Showing papers on "Weldability published in 2015"

Influence of tool design and process parameters on dissimilar friction stir welding of copper to AA6061-T651 joints

Abstract: In the present investigation, two different tool designs along with different process parameters such as tool pin offset, welding speed and axial plunge load were used to produce dissimilar copper to aluminium (6061-T651) friction stir welding joints. Macrostructure and microstructure analysis, tensile test, hardness measurement test, scattered electron microscopy and electron-dispersive tests were performed to evaluate the weldability and weld properties of dissimilar copper–aluminium joints. The results revealed that defect-free dissimilar friction stir welding was achieved using a cylindrical tool pin profile. On the other hand, the taper tool pin profile was not found to be suitable for dissimilar friction stir welding system (FSW). Maximum tensile strength of 133 MPa and hardness of 181 HV (in the nugget zone) were obtained when FSW process parameters such as rotational speed, welding speed, tilt angle, tool pin offset and tool pin profile were kept at 1500 rpm, 40 mm/min, 2°, 2 mm and cylindrical profile, respectively. Axial plunge load value depended on the shoulder diameter as well as on the tilt angle. Axial plunge load range from 600 to 700 kgf was used to achieve defect-free copper to AA6061-T651 (of 6.3 mm in thickness) friction stir welded joint.

Fiber laser welding of NiTi to Ti-6Al-4V

Abstract: Joining of multimaterials is a major issue for several industrial applications where the combination of individual material properties increases component performance. The objective of this experimental study is to assess the laser weldability of NiTi to Ti-6Al-4V. Dissimilar welds were performed on 1-mm-thick plates with a high-power fiber laser with different heat inputs to control the cooling rate. Fracture was always observed in the weld metal in a solidification cracking phenomena. Scanning electron microscopy with EDS was performed to analyze the fracture surfaces. Solidification cracking was observed in the fusion zone associated to Ti2Ni formation in two distinct fracture morphologies: brittle transgranular cracking in the Ti2Ni regions and dimple intergranular failure along the solidification dendrites. Thus, autogeneous welding of these two materials is difficult due to intermetallics formation and filler materials or interlayers are needed to prevent the formation of brittle intermetallics.

Marine titanium alloys: Present and future

Abstract: CRISM Prometey has pioneered the use of titanium alloys as structural materials for marine facilities. Specialized titanium alloys for ship hulls, marine power systems, and ship engineering are widely used in shipbuilding and other industries. Prometey has created titanium alloys with the yield strength of 785 MPa and technologies of manufacturing large semifinished products: boards with thickness up to 160 mm, sheet billets for stamping, and billet forgings. The 50-year experience of operation with titanium hull structures has demonstrated that pseudo-α alloys are the optimum variant of welded titanium alloys for marine equipment. These alloys as parts of welded structures are characterized by good weldability and adaptability and high corrosion and mechanical resistance in metallurgical works and shipbuilding. Currently, the company is working to improve the yield strength of pseudo-α-class alloys to 950 MPa, as well as developing the ultrastrong titanium alloy for autonomous manned submersibles, allowing the hydrogeological studies and works at depths up to 11 km. Work is in progress on titanium alloys designed for marine equipment operating in extreme conditions of the Arctic offshore.

Studies on the weldability, microstructure and mechanical properties of activated flux TIG weldments of Inconel 718

Abstract: This research article addresses the joining of 5 mm thick plates of Inconel 718 by activated flux tungsten inert gas (A-TIG) welding process using SiO 2 and TiO 2 fluxes. Microstructure studies inferred the presence of Nb rich eutectics and/or laves phase in the fusion zone of the A-TIG weldments. Tensile studies corroborated that the ultimate tensile strength of TiO 2 flux assisted weldments (885 MPa) was better compared to SiO 2 flux assisted weldments (815 MPa) and the failure was observed in the parent metal for both the cases. Impact test results portrayed that both the weldments were inferior in toughness as compared to the parent metal, which was due to the presence of oxide inclusions. Also, the study investigated the structure–property relationships of the A-TIG weldments of Inconel 718.

