Performance Of Welded Joints Research Articles

Diffusion Welding for TC4 Titanium Alloy/T2 Copper with Vanadium Foil

TC4 titanium alloy (TC4) was vacuum diffusion welded to T2 copper (T2) with vanadium (V) foil as an interlayer. The influence of process parameters on elemental diffusion behavior, microstructure evolution, and shear performance of welded joints was explored. An obvious solid-solution diffusion zone appeared in the welded interface between TC4 and V, but no distinct diffusion zone formed in the joint interface of V/T2. The solid-solution phases of (Ti6, V)ss, (Ti3, V)ss, and (Ti, V7)ss appeared in the interface of TC4/V. The crystallographic orientations of (Ti6, V)ss, (Ti3, V)ss, and (Ti, V7)ss phases in high-resolution transmission electron microscope images were (002), (201), and (121), respectively. The lattice mismatch between (Ti6, V)ss and (Ti3, V)ss was calculated to be 11.9%. The activation energy to form a stable solid solution between titanium and vanadium was 226.6 kJ/mol. The highest shear strength of the welded joint reached 160 MPa, obtained at 860°C (1580°F) for 60 min. The joint fractured along the interface of V/T2, illustrating that the solid-solution structure between Ti and V was stronger than the metallurgical bonding between V and Cu. The fracture surface of the welded joints revealed a river pattern and ladder topography, representing a cleavage fracture mode. FCC-Cu, BCC-V, and β-Ti were detected on both fracture surfaces of the TC4 titanium alloy and T2 pure copper sides. The influence of welding temperature on the diffusion of V in Ti was greater than on Ti in V, and Ti and Cu diffused faster than V in the joint.

Effect of Residual Stress on Mode-I Stress Intensity Factor: A Quantitative Evaluation and a Suggestion of an Estimating Equation

An extensive literature review was conducted primarily to develop a comprehensive understanding of the quantitative behavior of residual stress (RS) distribution in weld joints. Based on prior data, various levels of the peak RS and distribution profiles were applied to a finite element analyses (FEA) model as an initial loading to evaluate the effect of RS on the Mode-I stress intensity factor (SIF), KI. The RS was not found to have a significant effect on the SIF values when the peak RS was less than 300 MPa. The enhanced effect of RS on the KI values was found to be more pronounced at a lower crack ratio, while the analytical form of the RS distribution had a minor effect. The effective boundary corrections function, FResidual, was derived under the effect of RS for 1T CT specimen for various crack geometries of the crack ratio, (a/W) of 0.2, 0.40, 0.50, 0.60, and 0.75, and with peak RS varying from 100 MPa to 600 MPa. The obtained effective function of KI can be employed to quantitatively evaluate the effect of RS on the fatigue performance of welded joints.

Effect on the Property of 2195 Al-Li Alloy Laser-Welded Joints with Different Filler Materials

In order to improve the performance of welded joints in Al-Li alloys, butt joints consisting of 2 mm thick 2195-T8 Al-Li alloy plates are fabricated by laser beam welding with different filler wires in this paper. The joints welded by ER2319CT, ER4047, and without filler are investigated in the context of microstructure, the distribution of alloying elements, the burning loss of alloying elements, and tensile strength. From the fusion boundary to the center of the weld seam (WS), the crystal morphologies vary in the sequence of fine equiaxed grains, columnar dendrite, and equiaxed dendrite. The equiaxed grains and columnar dendrite disappear in certain areas of the WS by ER2319CT. The burning loss rates of Li and Cu in the WS by filler wires are higher than those by laser welding without filler. AlLiSi and Al2Cu are identified as the strengthening phases in the WS by ER4047, while Al2Cu, Al2CuLi, and Al6CuLi3 are the strengthening phases in the WS by ER2319CT. Compared with laser welding without filler wire, more strengthening phases improve the mechanical properties of the welded joints by filler wires. Both types of welding wires can improve the performance of welded joints, and ER2319CT is more effective.

