Showing papers on "Weldability published in 2019"

Intermetallic compounds (IMCs) formation during dissimilar friction-stir welding of AA5005 aluminum alloy to St-52 steel: numerical modeling and experimental study

Abstract: In this research, AA5005-O aluminum-magnesium alloy and St-52 low carbon steel sheets were friction-stir welded in a butt-dissimilar joint design. Effects of different processing parameters including tool rotational speed (w), traverse velocity (v), plunge depth, and offset distance on the solid-state weldability of these dissimilar materials were assessed in terms of formation of intermetallic compound (IMC) layer at the interface. A 3D thermo-mechanical finite element modeling procedure was employed to predict the nucleation and growth of IMC layer. Formation of various FeAl, FeAl3, and Fe2Al5 IMCs at the interface, layer morphology, and thickness were experimentally studied as well, by using X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) analysis techniques. A good agreement between the simulated thermal results and experimental data was noticed. The results showed that the thickness of IMC layer at the interface as the main controlling parameter in transverse tensile property and fracture behavior of produced dissimilar joints can be varied extremely as a function of processing parameters. By decreasing the heat input and suppressing the kinetics of IMCs layer formation, the tensile performance of dissimilar welded joints is improved, considerably. However, the soundness of these dissimilar welds played another main role as a restriction mechanism against this trend. The maximum joining efficiency is attained around 90% at an optimized working window of w = 1200 rpm, v = 90 mm/min, and a plunge depth of 0.3 mm with an offset distance of 0.5 mm toward the Al side. The hardness of this optimized dissimilar weld is enhanced even more than the steel base metal caused by the formation of IMC layer at the interface as well as the dispersion of reinforcing intermetallic particles (IMPs).

Hadfield manganese austenitic steel: a review of manufacturing processes and properties

Abstract: In this paper, manufacturing processes and properties of Hadfield manganese steel was studied. Due to good flexibility and excellent resistance to wear, the high strength steel is widely used in various industries such as cement, mining, road construction and railroads. Induction furnace is suitable for melting of Hadfield steel. Typically, silica, olivine and chromite sand are used to make mold in the casting process of Hadfield steel. This steel is in standard state, an alloy of Fe, C and Mn. But in certain applications, other elements such as Cr, Ti, Al, Mo, B, V, etc are added. Mn is used as the most important austenite stabilizer in Hadfield steel and its role is to delay the austenite to martensite transformation. Mn is a carbide forming element and forms Mn3C and (Fe, Mn)3C in Hadfield steel. The optimal structure for the Hadfield steels is the fully austenite structure and the single-phase. In non-heat-treated castings, the structure of the unit consists of austenitic and grain boundary carbide phase. To provide optimum toughness, the structure of the Hadfield steel should be austenitic single-phase. Twin strain has a great contribution to plastic deformation of this steel. Two phenomena of dislocation accumulation and the formation of twins during plastic deformation of these steels are the main reason of the strain hardness of this steel. The high rate of work hardening in Hadfield steel is due to strain induced transformation of γ to α or e martensite, mechanical twinning, dynamic strain aging, and the confrontation between dislocations with stacking faults. In the early stages of wear and slow wear conditions, the wear resistance of Hadfield steel is low. In conditions of slow wear, the surface is not sufficiently work hardening and thus the wear resistance of this steel is low. But with the work hardening of the surface, wear resistance rises sharply. The welding and weldability of this steel are strongly influenced by the heat input. In any case, the formation of carbide phases in the weld metal is acceptable, and often the weld metal has higher strength and lower toughness than the base metal. Carbides deposited in the heat affected zone (HAZ) of welded Hadfield steel, usually are Mn7C3 and Mn23C6.

Laser weldability of cast and rolled high-entropy alloys for cryogenic applications

Abstract: Laser similar welding of cast and rolled high-entropy alloys (HEAs) was performed using the cantor system (Co0.2Cr0.2Fe0.2Mn0.2Ni0.2). As the welding velocity was increased from 6 to 10 m min−1, the shrinkage voids, primary dendrite arm spacing, and dendrite packet size decreased, thus improving the mechanical properties of the cast and rolled HEA welds. The cast HEA welds showed tensile properties comparable to those of the base metal (BM). In all the specimens fracture occurred near the heat-affected zone and BM at 298 K. However, the rolled HEA welds showed lower tensile strength than the BM, and fracture occurred in the weld metal (WM). This can be attributed to the larger dendrite packet size of the WM than the grain size of the BM. In addition, the tensile properties of the specimens at the cryogenic temperature were superior to those observed at 298 K, regardless of the cast and rolled HEA welds. This is because the formation of deformation twins and dislocations was predominant at 77 K. Therefore, the laser similar welds of cast and rolled HEAs are suitable for cryogenic applications.