Weldability and weld performance of candidate nickel base superalloys for advanced ultrasupercritical fossil power plants part I: fundamentals

Abstract: Fossil fuel will continue to be the major source of energy for the foreseeable future To meet the demand for clean and affordable energy, an increase in the operating efficiency of fossil fired power plants is necessary There are several initiatives worldwide to achieve efficiencies >45% higher heating value (HHV) through an increase in steam temperature (700 to 760°C) and pressure (276 to 345 MPa) Realising this goal requires materials with excellent creep rupture properties and corrosion resistance at elevated temperatures In order to accomplish this, three classes of materials have been identified: creep strength enhanced ferritic steels, austenitic stainless steels and nickel base superalloys Although new alloys have been designed and developed to meet this need, welding can have a significant and often detrimental effect on the required mechanical and corrosion resistant properties Two previous papers addressed the welding and weldability of ferritic and austenitic stainless steels W

Characterization of metallurgical and mechanical properties on the multi-pass welding of Inconel 625 and AISI 316L

Abstract: This article investigated the weldability, metallurgical and mechanical properties of Inconel 625 and AISI 316L stainless steel weldments obtained by continuous current (CC) and pulsed current (PC) gas tungsten arc welding (GTAW) processes employing ERNiCr-3 and ER2209 fillers Microstructure studies showed the migrated grain boundaries at the weld zone of ERNiCr-3 weldments and multi-directional grain growth for ER2209 weldments It was inferred from the tension tests that the fracture occurred at the parent metal of AISI 316L in all the cases Charpy V-notch impact tests accentuated that the CCGTA weldments employing ERNiCr-3 filler offered better impact toughness of 77 J at room temperature Further a detailed study has been carried out to analyze the structure — property relationships of these weldments using the combined techniques of scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) analysis

Understanding grain refinement in aluminium welding

Abstract: Grain refinement is an important opportunity to improve mechanical properties of fusion welds and the weldability (susceptibility to solidification cracking) of the base metal. In this study, grain refinement was achieved in aluminium welds through additions of grain refiner to the weld metal. Increasing grain refiner additions led to a decrease of the weld metal mean grain size (down to −86 %). The grain refinement efficiency was the highest in commercial pure Al (Alloy 1050A, Al 99.5), followed by Alloy 6082 (Al Si1MgMn) and Alloy 5083 (Al Mg4.5Mn0.7). To investigate this clear influence of alloy content on grain size, the undercooling parameters P and Q were calculated. Temperature measurements revealed that solidification parameters such as solidification growth rate or cooling rate vary significantly along the solidification front, dependent upon torch speed and alloy. On the basis of this comparison, an analytical approach was used to model the columnar to equiaxed transition (CET). Moreover, wavelength dispersive X-ray spectroscopy (WDS) and transmission electron microscopy (TEM) analyses revealed particles rich in Ti and B that are probably TiB2 particles coated by Al3Ti nucleating Al grains during solidification. Also, Ti/B contents needed in commercial filler wires to allow optimum weld metal grain refinement were calculated dependent upon base alloy and welding process.

Weldability of Thermomechanically Treated Steels Having a High Yield Point

Abstract: The article concerns the issue of weldability of S700MC steel, treated thermo-mechanically, with high yield point. The weakest area of welded joints of this steel is a high temperature coarse heat affected zone (HAZ) in which due to the nucleation effect of the dissolved phases, strengthening the matrix and their subsequent uncontrolled separation precipitation in the form of finely disperse and rapid decrease impact strength is observed. Performed arc welding tests here have shown that in order to ensure high quality of welded joints, it is necessary to limit the welding linear heat input. During the welding process of S700MC steel, it is not recommended to use pre heating before the welding process and heat treatment after welding, and the number of repairs should be kept to a minimum, because it leads to a reduction of strength and plastic properties in the HAZ area, as a result of aging processes, dissolution of strengthening phases in the matrix and their subsequent uncontrolled precipitation during cooling.

