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Improvements in machinability by alloying of the workpiece often adversely impact the end user properties of a material. For example, the common use of non-metallic inclusions can lead to improved tool life during turning or milling, but often adversely affects weldability, corrosion, and wear resistance. A cutting tool material meets kilometers of workpiece material during a machining operation. Hence elements in small quantities in the workpiece may insignificantly affect the end user properties but may have large effects on tool wear. One such effect is the formation of refractory and wear resistant reaction products between the workpiece and tool. Such reaction products forming on tool surfaces may lead to improved machinability. This paper proposes the use of small amounts of alloying to induce such a Tool Protection Layer. Additionally, the paper develops a computational framework for designed alloying which balances formation of Tool Protection Layers, its in-process retention, and the functional properties of the alloy. The method has been validated for a case of manganese steel. The calculations were validated first by a wide range of diffusion experiments. Then by industrial turning of cast alloys, by comparing one reference and two newly designed alloys based on the alloying concept. The alloy with 0.003 mol fractions of Al resulted in more than 3 times increase in tool life, due to in-operando formation of Al 2 O 3 Tool Protection Layer. The designed manganese steel maintained its functional properties with respect to abrasive wear resistance and retained its ability to work harden. [Display omitted] • A thermodynamic modeling method for machinability improvement. • Microalloying leads to improved machinability, functional properties maintained. • The formation of alumina tool protection layers increases tool performance. [ABSTRACT FROM AUTHOR]

Wrought aluminum alloy AA 6063 is known for its favorable mechanical properties, corrosion resistance, and weldability in high-performance applications. Nonetheless, its limited fluidity hinders the cost-effective production of intricate structures through economical casting processes. To address this, a small fraction of TiC nanoparticles were dispersed into the AA 6063 melt to enhance its fluidity, eliminate hot cracking, and improve casting surface quality. Further investigation indicates that nanoparticles contribute to gradual latent heat release, grain growth restriction, and improved molten alloy wettability. The results demonstrate the potential of the emerging nano-treating technology in making traditionally difficult-to-cast alloys viable for low-cost casting operations to deliver products with enhanced high performance for numerous applications. • TiC nano-treating successfully demonstrates enhanced fluidity of aluminum alloy 6063 (AA 6063) by 10–25%. • Introduction of 1 vol% TiC nanoparticles eliminated hot cracking and reduced surface roughness average by 58%. • Nanoparticles enhance properties by reducing grain size, delaying solidification, and improving molten alloy wettability. [ABSTRACT FROM AUTHOR]

Magnetic pulse welding (MPW), as an environmentally friendly room temperature solid-state welding technology, usually involves low energy utilization efficiency, resulting in the need for higher energy to achieve metallurgical welding. This study proposed an innovative coil structure for increasing energy utilization efficiency during MPW. The current signal and structural strength of new coils with different turns were analyzed by numerical simulation. The results show that, different from traditional E-shaped and H-shaped single turn coils, the new structure can achieve nearly n-time amplification of current, which enabling the flyer plate to achieve the critical speed of metallurgical welding at lower energy. The 7-turn coil has higher structural strength and pulse current compared to the other coils in this study. The initial current was amplified 5.2 times by the 7-turn coil and welding of Al-Fe plates was achieved. The microstructures at the welding interface exhibit typical metallurgical features, including wave interfaces, element diffusion layers, and intermetallic compounds. The fracture location of the AA1060 (thickness δ: 0.5)-DP600 joint appeared on the base metal. The fracture morphology of AA5754 (thickness δ: 1.0)-DP600 joint shows that a large amount of aluminum element remains on the DP600 plate. Therefore, the new coil can increase the energy utilization rate during the welding process and achieve stable metallurgical welding of dissimilar materials. [Display omitted] • Proposed a new coil structure for improving the energy utilization rate of dissimilar sheet metals magnetic pulse welding. • The high pulse current was generated in the converging section of the new coil instead of each turn of the coil. • Numerical simulation results showed that the peak pulse current is amplified with the 7-turn coil and the error is 1.40 %. • The new coil requires less energy to realize magnetic pulse welding of dissimilar sheets. [ABSTRACT FROM AUTHOR]