Process parameter optimization in friction stir welding process using Taguchi method

Friction Stir Welding (FSW) process is an effective welding technique that is used to create high quality solid state joints in industries such as aerospace, automotive and shipbuilding. The significant advantages are no melting and recast issue. In FSW process, profile of tool pin plays a significant part which influence the performance of welded joints. In this investigation, experiments conducted to study the impact of tool pin profile and optimize the process variables in FSW process. Circular, square and triangular types are used as profiles of tool pin in this work. Taguchi orthogonal matrix is used for performing the experiments. Input parameters included are profile of tool pin geometry, rotational speed of tool and welding speed. Response includes tensile strength of the joint and weld’s micro hardness. Taguchi procedure is applied to analyzed the experimental results. Taguchi steps are unique optimization procedure for estimation of optimum selection of process parameters. The experimental result showed that enhanced tensile strength and microhardness with square tool pin profile. It is observed that weld quality is influenced by optimum selection of tool pin’s geometry in FSW process.

Refractory Performance of the Axial Tensile Welded Hollow Spherical Joint

To study the refractory performance of the axial tensile welded hollow spherical joint, the steady-state test of heating under constant load was carried out on the joint specimens with different load levels. The failure modes, temperature field, displacement-time curves, and refractory performance of the spherical joints exposed to fire are investigated and analyzed. The experimental results indicate that the failure modes of the joints exposed to fire are pull-out failures. The failure location is at the intersection of the steel tube-hollow sphere. The lowest temperature is located at the intersection of the steel tube-hollow sphere. The closer you get to the equator of the hollow sphere, the higher the spherical temperature. The smaller the load level, the higher the refractory temperature and the longer the refractory limit of the joints. The correctness of the numerical model was verified by comparison with the experimental result. Numerical simulations show that with the increase of the load levels, the refractory performance of the joints gradually decreases, and the downward trend gradually slows down. Compared to the refractory temperature code-recommended, the refractory temperature of the tensile joints is very conservative.

Influence of Vanadium Micro-Alloying on the Microstructure of Structural High Strength Steels Welded Joints.

The inter-critically reheated grain coarsened heat affected zone (IC GC HAZ) has been reported as one of the most brittle section of high-strength low-alloy (HSLA) steels welds. The presence of micro-alloying elements in HSLA steels induces the formation of microstructural constituents, capable to improve the mechanical performance of welded joints. Following double welding thermal cycle, with second peak temperature in the range between Ac1 and Ac3, the IC GC HAZ undergoes a strong loss of toughness and fatigue resistance, mainly caused by the formation of residual austenite (RA). The present study aims to investigate the behavior of IC GC HAZ of a S355 steel grade, with the addition of different vanadium contents. The influence of vanadium micro-alloying on the microstructural variation, RA fraction formation and precipitation state of samples subjected to thermal cycles experienced during double-pass welding was reported. Double-pass welding thermal cycles were reproduced by heat treatment using a dilatometer at five different maximum temperatures of the secondary peak in the inter-critical area, from 720 °C to 790 °C. Although after the heat treatment it appears that the addition of V favors the formation of residual austenite, the amount of residual austenite formed is not significant for inducing detrimental effects (from the EBSD analysis the values are always less than 0.6%). Moreover, the precipitation state for the variant with 0.1 wt.% of V (high content) showed the presence of vanadium rich precipitates with size smaller than 60 nm of which, more than 50% are smaller than 15 nm.

Effect of post-welding heat treatment on mechanical and microstructural properties of friction stir welded dissimilar magnesium alloys

Magnesium (Mg) alloys have undergone a huge exploration to expand their applications because of their exceptional unique characteristics and their status as one of the lightest metals. Friction stir welding (FSW) is a well-known welding practice for Mg alloys. Heat treatment can enhance the weld joint's physical properties and performance. In the current work, FSW joint of AZ31 and AZ61 Mg alloys were heat treated at 260 °C for 15 min. It has been examined how post-weld heat treatment (PWHT) affects the microstructure and mechanical characteristics of AZ31-AZ61 Mg alloy FSW joints. PWHT has been found to have a remarkable impact on the weld joint. The weld's stirring zone yielded noticeably coarser grains. After heat treatment, the joint's elongation improved by around 39%. After PWHT, the stir zone showed the highest microhardness 69 Hv (reduced by about 11.87%). The impact toughness of the FSW joint was reduced after PWHT by about 6%.