Microstructural control and mechanical properties in friction stir welding of medium carbon low alloy S45C steel

Abstract: Critical control of the welding conditions produced a fine ferrite–martensite duplex structure with the martensite volume fraction of around 33% in friction stir welding (FSW) of medium carbon (0.45 wt% C) low alloy steel sheets. This microstructure provides the preferable combination of tensile strength and ductility. The findings were achieved to clarify the effect of the welding speed on the weldability. The fraction of low angle grain boundaries (LAGBs) decrease with increasing welding speed. At the welding speed of 400 mm/min, the top region microstructure consists of lath martensite, while the bottom region shows a fine ferrite–pearlite structure. This microstructural variation can be linked with the distribution of the peak temperatures along the thickness of the weld. Additionally, it was shown that a non-contact thermal imaging system can be used as an effective tool for the online monitoring of several kinds of weld decays.

Effect of Continuous and Pulsed Current on the Metallurgical and Mechanical Properties of Gas Tungsten Arc Welded AISI 4340 Aeronautical and AISI 304 L Austenitic Stainless Steel Dissimilar Joints

Abstract: In this research work, the weldability of low alloyed AISI 4340 aeronautical steel and AISI 304L austenitic stainless steel joined by continuous current (CC) and pulsed current (PC) gas tungsten arc welding (GTAW) techniques, using ER309L and ERNiCr-3 filler metals was investigated. The main focus of the study involves the investigation on the effect of continuous and pulsed current mode of GTA welding process on the metallurgical and mechanical properties of these dissimilar weldments. Microstructure studies revealed the formation of different zones across the weldments, vis-a-vis martensite at the HAZ of AISI 4340, vermicular δ - ferrite /ferrite stringers at the HAZ of AISI 304L, pearlite colonies at the parent metal of AISI 4340 and equi-axed cellular and/or columnar dendrites at the weld zone. Tensile results showed that current pulsing accrued better tensile properties. The structure - property relationships of these weldments were established based on the current modes employed by utilizing combined techniques of optical microscopy, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS).

Microstructure, mechanical properties and texture of an AA6061/AA5754 composite fabricated by cross accumulative roll bonding

Abstract: AA6061 alloy is a widely used material in the automotive and aerospace industries, but is prone to hot cracking, which limits its weldability. To prevent this phenomenon, the AA6061/AA5754 composite was formed using a severe plastic deformation technique, Cross Accumulative Roll Bonding (CARB), at an elevated temperature (350 °C) to ensure good bonding between layers. This technique was efficient to maintain a small grain size, even under the process temperature conditions, and consequently, preserve good mechanical properties. The composite had better mechanical properties than the initial aluminium alloys. Microstructure and texture remained stable after two cycles and yield stress tended towards an equal value in the rolling and the transverse directions. After two cycles, the main component was the {001}〈110〉 rotated Cube, which was maintained for up to 10 cycles. Diffusion was more effective as the strain increased. Finally, a tungsten inert gas (TIG) welding process was performed on the composite and confirmed resistance to hot cracking.

Fiber Laser Welding of Direct-Quenched Ultrahigh Strength Steels: Evaluation of Hardness, Tensile Strength, and Toughness Properties at Subzero Temperatures

Abstract: The recently developed direct-quenched ultrahigh strength steels (UHSS) possess an appropriate combination of high tensile strength and toughness properties at subzero temperatures down to −80 °C, while simultaneously having low carbon contents, which is beneficial for weldability. In this study, butt joints of Optim 960 QC direct-quenched UHSS with a thickness of 8 mm were welded with a 10 kW fiber laser to evaluate the characteristics of the joints within the range of low to high heat inputs possible for this welding process. The mechanical properties of the joints were studied by subjecting the specimens to a number of destructive tests, namely, hardness and tensile testing, as well as impact toughness testing at temperatures of −40 °C and −60 °C. It was found that high quality butt joints with superior tensile strength and good impact toughness properties at −40 °C could be obtained. However, having a high level of all these properties in the joint narrows the process parameters’ window, and the heat input needs to be strictly controlled.