Advances in Maraging Steels for Additive Manufacturing

Abstract: Maraging steels such as 1.2709 are high strength—high toughness alloys that gain their exceptional mechanical properties by the combination of nanometer-sized intermetallic precipitates and a martensitic matrix. Here the martensitic microstructure is not achieved by a high carbon content but by adding nickel to the chemical composition. In turn, the lack of carbon leads to good weldability and therefore makes these materials preferred candidates for additive manufacturing techniques, such as selective laser melting (SLM). Applications for SLM produced components are found especially in the tooling industry, where the implementation of inserts with intelligent conformal cooling channels in dies and moulds has already shown to drastically increase the tool lifetime. In this study, different maraging steels are investigated with respect to typical powder characteristics, such as sphericity, particle size distribution, on the one hand, and the microstructure as well as the achieved mechanical properties of the respective SLM printed parts, on the other hand.

Study of 3D printing direction and effects of heat treatment on mechanical properties of MS1 maraging steel

Abstract: The objective of this paper is to investigate the mechanical properties of samples of MS1 Maraging Steel (untreated and heat treated), which were produced by additive technology in various orientations in the working area of the building machine. MS1 steel (European 1.2709 and German X3NiCoMoTi 18-9-5) is well known for its high strength, high fracture toughness, good weldability, and dimensional stability during aging. The literature review, related to the mechanical properties and fracture of MS1 steel, found that there are no available studies of the effects of both building direction and heat treatment on the mechanical properties of MS1 steel. The authors decided to address this omission and present this entirely new research in this article. The uniaxial tensile tests to fracture were completed at two of the authors’ workplaces. The results were statistically assessed using Grubbs’ test for outliers, and then the data were processed using box plots to be easily comparable from the point of view of print direction, heat treatment, and the values declared by the metal powder producer or in the tables (for conventionally produced steel). Scanning electron microscopy was used to analyze the fracture surfaces obtained after tensile testing cylindrical samples. The results showed that there was an impact on the mechanical properties depending on the sample orientation within the same heat treatment type; there was also significant influence of heat treatment, while the possibility of the natural aging effect on mechanical properties was also noted.

Effect of Welding Heat Input on Simulated HAZ Areas in S960QL High Strength Steel

Abstract: When the weldability of high strength steels is analyzed, it is the softening in the heat-affected zone (HAZ) that is mostly investigated, and the reduction of toughness properties is generally less considered. The outstanding toughness properties of quenched and tempered high strength steels cannot be adequately preserved during the welding due to the unfavorable microstructural changes in the HAZ. Relevant technological variants (t8/5 = 2.5–100 s) for arc welding technologies were applied during the HAZ simulation of S960QL steel (EN 10025-6) in a Gleeble 3500 physical simulator, and the effect of cooling time on the critical HAZ areas of single and multipass welded joints was analyzed. Thermal cycles were determined according to the Rykalin 3D model. The properties of the selected coarse-grained (CGHAZ), intercritical (ICHAZ) and intercritically reheated coarse-grained (ICCGHAZ) zones were investigated by scanning electron microscope, macro and micro hardness tests and instrumented Charpy V-notch pendulum impact tests. The examined HAZ subzones indicated higher sensitivity to the welding heat input compared to conventional structural steels. Due to the observed brittle behavior of all subzones in the whole t8/5 range, the possible lowest welding heat input should be applied in order to minimize the volume of HAZ that does not put fulfillment of the allowed maximal (450 HV10) hardness at risk and does not lead to the formation of cold cracks.

Advantages of the Application of the Temper Bead Welding Technique During Wet Welding.