Experimental study on fatigue behavior of trapezoidal rib-to-deck welded joints in orthotropic steel decks strengthened with CFRP sheets

Due to the unavoidable stress concentrations and welding defects, the trapezoidal rib-to-deck welded joints of Orthotropic Steel Bridge Decks (OSBD) are prone to fatigue cracking. It is a new exploration to apply Carbon Fiber Reinforced Polymer (CFRP) sheets to strengthen the complex welded joints to improve the fatigue strength. In this paper, the comparative tests of un-strengthened and CFRP strengthened welded joints were carried out. The hot spot stress distribution under static load and fatigue behavior under cyclic load were studied, considering the influence of the number of CFRP sheet layers. The experimental results indicate that CFRP reinforcement can effectively reduce the stress concentrations at weld toe of the deck, and three-layers reinforcement has a greater effect than one-layer reinforcement. There was no significant difference in failure modes between the un-strengthened and CFRP strengthened welded joints. The fatigue cracks of all joints originated from weld toe of the deck, and then expanded along the width and thickness of the deck which caused the deck to break. CFRP reinforcement can significantly improve the fatigue life of trapezoidal rib-to-deck welded joints under the same nominal stress range and three-layers reinforcement presented a longer fatigue life. The S-N curve [Formula: see text] based on the hot spot stress range at weld toe of the deck was established, which can be applied to the fatigue strength design of un-strengthened and CFRP strengthened rib-to-deck welded joints. The mechanism that CFRP reinforcement can significantly improve the fatigue performance of welded joints can be concluded to less stress concentrations and slower growth rate of the crack.

Effect of welding parameters and post-welding heat treatment on the microstructure and properties of weld seam of 20# steel and 304 stainless steel

According to the influence of welding process between 304 austenitic stainless steel and 20 steel dissimilar steel on the weld seam, the effects of welding current of 150A, 180A and 200A, normalizing and solution treatment on the microstructure and properties of the weld seam were studied by using MAG. The results show that the 150A current welding seam has incomplete fusion, which leads to its low strength and fracture toughness. With the increase of current, the necking fracture occurred on one side of 20 steel, and the brittleness and hardness of weld increased, all of which indicated that carbon element diffused from 20 steel to weld and 304 stainless steel. Although the corresponding post-welding heat treatment can reduce the hardness to a certain extent, improve the machining performance of welded joints and homogenize the microstructure of welded joints, it can’t significantly improve the performance of welded joints of dissimilar steels.

Investigation of Low Cycle Fatigue Behaviors of Inertia-Friction-Welded Joints of the TC21 Titanium Alloy

As a new highly damage-tolerant structural material, the TC21 titanium alloy has been widely used in aerospace applications. Inertial friction welding (IFW) is a form of pressure welding technology with less welding parameters and high welding joint performance, which is especially suitable for the connection of rotors of aero-compressors and engines. In this paper, inertia friction welding of TC21 titanium alloys was successfully carried out, and the microhardness, tensile properties and low cycle fatigue (LCF) behaviors of IFW joints were studied. Based on the mechanical parametric results of the tensile test, the true stress–strain curves of the IFW joint of TC21 titanium alloys are obtained by further calculation. Based on the LCF test results under different strain amplitudes, life prediction of IFW joints was investigated. The results of the LCF test show that there is no obvious cyclic hardening and cyclic softening of the IFW joints. Moreover, the fracture morphology of LCF samples under high strain amplitude (0.9%) and low strain amplitude (0.6%) was observed. The results show that the fatigue cracks initiate and propagate at multiple points in the LCF samples, and the transient fracture zone is larger under high strain amplitude. However, under low strain amplitude, a fatigue crack nucleates and propagates at a single point, and the crack propagation zone is larger.

