Effect of Oscillation Modes on Microstructure and Properties of WE43 Rare‐Earth Magnesium Alloy Welded Joints

The effect of one two-step high-temperature post-weld heat treatment on the microstructure of TC4 weld joints has been studied in our experiment, and as a result, the weld joints with attractive mechanical property have been obtained. The weld joints consisted of lamellar martensitic α, retained β and primary α, therefore microstructure of the weld joints would be kept in balance, and spheroidised α phase both in the crystalline grain and grain boundary, which could improve attractive balance of mechanical properties.

To explore the influence of different welding modes on the properties of 316L thin-plate welded joints, a new type of laser arc compound gun head similar to a coaxial one was used in this experiment. A high-speed camera was used to record the welding process and analyze the droplet splash behavior of the molten pool. The microstructure, microhardness change, and tensile test results of welded joints under different welding modes were analyzed. The results showed that laser welding (LW) is more prone to molten pool splash than hybrid laser arc welding (HLAW). The HLAW pool area was significantly increased compared with that of LW. The HLAW joint microstructure was more uniform than that of LW, which can improve the microhardness of welded joints. HLAW improved the tensile properties of the joint, with the maximum tensile strength of the joint increasing from 433 to 533 MPa. This test can provide guidance for the HLAW process.

Effects of Welding Speed on the Microstructure and Corrosion Behavior of Dissimilar Gas Metal Arc Weld Joints of AISI 304 Stainless Steel and Low Carbon Steel

Influence of filler metals and PWHT regime on the microstructure and mechanical property relationships of CSEF steels dissimilar welded joints

Heat treatment was carried out to the 1420 Al-Li alloy electron beam welding (EBW) joints after welding, and the microstructures of welded joints are analyzed systematically before and after post-weld heat treatment (PWHT). The observation of joint microstructure demonstrates that the grain morphology of weldment changes from equiaxed dendrites in as-welded (AW) condition into equiaxed grains after PWHT, and that the fine strengthening phases precipitate within the grain. The XRD analysis of phase constituent and TEM observation of weldment indicate that the main strengthening phases in 1420 Al-Li alloy weldment are spheroidal δ′(Al3Li), β′(Al3Zr) and rod-like T(Al2MgLi) after PWHT. Furthermore, the δ′ phase precipitate free zone (PFZ) is found along the grain boundary. The scanning observation of joint fracture shows that Al-Li alloy EBW joint presents the characteristic of transgranular ductile fracture in AW condition. After PWHT, the Al-Li alloy welded joint presents the pattern of intergranular fracture. The variation of fracture mode is related to dispersed precipitation of δ′ phase and the formation of PFZ at the grain boundary in weldment after heat treatment.

Mechanical and microstructural properties of dissimilar copper and stainless-steel butt welds prepared using zigzag and circular fiber laser oscillation methods

The magnetic field-assisted laser wire-filled welding test of 1.5 mm automotive 22MnB5 steel is performed to investigate the influence of magnetic field on the microstructure and properties of the welded joints. When no magnetic field is applied, and the laser heat input is 190 J mm−1, the welded joint width and the grain size of the coarse grain region are large. Also, there is an obvious hump defect at the bottom of the weld. Under the same heat input conditions, when a 5 mT and 15 mT steady magnetic field is applied, the thermoelectric magnetic force generated by the magnetic field promoted the flow of molten pool and concentrated laser energy. It is found that the hump defect is eliminated, the width of the welded joint is reduced, the grain size of the coarse grain region is significantly reduced, and the overall hardness of the welded joint is improved. However, different magnetic induction intensities have different effects on the solid phase transformation of the weld. When no magnetic field is added, the weld center is mainly composed of granular bainite and polygonal ferrite due to the slow cooling rate of the molten pool. When the applied magnetic field is 5 mT, the center of the weld is mainly composed of brittle and hard upper bainite because the thermoelectric magnetic force stirs the molten pool and accelerates the cooling rate of the molten pool but the overall mechanical properties of the welded joint were relatively poor. At 15 mT, lath martensite and lower bainite predominate in the weld center due to the increased cooling rate of the molten pool, thereby increasing the overall mechanical properties of the welded joint. Therefore, choosing the appropriate magnetic induction intensity is critical for improving the microstructure and properties of welded joints.

The morphology and microstructure of the weld joint have significant influence on mechanical properties of welded specimens. In this paper, the mechanism on how the external magnetic field affected weld profile and microstructure was discussed by applying the longitudinal steady magnetic field to laser welding for SUS301 stainless steel. The optimal and scanning electron microscopes were used to measure the shape of the cross section and observe the microstructure after welding. The results showed that the shape of the cross section and microstructure could be significantly changed using the external magnetic field. Moreover, joint shape changed distinctly with the magnetic field intensity changing. With the increasing of magnetic flux density, the weld profile of the full penetration model changed from funnel to X type; meanwhile, the bottom weld width increased by 40%. In addition, the partial fusion zone occurred, and the weld width decreased by 20% while penetration increased by 18% when magnetic flux density turned into 380 mT. As far as microstructure of weld joint was concerned, it appeared that application of axial magnetic field led to indistinct fusion line and blocky austenite in big size rather than columnar grain in the center of the cross section. This phenomenon could be explained by numerical simulation results.