Resistance spot welding (RSW) of galvannealed and bare dual phase (DP600) steel is a challenging task as it involves the additional complexity of zinc coating layer. This study is focused on optimization of spot welding parameters, viz., welding current and time to achieve maximum load bearing capacity in tensile-shear and coach-peel configurations. Study revealed a minimum critical nugget diameter is needed above which favorable pull-out failure is observed. Critical nugget diameter for pull-out failure is determined to be 4.4 mm. Applicability of different empirical and metallurgical models for determination of critical nugget diameter were assessed. Transition from partial interfacial to pullout failure mode has been explained on the basis of combined effect of increased nugget diameter and micro-mechanism of fracture. It was observed that the there was an increase in nugget diameter and load bearing capacity of the spot welds with an increase in welding current as well as welding time. Best fit equations have been proposed for maximum load bearing capacity as a function of spot welding parameters and nugget diameter. Microstructural evolution and hardness variation across different welding zones have been presented in detail. Redistribution of zinc in different zones of welding has been evaluated using electron probe micro-analysis. [ABSTRACT FROM AUTHOR]

The fusion zone microstructure and mechanical properties of UNS S32750 joints obtained from gas tungsten arc (GTA), gas metal arc (GMA) and flux cored arc (FCA) welding processes were investigated. The formation of grain boundary, Widmanstätten and intragranular austenite were observed in the fusion zone of the weldments. Electron back scattered diffraction (EBSD) analysis confirmed the presence of chi (ψ) and sigma (σ) phases in the reheated fusion zones of all the weldments. Tensile failures occurred at the fusion zone for all the weldments and the joint efficiency was found to be greater for GTA welds than the others. The number of welding passes and heat input had a significant impact on the ferrite: austenite ratio. FCA weldments experienced inferior notch toughness at both room temperature and sub-zero temperature owing to the prominent amount of secondary austenite and precipitation of intermetallic phases compared to the other weldments. [ABSTRACT FROM AUTHOR]

The cast aluminum alloys with light weight and good castability show great potential in aerospace and automotive applications. Due to their poor weldability and the low strength of welded joints, these alloys are difficult to fuse using conventional fusion welding techniques. Here, through friction stir welding (FSW) for cast Al-Si 7 -Cu 4 -Mg 0.3 alloy manipulated by in-situ nanocrystals, a novel method to realize the automatic solid-state joining of cast aluminum alloys was proposed, along with the guarantee of high strength-plasticity combination of the joints. The microstructure of cast Al-Si 7 -Cu 4 -Mg 0.3 alloy comprehensively manipulated by in-situ nanocrystals ensured the complete globalization of eutectic silicon and comprehensive mechanical performances of base materials to fulfill FSW. The microstructure evolution across various welded regions of the joints was revealed. The dendritic grains with a certain degree of coarsening and short needle-like eutectic silicon were formed in the heat affected zone (HAZ), and the mechanism of microstructure evolution was mainly dynamic recovery (DRV). The dynamic recrystallization (DRX) of grains in the nugget zone (NZ) resulted in regular fine equiaxed grains, and nearly spherical eutectic silicon distributed uniformly in the matrix. The optimal yield strength (YS) and ultimate tensile strength (UTS) of friction stir welded joints were 280 MPa and 400 MPa, which achieved 84.8% and 83.3% of the base material respectively (330 MPa and 480 MPa). This study contributes to producing friction stir joint of cast aluminum alloys with complex structures, as an alternative to traditional stamping-welding process of deformed aluminum alloys. Keywords • A novel method to realize the automatic solid-state joining of cast aluminum alloys was proposed. • The overall microstructure of base materials was refined by in-situ nanocrystals. • The microstructure evolution behavior of friction stir joints in different regions was revealed. • The friction stir joints exhibited excellent strength-plasticity combination. [ABSTRACT FROM AUTHOR]

Composition effect of Inconel 625, Incoloy 65 and ER347 fillers on microstructural evolution and solidification crack (SC) sensitivity of gas tungsten arc welded Incoloy 825 to AISI 321 SS was investigated. The structure of welds had been mostly austenitic, and solute segregation caused formation of eutectic-nature secondary phases in inter-dendritic/cellular spaces of three weld alloys. The dilution effect led to a transition from FA to AF mode of solidification in ER347 weld and decreased its ferrite content. Inconel 625 and ER347 welds had the highest and lowest resistance to SC during Longitudinal Varestraint Test, respectively. Fine dendritic structure of Inconel 625 weld resulted in easier strain accommodation and better weldability properties of this alloy. Severe cracking and high sensitivity of ER347 weld to SC were characterized because of low ferrite content and easier wettability of solidification grain boundaries due to formation of low-melting Nb and Ti-rich phases. Inconel 625 filler could play an effective role in establishing an appropriate bridge in terms of thermal expansion coefficient between dissimilar parent metals. [ABSTRACT FROM AUTHOR]

