Microstructure Of Welded Joints Research Articles

The Effect of Electron Beam Welding on the Microstructure and Microhardness of 3D-Printed Products from Titanium Alloy Ti–6Al–4V

The microstructure of double-sided welded joints of 3D-printed items made of titanium alloy Ti‒6Al–4V by the electron-beam freeform fabrication (EBF3) method has been investigated using the methods of X-ray diffraction analysis, optical metallography, and scanning and transmission electron microscopy. It is found that columnar epitaxial growth of primary β grains with transverse dimensions close to the sizes of primary β grains in the base material occurs in the process of electron-beam welding with a double-sided welded joint. Inside the primary β grains, there are grains of the α-phase with a lamellar shape inherited from the α' martensite, which is formed in the course of transformation β → α'. As in the printed samples, there is a nanocrystalline α"-phase in the metal of the welded joint inside grains of the α-phase and in interlayers of the β-phase. However, the density of particles of this phase in the metal of the welded joint is higher than in the base material. In the metal of the welded joint, tensile macrostresses and elastic residual microstrains also increase. The microhardness of the metal of the welded joint is greater than the microhardness of the base material.

Microstructure and mechanical properties of flash butt welding joint of high nitrogen austenitic stainless steel

The microstructure and properties of high nitrogen stainless steel welded joints under different flash currents were studied by flash butt welding. The results show that, the flash welding parameters have obvious influence on the joint structure and mechanical properties. The joint is organized into symmetrical distribution, and the grains obtained in the interface area are small, mostly pearlite and ferrite. With the increase of flash current, grain coarsening in overheated zone (OZ) and welding zone (WZ) of joint, which was mainly attributed to the increase of welding heat input. Martensite exists on both sides of the weld, in which the hardness reaches the peak. The tensile strength of welded parts can reach up to 97% of the base material, and the fracture is in the form of ductile fracture.

Analysis and characterization of dynamic recrystallization and grain structure evolution in friction stir welding of aluminum plates

The dynamic recrystallization (DRX) process and grain structure evolution during friction stir welding determine the final microstructure and performance of weld joints. In this study, Monte Carlo method is applied to develop a model for numerical simulation of dynamic recrystallization in friction stir welding of aluminum plates. An appropriate DRX nucleation model suitable for Monte Carlo simulation is selected, and the correlation of the Monte Carlo simulation step and the real time is calibrated. The transient evolution and the final distribution of grain structures in welds are predicted numerically. The calculated grain sizes in weld nugget zone are in good agreement with the experimentally measured ones. The dynamic recrystallization mechanism during friction stir welding of 1060 aluminum plate is analyzed by combining the finite element simulation and Monte Carlo simulation results with the characterization results of electron backscatter diffraction. It is found that along the material flowing path during friction stir welding, the main DRX mechanisms are different at leading, retreating and trailing sides around the tool, and the tool rotation speed (associated with the heat input level) determines which type of DRX is easier to occur at different positions along material flowing path.

Investigating the heat input effect of the GTAW process upon the microstructure and HAZ extension of HSLA-100 steel weld joints using thermal cycles

In the current research, the welding of HSLA-100 steel was accomplished with three different heat inputs using the GTAW process. The microstructure of various joint zones was investigated utilizing an optical microscope and scanning electron microscope. For the purpose of assessing the impact of thermal cycles upon the extension and alterations in the heat-affected zone, the thermocouples were placed at distinct distances from the fusion line. The results indicated that the weld metal microstructure comprised of acicular ferrite and a number of polygonal and quasi-polygonal Ferrite with M/A constituent. An epitaxial growth was observed in the fusion line in all heat inputs. It was determined that the heat-affected zone microstructure consisted of two regions, namely a coarse-grained heat-affected zone with a granular and lath bainite microstructure and a fine-grained heat-affected zone with the prevailing microstructure of granular Bainite. The results indicated that increasing the heat input leads to a decrease in the amount of acicular ferrite and M/A constituent volume fraction in the weld metal and an increase in lath bainite in coarse-grained zone. It was found that by increasing the heat input from 0.78kJ/mm to 1.42 kJ/mm, the grain size increases from 29.2μm to 76.5 μm and from 15.7μm to 32.5μm in coarse-grained and fine-grained zone, respectively. The thermal cycles evaluation pertinent to the implanting of a thermocouple disclosed that the heat-affected zone width is extended from 3.6 mm to 4.5mm by increasing the heat input from 0.78kJ/mm to 1.42 kJ/mm.