Microstructure and fracture behavior of laser welded joints of DP steels with different heat inputs

400Mpa grade ultrafine grained steel was welded by manual arc welding with J506 electrode and I type grove butt welding. The microstructure and hardness change of welded joints were also studied. The welded joints were quenching heat treated and the change of microstructure and hardness were studied before and after heat treatment. The result showed that the microstructure grain size in the weld zone and overheated zone increased with the increase of current. Both the weld zone and the overheated zone were coarse ferrite and pearlite, and the weld zone was dendritic morphology. The weld zone had the highest hardness in the welded joint, followed by the overheated zone, the normalized zone and the base metal. The weld joints did not soften. After heat treatment, the microstructure of welded joints were the mixed structure of low carbon martensite, pearlite, ferrite and bainite. The hardness of welded joints were all improved.

ABSTRACTThe laser–tungsten inert gas hybrid welding method was adopted to realize the welding process between Q460 high-strength steel and 6061 aluminum alloy. The influence of the dual heat source on the mechanical properties and microstructure of the welded joints are discussed. In addition, the effects of including a copper–zinc interlayer on the microstructure, elemental distribution, and mechanical properties of welded joints are also studied. The results show that the mechanical properties of the welded joints are influenced by the relative heat inputs of the two heat sources and the Cu-Zn interlayer. The braze welded joint fabricated without a Cu-Zn interlayer fractured at an Al-Fe intermetallic compound (IMC) layer formed at the interface, whereas the braze welded joint fabricated with a Cu-Zn interlayer fractured at an Al-Cu IMC layer formed at the interface. Comparisons show that the maximum tensile shear load of the brazed welded joint with the Cu-Zn interlayer was increased by about 20% relative to that formed without the interlayer. The formation of Al-Fe IMC layer in the deep penetration joint was inhibited by the combined effect of the dual heating sources and the Cu-Zn interlayer.

In order to improve the poor weldability and low quality of welded joints during the welding of magnesium alloys, a longitudinal magnetic field is introduced in the welding process of A-TIG welding with a fixed magnetic field frequency (30 Hz) and magnetic field current (1.5 A). Experimental analysis is performed on the effect of the magnetic field on the microstructure and mechanical properties of welded joints under different TiO2 active agent coating amounts. The results show that the grain size tends to decrease and then increase with the increase in the active agent coating under the magnetic field. This is mainly because the active agent changes the arc morphology, which in turn affects the melt pool motion. The Lorentz force generated by the longitudinal magnetic field acts on the molten pool and will have an agitating effect on the pool. Both the magnetic field and the active agent are convective to the melt pool, and when the magnetic field and the active agent act together will further enhance the convective effect. However, when the active agent is too thick, it will affect the fluidity of the molten pool during welding and reduce the quality of the welded joint. Under the action of magnetic field, when the active agent coating amount is 3 mg/cm2, the grain size is the finest and the mechanical properties are the best. At this time, the tensile strength was 292 MPa, elongation was 11.2%, and hardness was 78.9 HV in the weld zone and 77.8 HV in the heat-affected zone. Further analysis of the melt pool change and grain refinement mechanism under the combined effect of the magnetic field and active agent revealed that the magnetic field promotes the solidification of the second phase in the weld tissue, but the effect on the heat-affected zone is not obvious. The addition of the magnetic field was found to refine the grains by EBSD testing, reducing the average grain size by 1.43 μm. This indicates that the introduction of the magnetic field in the A-TIG welding process improves the mechanical properties and microstructure of the welded joint, which is conducive to solving the problem of poor weldability in the welding process of magnesium alloys.

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.

The 1.3 mm thick plate of ODS high temperature alloy MGH956 was TIG welded with fillers containing different B4 C(0, 0.25 and 0.5 mass %), then the effect of B4 C content on the microstructure and mechanical properties of the weld joints was investigated. The results show that the microstructure of the weld metal with B4 C exhibits mainly equiaxed grains, which are fine and uniform, without significant agglomeration of oxide dispersoids, while the strengthening particulates of the alloy distribute in both grains and grain boundaries. The microstructure of weld joint was finer as the filler with B4 C content in a range from 0.25 to 0.5 mass%. However nearly almost the strengthening particulates of the alloy concentrate in the grain boundaries but disappear in the grains for the weld joints by filler with 0.5% B4 C. The tensile strength of the weld joints firstly increases and then decreases when the B 4 C content of the fillers ranged from 0% to 0.5 mass%, but their toughness decreases with the induce of B4 C. The tensile strength of the weld joint with filler material containing 0.25% B4 C is the highest i.e. 630 MPa, reaching 87.5% of the parent material. The fractured surface exhibited characteristics of brittle fracture.

Investigation on the microstructure and mechanical properties of autogenous laser welding joint of ITER BTCC case lid