Dislocation structures and their evolution of 304L stainless steel and weld metal made with ER308L stainless steel welding wire subjected to uniaxial symmetric strain-controlled loading and ...stress-controlled ratcheting loading were observed by transmission electron microscopy (TEM). The correlation between the cyclic response and the dislocation structure has been studied. The experiment results show that the cyclic behaviour of base metal and weld metal are different. The cyclic behaviour of the base metal consists of primary hardening, slight softening and secondary hardening, while the weld metal shows a short hardening within several cycles followed by the cyclic softening behaviour. The microscopic observations indicate that in base metal, the dislocation structures evolve from low density patterns to those with higher dislocation density during both strain cycling and ratcheting deformation. However, the dislocation structures of weld metal change oppositely form initial complicated structures to simple patterns and the dislocation density gradually decrease. The dislocation evolution presented during the strain cycling and ratcheting deformation is summarized, which can qualitatively explain the cyclic behaviour and the uniaxial ratcheting behaviour of two materials. Moreover, the dislocation evolution in the two types of tests is compared, which shows that the mean stress has an effect on the rate of dislocation evolution during the cyclic loading.
The effect of ER5356 and ER5087 welding wires on fatigue property of MIG-welded 7N01-T4 aluminium alloy joints was investigated. The microstructure of ER5087 welded joint is similar to that of ER5356 ...joint. However, the fusion zone of the welding joint with ER5087 has a smaller grain size than that of the joint with ER5356. The fatigue strength of joints welded with ER5356 and ER5087 is 105.9 and 103.2 MPa at 10
7
cycles. During the fatigue process, the crack initiation for joints welded using ER5087 is due to porosity while for ER5356 is due to microcracks from eutectic melting in the heat-affected zone.
The A7N01-T5 aluminum alloy plates with the thickness of 12 mm were welded with the ER5356 and ER5087 welding wires, respectively, by the method of Metal Inert Gas (MIG) welding. The mechanical ...properties and microstructures of the welded joints were investigated by micro-hardness measurement, tensile test, energy dispersive spectroscopy (EDS), electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM). The results showed that the tensile strength and elongation of 7N01/5087 welded joint (the 7N01 aluminum alloy plate welded with ER5087 wire) were greater than those of 7N01/5356 welded joint (the 7N01 aluminum alloy plate welded with ER5356 wires), respectively. The high strength and the good elongation of 7N01/5087 welded joint were mainly attributed to the microstructure refinement in the weld zone through adding Zr element to promote the nucleation of Al grains around the Al3Zr sites.
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Porosity was measured for 21 AA2319 wire and arc additive manufacture (WAAM) panels built using different wire batches, cold metal transfer (CMT) modes, wire feed speed (WFS) and ...travel speed (TS). Image analysis software was used to measure the porosity across two different planes, totalling an area of 84 mm2 approximately 20 layers in height. Porosity was not strongly dependent on CMT mode, WFS and WFS to TS ratio within the ranges tested but batch-to-batch variability in feedstock wire had a significant influence on area of porosity and size distribution. Wire characterisation showed that porosity did not appear to depend on bulk composition but was influenced by surface finish. Surface finish could affect hydrogen content on the wire surface and arc stability which would affect porosity. Further investigation of the relationships between surface finish and surface hydrogen content, and surface finish and arc stability is required to understand porosity formation in aluminium WAAM components.
A multi-strand composite welding wire was applied to join high nitrogen austenitic stainless steel, and microstructures and mechanical properties were investigated. The electrical signals demonstrate ...that the welding process using a multi-strand composite welding wire is highly stable. The welded joints are composed of columnar austenite and dendritic ferrite and welded joints obtained under high heat input and cooling rate have a noticeable coarse-grained heat-affected zone and larger columnar austenite in weld seam. Compared with welded joints obtained under the high heat input and cooling rate, welded joints have the higher fractions of deformed grains, high angle grain boundaries, Schmid factor, and lower dislocation density under the low heat input and cooling rate, which indicate a lower tensile strength and higher yield strength. The rotated Goss (G
) ({110}〈1 1 ¯ 0〉) orientation of a thin plate and the cube (C) ({001}〈100〉) orientation of a thick plate are obvious after welding, but the S ({123}〈63 4 ¯ 〉) orientation at 65° sections of Euler's space is weak. The δ-ferrite was studied based on the primary ferrite solidification mode. It was observed that low heat input and a high cooling rate results in an increase of δ-ferrite, and a high dislocation density was obtained in grain boundaries of δ-ferrite. M
C
precipitates due to a low cooling rate and heat input in the weld seam and deteriorates the elongation of welded joints. The engineering Stress-strain curves also show the low elongation and tensile strength of welded joints under low heat input and cooling rate, which is mainly caused by the high fraction of δ-ferrite and the precipitation of M
C
.
