Showing papers in "Science and Technology of Welding and Joining in 2018"
TL;DR: In this article, the theoretical requirements are explored through the understanding of joining mechanism and heat generation in aluminium-magnesium dissimilar friction stir welding (FSW), and the observed trends in microstructural characterisation and mechanical properties are analysed.
Abstract: The paper critically assesses the research progress towards aluminium–magnesium dissimilar friction stir welding (FSW). First, the theoretical requirements are explored through the understanding of joining mechanism and heat generation in aluminium–magnesium FSW. Next, the observed trends in microstructural characterisation and mechanical properties are analysed. Finally, the effects of welding parameters and how it influences process variables and materials responses are discussed in detail, and several suggestions are made based on these discussions.
102 citations
TL;DR: In this paper, the response of the CoCrFeMnNi high-entropy alloy to weld thermal cycles was investigated to determine its applicability as an engineering structural material.
Abstract: The response of the CoCrFeMnNi high-entropy alloy to weld thermal cycles was investigated to determine its applicability as an engineering structural material. Two processes were used: high-energy-...
71 citations
TL;DR: In this article, the feasibility of FSW for dissimilar lap-joining of an aluminium-magnesium alloy (AA5058) and poly-methyl-methacrylate sheets to attain sound and defect-free joints was examined.
Abstract: In this research, the feasibility of friction-stir welding (FSW) for dissimilar lap-joining of an aluminium-magnesium alloy (AA5058) and poly-methyl-methacrylate sheets to attain sound and defect-free joints was examined. The inter-mixing flow patterns between the metal and polymer counterparts during FSW were predicted by employing three-dimensional finite element models. It is shown that the bonding mechanism between the dissimilar materials is mechanical interlocking at the interface which controls the joint strength depending on the processing parameters. The most suitable dissimilar lap-joining regarding microstructural soundness is attained at w= 1600 rev min−1 and v = 25 mm min−1. Under this condition, the maximum joint strength, which is about ∼60% of the weakest base material, is attained. Fractography indicates that the rupture occurs from the aluminium side.
68 citations
TL;DR: In this paper, the feasibility of friction stir welding of poly(methyl methacrylate) sheets was studied experimentally and theoretically by employing thermomechanical simulations, and the effect of processing parameters including tool plunge depth, tilt angle, tool rotational speed (w), and transverse velocity (v) was investigated to determine suitable conditions to attain sound and defect-free joints.
Abstract: In the present work, the feasibility of friction stir welding (FSW) of poly(methyl methacrylate) sheets was studied experimentally and theoretically by employing thermomechanical simulations. The effect of processing parameters including tool plunge depth, tilt angle, tool rotational speed (w), and transverse velocity (v) was investigated to determine suitable conditions to attain sound and defect-free joints. It is shown that a low tool plunge depth of 0.2 mm and a tilt angle of 2° provide suitable material flow to gain sound joints. By controlling the heat input into stir zone by increasing the tool rotational speed and decreasing linear velocity, the formation of defects can be minimised. Mechanical examinations in both longitudinal (LS) and transverse (TS) directions indicate that the highest joint strength of 57 MPa (for LS) and 42 MPa (for TS) are obtained at processing conditions of w = 25 mm min−1 and v = 1600 rev min−1. The measured tensile strengths are 81 and 60% of the base polymer, re...
62 citations
TL;DR: In this paper, a 3D print device using a cold metal transfer arc welding station to melt a metallic filler wire is developed to build aluminium part by optimising the process parameters.
Abstract: A 3D print device using a cold metal transfer arc welding station to melt a metallic filler wire is developed to build aluminium part by optimising the process parameters. First tests achieved using standard pre-recorded process parameters allow to study the effect of the travel speed and the average welding power on the geometrical characteristics of mono-layer deposits and on walls built by layers superposition. Finally, a parametric study of the effect of each process parameter controlling the shape of the arc current or voltage and the filler wire feeding is carried out in order to try to improve the geometrical regularity of the deposits, and to better understand the effect of each parameter on the melting of the filler wire, its transfer on the support plate, and the geometry of the formed bead.