Abstract: Thermo-mechanically rolled S460ML steel was chosen for welding in underwater wet welding conditions by covered electrodes. The main aim of this study was to check the weldability for fillet welds in a water environment by controlled thermal severity (CTS) tests and to check the influence of temper bead welding (TBW) on the weldability of the investigated steel. Non-destructive and destructive tests showed that S460ML steel has a high susceptibility to cold cracking. In all joints, hardness in the heat-affected zone (HAZ) was extended to the 400 HV10 values. Microscopic testing showed the presence of microcracks in the HAZ of all welded joints. TBW was chosen as the method to improve the weldability of the investigated steel. This technique allows for the reduction of the maximum hardness in the HAZ below the critical value of 380 HV10, as stated by the EN-ISO 15614-1:2017. It was determined that for S460ML steel, from the point of view of weldability, the pitch between two beads should be in the range 75%⁻100%. Also, if the pitch between two beads increases, the hardness, grain size, and number of cracks decreases. In all specimens where the hardness of the HAZ was below 380 HV10, there were no microcracks.

Activated flux TIG welding of Inconel 718 super alloy in presence of tri-component flux

Abstract: In this study, we have explored the influence of newly developed tri-component oxide flux (Cr2O3, FeO, and MoO3) on weldability, bead geometry, weld pool temperature variation, and mechanic...

Process robustness and strength analysis of multi-layered dissimilar joints using ultrasonic metal welding

Abstract: This paper investigates the effects of process parameters on the joint strength and process robustness when multi-layered joints of dissimilar metals are produced by ultrasonic metal welding (UMW). Three layers of 0.3-mm aluminium sheet are welded with a single 1.0-mm copper sheet which is representative of electric vehicle battery interconnects. A process robustness study in which welding pressure, amplitude of vibration and welding time are varied to produce satisfactory welds is reported. The weld quality is evaluated by performing lap shear and T-peel tests where maximum loads are considered as the quality indicator. Response surfaces are developed to identify the relationship and sensitivity between the input process parameters and output quality indicators. A feasible weldability zone is defined for the first time by identifying the under-weld, good-weld and over-weld conditions based on load-displacement curves and corresponding failure modes. Relying on the weldability zone and response surfaces, multi-objective optimisation is performed to obtain maximum lap shear and T-peel strength which resulted in Pareto frontier or trade-off curve between both objectives. An optimal joint is selected from the Pareto front which is verified and validated by performing confirmation experiments, and further, used for T-peel strength analysis of different interfaces of the multi-layered joint. To conclude, this paper determines both the optimal weld parameters and the robust operating range.

Effect of different carbides on the wear resistance of Fe-based hardfacing alloys

Abstract: Hardfacing plates are being used in raw material conveying system of an integrated steel plants to mitigate the wear of chutes and hoppers. Four Fe-based commercial hardfacing alloys were studied in this work. To prepare test samples, mild steel base plates was used. In hardfaced plates, mild steel backing provides the weldability, formability, and ductility whereas the hard weld deposit provides the required wear resistance. This investigation aims to correlate microstructural, tribological and hardness properties of hardfacing plate samples with varying chemical composition. Microstructural characterization involved the morphological study and elemental analysis of different types of carbides through EDS, hardness evaluation mainly involved measurement of bulk hardness and micro-hardness, whereas tribological studies involved pin-on-disc wear test. Higher hardness doesn't always mean higher wear resistance. Presence of alloying elements resists the material removal by abrasive action and increases the wear resistance.

Welding of High Entropy Alloys-A Review.

Abstract: High-entropy alloy (HEA) offers great flexibility in materials design with 3–5 principal elements and a range of unique advantages such as good microstructure stability, mechanical strength over a broad range of temperatures and corrosion resistance, etc. Welding of high entropy alloy, as a key joining method, is an important emerging area with significant potential impact to future application-oriented research and technological developments in HEAs. The selection of feasible welding processes with optimized parameters is essential to enhance the applications of HEAs. However, the structure of the welded joints varies with material systems, welding methods and parameters. A systemic understanding of the structures and properties of the weldment is directly relevant to the application of HEAs as well as managing the effect of welding on situations such as corrosion that are known to be a service life limiting factor of welded structures in conditions such as marine environments. In this paper, key recent work on welding of HEAs is reviewed in detail focusing on the research of main HEA systems when applying different welding techniques. The experimental details including sample preparation, sample size (thickness) and welding conditions reflecting energy input are summarized and key issues are highlighted. The microstructures and properties of different welding zones, in particular the fusion zone (FZ) and the heat affected zones (HAZ), formed with different welding methods are compared and presented in details and the structure-property relationships are discussed. The work shows that the weldability of HEAs varies with the HEA composition groups and the welding method employed. Arc and laser welding of AlCoCrFeNi HEAs results in lower hardness in the FZ and HAZ and reduced overall strength. Friction stir welding results in higher hardness in the FZ and achieves comparable/higher strength of the welded joints in tensile tests. The welded HEAs are capable of maintaining a reasonable proportion of the ductility. The key structure changes including element distribution, the volume fraction of face centered cubic (FCC) and body centered cubic (BCC) phase as well as reported changes in the lattice constants are summarized and analyzed. Detailed mechanisms governing the mechanical properties including the grain size-property/hardness relationship in the form of Hall–Petch (H–P) effect for both bulk and welded structure of HEAs are compared. Finally, future challenges and main areas to research are highlighted.