The normalized S355G10 + N steel was chosen for testing, it is used in a variety of applications including the building of offshore structures, which may require repairs in water environment. The main aim of the work was to check susceptibility to cold cracking for fillet welds – Controlled Thermal Severity (CTS) tests and butt welds – Tekken tests and in the next step evaluation of effectiveness of Temper Bead Welding (TBW) application in wet welding conditions for joints welded by covered electrodes. The TBW effectiveness was experimentally verified as a method that may reduce the susceptibility to cold cracking in water environment. An application of the TBW technique caused the maximum hardness of the heat affected zone to fulfill the criterion of EN ISO 15614-1 standard in level of 380 HV10. It was determined that for S355G10 + N steel the beneficial range of the pitch value between beads is 75%–100%. [ABSTRACT FROM AUTHOR]

Explosive welds of stainless steel and aluminium could only be achieved with the steel positioned as the baseplate. Using stainless steel as the flyer plate, the tensile stresses arrive at the interface before the complete solidification of the localised melting and no bonding is achieved. The poor weldability in this configuration is mainly related to the very low thermal conductivity of the flyer compared to the baseplate. The position of the materials significantly influences the weldability, and the ideal material for the flyer should have a higher melting temperature, specific heat and thermal conductivity, and a lower density compared to the baseplate. Some intermetallic formation is inevitable in dissimilar welds of combinations that can easily form intermetallic phases. The time-velocity diagram proved to be a reliable tool to analyse the weldability, especially when used in conjunction with the weldability window. [ABSTRACT FROM AUTHOR]

The mechanical and microstructural effects induced by high and low heat input of autogenous Gas Tungsten Arc Welding (GTAW) process in Fe-22Mn-1.8Al-1.2Si-0.57C TWIP steel microalloyed with titanium (TWIP-Ti) were evaluated through weld experiments. Different butt joints preparations in TWIP-Ti steel 5.8 mm thickness plates were used. A Finite Element (FE) model was applied to evaluate the deformation during welding process. The peak temperatures estimated numerically by the FE model were correlated with microhardness measurements carried out in high and low heat input welds. The lack of segregation of Mn and C at the melting zone interface contributed to avoid the hot-cracking in the welded joints at high and low heat input. The heterogeneous grain size microstructure in the welded specimens was affected by the heat input, which was correlated with the heat affected zone hardness measurements. An increase in both yield strength and ultimate tensile strength was measured in the low heat input weld as a result of the lack of hot cracking in the FZ-HAZ interface and the heterogeneous grain size distribution. [ABSTRACT FROM AUTHOR]

A novel sheet metal forming process, by manufacturing parts in a single sheet with varying thickness, has been employed in this work. It combines hot forming and cold-die quenching, also known as HFQ®, and the use of aluminium tailor welded blanks (TWBs) into a hybrid process. A series of hot stamping tests on the AA6082 TWBs were performed to investigate the deformation behaviour and failure features. Two failure modes, i.e. circumferential necking and parallel weld necking have been observed in the formed parts depending on the forming speed and thickness ratio of the TWBs. An advanced forming limit prediction model has been developed and further integrated into finite element simulation via a cloud-based multi-objective platform 1 1 All the models presented in this paper are available as open access numerical modules at www.smartforming.com, an online knowledge-based cloud platform. to investigate the failure/necking features of AA6082 TWBs. The model incorporates the theories of Hosford yield function, the anisotropic nature of plastic deformation in sheet metals and the Marciniak-Kaczynski (M-K) theory. According to the theories, the incremental work per unit volume ratio ( d ε ¯ B ∙ σ ¯ B / d ε ¯ A ∙ σ ¯ A ) between Zone B (thickness imperfect zone) and Zone A (the remainder of the material) is a key parameter determining the formability, by which the complex failure features have been fundamentally studied. The transition of failure mode in a TWB was attributed to the joint effects of temperature, strain rate and loading path changes. Strain rate could accelerate the development of localised necking in the TWBs when the failure mode was in transition from the circumferential mode to parallel mode. [ABSTRACT FROM AUTHOR]

The nickel interlayer improved the laser weldability of Zr-2.5Nb to AISI 410 stainless steel. The fusion zone contained a large amount of refined and tough dendritic γ-Ni(Fe, Cr) solid solution (182 ∼ 268 HV), while the brittle Zr(Fe, Cr) 2 intermetallic compound (1171 ∼ 1460 HV), which was the main phase as the result of direct welding of Zr-2.5Nb to SS410 as well as the source responsible for the welding cracks, disappeared. Only limited quantities of Zr 2 (Ni, Fe), Zr 7 Ni 10 (and/or Zr 2 Ni 7 ) intermetallics were present mainly in the form of thin layers (less than 200 μm thick in total) near the fusion interface with Zr-2.5Nb. Those Zr-Ni based intermetallics showed relatively higher toughness and lower hardness (301 ∼ 497 HV) than the brittle Zr(Fe, Cr) 2 , which reduced the overall cracking sensitivity of the laser-weld. [ABSTRACT FROM AUTHOR]