Investigation on microstructure and properties of dissimilar joint between TRIP800 and QP980 fabricated by laser welding

Dissimilar weld joints of QP980 and TRIP800 were fabricated by a fibre laser. The microstructure and mechanical properties of dissimilar weld joints were studied. The tensile properties of weld joints were not influenced by the narrow softening zone with a less reduction in hardness of ∼25 HV from the QP980, which contributed to fracture in TRIP800. The DIC images showed that the location of maximum strain was changed from the QP980 side to TRIP800 side during the tensile test of QP980 (1.2 mm)–TRIP800 (1.4 mm) joints. The dissimilar weld joints were characterised by the limited dome height test (LDH). The LDH values were varied with the punch pole location, as a result of the softening zone and non-uniform microstructure on the heat-affected zone of joints.

The role of ERNi-1 wire on Microstructure and Properties of Pure Nickel N6 Plasma Arc Welding joint

The butt welding tests of 5.5mm thick pure nickel N6 plate were carried out by plasma arc welding (PAW) and ERNi-1wire-filled PAW. And the differences in microstructure and properties between two kinds of joints were studied. The results show that the wire-filled pure nickel N6 joint has good appearance without defects such as pores, cracks, and undercuts. Pure nickel N6 weld is single-phase austenite structure, and no phase transformation occurs during heating or cooling. The weld zone of PAW joint is characterized by coarse columnar grain with average grain size of 125.8 μm, while the weld zone of wire-filled joint is equiaxed grain with average grain size of 54.8 μm. The tensile strength of the wire-filled PAW joint is 337MPa and the elongation after fracture is 44%, which is 11.6% and 85.5% higher than that of the PAW joint. The corrosion rate of wire-filled PAW joint is 2.6908g/m2h, which is lower than that of PAW joint of2.8820g/m2h, and the corrosion rates of both joint are higher than the base metal. The alloy elements in the welding wire can supplement the alloy elements burned in the welding process. As the filler metal, the melted wire forms the joint with the melted base metal, avoiding the defects such as undercut and depression. Al and Ti elements in ERNi-1 wire have deoxidation and nitrogen fixation effect during welding thermal cycle process, which improves the resistance of weld to carbon monoxide and nitrogen porosity. In the process of nitrogen fixation, TiN particles are formed in the crystal or grain boundary. TiN particles at the grain becomes heterogeneous nucleation particles in the grain, which makes a large number of nucleation and increases the nucleation rate. TiN particles at grain boundaries act as "nails" to hinder the migration of austenite grain boundaries. In the deoxidization process, the deoxidized products Al2O3 and TiO2 are formed. However, large-size inclusions are formed owing to the high content of Al and Ti in the molten pool, which affects the performance of the joint. Therefore, the structure and performance of filler wire-filled PAW joint are better than those of PAW joint.

Effects of Pulsed Laser on the Microstructure and Fatigue Properties of B950CF High-Strength Steel Hybrid Welding Joint

Effects of Pulsed Laser on the Microstructure and Fatigue Properties of B950CF High-Strength Steel Hybrid Welding Joint

调修温度对6005A铝合金焊接接头组织及性能的影响

调修温度对6005A铝合金焊接接头组织及性能的影响

Microstructure and mechanical behavior of P91 steel dissimilar welded joints made with IN718 filler