Microstructural formation and mechanical performance of friction stir double-riveting welded Al-Cu joints

A novel friction stir double-riveting welding (FSDRW) technology was proposed in order to realize the high-quality joining of upper aluminum (Al) and lower copper (Cu) plates, and this technology employed a Cu column as a rivet and a specially designed welding tool with a large concave-angle shoulder. The formations, interfacial characteristics, mechanical properties and fracture features of Al/Cu FSDRW joints under different rotational velocities and dwell times were investigated. The results showed that the well-formed FSDRW joint was successfully obtained. The cylindrical Cu column was transformed into a double riveting heads structure with a Cu anchor at the top and an Al anchor at the bottom, thereby providing an excellent mechanical interlocking. The defect-free Cu/Cu interface was formed at the lap interface due to the sufficient metallurgical bonding between the Cu column and the Cu plate, thereby effectively inhibiting the propagation of crack from the intermetallic compound layer at the lap interface between the Al and Cu plates. The tensile shear load of joint was increased first and then decreased when the rotational velocity and dwell time of welding tool increased, and the maximum value was 5.52 kN. The FSDRW joint presented a mixed mode of ductile and brittle fractures.

Methods and Equipment for Experimental Evaluation of the Performance of Shell and Hull Structures

Introduction. Pressure-operated thick-walled hull structures are the most common type of high-duty welded structures. When these structures are loaded with internal pressure, a complex biaxial stress field arises in them, which is summed up with the fields of residual welding stresses. Therefore, when selecting a technology for manufacturing critical welded structures, the results obtained during conventional uniaxial tests of samples are insufficient. The variety of factors affecting the performance of structures, and the difficulties of separate assessment of their influence, caused the need to maximize the approximation of experimental conditions to the real working conditions of the structure.Materials and Methods. Testing of full-scale structures has a number of advantages, but they are extremely expensive, and, as a rule, only one, the weakest link, is identified, the bearing capacity of the other structural elements remains unclear. For testing, UDI radiometric installations designed for different sample sizes were used. The presented installations allow testing samples of various shapes, types of welded joints (butt, T-bar), changing the position of welded parts.Results. Without rejecting the results obtained during the testing of full-scale structures in the works of the Bauman Moscow State Technical University, DSTU, NRC «Kurchatov Institute» – CRISM «Prometey», and the authors proposed to conduct the basic scope of the research on individual structural elements that would reflect the characteristic features of loading, manufacturing technology, and operating conditions. The design of the «fitting-sheet» connections was applied, which made it possible to increase the indicators of the failure initiation and propagation to the level of the base metal.Discussion and Conclusions. Schemes of structures for obtaining a biaxial tension or bending field in samples were presented. Samples tested according to the proposed schemes allowed us to draw conclusions about the performance of welded joints under conditions close to the actual operation of the structures under study. The proposed test scheme is used by research laboratories in our country and around the world.

Development of a Novel Welding Technique With Reduced Heat-Input by Employing Double-Pulsed Gas Metal Arc Welding for Aerospace Grade 18% Ni Maraging Steel

Abstract Eighteen percent Ni maraging steels are high performance Fe–Ni martensite-based alloys with ultra-high strength and good toughness. They find applications in strategic sectors, joining of thick sections often coming into picture. Welding of thick section involves a longer processing time, more passes, and a higher heat-input. Double-pulsed gas metal arc welding (DP-GMAW) is an emerging welding technique, well suited for joining thick sections. DP-GMAW is capable of controlling the solidification parameters, weld pool geometry, and cooling rate at a reduced heat-input. The major concern regarding the welding of maraging steel is the formation of the reverted austenite (RA) phase in the fusion zone (FZ). The formation of RA deteriorates the mechanical performance of welded joints. The presence of RA can be supressed by the usage of suitable welding techniques and proper post-weld heat treatments (PWHTs). DP-GMAW process was employed to carry out the welding; studies on the joints produced are reported in this research paper. The studies also included the effect of various PWHTs on the metallurgical and mechanical properties of the maraging steel weldments. The research used three distinct PWHTs: direct aging (DA), solutionizing + aging (SA), and homogenizing + solutionizing + aging (HSA). The FZ microstructures under DA and SA conditions show that there is RA at the cell boundaries. However, there was no evidence of RA in FZ following HSA. The energy dispersive spectra (EDS) analysis of the as-welded FZ showed segregation along the grain boundaries (GBs). This led to the premature formation of RA upon subsequent aging. The SA treatments proved inadequate to totally eliminate RA in the microstructure. On the other hand, the HSA treatments were effective in evening out concentration differences and preventing formation of RA. This study demonstrates that DP-GMAW combined with HSA treatment has the best mechanical properties.

