Showing papers on "Weldability published in 2011"

Achieving high property friction stir welded aluminium/copper lap joint at low heat input

Abstract: Aluminium and copper plates with 3 mm thickness were successfully friction stir lap welded at a lower rotation rate of 600 rev min 21 using a larger pin 8 mm in diameter. Good metallurgical bonding on the Al/Cu interface was achieved due to the formation of a thin, continuous and uniform Al-Cu intermetallic compound layer. Furthermore, many Cu particles consisting of pure Cu and intermetallic compound layers were generated at the lower part of the nugget zone, forming a composite structure with increased hardness. A lower rotation rate resulted in a decrease in annealing softening in the heat affected zone (HAZ), and a larger diameter pin increased the Al-Cu bonding area. These factors resulted in that the friction stir welded lap joint exhibited a high failure load of 2680 N with failure in the HAZ on the aluminium side.

Dissimilar Metal Joining of 2024 and 7075 Aluminium Alloys to Titanium Alloys by Friction Stir Welding

Abstract: The friction stir welding (FSW) process is a solid-state joining process and the joining temperature is lower than that used in the fusion welding processes. Therefore, for dissimilar metal welding, FSW is considered to offer several advantages over fusion welding. The present work investigated the weldability of duralumin and titanium alloys using friction stir welding. The aluminum plates used in this work were 2024T3 and 7075-T651, and the titanium plates used were pure titanium and Ti-6Al-4V. The average tensile strength of the Ti/2024 FSW joints was 311 MPa, and the tensile strength of the Ti/2024 joint was higher than that of the Ti/7075 FSW joint when the joining conditions were the same. A mixed region of Ti alloy and Al alloy was observed at the joint interface, and the joints mainly fractured at this region, where there was an intermetallic compound layer. In this region, a TiAl3 intermetallic compound was detected by XRD. Therefore, it can be understood that this TiAl3 intermetallic compound affects the tensile strength of butt joints. [doi:10.2320/matertrans.L-MZ201102]

Evaluation of weldability for resistance spot welded single-lap joint between GA780DP and hot-stamped 22MnB5 steel sheets †

Abstract: Recently, in the automotive industry, Al-coated boron steel sheets (22MnB5) have been used for hot stamping, and the use of these sheets makes it possible to achieve a tensile strength of over 1,500 MPa, since a metallurgical transformation from austenite to martensite occurs during the process. In this study, resistance spot welding (RSW) experiments were performed in order to evaluate the weldability of single-lap joints between GA780DP and 22MnB5. The effect of the weld current on the nugget diameter and load-carrying capacity was evaluated by observing the nugget diameter and performing a tensile-shear test. Furthermore, the fracture behavior was evaluated by carrying out optical microscopy, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX) observations. Ductile regions were observed on the interfacially fractured surface of the weld, and this implies that a high load-carrying capacity can be obtained even when interfacial fracture (IF) occurs. IF is caused by the stress concentration resulting from the presence of the sharp notch at the boundary of the nugget as well as by the high hardness and the brittle microstructure of the weld; the microstructure is brittle because of the high carbon equivalent (Ceq) and the penetration of Al in the weld.

High-strength molten-zinc-plated steel sheet having excellent bendability and weldability, and process for production thereof

Abstract: A steel sheet is coated with a molten zinc plating layer, wherein the steel sheet comprises, in mass%, not less than 0.05% and less than 0.12% of C, 0.001 to 0.040% of P and 0.0050% or less of S, has a steel sheet surface layer part (which is a part lying between each of surfaces of the steel sheet and a depth of 10 μm of the steel sheet) and a steel sheet inner layer part (which is a inside part from the depth of 10 μm from each of the surfaces of the steel sheet), and has a tensile strength of 980 MPa or more, wherein the steel sheet surface layer part has a structure that contains a ferrite phase at a volume fraction of more than 70% and the steel sheet inner layer part has a structure that contains a ferrite phase having an average crystal particle diameter of 5 μm or less at a volume fraction of at least 20 to 70%. In this manner, it is possible to produce a high-strength molten-zinc-plated steel sheet having a tensile strength (TS) as high as 980 MPa or more and also having excellent bendability and weldability.