62 citations
TL;DR: In this article, the effect of post weld heat treatment (PWHT) temperature on laser beam welds in high-entropy alloys (HEAs) using a cold-rolled cantor system (CoCrFeMnNi) was investigated.
Abstract: The effect of post weld heat treatment (PWHT) temperature on laser beam welds in high-entropy alloys (HEAs) using a cold-rolled cantor system (CoCrFeMnNi) was investigated. Laser welding of low heat input was applied to reduce thermal distortion. The cold-rolled HEA welds indicated larger grain size and inferior tensile/hardness properties as compared to the base metal (BM). By applying PWHT, the welds showed superior hardness to the BM with no variation in the face-centred cubic phase and a decrease in the size and fraction of CrMn oxide inclusions. As the PWHT temperature increased (800–1000°C), the variation in the grain size decreased between the weld metal and heat-affected zone, thus resulting in approximately the same tensile strength and elongation of the transverse welds as compared to the BM.
58 citations
TL;DR: In this article, the authors provide a perspective on the current development of the friction stir welding (FSW) technology and the industrialisation of the technology and related research were assessed by a...
Abstract: This paper intends to provide a perspective on the current development of the friction stir welding (FSW) technology. The industrialisation of the technology and related research were assessed by a...
54 citations
TL;DR: In this paper, the influence of welding process, constraints, solid phase transformation and multi-pass welding on deformation and residual stress was discussed, and computation accuracy and efficiency were summarised.
Abstract: Welding deformation and residual stress have negative influence on assembly accuracy and service performance. Thermal elastic plastic (TEP) and inherent strain finite element analysis (FEA) methods were used to study this challenge. Basic principle of these two methods was first introduced. The influence of welding process, constraints, solid phase transformation and multi-pass welding on deformation and residual stress was discussed, and computation accuracy and efficiency were summarised. Loading method of inherent strain in inherent strain FEA was analysed, interface element was introduced to simulate effects of the gap on deformation in assembly welding especially for large structures. The future work, including accurately multiscale TEP model, efficiently transient prediction method of large structures, and flexible evaluation software, was planned.
45 citations
TL;DR: In this article, the macro-structure, microstructure and mechanical properties of 4043 aluminium-alloy parts manufactured by variable polarity cold metal transfer welding (CMT+Advance) have been investigated.
Abstract: The macro-structure, microstructure and mechanical properties of 4043 aluminium-alloy parts manufactured by variable polarity cold metal transfer welding (CMT + Advance) have been investigated. The...
39 citations
TL;DR: In this paper, the 5mm-thick AZ61 magnesium alloy was friction stir welded by using the specially designed bobbin tool with various rotation speeds. Defect-free welds were successfully obtained with rotation spe...
Abstract: The 5-mm-thick AZ61 magnesium alloy was friction stir welded by using the specially designed bobbin tool with various rotation speeds. Defect-free welds were successfully obtained with rotation spe...
38 citations
TL;DR: In this article, the effect of three different types of in situ postweld heat treatment (PWHT) on the mechanical properties of TRIP steel resistance spot welds was addressed.
Abstract: Transformation-induced plasticity (TRIP) steel resistance spot welds are delicate to low-energy interfacial failure via crack propagation through martensitic fusion zone during cross-tension (CT) loading. This paper addresses the effect of three different types of in situ postweld heat treatment (PWHT) on the mechanical properties of TRIP steel resistance spot welds. Depending on the post weld second pulse current level, three different strengthening mechanisms were found including (i) martensite tempering with reduced hardness, (ii) refining of martensite packets with improved toughness and (iii) nugget re-melting/enlargement combined with possible reduction of grain boundary impurity segregation. All designed in situ PWHTs were enabled to promote pullout failure mode with improved load-bearing capacity and energy absorption capability during CT loading.