Poor miscibility is an important reason for the non-weldable performance of most dissimilar polymers and their composites, and traditional surface treatments cannot effectively improve the weldability of dissimilar polymers. Therefore, the non-weldability of dissimilar polymers is one of the important factors that limit the application of polymers and their composites. We proposed a surface modification scheme of laser ablation or etching to improve the weldability of immiscible polymers effectively. Experimental studies on femtosecond ultraviolet (UV) laser ablation/etching, mid-infrared laser transmission welding (LTW), and related characterization and mechanical tests were carried out. The experimental results showed that laser ablation induced the deposition of abundant polar oxygen-containing groups on the surface of polycarbonate (PC), which improved the miscibility of PC and polyamide 66 with a glass fiber volume ratio of 30 % (PA66GF30) and reduced the weak boundary layer (WBL), thereby improving their chemical bonding performance. Using the compatibilization mechanism induced by laser ablation, the bonding strength of the PC/PA66GF30 joint obtained by LTW was 13.7 MPa, which was much higher than that of the untreated joint (1.4 MPa). However, the grooves generated by laser etching could induce macro-anchoring effect of the hybrid joint. Based on the compatibilization mechanism and macro-anchoring effect, with the selection of appropriate welding power and etching parameters, the bonding strength of the PC/PA66GF30 joint was further increased to 29.7 MPa. This work has demonstrated the feasibility of laser surface treatment (especially etching) to significantly improve the welding strength of immiscible polymers and their composites. • Laser surface treatment was used to improve the weldability of dissimilar polymers and their composites for the first time. • The method induced the deposition of abundant oxygen-containing functional groups on the surface. • Laser ablation or etching improved the miscibility of immiscible polycarbonate/GFRP. • Laser etching induced macro-anchoring effect of the hybrid joints. • The bonding strength of the hybrid joints was significantly increased. [ABSTRACT FROM AUTHOR]

Gas metal arc (GMA) brazing was employed to join hot-dip galvanized steel sheets (GI) in lap joint configuration using CuSi 3 filler. The effects of brazing current and speed on the joint characteristics such as bead geometry, microstructure, weldability, microhardness and tensile shear strength were studied. The bead geometry was assessed by examining the bead shape, width, contact angle, penetration width and depth of the fused zone. The microstructural investigations were performed using scanning electron microscopy (SEM), and composition was determined using energy dispersive spectroscopy (EDS). The formation of Fe-Si phases was noticed in the bead which was found to increase with brazing current and brazing speed. The pores were nucleated in GI lap joint at highest current 80 A and lower brazing speeds 60–70 cm/min. The bead shape and size, joint strength, weldability were found best at a combination of 70 A and 80 cm/min which could be attributed to a uniform distribution of Fe 5 Si 3 (Cu) in the bead. It is suggested that for a pore-free bead structure, the heat input should lie in the range of 58.5–93.6 J/mm for the arc brazing of GI sheets. [ABSTRACT FROM AUTHOR]

A series of ultrasonic spot welding experiments with similar Mg alloy (AZ31B) were performed to determine the process parameters and their effect on weld quality, including weld strength and fracture morphologies. Two dominant welding parameters including vibration amplitude and welding time were evaluated independently to obtain good weld quality. A horn and an anvil tip surfaces were designed with pyramidal patterns to prevent slippage of lap-structured Mg alloy sheets among tool tips during ultrasonic spot welding process. The lap joint thinning was significant at higher vibration amplitudes and longer welding times and resulted in the variation of fracture types at the weld interface. Lap-shear tests on the ultrasonic spot welded Mg alloy lap joints yielded two fracture types: shear and pullout fracture. Metallographic examinations of the fracture surfaces provided insights on the fracture characteristics of the ultrasonic spot welded Mg alloys. Variations in the fracture morphologies were the results of the actual weld nugget development and closely related to weld quality. Higher weld strength was obtained at a low welding energy range of 100–140 J. [ABSTRACT FROM AUTHOR]

The theoretical fundamentals of laser weldability of metals are surveyed and relevant thermophysical parameters are identified – such as vapour pressure, keyhole pressure, beam irradiance, surface tension and viscosity. The derived approach for improving the laser weldability implies the use of a Yb fibre laser with an initial large beam diameter, a top-hat beam profile and a high laser power, which enables the formation of a large and stable keyhole during deep penetration welding. For validating the effectiveness of the developed approach, it is applied to various high-alloyed and hard-to-weld Al–Zn–Mg–Cu alloys. Defect-free welds are obtained even for AA7034 – the alloy with the highest (Zn + Mg + Cu) content commercially available. As reference, the same alloys are welded by using a conventional Nd:YAG laser with a small beam diameter, a Gaussian beam profile and medium laser power. The laser weldability deteriorates with increasing (Zn + Mg + Cu) content in terms of porosity and excess of penetration. The obtained results highlight the importance of the laser system used on the laser weldability of Al–Zn–Mg–Cu alloys. [ABSTRACT FROM AUTHOR]