Corrosion Performance and Mechanical Strength in Aluminum 6061 Joints by Pulsed Gas Metal Arc Welding.

In this paper, the analysis of electrochemical corrosion performance and mechanical strength of weld joints of aluminum 6061 in two-heat treatment conditions was performed. The joints were produced by gas metal arc welding in pulsed mode. The original material exhibited precipitates of and ” phases in a volume fraction (Vf) of 2.35%. When it was subjected to a solubilization process, these phases were present in a Vf = 2.97%. This increase is due to their change in shape and distribution in clusters within the aluminum matrix. After the welding process, the best sample in the solubilization condition reached 117 MPa, while the original material achieved 104 MPa, but all samples showed a fracture in the fusion zone. This is attributed to the heat input that produces high and low hardness zones along the heat-affected zone and the welding zone, respectively. Moreover, the change in microstructure and phase composition creates a galvanic couple, susceptible to electrochemical corrosion, which is more evident in the heat-affected zone than in the other weld regions, exhibiting uniform and localized corrosion, as was evident by electrochemical impedance spectroscopy. The heat from the welding process negatively affects the corrosion resistance, mainly in the heat-affected zone.

Characteristics of Laser-arc Hybrid Welding and the Effect of Heat Input Ratio on Welded Joint Performance

Characteristics of Laser-arc Hybrid Welding and the Effect of Heat Input Ratio on Welded Joint Performance

Study on the Effects of Multiple Laser Shock Peening Treatments on the Electrochemical Corrosion Performance of Welded 316L Stainless Steel Joints

To study the influence of laser shock peening on the electrochemical corrosion resistance of welded 316L stainless steel joints, welded 316L stainless steel joints are treated with different laser shock peening treatments (i.e., one, two, and three times). Our analysis employs electron backscattering diffraction (EBSD), scanning electron microscopy (SEM), X-ray diffraction (XRD), an X-ray stress meter, and electrochemical corrosion tests to observe and analyze the microstructure, structural composition, residual stress, and corrosion resistance in different areas of the surface of 316L before and after the laser shock peening. The results show that the residual stress distribution of the welded joints is optimized after laser shock peening, with a maximum residual compressive stress near the matrix of 171 MPa. When the number of laser shock peening treatments is two, the corrosion current reaches a minimum of 9.684×10−7 A/cm2, and optimal pitting resistance is obtained. However, when the number of laser shock peening treatments is further increased to three, the corrosion current increase and the pitting resistance decreases. In summary, the electrochemical corrosion resistance of the welded joints effectively improves after laser shock peening, but its performance begins to decline after three repeated shocks, which is related to the combined effects of stress change and microstructure phase transformation.

Microstructure and Mechanical Characteristics of the First Wall Welded Joints

Vacuum electron beam welding (EBW) is selected as the welding of the water-cooled ceramic breeder (WCCB) blanket. In the process of welding the first wall (FW) of WCCB blanket, it is necessary to add a backing plate to the arc section. At this stage, the thickness of reduced activation ferrite/martensite (RAFM) steels is up to 31 mm. In this article, thick plate RAFM steels after hot isostatic pressing (HIP) are welded by EBW, and then different heat treatments are performed. The results showed that, in the welding condition, hardness of welded joints was changed slightly. The highest hardness of the joint is 440 HV while the lowest is 290 HV, and a softening zone was observed in the heat-affected zone (HAZ). Moreover, after different heat treatments, the welding seam changed into the tempered martensite. In addition, the hardness of base metal and welded joints is all reduced, and the performance of welded joints in quenched and tempered conditions is better than that in normalized and tempered conditions.