Hybrid Laser-arc Welding of 17-4 PH Martensitic Stainless Steel

Abstract: PH stainless steel has wide applications in severe working conditions due to its combination of good corrosion resistance and high strength The weldability of 17-4 PH stainless steel is challenging In this work, hybrid laser-arc welding was developed to weld 17-4 PH stainless steel This method was chosen based on its advantages, such as deep weld penetration, less filler materials, and high welding speed The 17-4 PH stainless steel plates with a thickness of 19 mm were successfully welded in a single pass During the hybrid welding, the 17-4 PH stainless steel was immensely susceptible to porosity and solidification cracking The porosity was avoided by using nitrogen as the shielding gas The nitrogen stabilized the keyhole and inhibited the formation of bubbles during welding Solidification cracking easily occurred along the weld centerline at the root of the hybrid laser-arc welds The microstructural evolution and the cracking susceptibility of 17-4 PH stainless steel were investigated to remove these centerline cracks The results showed that the solidification mode of the material changed due to high cooling rate at the root of the weld The rapid cooling rate caused the transformation from ferrite to austenite during the solidification stage The solidification cracking was likely formed as a result of this cracking-susceptible microstructure and a high depth/width ratio that led to a high tensile stress concentration Furthermore, the solidification cracking was prevented by preheating the base metal It was found that the preheating slowed the cooling rate at the root of the weld, and the ferrite-to-austenite transformation during the solidification stage was suppressed Delta ferrite formation was observed in the weld bead as well no solidification cracking occurred by optimizing the preheating temperature

Cold cracking of underwater wet welded S355G10+N high strength steel

Abstract: Water as the welding environment determines some essential problems influencing steel weldability. Underwater welding of high strength steel joints causes increase susceptibility to cold cracking, which is an effect of much faster heat transfer from the weld area and presence of diffusible hydrogen causing increased metal fragility. The paper evaluates the susceptibility to cold cracking of the high strength S355G10+N steel used, among others, for ocean engineering and hydrotechnical structures, which require underwater welding. It has been found from the CTS test results that the investigated steel is susceptible to cold cracking in the wet welding process.

Numerical analysis of thermoplastic composites laser welding using ray tracing method

Abstract: Laser technology is a good alternative for continuous joining of thermoplastics composites structures. Presence of continuous fibers at a high fiber volume fraction (superior to 30%) does not allow using traditional development as for pure thermoplastic materials, due to the presence of fiber clusters or polymer rich areas. Those heterogeneities induce macroscopic light scattering through the structure, reducing the resulting energy level absorbed at the welding interface. The study proposed here takes into account the real microstructure of the composite in order to evaluate changes in local energy diffusion directly linked with local fiber arrangements. The objective of this work is to develop an affordable numerical simulation of the laser welding process modeled with adapted physics mechanism and taking into account the microstructure heterogeneity of the considered materials regarding optical and thermal properties. To model the optical path of the laser beam through the composite fibrous structure, a simulation tool based on geometrical optic is developed. Weldability is considered on composites with different thicknesses, showing the non linear relationship between welding energy and substrate thickness.

Ultrasonic welding of plastics and polymeric composites

Abstract: Ultrasonic welding is one of the most popular methods for joining plastics and it is becoming an important method for welding polymeric composites. This chapter first describes the theory of ultrasonic welding including viscoelastic heating and the difference between near-field and far-field ultrasonic welding. The chapter then includes a process description of plunge and continuous ultrasonic welding. The chapter then discusses ultrasonic welding equipment including power supply and controller, stack, actuator, and fixture and a description of the different process control modes. Finally, the chapter discusses joint and part design and thermoplastic material weldability.

Weld nugget formation in resistance spot welding of new lightweight sandwich material

Abstract: Weldability of a new lightweight sandwich material, LITECOR®, by resistance spot welding is analyzed by experiments and numerical simulations The spot welding process is accommodated by a first pulse squeezing out the non-conductive polymer core of the sandwich material locally to allow metal–metal contact This is facilitated by the use of a shunt tool and is followed by a second pulse for the actual spot welding and nugget formation A weldability lobe in the time-current space of the second pulse reveals a process window of acceptable size for automotive assembly lines Weld growth curves are presented together with results of numerical simulations made in the finite element computer program SORPAS® 3D, which is based on an electro-thermo-mechanical formulation The numerical models are presented together with the specific modeling conditions leading to numerical simulations in good agreement with experimental results in the range of welding parameters leading to acceptable weld nugget sizes The validated accuracy of the commercially available software proves the tool useful for assisting the choice of welding parameters