Weldability Studies of High-Cr , Ni-Base filler metals for power generation applications

Abstract: The solidification behaviour and weld solidification cracking susceptibility of high-Cr, Ni-base filler metals that are widely used, or proposed for use, in the nuclear power industry have been investigated. Two heats of ERNiCrFe-13 (filler metal 52MSS), one heat of ERNiCrFe-7A (filler metal 52M), and one heat of a modified ERNiCr-3 (filler metal 82 with higher Cr content, designated here as filler metal 52i) have been tested using both the Transvarestraint test and the Cast Pin Tear test (CPTT). The solidification behaviour in these alloys has been studied by a newly developed procedure that accurately replicates the solidification process in fusion welds of Ni-base alloys and is based on the patented technique for Single Sensor Differential Thermal Analysis (SS DTA™). Results of the solidification studies showed that filler metal 52i has the widest solidification range, followed by the two heats of filler metal 52MSS, and filler metal 52M. The filler metal 52i also has the widest eutectic temperature range. The interdendritic eutectic constituent formed in weld metal of this filler metal and filler metal 52MSS is enriched in Nb and results from the eutectic reaction of γ + L → γ + NbC at the end of solidification. Both the CPTT and the Transvarestraint test provided the same ranking of solidification cracking susceptibility among these filler metals. Both heats of 52MSS and the heat of 52i were found to be more susceptible to solidification cracking than filler metal 52M. The slightly higher resistance to solidification cracking of filler metal 52i relative to the 52MSS filler metals is attributed to crack “healing” during the final stages of solidification. This is the result of the higher fraction of eutectic liquid of filler metal 52i, as confirmed by metallographic studies. The results of this study confirm the higher solidification cracking susceptibility of high-Cr, Ni-base filler metals that contain higher Nb levels to counteract ductility-dip cracking, relative to filler metals that are Nb-free. This study has also shown that the CPTT can be used as an alternative, and reliable, tool for ranking the solidification cracking susceptibility of high-Cr, Ni-base filler metals proposed for use in nuclear power plants and other applications.

Three-Sheet Spot Welding of Advanced High-Strength Steels

Abstract: With the introduction of advanced high strength steels (AHSS), welding has become more difficult to model and execute, as the material data is more complex than the more common materials in use today Especially car manufactures are interested, as they would utilise the materials in the supports that make the chassis, which is welded together by resistance welding Three sheet spot welding of advanced high strength steel studies the option of welding a thin sheet of mild steel with two thicker sheets of AHSS Industry wise the thin mild steel could be the sheets covering the car body Initially a simulation study was conducted using SORPAS so establish welding parameters for experimental welding of seven different material combinations The three first were a combination of DC06(06mm), Docol350yp(08mm), DP600(15mm) and TRIP700(12mm): DC06-Docol350yp-DP600, DC06-Docol350yp-TRIP700 and a comparison DC06-Docol350yp-DP600/TRIP700 The last four were a combination of DC06, DP600 and TRIP700: DC06-DP600-TRIP700, DC06-TRIP700-DP600, DC06-TRIP700-TRIP700 and DC06-DP600-DP600 Based on the simulation results and with the use of 2k Factorial Design, the weld experiments were planned and executed The test welds were then shear tested to find the weld strength for later comparison and analysis To analyse the experimental results a variance analysis was used to identify key parameters influence on the weld strength A comparison of the measured IRMS value and weld strength together with splash was also conducted It was found that changing the lower electrode size from a smaller type to a larger had positive effect on the weld strength for DC06-Docol350yp-DP600 Alternately it had no effect with the DC06-Docol350yp-TRIP700 combination For the DC06-Docol350yp-DP600/TRIP700 comparison test, splash occurred with TRIP but not with DP This shows that the TRIP weldability range is narrow compared to the DP Changing the material from TRIP to DP showed a clear connection between weld time and sheet thickness In all of the tests the DC06 was successfully welded to the two sheets of AHSS For the last four material combinations, TRIP showed to have a detrimental effect on the welding when in contact with the DC06 The combinations: DC06-TRIP700-DP600 and DC06-TRIP700-TRIP700 were highly unstable, with no welding of the DC06 occurring at certain points DC06-DP600-TRIP700 was more stable and generating the highest average weld strength of all the tests The combination DC06-DP600-DP600 was close to completely stable in stark contrast to the tests involving TRIP The problems with the TRIP are two fold: One is the fact that TRIP is coated; this slows down the nugget growth and adds some instability to the experiment The second problem is TRIP it self, as TRIP has a very narrow window of weldability and does not take much to either hit splash or not get any weld

Weather resistant steel plate and manufacturing method thereof

Abstract: The present invention provides a weather resistant steel plate, which comprises components of, by mass percent, 002 to 010 of C, 010 to 040 of Si, 10 to 16 of Mn, less than or equal to 0025 of P, less than or equal to 0015 of S, 020 to 050 of Cu, 030 to 060 of Cr, 010 to 050 of Ni, less than or equal to 040 of Mo, less than or equal to 0060 of Nb, less than or equal to 0060 of V,0010 to 0035 of Ti, less than or equal to 00030 of B, less than or equal to 00050 of Ca, 0015 to 0050 of Al, and the balance Fe and other unavoidable impurities Correspondingly, the present invention also provides a manufacturing method of the weather resistant steel plate Through reasonable distribution ratio of alloy components, the method provided in the invention can obtain a high-strength and high-toughness weather resistant steel plate with good corrosion resisting performance, high yield strength and tensile strength, and excellent low temperature impact toughness The steel plate also possesses good weldability, being able to carry out welding without preheating or employ lower preheating temperature welding The steel plate provided in the invention can be widely applied to large-scale steel structure engineering such as building structures, bridges, etc