Development of Multipass Gas Tungsten Arc Welding Technique for Aerospace Grade 18% Ni-Co-Mo Based Maraging Steel to Improve the Metallurgical and Mechanical Properties by Reducing Austenite Pools

Abstract The maraging steel is an impeccable choice for aerospace applications due to its high strength and excellent toughness. Welding is importantly involved in fabricating various structures out of maraging steel. Gas tungsten arc welding (GTAW) is the most commonly adopted technique for joining maraging steel. However, the major concern regarding the welding of maraging steel is the formation of the reverted austenite phase in the fusion zone and the heat affected zone. This reverted austenite deteriorates the mechanical property performance of welded joints. The present study focuses on GTAW of 12 mm thick MDN 250 maraging steel. An attempt was made to suppress the reverted austenite by employing suitable post-weld heat treatments. Three different types of post-weld heat treatments were adopted, i.e, (i) direct aging (W-DA), (ii) solutionizing + aging (W-SA), and (iii) homogenizing + solutionizing + aging (W-HSA). The micrograph and XRD analysis of the fusion zone with W-DA and W-SA conditions reveal the presence of reverted austenite. The SEM/EDAX examination of the fusion zone of as-welded, W-DA, and W-SA conditions revealed micro-segregation of Ni, Mo, and Ti elements from the matrix to the grain boundaries. On the other hand, the W-HSA condition was free from micro-segregation and austenite reversion. Electron backscatter diffraction (EBSD) analysis was used to estimate the percentage of reverted austenite in the fusion zone. The tensile test shows the highest strength of 1721 MPa (UTS) in W-HSA conditions. Similarly, the microhardness of the W-HSA conditions depicts a higher hardness with an even distribution in the microhardness values across the weldment. Hence, considering both metallurgical and mechanical examination of the weldment, the W-HSA heat treatments give superior properties in the case of GTA welded MDN 250 grade maraging steel.

The influence of holding time on the characteristics of friction stir welded dissimilar magnesium alloy joints during post welding heat treatment

Magnesium (Mg) alloys have been extensively researched to widen their uses due to their outstanding particular features and the fact that they are one of the lightest metals. Mg alloys could be used in a variety of industries, including aircraft, shipbuilding, automobiles, railways, and many more. Mg alloy welding is recognized as one of the most difficult processes in a variety of industries. Because of its ability to generate a high-quality joint, friction stir welding (FSW) of Mg alloys has sparked a lot of research and industry interest. Heat treatment after welding is an effective way to improve the characteristics and performance of welded joints. Therefore, the FSW process was used to prepare Mg alloy weld joints and diverse heat treatment conditions were applied. The microstructure and mechanical properties of as-welded and heat-treated FSW butt-joints made of dissimilar AZ31 and AZ91 plates were studied. It was observed that holding times of 30 min and 60 min were prosperous in recrystallizing the grain and enhancing the microstructure of the weld zones. The holding time of the heat treatment cycle was found to smooth the microhardness profile in this order: 60 min>30 min>15 min. The post-weld heat treatment (PWHT) for 60 min has been found to improve both tensile strength and percentage elongation. Heat treatment enhanced the ductility of joints. As a result, the tensile failure mode was altered from brittle to ductile. PWHT joints had the highest impact energy of 4.2 J for 30 min, which was around 93% that of welded joints.

Microstructure and mechanical properties of vacuum brazed diamond abrasive segments with zirconium carbide reinforced Cu-based active filler metals

Herein, by using Cu–Sn–Ti alloys addition zirconium carbide (ZrC) reinforcement to provide a way of enhancing the strength of brazed joint between diamond and solder. Microtopography of brazed segments was observed and interfacial characteristics of the brazing diamond were analyzed in detail via Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The wear machining performance of the diamond segment at different braze process was measured by changing the brazing temperature and holding time, respectively. Experiments indicated the microtopography of brazed segments with composite alloy of 15 wt% ZrC addition was optimal which the diamond edge was obvious, and the brazing filler metal spread more continuously and uniformly around the diamond without cracks and holes. Interfacial characterization results indicated that 10% wt% ZrC addition can promote titanium carbides produced on the diamond surface owing to the capillary force can improve the wettability. 15% wt% ZrC addition can further promote titanium carbides produced and improve the wettability by increasing the capillary force. However, higher ZrC addition (x ≥ 20 wt%) reduced performance of welded joints. Different braze process results showed that the brazed joint with the best grinding performance was obtained when the brazing temperature was 980 °C and the holding time was 15 min.