed infrared camera, evolution of the plastic strain within tensile specimens corresponding to LBW and TIG welding were recorded and analyzed. Compared with the TIG, the welded joint by LBW has the characters of small overall residual distortion, fine microstructure, narrow heat-affected zone (HAZ), high Vickers hardness. LBW welding method can produce joints with higher strength and ductility. It can be concluded that Pulsed Nd:YAG laser welding is much more suitable for welding the thin Ti6Al4V titanium alloy plate than TIG welding.
Tensile properties of 2219-T8 aluminum alloy TIG welding joints were seriously restricted by partially melted zone (PMZ) properties and stress concentration at weld toe. In this work, PMZ local ...properties were enhanced by refining grains size and θ phase particles in base metal. And the stress concentration at weld toe was adjusted using three-pass welding with swing. The results showed that tensile strength of PMZ was increased by ∼16–21 MPa, due to the higher Cu content of matrix, as well as reduced coarse and continuous eutectic. The joint tensile strength of ∼318 MPa (∼10% increase) and elongation of ∼5.8% (∼26% increase) were obtained by improving PMZ local properties and matching proper stress distribution.
An applicable method to improve the tensile properties of 2219-T8 aluminum alloy TIG welding joints is attractive in manufacturing of large propellant tanks. In this work, tensile properties of ...2219-T8 TIG welded joints was improved by adjusting the weld geometry using multi -pass welding with swing. The effects of weld geometry on the tensile properties of joint were investigated. And the geometry parameters were optimized by an orthogonal experiment design. The joints with tensile strength coefficient of 70 % and elongation over 4% were acquired after weld geometry optimization. The improvement mechanisms of weld geometry attributed to the reduced strain variation rate and stress concentration at the weld toe.
The 12 mm-thick Ti–6Al–4V (TC4) titanium alloy plates were welded using keyhole tungsten inert gas (K-TIG) welding at various heat inputs. The microstructure, grain boundary (GB) characteristics and ...mechanical properties of the weld metal zone (WMZ) were analyzed. The test results show that the K-TIG welds are well formed, and no obvious defects are observed when the heat input is 2.30–2.62 kJ/mm. When the heat input gradually increases, α laths increase in length, and α′ phase and residual β phase are reduced. The electron backscatter diffraction (EBSD) test results indicate that the high-angle GB proportion in the WMZ increases with the increase of heat input. The tensile strength of the WMZ gradually decreases and the elongation of the WMZ increases when the heat input increases from 2.30 to 2.62 kJ/mm. The impact toughness of the WMZ increases as the heat input increases.
In this paper, high-temperature impact fatigue (HTIF) was carried out on a Co-based surface layer cladded by TIG welding, and cracks emerged at 400-cycle condition. The reasons for cracking were ...investigated from three aspects: microstructure, stress distribution, and crystal orientation. Crack generation was induced by high stress distribution in eutectic carbides at grain boundaries and the great disparity in orientations between grains on two sides of the crack path. The microstructural advantage for cracking behavior played a key role in emergence of cracks, which was verified by the investigation and comparison of three distances from the weld interface. Moreover, the interface microstructure of Co-based layer and FB2 substrate was characterized by transmission electron microscopy, and the phase composition of the weld interface comprised FeCo and M23C6. The results presented that the addition of Ni-based transition layer caused the acquisition of the crack-free surface layer after HTIF. Finally, microhardness test was conducted on samples with and without a transition layer. The hardness of Co-based surface layer without the transition layer was mainly affected by the transformation of carbides, dilution of Fe, and work hardening during HTIF. The hardness of Co-based surface layer with the transition layer showed minimal change during HTIF, and this finding was attributed to the slight variation in the microstructure.
•The microstructural evolution of Stellite 6 layer was revealed.•Mechanisms of cracks generation during HTIF were illustrated.•Crack problem was solved by the addition of Inconel 625 transition layer.•The phase composition of interfacial layer was determined.•Reasons for hardness variation during HTIF was explained.
Magnesium alloys have many advantages, such as light weight, anti-seismic, anti-electromagnetic interference, high damping, high negative electricity and easy recycling. They are widely used in ...automobiles, motorcycles, and aerospace and are known as green engineering materials in the 21st century. Because of the special physical and chemical properties of magnesium alloys, the weldability of magnesium alloys is poor, which seriously hinders the use of magnesium alloy structural parts. Therefore, this paper analyses the welding problems of magnesium alloys, and discusses the fatigue properties of magnesium alloys.
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