The paper presents the detailed microstructure study and mechanical behavior of P91 welded joint produced by gas tungsten arc welding process (GTAW) using the dissimilar nickel grade superalloy Inconel 718 filler (ERNiFeCr2). The microstructural changes in the weld fusion zone (WFZ) and heat-affected zone (HAZ) were also studied for varying heat treatment conditions. The effect of the Inconel 718 filler on the tensile properties, hardness and Charpy impact toughness (CIT) of the welded joint was also studied for as-welded and heat-treated conditions. The post-weld heat treatment (PWHT) was performed in a temperature range of 650–1060 °C. The microstructure study showed the formation of an unmixed zone at the interface of the HAZ and weld metal and remain unaffected during the PWHT. The region of weld metal near the boat fusion line showed the cellular and columnar dendrites. The center region of the bulk weld metal was solidified as the columnar dendrites and cellular dendrites along with segregation of the elements at inter-dendritic boundaries. The dendrite core showed the segregation of the Ni, and Cr; however, at dendrite boundaries, major segregation was observed for the elements Nb, Mo and Ti. The heat treatment up to a temperature of 810 °C has observed a negligible effect on the WFZ microstructure; however, a significant change in microstructure was observed for the P91 HAZ region. A significant change in the microstructure of the WFZ was measured after the normalizing at 1060 °C, followed by tempering at 760 °C for 2 h (complex heat treatment). The tensile strength of the welded joint was measured 817 MPa with a joint efficiency of 146% for as-welded condition and a maximum of 901 MPa with a joint efficiency of 161% for complex heat treatment. The welded joint CIT was measured a maximum of 48 J in as-welded condition and get reduced after the PWHT and measured a minimum of 35 J after complex heat treatment. A hardness variation was observed along the welded joint for as-welded and PWHT condition. In the as-welded condition, the hardness of the WFZ was measured about 417 ± 21 HV and showed a minute change with an increase in tempering temperature. The minimum hardness was measured in the inter-critical HAZ region for the as-welded joint and produce a significant level of heterogeneity in hardness variation along the P91 HAZ. PWHT has observed a considerable reduction in the hardness value of the P91 HAZs except for ICHAZ. A negligible level of hardness variation along P91 HAZ was measured after PW 4.

Effects of tool shoulder geometry on mechanical properties and microstructure of friction-stir welded joints of AA5083-0 aluminium alloys

Shoulder geometry is an important geometrical feature of tool design in friction stir welding since it has a strong effect on heat generation and material flow. In this paper the effect of shoulder geometry of tool on mechanical properties, microstructure evolution, and thermal history of friction stir welded joints of AA5083-O aluminium alloy. Two different shoulder geometries of tool named concave and featured (concentric circles) were used, both with cylindrical threaded pin. A set of samples were fabricated using a milling machine and a factorial experimental design to estimate the effects of process parameters (rotational and welding speed) and shoulder geometry on welded joints. Tensile strength, hardness, and microstructure evolution were experimentally measured. These observations were complemented with results obtained from a finite element modelling to calculate thermal history in welded joints. The results showed that the combination of revolution pitch R-value and shoulder geometry of tool were the most significant factors, affecting to mechanical properties, thermal behaviour, and microstructure evolution. The best tensile properties were obtained with a featured shoulder tool using 1400 rpm and 16 mm.min-1, and 1085 rpm and 11 mm.min-1 for rotational and welding speed. The same parameter combination resulted in a joint efficiency of 70% and 65%, respectively. In addition, the results of evaluation using an ANOVA analysis with fixed factors showed that increasing R-values produces statistically significant differences in ultimate strength (Sut) values.

Mechanical behaviors of electron beam welded titanium alloy up to very high cycle fatigue under different process conditions

The mechanical behavior of electron beam welded joints for titanium alloy has been investigated in static and cyclic loading up to very high cycle fatigue. It can be concluded that a higher welding voltage parameter and optimal heat treatment condition in combination will produce higher static and cyclic properties of titanium alloy welded joints. The metastable martensite α′ structures in the β grains of the fusion and heat-affected zones are wholly decomposed into small lamellar α phases, forming α + β phases through the post-weld heat treatment (PWHT). Hence, the welded joints by PWHT could transform the “concave” shape microhardness distribution into “convex” shape distribution. The fatigue cracks are initiated from the internal pores of the material in very high cycle fatigue regime. The higher voltage parameter applied to the welding process could reduce the density of pores in the material, which is in favour of the fatigue life of the welded joints. • A higher voltage and optimal heat treatment in combination produce higher mechanical properties of welded joints. • Microstructure and microhardness of welded joints were analyzed before and after heat treatment. • The higher voltage reduced the pores density in the welded joints, which improved fatigue life.

Влияние направления проката АМг5 на микроструктуру и свойства сварных соединений, полученных сваркой трением с перемешиванием