Laser cladding of NiCoCr alloy powder on cast iron was performed with a 1 kW Nd:YAG continuous laser. Despite numerous advantages, one of the most critical issues is the formation of martensite and a brittle layer in the vicinity of the bonding interface due to the inherent rapid cooling, which might result in cracking nearby and a decrease in bonding strength. The objective of this research is to produce well bonded NiCrCo alloy coating that is free of pores and cracks on cast iron without preheating the whole substrate. Considering the poor weldability of cast iron, the strategy of reciprocated deposition, namely multi-layer laser cladding, was applied. The microstructural evolution of the multi-layer coating on the cast iron was investigated with the emphasis on the variation of the bonding zone. The results showed that NiCoCr coatings with different layers consisted of fine solid solution dendrites surrounded by an inter-dendritic network of precipitates. The multi-layer clad coating had a gradual distribution of elements, which was different from that in the single layer coating. The martensite near the bonding interface was transformed into tempered sorbite under the thermal influence of multi-layer deposition, leading to a decrease in the high micro-hardness zone width. A bending test confirmed that the bonding brittleness was reduced and the mechanical properties were improved through the use of the multi-layer laser cladding approach. [ABSTRACT FROM AUTHOR]

This study investigated the effect of using a rooftop piercing punch on the hole-expansion ratio of high-strength steels. The holes made using the piercing punch showed very high hole-expansion ratios under certain conditions. Regarding the rooftop-vertical angles, the hole-expansion ratio increased at 80° and decreased at 45°. The sheet bending effect caused by the rooftop shape contributed to these results. The small amount of bending in the case of 80° induced tensile stress around the punch edge without plastic deformation, which accelerated the material fracture. This acceleration decreased the plastic strain on the pierced surface and led to a high hole-expansion ratio. In the case of 45°, a large amount of bending caused plastic deformation around the punch edge, which deteriorated the hole-expansion ratio. Regarding the material direction when set on a die face, the hole-expansion ratio increased when the material direction with the highest ductility on the pierced surface was at 90° to the rooftop line. In this condition, the ductility at the weakest position on the pierced surface resulting from piercing using the rooftop punch reaches a maximum in the other material directions. [ABSTRACT FROM AUTHOR]

Cold rolled samples of a low carbon Mo–Ti–Nb microalloyed steel were subjected to simulated continuous annealing cycles using a Gleeble 3500 thermomechanical simulator to suitably optimize the base metal micro-constituents in order to improve weldability. The cycles, CR-1 and CR-2 were designed to assess the cooling rate effect (i) CR-1: 10 °C/s–780 °C(120s)–2 °C/s-730 °C–100 °C/s, (ii) CR-2: 10 °C/s–780 °C(120s)–2 °C/s–730 °C–50 °C/s], CR-1-T to assess the tempering effect [CR-1-T: 10 °C/s–750 °C(120s)–2 °C/s–730 °C–100 °C/s–10 °C/s–200 °C/s (120s)–60 °C/s] and B-1 and B-2, to assess the effect of bainite [B-1: 10 °C/s–780 °C(60s)–2 °C/s–760 °C–40 °C/s–470 °C/s (60s)–70 °C/s and B-2: 10 °C/s–780 °C(120 s)–2 °C/s–760 °C–20 °C/s–470 °C/s (60s)–10 °C/s] on weldability of the steel. Dilatometric studies were conducted on a Gleeble 1500D to obtain the intercritical temperature regime (Ar 1 –Ar 3 ) and the transformation temperatures for the low temperature transformation products. It was recorded that the cycle with 100 °C/s cooling rate (CR-1) resulted in a weldment full of cracks at the (Mn–Fe)S interfaces. A cooling rate of 50 °C/s (CR-2) caused cracks at the (Mn–Fe)S inclusions in the weld zone and the HAZ, and also softening of the heat affected zone (HAZ). The cracks generated by the CR-1 cycle could be completely avoided by introducing a short tempering cycle of 120 s at 200 °C to the CR-1 cycle (CR-1-T). CR-1-T cycle resulted in tempering of martensite (31% by volume) and precipitation of Ti–C in the ferrite that helped avoid the weldment cracks and retain the tensile properties close to that of the CR-1 cycle. B-1 cycle with a nominal presence of bainite in the ferritie-martensite structure resulted in cracks in the weldment. However, in B-2 cycle with the introduction of an optimized amount of bainite (37%) in a ferritic-martensitic matrix in association with Mo–C precipitation in ferrite, a crack-free weldment with improved tensile properties could be obtained. Among the studied thermal cycles, CR-1-T and B-2 manifested the best combination of weldability and tensile properties. [ABSTRACT FROM AUTHOR]