Pulsed Nd:YAG laser welding of 17-4 PH stainless steel: Microstructure, mechanical properties, and weldability investigation

Abstract: Pulsed Nd:YAG laser welding of 17-4 martensitic precipitation hardening (PH) stainless steel (SS) is investigated. In order to achieve optimum laser welding parameters, bead on plate (BOP) welding was conducted on 17-4 PH SS. No crack was detected in the weldments, and microstructure of weld metal was δ-ferrite in the martensite matrix. Resistance to cracking of weldment was correlated to the presence of δ-ferrite in the weld metal, and using pulsed Nd:YAG laser as a low heat input welding method. Four HAZs were distinguished and microstructure evaluation in each zone is discussed. In the second part of this research, pulsed Nd:YAG laser welding of similar 17-4 PH SS in butt joint configuration was performed. Microstructure characterization and mechanical properties of weldment in as-welded and aged in 550 °C for 30 min conditions were investigated and compared. Aging caused precipitation of copper-rich clusters and increasing hardness of weld metal and homogenizing the hardness in HAZ. Tensile test results demonstrated that the failure occurred in the base metal and showed features of ductile fracture.

Numerical study for prediction of optimum operational parameters in laser welding of NiTi alloy

Abstract: Laser welding of NiTi alloy is a challenging process since it strongly affects the functionality of the material in the heat affected and fusion zones. In fact, the inherent thermal process can remarkably change the transformation temperature of NiTi alloy in the welding zone because of variation in the material composition. Accordingly, the laser parameters such as laser power and velocity effectively determine the quality of the welded component. The functional and mechanical behavior of the resulting welded NiTi parts can also be effectively improved by controlling laser parameters, and consequently, improve the weldability quality. The purpose of the present study was to establish a reliable finite element model to predict the thermal behavior induced by the laser welding process. To this end, a numerical model was employed to estimate the optimum laser parameters, which can reduce the heat affected and the fusion regions and thus result in a better weld. The results of the finite element model show good accuracy compared to the experimental results including the transient temperature and the dimension of the heat affected and fusion zones. In addition, an Artificial Neural Network (ANN) approach was applied, as a predictable tool, to perform a nonlinear mapping between inputs and outputs of the welding process in order to find the optimum laser parameters.

A Novel Shim-Assisted Resistance Spot Welding Process to Improve Weldability of Medium-Mn Transformation-Induced Plasticity Steel

Abstract: Medium-Mn transformation-induced plasticity steels have great potential to significantly reduce vehicle weight and improve fuel economy due to their outstanding combination of high strength and excellent ductility. One bottleneck to the application is their poor weldability resulting from their high Mn contents. In this paper, three resistance spot welding set-ups, including no shim, an interstitial-free steel shim at the faying interface (shim-in) and shims against the electrodes (shim-out), were incorporated to investigate the weldability of Fe-7Mn-0.14C medium-Mn steel. Tensile-shear, cross-tension, and microhardness tests were used to evaluate the mechanical properties of the welds. Experimental results demonstrated that the failure mode of the welds transitioned from the interfacial fracture in the case of no shim to the desired nugget pull-out fracture in the shim-out set-up, resulting in dramatical improvements in both peak loads and their corresponding extensions during the tensile-shear and cross-tension tests. In contrast, the shim-in set-up made no improvement. What can contribute to such improvement was then discussed on the basis of observed morphologies and microstructures of welds.