Introduction. Heat emission and plastic deformation during friction stir welding (FSW) cause profound changes in the microstructure and structural properties of weld joints. The grain size, crystallographic texture evolution and second-phase precipitate are the most important microstructural changes during welding of aluminum alloys, which largely influence the strength properties of weld joints. In addition to process-dependent parameters (instrument sump force, its rotation frequency, and travel rate) of the FSW process, a significant factor, determining the properties of the obtained weld joints, is also a mutual orientation of structural elements of the weld material and the direction of the instruments impact on the material during welding. In this regard, the purpose of the work is to analyze the combined influence of the direction of the initial rolling and the instrument pressure during FSW on the structure and properties of weld joints from the AA5056 aluminum alloy. Methods. Research methods are mechanical tests for statistical tension, microhardness as well as metallographic analysis of the structure of welded joints. Results and discussion. As a result, it is established that at low values of the axial force on the instrument (7 kN), defects such as the joint line and voids are observed in welded joints both rolling and transverse directions. When the load increases from 8 kN to 12 kN, defect-free weld joints with enhanced mechanical properties form. It is determined that the rolling direction of AA5056 during FSW does not influence the structure and tensile strength of the weld joints, but it influences the relative elongation and microhardness. It is shown that in the stir zone of the weld joint, obtained by FSW in the transverse direction of AA5056 flats, the relative elongation is 1.3-2 times greater, and the microhardness is by 4-10% greater than that in the stir zone of weld joints, obtained by FSW in the rolling direction of AA5056 flats.

Influence of inhibitors on the corrosion behavior of the X5CrNi18 10 stainless steel‐welded joint

AbstractThis study considers the corrosion behavior of the X5CrNi18 10 stainless steel‐welded joint in NaCl solution, with and without the presence of several corrosion inhibitors (NaNO3, Ce(NO3)3, and CeCl3). The degree of sensitization of the welded joint to intergranular corrosion is determined using the electrochemical potentiokinetic reactivation method with a double‐loop method. Pitting corrosion tests are performed by the potentiodynamic method. Resistance to general corrosion and the stability of the passive film is assessed based on the results of electrochemical impedance spectroscopy measurements, as well as on the values of the corrosion and passivation current. The main goal of this study is to determine the relation of the welded joint microstructure to general and pitting corrosion in the presence of the corrosion inhibitors. The value of pitting potential for the base metal and weld metal in the presence of the NaNO3 or Ce(NO3)3 inhibitor is shifted to potentials in the transpassive area. The pitting potential for the heat‐affected zone also possesses a noticeable higher value. However, nitrate ions do not increase the general corrosion resistance of any part of the welded joint. CeCl3 does not increase resistance to general or pitting corrosion.

Microstructure and Mechanical Properties of Linear Friction Welding Joint of GH4169 Alloy/S31042 Steel

Microstructure and Mechanical Properties of Linear Friction Welding Joint of GH4169 Alloy/S31042 Steel

Research Progress on Numerical Simulation of Welded Joints Microstructure

Since the integrity and mechanical properties of welded joints mainly depend on the solidification behavior of the weld pool and the microstructure characteristics of the welding heat affected zone, it is crucial for engineers and scientists to reveal the solidification behavior of the weld pool and the structural transformation of the welding heat-affected zone. With the dramatical improve of material calculation methods, the formation mechanism of the microstructure of some metal welded joints has been continuously revealed. In this article, the application of computer simulation in the study of welded joint microstructure is comprehensively analyzed. It focuses on the difficulties of simulating each area of welded joints, the advanced simulation methods applicable to each area and the current research status. Based on the characteristics of welded joint formation and simulation methods, some hot issues in research are proposed, aiming to provide effective help for researchers in related fields and open up new research ideas.

The Effect of Process Parameters on the Microstructure and Mechanical Properties of AW5083 Aluminum Laser Weld Joints

In this article, the effect of process parameters on the microstructure and mechanical properties of AW5083 aluminum alloy weld joints welded by a disk laser were studied. Butt welds were produced using 5087 (AlMg4.5MnZr) filler wire, with a diameter of 1.2 mm, and were protected from the ambient atmosphere by a mixture of argon and 30 vol.% of helium (Aluline He30). The widest weld joint (4.69 mm) and the highest tensile strength (309 MPa) were observed when a 30 L/min shielding gas flow rate was used. Conversely, the narrowest weld joint (4.15 mm) and the lowest tensile strength (160 MPa) were found when no shielding gas was used. The lowest average microhardness (55.4 HV0.1) was recorded when a 30 L/min shielding gas flow rate was used. The highest average microhardness (63.9 HV0.1) was observed when no shielding gas was used. In addition to the intermetallic compounds, β-Al3Mg2 and γ-Al12Mg17, in the inter-dendritic areas of the fusion zone (FZ), Al49Mg32, which has an irregular shape, was recorded. The application of the filler wire, which contains zirconium, resulted in grain refinement in the fusion zone. The protected weld joint was characterized by a ductile fracture in the base material (BM). A brittle fracture of the unshielded weld joint was caused by the presence of Al2O3 particles. The research results show that we achieved the optimal welding parameters, because no cracks and pores were present in the shielded weld metal (WM).