The production of parts involving the combination of different materials has gained a lot of interest in recent years as a strategy for achieving weight reduction. Particular attention has been paid to the joining process of mechanical components obtained with different production processes. This paper aims at studying the feasibility of laser welding to join rolled 6082-T6 thin sheet to A357 sheet produced by Laser-based Powder Bed Fusion (LPBF). The role of welding parameters, LPBF scan strategy and post heat treatment on the weld bead formation has been studied by means of microstructural and mechanical characterization. The results showed that a higher welding speed reduces the porosity in the weld bead obtaining values of about 5% in terms of percentage of fused area, while the post heat treatment of the LPBF sheet has the greatest influence on the final properties of the joint compared to the scanning strategy used. In particular, a complete T6 heat treatment of the additive sheets leads to an ultimate tensile strength of about 200 MPa closes to the reference condition 6082−6082. Hardness measurements showed that a drop in the values occurred at the center of the bead regardless of the treatment conditions while Digital Image Correlation (DIC) strain analysis confirmed that higher deformation occurred in the Fused Zone and in the Heat Affected Zone. SEM-EDS analysis revealed the presence of intergranular precipitates which contain Fe, Si, Mg and Mn in the fused zone. [ABSTRACT FROM AUTHOR]

Highlights: [•] A potentially permanent weld has a wavy shape interface and is able to undergo plastic deformation. [•] The wave height increases with the increase of both charging voltage and gap. [•] The weld variance in terms of wave height isovalues provides an operative welding range. [•] The welding range in a charging voltage–gap diagram is determined by a lower straight/wavy transition limit and an upper critical limit. [•] The weldability window has a potential convex shape and is determinable by the impact velocity isovalues. [Copyright &y& Elsevier]

Abstract: A new mathematical-solidification-weldability model has been developed to obtain the optimum chemical composition in the γ-Ti–Al–Nb precipitation-strengthened nickel-base superalloys, in which, the best resistance to hot cracking be achieved. To solve the weldability model, SEM microphotographs and EDAX analysis extracted from microstructure of the welds and phase diagrams were used as model data inputs. The relation between the segregating elements versus the retained weld liquid, and as well as, solidification path of welds (L→γ) were attained. The model is able to predict the brittleness temperature range (BTR) and the extent of weld mushy zone as a direct criterion of weldability determination. For the weld type A (alloy Inconel 718), formation of secondary phases or eutectics is too probable. In case of weld type B (alloy Udimet 500), formation of secondary phases enriched in Ti in the interdendritic locations can be anticipated. The BTRs and the size of mushy zones for welds type A, B and C (65wt% alloy 500+35wt% alloy 718) have been calculated. The solidification-weldability model showed that weld type C with dilution level of 65% and the ratio Nb/(Ti+Al)=0.53 has the best weldability among the dilutions studied and can be offered as a new-weldable nickel-base superalloy. [Copyright &y& Elsevier]

Abstract: The extended use of powder metal components can be improved by the use of welding joining methods. This work investigates the weldability of iron-based powder metal alloys (Fe–Ni, Fe–Ni–P alloys) using the pulsed gas tungsten arc welding process (GTAW) with three different filler metals (AWS R 70S-6, AWS R 309L, AWS R Fe–Ni). Results revealed that the Fe–Ni powder metal alloy does not present any metallurgical difficulty concerning the weldability for all types of filler metal studied. The Fe–Ni–P powder metal alloy, microstructural examinations showed that, despite its high content of phosphorus (0.25wt%), the utilization of pulsed GTAW process with stainless steel 309L filler metal resulted in welds free of porosities and solidification cracks. Metallographics examinations suggest that the absence of solidification cracks in this alloy can be mainly attributed to the presence of delta ferrite in the stainless steel weld metal which absorbed part of the phosphorus and significantly reduced the formation of the Fe3P low-melting eutectic in the weld pool during cooling. In contrast, solidification cracks were observed when joining the Fe–Ni–P powder metal alloy using RFe–NI and R70S-6 filler metals. Hardness tests carried out indicated a heat affected zone (HAZ) with no excessive hardening for all alloys studied. Furthermore, tensile tests showed that the fractures always occurred in the base metal with tensile strength slightly superior to the value of unwelded samples. As a result, this investigation showed the feasibility of joining iron-based powder metal alloys by the pulsed GTAW process since a rigid control of the heat input is implemented together with an adequate choice of the filler metal, especially when welding the Fe–Ni–P alloy. [Copyright &y& Elsevier]