TL;DR: Friction stir scribe technology, a derivative of friction stir welding, was applied for the dissimilar lap welding of an aluminium alloy and galvanised mild steel sheets as discussed by the authors, and the results showed that the process was more efficient than traditional friction-stir welding.
Abstract: Friction stir scribe technology, a derivative of friction stir welding, was applied for the dissimilar lap welding of an aluminium alloy and galvanised mild steel sheets. During the process, the ro...
TL;DR: In this paper, Aluminium alloy and magnesium alloy were successfully joined by using laser welding/brazing technology via a nickel interlayer, and the results showed the properties of the dissimilar Al/Mg join.
Abstract: Aluminium alloy and magnesium alloy were successfully joined by using laser welding/brazing technology via a nickel interlayer. Microstructure and mechanical properties of the dissimilar Al/Mg join...
TL;DR: In this paper, the authors showed that the composition of the nickel-based superalloys plays a strong role in determining the required time for obtaining intermetallic-free joint during diffusion brazing.
Abstract: The key feature of diffusion brazing, also referred to as transient liquid phase bonding, is isothermal solidification which precludes the formation of intermetallic in the joint centreline Analysing the available data published in the literature showed that the composition of the nickel-based superalloys plays a strong role in determining the required time for obtaining intermetallic-free joint during diffusion brazing This effect is not predictable by the standard conventional models It is proposed that increasing the boride-forming elements in the base superalloy which promotes in situ boride precipitation at the diffusion-affected zone can accelerate the diffusion flux of the boron into the base superalloy, leading to faster isothermal solidification The higher the Cr + Mo + Nb + Ta + W content in base superalloy, the shorter the isothermal solidification time
TL;DR: In this paper, solidification phenomena and solid state precipitations during diffusion brazing of Hastelloy X nickel base superalloy using a ternary Ni−4.5Si−3.2 B (in wt-%) fille
Abstract: The paper aims at understanding solidification phenomena and solid state precipitations during diffusion brazing of Hastelloy X nickel base superalloy using a ternary Ni–4.5Si–3.2 B (in wt-%) fille...
TL;DR: In this article, the authors investigated the underlying factors of the tensile shear strength of automotive steels' resistance spot welds during interfacial failure and found that the ratio of the fracture toughness to the hardness of the fusion zone is the critical factor governing the interfacer failure mechanism.
Abstract: The failure of advanced high-strength steels’ spot welds is a critical issue for automotive crashworthiness. This paper deals with understanding the underlying factors of the tensile-shear strength of automotive steels’ resistance spot welds during interfacial failure. It was found that the ratio of the fracture toughness to the hardness of the fusion zone is the critical factor governing the interfacial failure mechanism: ductile shear failure (controlled by the fusion zone hardness) vs. cleavage crack propagation (controlled by the fracture toughness). This clarification could pave the way for more accurate modelling of interfacial failure of advanced steel resistance spot welds and shed light on the design of proper post-weld heat treatment for improving the weld mechanical performance.
TL;DR: In this paper, the welding parameters were optimized based on the clamping ring temperature and weld strength, and 85.7% of welds achieved a strength which exceeds the American Welding Society requirement when the clamping ring temperature ranges from 230 to 265°C.
Abstract: Al/steel welds were successfully fabricated by refill friction stir spot welding. The welding parameters were optimised based on the clamping ring temperature and weld strength. 85.7% of welds achieve a strength which exceeds the American Welding Society requirement when the clamping ring temperature ranges from 230 to 265°C. Cracks are formed under the pin and sleeve in the Al substrate at the Al/steel interface, which are associated with the tool sleeve plunging period and attributed to the α-Al + Al–Zn eutectic structure. The interdiffusion between Al and Zn at the steel surface produced an Al–Zn eutectic structure layer at the Al/steel interface, while part of the zinc coating materials is squeezed out of the sleeve periphery, leading to a brazing effect which contributes to weld strength. Nanoscale discontinuous Fe4Al13 and FeAl intermetallics form as a layer localised at the Al–Zn layer/steel substrate interface.