Remarkable improvement in resistance spot weldability of medium-Mn TRIP steel by paint-baking heat treatment

Abstract: In this study, a remarkable improvement in resistance spot weldability of medium-Mn transformation-induced plasticity (MT) steel through a paint-baking heat treatment was addressed using dissimilar resistance spot weldments between MT and dual phase (DP) steels with various soaking temperatures. Experimental results showed that the cross-tension strength in the dissimilar MT/DP weldment increased up to 128% when the soaking temperature was more than 110 °C, and was at its highest at 210 °C. The improved cross-tension strength is attributed to the failure mode change from a pull-out to a partial pull-out failure. The brittle-to-ductile transition of martensitic matrix in coarse-grained heat-affected zone in MT steel was also considered to be a factor. Austenite reversion and carbide precipitation occurred in the martensitic matrix during the paint-baking heat treatment, whereas there was no significant change in alloying element segregation at the prior austenitic grain boundary. The driving force for the tempering was discussed based on the calculated carbon diffusion distance.

Weldability of high-strength aluminium alloy EN AW-7475-T761 sheets for aerospace applications, using refill friction stir spot welding

Abstract: Refill friction stir spot welding is a solid-state welding process for joining lightweight sheets in the overlap configuration by means of frictional heat and mechanical work. The objective is to investigate refill friction stir spot welding of aluminium alloy EN AW-7475-T761, since fusion welding of such high-strength alloys is problematic due to solidification and liquation cracking. This alloy is used in highly stressed structural parts in aerospace applications, because of its low weight, superior strength, high corrosion resistance and corrosion fatigue behaviour. The process parameter optimization and the effect of the parameters on the weld characteristics were examined. The dwell time, the plunge depth and the rotational speed were varied according to a multi-level factorial design. An increase of the dwell time resulted in a larger stir zone area and smaller amount of defects. The width of the central coarse-grained band became smaller, containing a more refined grain size. An increase of the rotational speed lead to a smaller stir zone area, a discontinuous joint line remnant and a larger width of the central coarse-grained band. An increase of the plunge depth lead to a larger stir zone area. Welds produced with a high heat input exhibited a lower average hardness and a higher hardness drop, compared to welds with a low high heat input. Analysis of variance has shown that the dwell time, the plunge depth and their interaction have a statistically significant effect on the lap shear strength: a longer dwell time, a higher plunge depth and their interaction resulted into a higher lap shear strength.

Solid-state joining of powder metallurgy Al-Al2O3 nanocomposites via friction-stir welding: Effects of powder particle size on the weldability, microstructure, and mechanical property

Abstract: Solid-state butt-joining of powder metallurgy (PM) fabricated Al-Al2O3 nanocomposites was assessed using friction-stir welding (FSW), in which the PM materials were prepared from aluminum powder with different particle size distributions of

MAG Welding tests of modern high strength steels with minimum yield strength of 700 MPa

Abstract: The modern high strength steel plates have an excellent combination of strength and toughness based on micro-alloying and complex microstructure. Retaining this combination of properties in the weld zone is a major challenge for applications in high-demanding structural construction. This work investigates the weldability of three different modern high strength steel plates, with a thickness of 8 mm. Two of the test materials were produced by a thermo-mechanically controlled process (TMCP) and one by a quenching and tempering method (Q&T). Two-passes MAG (metal active gas) welding was used with four different heat inputs. The tests implemented on all the materials included tensile, hardness profiles (HV5), Charpy-V impact toughness tests, and microstructure analysis using scanning electron microscope (SEM). For one of the TMCP steels, some extended tests were conducted to define how the tensile properties change along the weld line. These tests included tensile tests with digital image correlation (DIC), and 3-point bending tests. The most notable differences in mechanical properties of the welds between the materials were observed in Charpy-V impact toughness tests, mostly at the vicinity of the fusion line, with the Q&T steel more prone to embrittlement of the heat affected zone (HAZ) than the TMCP steels. Microstructural analysis revealed carbide concentration combined with coarse bainitic structures in HAZ of Q&T steel, explaining the more severe embrittlement. During the tensile tests, the DIC measurements have shown a strain localization in the softest region of the HAZ. Increasing the heat input resulted in earlier localization of the strain and less maximum strength. The tensile properties along the weld line were investigated in all welding conditions, and the results emphasize relevant and systematic differences of the yield strength at the transient zones near the start and end of the weld compared with the intermediate stationary domain.