Abstract: The current work was carried out to characterize welding of AISI 310 austenitic stainless steel to Inconel 657 nickel–chromium superalloy. The welds were produced using four types of filler materials; the nickel-based corresponding to Inconel 82, Inconel A, Inconel 617 and 310 austenitic stainless steels. This paper describes the selection of welding consumables for the joint. The comparative evaluation was based on hot-cracking tests (Varestraint test) and estimation of mechanical properties. According to Varestraint tests, Inconel A showed the least susceptibility to hot cracking. In tension tests, all weldments failed in the weaker parent metals (i.e., Inconel 657). Moreover, Inconel A weldment had the highest strength and total elongation. On the other hand, the weld metals failed by ductile fracture except Inconel 617, which exhibited mixed fracture mode. At last, it was concluded that Inconel A filler material offered the best compromise for the joint between Inconel 657 and 310 stainless steel. [Copyright &y& Elsevier]

[Display omitted] While the automotive industry is striving for the reduction of car body weight to increase the fuel efficiency and to reduce CO 2 emission without compromising the safety and crashworthiness of vehicles, a new generation of advanced high strength steels (AHSS) have emerged as excellent candidates to meet these requirements. However, their integration into the car body structure is associated with welding-related problems. This research utilizes a novel approach to establish a fundamental correlation between welding parameters, microstructure and mechanical performance of AHSS resistance spot welds. In-situ micro-cantilever bending experiments are executed and analyzed in a quantitative manner to evaluate the effect of texture and post-welding heat treatment on the local fracture toughness of spot welds. A striking finding is that, through a switch from single to double pulse weld scheme, the texture of martensite formed in the fusion zone becomes responsible for a significantly higher fracture toughness of the area in front of the pre-crack. In addition, it is found that paint baking heat treatment also results in a much enhanced fracture toughness through tempering of the martensitic microstructure. A quantitative correlation is made between the micro-scale fracture toughness and macro-scale mechanical performance of advanced high strength steel welds. [ABSTRACT FROM AUTHOR]

Abstract: Dual-phase (DP) steel is a kind of advanced high-strength steels (AHSS) developed specifically for automotive application due to its excellent formability and better crash absorption than other conventional AHSS. Resistance spot welding (RSW) is the dominant sheet metal joining method in automobile industry, whereas the weldability of dual-phase steel using conventional air gun is not so excellent for the weld lobe diagram under constant electrode force is too narrow. However, this disadvantage can be easily overcome by servo gun''s electrode force control function. This paper mainly relates how to improve weldability of dual-phase steel by adjusting electrode force during spot welding process. By modifying the electrode force using an orthogonal experimental design method, the result shows that the width of weld lobe diagram of dual-phase steel can be nearly doubled. [Copyright &y& Elsevier]

Abstract: This study investigates the effect of welding condition according to mechanical properties of pure titanium and presents the optimum welding condition through the evaluation about the weldability of pure titanium by the welding conditions such as the welding pass, the amount of shielded gas and the welding time interval. In order to find out optimum welding condition by the mechanical properties of pure titanium, the annealed pure titanium of the ASTM B265 grade 2 is selected as a specimen and is classified by several welding conditions. And then, the experiments performed the test of tension, impact and hardness under the welding condition, respectively. The experimental result revealed that the specimen of 4-pass has the highest tensile strength in case of the welding pass condition. And, in case of the shielding gas condition, the tensile strength and elongation occurs the highest to the specimen of 25l/min. The hardness value at the HAZ (heated affected zone) is higher than that for the WMZ (welding metal zone) and reveals almost the constant value more and more distance at the HAZ. Also, the impact absorption energy shows the high tendency by an increase in the number of pass. [Copyright &y& Elsevier]

Abstract: The objective of this study was to investigate the weldability of three different iron-based powder metal alloys (pure Fe, Fe–Ni and Fe–P–Ni alloys) using the keyhole pulsed plasma arc process (PAW). The work undertaken included the effect of pulsed welding parameters on the microstructure and mechanical characteristics of the welded joints. Microstructural examination results revealed that for the pure Fe and Fe–Ni alloys, the fusion-welded zone was free of porosity and cracks. However, the Fe–P–Ni powder metal alloy with a high level of phosphorus content (0.25wt%) and 7mm thickness specimen presented solidification cracks and tunneling failure as a result of high shrinking stress due to the higher volume of molten metal and faster cooling rates. This problem was overcome by reducing the thickness of the specimen to 4mm. No significant differences were noted in the hardness profile of the welded specimens, which warranted a heating affected zone with no excessive hardness. Furthermore, tensile tests showed that the failures of the specimen occurred always in the base metal with tensile strength slightly superior to the value of unwelded samples. Therefore, this study indicates that iron-based powder metal alloys can be successfully joined by keyhole pulsed PAW process without filler metal. [Copyright &y& Elsevier]