TL;DR: In this article, the effect of single and double pulse welding on the mechanical behavior of resistance spot-welded DP1000-GI steel is investigated, and the results show that double-pulse welding is more effective than single pulse welding.
Abstract: In the present study, the effect of resistance spot welding scheme (i.e. single and double pulse welding) on the mechanical behaviour of resistance spot-welded DP1000-GI steel is investigated. It i...
TL;DR: In this article, a series resistance spot welding was used to join SUS304 and carbon-fibre-reinforced polyamide and modified polypropylene, but not to polyphenylene sulphide.
Abstract: Dissimilar materials joining of SUS304 and carbon-fibre-reinforced plastics consisting of short fibres and thermoplastics was performed. The materials were joined by series resistance spot welding. The electrodes were pressed on the metal plate of the lap joint of metal/carbon-fibre-reinforced plastics. The SUS304 plate was heated by resistance heating, causing the thermoplastic near the interface to melt slightly because of heat conduction. SUS304 could be joined directly to carbon-fibre-reinforced polyamide and modified polypropylene, but not to polyphenylene sulphide. The joining area increased with an increase in the welding current and welding time, so did the tensile shear fracture load. Furthermore, the silane coupling agent treatment of SUS304 was highly effective in increasing the joining strength.
TL;DR: In this article, an analysis of the wetting behavior of the Zn-xAl filler metal spreading on the stainless steel is presented, showing that the spreading area of the filler metal after re-solidification decreases with an increase of the content of Al.
Abstract: This work offers an analysis of the wetting behaviour of the Zn–xAl filler metal spreading on the stainless steel. Effects of Al content on wetting kinetics and microstructures of the re-solidified filler metal were studied in this important system of dissimilar substrates. Experimental results have confirmed that the wetting of Zn–xAl filler metal on stainless steel features the trend of triple-line kinetics. In the main spreading phase, the spreading radius and time can be correlated with a power law of Rn ∼ t, n = ∼0.4. The content of Al in the filler metal has a minimal effect on the value of n for the investigated range of Al concentrations. However, the spreading area of the filler metal after re-solidification decreases with an increase of the content of Al. Moreover, the thickness of the Fe–Al intermetallic layer at the cross-section increases with an increasing Al content.
TL;DR: Acicular ferrite is recognized as a desirable microstructural constituent in C-Mn and low-alloy steel weld metals as mentioned in this paper, it is Widmanstatten ferrite that nucleates on the spheroidal non-metallic inclusio...
Abstract: Acicular ferrite is recognised as a desirable microstructural constituent in C–Mn and low-alloy steel weld metals. It is Widmanstatten ferrite that nucleates on the spheroidal non-metallic inclusio...
TL;DR: A finite element model based on software Abaqus/Explicit and experimentation was established to describe the probeless friction stir spot welding process of 2198-T8 aluminium alloy as mentioned in this paper.
Abstract: A finite element model based on software Abaqus/Explicit and experimentation was established to describe the probeless friction stir spot welding process of 2198-T8 aluminium alloy. An Arbitrary La...
TL;DR: In this article, the effects of pin thread and thread interruptions on weld quality and process response parameters during friction stir welding (FSW) of 6061 aluminium alloy were quantified.
Abstract: In this work, effects of pin thread and thread interruptions (flats) on weld quality and process response parameters during friction stir welding (FSW) of 6061 aluminium alloy were quantified. Otherwise, identical smooth and threaded pins with zero to four flats were adopted for FSW. Weldability and process response variables were examined. Results showed that threads with flats significantly improved weld quality and reduced in-plane forces. A three-flat threaded pin led to production of defect-free welds under all examined welding conditions. Spectral analyses of in-plane forces and weld cross-sectional analysis were performed to establish correlation among pin flats, force dynamics and defect formation. The lowest in-plane force spectra amplitudes were consistently observed for defect-free welds.
TL;DR: An experimental program by combining artificially thickened oxide layer as marker material and stop-action welding were used to study the material flow and defect formation in frictio... as mentioned in this paper.