Effect of the laser power on the microstructure and mechanical properties of the laser-MIG hybrid welding joints of the 2195 Al–Li alloy

ABSTRACT In the present study, 2195 aluminium–lithium (Al–Li) alloy joints were welded by laser-metal inert gas (laser-MIG) hybrid welding. The effect of different laser powers (700, 1000, and 1300 W) on the microstructures and mechanical properties of the weld joints was investigated. The dendritic solidification structure of the weld joint comprised the α-Al, θ-(Al2Cu), and T-(AlLiSi) phases. When the laser power increased, the grains coarsened, and the amount of the precipitated phase decreased. Consequently, the micro-hardness of the weld decreased. The heat input also increased with the increase in laser power. This increased the fluidity and solidification time of the liquid metal at the bottom of the molten pool. Therefore, the deposition of the particles of the refractory metal compounds and the formation of the equiaxed grain zone (EQZ) was hindered.

Microstructure and fatigue crack growth behavior in welding joint of Al-Mg alloy

In this paper, the microstructure and fatigue crack growth behavior of Al-Mg alloy welding joint by metal inert-gas welding (MIG) were studied by means of metallographic microscope, scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD). The results show that the welded joint is characterized by obvious heterogeneous microstructure. The weld zone is dominated by equiaxed cellular dendritic crystals, with a small amount of welding bubbles and microcracks. The position of welding joint with bubble, grain boundary, interface between hard phase particles and matrix, and hole of coarse impurity particles debonded tend to generate fatigue crack origins, and further develop into the main crack. Due to the influence of stress state, grain orientation, welding bubble and coarse phase particle, the fatigue crack propagation in the weld zone will appear deflection, bifurcation, convergence, bridging connection and other path choices, which will affect the direction and rate of fatigue crack propagation.

Numerical Simulation and Experimental Investigation on Electron Beam Welding of Spray-Formed 7055 Aluminum Alloy

The spray-formed 7055 aluminum alloy is welded by electron beam welding. Combined with the numerical simulation of a welding temperature field, the effect of different welding procedures on the microstructure and mechanical properties of welded joints is investigated in this study. Results show that the joints with good properties can be obtained under proper welding procedures. The microstructure analysis demonstrates that the fusion zone mainly consists of equiaxed grains, while a fine equiaxed grain zone is formed near the fusion line. There are mainly α(Al), MgZn2, Al2CuMg, and Mg32(Al,Zn)49 phases in the weld metal. The morphology of the weld can be improved by modification welding after the first bead welding, which is also advantageous to the mechanical properties of a welded joint. In the as-welded condition, compared with that of the base metal, the hardness of the weld zone decreased to a certain extent. The maximum tensile strength of a welded joint reaches 371.7 MPa. There are many dimples on the tensile fracture surface of a welded joint, and it dominantly presents the characteristic of ductile fracture. The simulated molten pool is consistent with the experimental weld morphology, and the reliability and accuracy of the simulation analysis are verified.

Effect of Welding Speed and Post Quenching on the Microstructure and Mechanical Properties of Laser-Welded B1500HS Joints

In this research, B1500HS high-strength steel with different thicknesses were laser welded, and the effects of welding speed and post quenching were investigated by analyzing the microstructure, microhardness distribution, and high-temperature tensile properties of weld joints. The results show that an obvious difference can be found in the metallographic structure and grain morphology of the weld joint at different locations, which also lead to the significant uneven distribution of hardness. After quenching, the grain size of the original heat-affected zone was uniform, the columnar grains in the fusion zone were transformed into fine equiaxed grains, and no obvious hardness difference can be found in the weld joint. For the weld joint without quenching, the increase of welding speed can reduce the dimensions of grains of fusion zone and coarse grain zone, and slightly increase the hardness of these regions. In contrast, welding speed change has little influence on the microstructure and hardness of the weld joint after quenching. The high-temperature flow stress–strain curves of fusion zone welded under different welding speeds were calculated based on the mixture rule. The analysis results indicated that the fusion zone has higher strength but lower elongation than the base metal. In addition, the change of welding speed has a small impact on the high-temperature tensile properties of the fusion zone.