Study of Inconel 718 weldability using MIG CMT process

Abstract: This work investigates the weldability of Inconel 718 using the metal inert gas (MIG) welding process called ‘cold metal transfer’. This arc welding process is reported for working with a lower heat input compared to other arc processes. The consequences are less base metal impaired, low deformation and low residual stress level in assembly. In order to check these abilities, metallographic, texture, chemical and residual stress analyses have been carried out. Results show that MIG cold metal transfer has good properties for the welding of Inconel 718 inasmuch as no defect has been detected and a lower level of residual stresses has been introduced in metal compared to classic MIG.

Weldability of Precipitation Hardening Superalloys – Influence of Microstructure

Abstract: Superalloys and in particular the precipitation hardened Ni-based superalloys have always been used extensively in the hot sections of jet engines. Large hot structural engine components with complex geometry have preferably been cast as single piece components since the large scale vacuum investment casting process became available about fifty years ago. However, a recent trend is to cast smaller pieces which can be joined with sheet or forged parts to fabricate structural components. The rationale for this fabrication strategy is the possibility to save weight by the use of higher strength wrought material, where geometry allows, and join these wrought parts with cast material where complex geometry is needed and where the demand for strength is moderate. One of the major challenges using this strategy is the obvious fact that numerous welds must be made which requires the fundamental understanding, not least metallurgical, of how different materials may be joined by specific welding processes. The main objective of this research has, for this reason, been to examine and interpret the weldability of precipitation hardened superalloys from a metallurgical standpoint. Two newly developed superalloys Allvac® 718PlusTM and Haynes® 282® are compared with the two well established Alloy 718 and Waspaloy. The understanding of the influence of secondary phases such as carbides and δ phase in the microstructure was addressed by systematic hot ductility testing (Gleeble) and by weldability testing (Varestraint). The effect of secondary phases were also analysed through practical welding as by electron beam welding (EBW), and by gas tungsten arc welding (GTAW). The research showed that all the techniques used (Varestraint testing, Gleeble testing, DSC thermal analysis and welding (GTAW repair and EBW)) in studying the weldability independently provided important knowledge and most importantly that a combination of the results from these different techniques were necessary for the understanding of the weldability of these four alloys. From a microstructural point of view it has been possible to show that δ phase contrary to what has generally been assumed improves the weldability due to its ability to inhibit grain growth and to assist in the healing of cracks. For future research, a new modified weldability testing method was developed where it is possible to perform Varestraint, Transvarestraint and spot-varestraint testing at ram speeds from 15 to 300 mm/s using GTAW, plasma arc welding and laser welding.

Keyhole behaviour during laser welding of zinc-coated steel

Abstract: The production of consistent, high-quality laser welds on zinc-coated steels for the automotive industry remains a challenge. A simple overlap joint geometry is desirable in these applications but has been shown to be extremely detrimental to laser welding because the zinc vapour formed at the interface between the two sheets expands into the keyhole and disrupts fluid flow in the melt pool, which often leads to metal ejection. In this work, laser welding on sheets with various coating thicknesses has been performed and it is observed that the sheets with thick coatings (?20 ?m) show surprisingly good weldability. High speed video camera visualizations of the keyhole provide insight into the keyhole dynamics during the process. It appears that the dynamic pressure of zinc vapour can effectively elongate the keyhole and the process can reach a stable state when an elongated keyhole is continuously present. A simple analytical model has been developed to describe the influence of zinc vapour on keyhole elongation.

Effect of shielded-electrode wet welding conditions on diffusion hydrogen content in deposited metal

Abstract: Wet welding is the most popular method of joining in aquatic environments. During underwater joining, the weldability of steel is limited by the higher cooling rates and hydrogen content in the welded metals. This article presents the results of preliminary tests on the effect of wet welding conditions on diffusion hydrogen amounts. Seven parameters were optimized using a Plackett–Burman design to get the most relevant variables. These parameters were salinity of water, contamination of electrode, electrode polarity, and welding current.