In this paper, ER70-Ti welding wire steel produced by an enterprise was used as the test material. The final rolling temperature was set at 960 °C, 930 °C and 900 °C, and the spinning temperature was ...set at 880 °C, 860 °C and 840 °C. The results showed that the microhardness of the steel decreased from 303HV to 248HV and from 317HV to 276HV as the spinning temperature decreased from 880 °C to 840 °C. The microstructure and mechanical properties of the wires with the diameters of 5.5mm, 4mm, 2.5mm, 1.4 mm and 1.2mm were examined. It was observed that the microstructure of each sample had bainite and ferrite dual phase structure. With the decrease of wire diameter, the strength gradually increased and the ductility decreased. The experimental results show that the existence of bainite structure in the welding wire is the main reason for the high strength of the welding wire and easy fracture in drawing. Based on this, the final rolling temperature of 900 °C and the spinning temperature of 840 °C should be adopted in the production of ER70-Ti welding wire steel.
A method of narrow gap gas metal arc welding (NG-GMAW) with a self-rotating arc was established using cable-type welding wire. The wire melting speed, metal deposition, and welding seam thermal ...cycles of cable-type welding wire (CWW) GMAW and single-wire GMAW at the same welding parameters were studied and analyzed. The microstructural characteristics and mechanical properties of the weld were analyzed. The results showed that CWW was highly efficient and exhibited satisfactory sidewall penetration in the welding process. With its special structure, the surface area and the heating provided by the electrical resistance of CWW were distinctly higher than those of the single wire, thus resulting in CWW GMAW exhibiting higher efficiency than single-wire GMAW. The sidewall penetration of CWW NG-GMAW was analyzed in terms of arc rotation, droplet transfer motion, and regular molten pool flow. The combination of the arc rotating force and droplet transfer force on the molten pool promoted heat transfer to both sidewalls, affecting the features of the sidewall and the bottom width of the molten pool.
The effects of welding wire composition on microstructure and mechanical properties of welded joint in Al-Mg-Si alloy were studied by electrochemical test, X-ray diffraction (XRD) analysis and ...metallographic analysis. The results show that the weld zone is composed of coarse columnar dendrites and fine equated grains. Recrystallized grains are observed in the fusion zone, and the microstructure in the heat affected zone is coarsened by welding heat. The hardness curve of welded joint is like W-shaped, the highest hardness point appears near the fusion zone, and the lowest hardness point is in the heat affected zone. The main second phases of welded joints are: matrix α-Al, Mg2Si, AlMnSi, elemental Si and SiO2. The addition of rare earth in welding wire can refine the grain in weld zone obviously, produce fine grain strengthening effect, and improve the electrochemical performance of weld.
7N01-T4 aluminum alloy were welded into three layers by metal inert gas (MIG) welding, with ER5087 welding wire containing Zr and ER5356 welding wire without Zr, respectively. The microstructures and ...face bend properties of the ER5356 and ER5087 welded joints were investigated. The weld zone (WZ) of the ER5087 welded joint had a smaller grain size than that of the ER5356 welded joint. Two kinds of welded joints were not broken via the face-bend test. However, there were some small holes and microcracks on the surface of the ER5356 welded joint, and there were no obvious defects on the surface of the ER5087 welded joint. The face bending specimen metallography shows that the grains of the cover layer were elongated, and the grains of the bottom layer were extruded. The ER5087 welded joint had a better bending performance than the ER5356 welded joint due to the microstructure refinement of the WZ through adding Zr element in ER5087 welding wire.
Abstract
The triple-arc (Tri-Arc) twin wire gas metal arc welding (GMAW) is an innovative approach to twin-wire welding. It establishes two arcs between the welding wires and the workpiece and ...introduces a third arc, called the “M arc” between the two wires. To theoretically analyze how various welding parameters affect this process, an equivalent circuit method is employed to establish a dynamic mathematical model for Tri-Arc twin wire gas metal arc welding. The welding process is characterized and simulated using MATLAB simulations to analyze variations in current signals and the wire stick-out. The results indicate that the main arc burns in a dynamic equilibrium state with periodic fluctuations, the current gradually decreases over time, and the arc is elongated. These simulation outcomes closely mirror real welding processes.
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