Abstract: An ingenious experimental programme by combining artificially thickened oxide layer as marker material and ‘stop-action’ welding were used to study the material flow and defect formation in frictio...
TL;DR: In this article, the longitudinal residual stresses in the friction stir-welded plates of 5A06 aluminium and pure copper were determined using the contour method, which revealed the presence of high tensile and compressive residual stresses on the aluminium and copper sides, respectively.
Abstract: The longitudinal residual stresses in the friction stir-welded plates of 5A06 aluminium and pure copper were determined using the contour method. The results revealed the presence of high tensile and compressive residual stresses on the aluminium and copper sides, respectively. The residual stresses were detected on the weld zone as well as the thermo-mechanically affected zone (TMAZ) of the aluminium plate. In contrast, the compressive residual stresses in the copper plate had a much narrower width along the weld line. Peak tensile stresses up to 240 MPa were found in the TMAZ of the aluminium plate.
TL;DR: In this paper, a ring-shaped permanent magnet is applied in resistance spot welding to improve the weld quality of austenitic stainless steel, under the action of an external magnetic field.
Abstract: A ring-shaped permanent magnet is applied in resistance spot welding to improve the weld quality of austenitic stainless steel. Under the action of an external magnetic field, the profile of the we...
TL;DR: In this article, a special experimental setup with a high-speed camera was employed to measure the strain during the welding process, and the critical strain required for solidification crack formation was locally and globally determined.
Abstract: In recent years, laser beam welding has found wide applications in many industrial fields. Solidification cracks are one of the most frequently encountered welding defects that hinder obtaining a safe weld joint. Decades of research have shown that one of the main causes of such cracks are the strain and the strain rate. Obtaining meaningful measurements of these strains has always been a major challenge for scientists, because of the specific environment of the measurement range and the many obstacles, as well as the high temperature and the plasma plume. In this study, a special experimental setup with a high-speed camera was employed to measure the strain during the welding process. The hot cracking susceptibility was investigated for 1.4301 stainless steel, and the critical strain required for solidification crack formation was locally and globally determined.
TL;DR: An integrated model of ultrasonic vibration enhanced friction stir welding (UVeFSW) was developed by integrating the thermal-fluid model with the ultrasonic field model and tool torque model.
Abstract: An integrated model of ultrasonic vibration enhanced friction stir welding (UVeFSW) is developed by integrating the thermal-fluid model with the ultrasonic field model and tool torque model. The to...
TL;DR: In this paper, the influence of base material properties on the interfacial phenomena in copper and aluminium-copper explosive welds was studied and two explosive mixtures with different detonation velocities were compared.
Abstract: The influence of base material properties on the interfacial phenomena in copper and aluminium–copper explosive welds was studied. Two explosive mixtures with different detonation velocities were t...
TL;DR: In this paper, an ultrasonic-assisted reactive brazing method, without flux and conducted in air, was developed to braze Mg/Al dissimilar alloys, and the effect of Al content on the shear strength was investigated based on the analysis of the microstructure and the fracture behaviour of the brazed joint.
Abstract: An ultrasonic-assisted reactive brazing method, without flux and conducted in air, was developed to braze Mg/Al dissimilar alloys. By using pre-coated Zn–Al solders on the Al sheet and a short-time ultrasonic (3 s) assistance, the Mg/Al dissimilar sheets were successfully brazed at a low temperature (340°C). The effect of Al content of the solder on the shear strength was investigated based on the analysis of the microstructure and the fracture behaviour of the brazed joint. The results indicated that the microstructure and the shear strength of the ultrasonic-assisted brazed joint were significantly affected by Al content in Zn–Al solders. Increasing Al content in Zn–Al solder prevented the joint from forming the continuous brittle MgZn2 layer. The maximum shear strength of 110.5 MPa was obtained when Zn–15Al solder was used, because the joint possessed the optimum microstructure of the soft (Al, Zn) eutectoid matrix with the MgZn2 dispersed particles.