Microstructural mapping of friction stir welded AA 7075-T6 and AlMgSc alloys using electrical conductivity

Abstract: AlMgSc and AA 7075-T6 alloys find applications in the aeronautic industry due to their lightweight associated with high mechanical strength and fatigue resistance. Both alloys have poor weldability when joined by fusion welding processes, which is overcome with the use of friction stir welding (FSW). Recent research work shows that electrical conductivity field analysis can be used as a material characterisation technique for solid state material welding exhibiting a microstructure gradient. This study aims to apply electrical conductivity field analysis to bead on plate FSW to identify the potential application of this technique to map and characterise microstructural transformations. The FSW was conducted on AlMgSc and AA 7075-T6 plates with different parameters, and electrical conductivity measurements were performed at half thickness, complemented by other techniques as hardness, scanning electron microscopy and energy dispersive spectroscopy. A good correlation was observed among electrical c...

Review of creep resistant alloys for power plant applications

Abstract: SUMMARY The environmental protection and economics havebeen driving force for development new alloys with im-proved creep strength, better corrosion and crack resis-tance and good weldability. Thus, significant advanceshave been made in developing of creep resisting materi-als. The 10 5 h creep rupture strength of ferritic/mar-tensitic steels at 600 °C has increased from about 35 MPato 180 MPa in last few decades and the operating temper-ature is 50 °C – 100 °C higher. Besides ferritic/mar-tensitic steels also ODS ferritic steels and nickel based al-loys are also very promising for power plants operating attemperaturesbeyond650°Corevenhigher(700°C).Theefficiency of power plant would increase to around 55 %and the CO 2 emission would decrease for almost 15 %.The austenitic stainless steel, on the other hand, poseshigh corrosion resistance and mechanical properties athigher temperatures; however, due to the poor thermalconductivity and large coefficient of thermal expansionthey are not appropriate for thick components.

Underwater Welding of Duplex Stainless Steel

Abstract: The present work was conducted to assess the weldability of duplex stainless steel at underwater conditions. Interest of underwater welding of this steel grade is connected with necessity of preparing welding repair technologies for subsea pipelines widely used in offshore oil and gas industry. The GMA local cavity welding method was used in the investigations. Welded beads were performed underwater at 0.5 m depth and in the air. Metallographic examinations of welds, ferrite content assessment in microstructure and hardness test were performed. The good weldability at underwater conditions of duplex stainless with the use of GMA local cavity method was confirmed.

On the effect of nitrogen on duplex stainless steels

Abstract: One of the key issues in the development of the modern duplex stainless steels was the introduction of nitrogen as an alloying element. This was made possible by e.g. the AOD process and has meant that the problems with earlier grades regarding weldability could be solved. The prime reason for the lower weldability, namely a coarse-grained heat affected zone with inferior properties was then removed. Further beneficial effects of nitrogen increases in the new generation of duplex grades were pointed out: localized corrosion resistance particularly in chloride containing solutions, enhancement of fatigue properties, improved creep properties particularly when considering heat treatment...The paper will outline the influence of nitrogen additions in duplex grades by means of thermodynamic calculations including phase diagrams, TTT phase precipitation diagrams from metallographic investigations, mechanical and corrosion properties. Metallographic investigations, corrosion resistance properties and mechanical properties will be presented. The specific links between welded joints microstructures and properties with different nitrogen contents will be discussed.

Parameter optimization using a regression model and fitness function in laser welding of aluminum alloys for car bodies

Abstract: The objective of this paper is to determine the optimal welding conditions in terms of the productivity and weldability for laser welding of aluminum alloy AA5182 using filler wire AA 5356. The experiments were performed with laser power, welding speed, and wire feed rate as control factors. Tensile tests were carried out in order to evaluate the weldability under each welding condition. In order to estimate the tensile strength, three regression models are proposed. One is a multiple linear regression model, another is a second order polynomial regression model, and the last is a multiple nonlinear regression model. Of the three models, the second order polynomial regression model had the best estimation performance with respect to ANOVA (analysis of variation) and average error rate. Also, this study defines objective functions for tensile strength, which represents weldability, and for the welding speed and wire feed rate, which represent productivity. In addition, fitness functions are obtained using the objective functions and a weight matrix which shows the importance of each objective function. The steepest descent method is used to find the optimal point where the fitness function was maximized. Optimal welding conditions were found at a filler wire feed rate of 2.7 m/min, laser power of 4 kW, and welding speed of 7.95 m/min.

Thermal cycle simulation of welding process in low carbon steel

Abstract: This paper is a contribution to the study of weldability of low carbon steel. It presents the microstructures obtained after thermal cycle simulation of welding by rapid heating and cooling treatments in a specific simulation equipment. Optical microscopy and microhardness measurements are used as characterization techniques. We have found that the obtained microstructures correspond exactly to those observed in real welded joint realized by arc welding.