Abstract: The addition of copper to microalloyed steels in order to promote precipitation hardening is one of the approaches adopted to develop new materials with high mechanical strength but minimized carbon content to assure good weldability. Besides that, the thermomechanical processing of such alloys can eliminate the subsequent quench and tempering heat treatments required by conventional steels. The effects of controlled-rolling parameters over the ageing response of an HSLA-80 microalloyed steel with 1.10% copper were studied in this work. The relatively weak influence over the ageing response verified when the reheating temperature was elevated from 1100°C to 1200°C indicated that copper precipitation is the main mechanism behind the hardening promoted by the ageing treatment; niobium had a secondary role. The strain degree applied during the roughing phase increased the ageing response of the alloy, but an increase in the strain degree applied during the finishing phase had no effect over this aspect. Also, a finishing temperature variation had no significant effect on the ageing response of the HSLA-80 steel. [Copyright &y& Elsevier]

Abstract: This paper reports the determination of optimum welding conditions (welding intensity and travel speed) for butt joints of 2205 duplex stainless steel sheets using plasma-arc welding (PAW). Minimum net energy input for proper operative and metallurgical weldabilities is studied using two different welding modes: the melt-in or conduction mode and the keyhole mode. The influence of the welding parameter for each mode on the dimensions and shape of the welds and on their ferrite contents is investigated. [Copyright &y& Elsevier]

Abstract: The design of cold forming processes requires the availability of a procedure able to deal with the prevention of ductile fracture. In fact, the ability to predict fracture represents a powerful tool to improve the production quality in mechanical industry. In this paper, artificial intelligence (AI) techniques are applied to ductile fracture prediction in cold forming operations. The main advantage of the application of AI tools and in particular, of artificial neural networks (ANN), is the possibility to obtain a predictive tool with a wide applicability. The prediction results obtained in this paper fully demonstrate the usefulness of the proposed approach. [Copyright &y& Elsevier]

Abstract: Forging of sintered porous powder is currently popular in many parts of the world as an economic method of producing high strength, high ductility parts from mental powder. The upsetting of porous metal is one of the main processes in powder forging. It is important to understand the upsetting bulging and the density variation of the billet in the forging of porous metal. In this paper, the finite element method is used to investigate the bulging deformation, forging force and density variation of the porous metal in upsetting. The influences of the parameters such as the initial height, the initial diameter, the initial relative density of the billets and the friction coefficient on the bulging deformation, forging force and the variation of relative density in the billets are also examined. [Copyright &y& Elsevier]

Hadfield’s manganese steel, nominally Fe–1.2%C–13%Mn, is an alloy of inherent toughness, work-hardening characteristics and excellent resistance to some types of adhesive and abrasive wear. However, due to its low yield strength, it may be deformed markedly before its work-hardening become effective. In certain applications, such as railroad crossings and rock-crushers, this can be a disadvantage. In practice, when this deformation becomes excessive, welding is employed to restore the casting to its original dimensions. During welding, precautions have to be taken to avoid overheating and the attendant carbide precipitation which may lead to subsequent early failure.Three different electrode compositions were used to overlay-weld austenitic manganese steel cast in the form of rail heads. Two of the electrodes were obtained commercially and the third was of novel chemical composition and was produced in our laboratory. Mechanical tests were then carried out to simulate the battering deformation likely to result from in-service exposure. The procedure highlighted the work-hardening characteristics and resistance to plastic flow of the weld deposit and base material, one of which consisted of the standard Hadfield’s alloy whilst two others had minor transition element additions. The electrode containing molybdenum produced a weld overlay which showed better work-hardening characteristics and deformation resistance than those of the other two commercial electrodes studied. [Copyright &y& Elsevier]

This paper presents development of an intelligent algorithm to understand relationships between process parameters and bead height, and to predict process parameters on bead height through a neural network and multiple regression methods for robotic multi-pass welding process. Using a series of robotic arc welding, additional multi-pass butt welds were carried out in order to verify the performance of the neural network estimator and multiple regression methods as well as to select the most suitable model. The results show that not only the proposed models can predict the bead height with reasonable accuracy and guarantee the uniform weld quality, but also a neural network model could be better than the empirical models (linear and curvilinear equations). [Copyright &y& Elsevier]