Showing papers on "Weldability published in 2021"

A novel strategy to additively manufacture 7075 aluminium alloy with selective laser melting

Abstract: Selective laser melting (SLM) has been successful in fabricating advanced engineering parts with high geometrical complexities. However, some metals or alloys with high strength, low weldability, and large freezing range, such as 7075 aluminium alloy, have low SLM-processability and are hard to be directly SLM-fabricated. Here, we proposed a novel strategy, combining substrate modification and inoculation treatment, to fabricate a crack-free and dense high-strength 7075 alloy using SLM at a broad processing window. Inoculation of the 7075 alloy powder with 1 wt% Ti submicron particles substantially refine the Al grains, effectively increasing the cracking resistance. Furthermore, the SLM substrate was modified, which allows integration of thermal insulation materials, such as vermiculite, to the substrate. As a result, the melt pool cooling rate and thermal gradient during solidification were significantly reduced. This directly led to a reduction in thermal stress within the melt pool. With combination of the substrate modification and Ti inoculation, crack-free, fine-equiaxed microstructure was obtained in the SLM-fabricated 7075 alloy that has the mechanical properties comparable to its wrought counterpart. This strategy can be implemented to SLM of other engineering alloys with low AM processability, providing a foundation for broadening industrial applications of SLM.

Comparison of the Weldability of AA6061-T6 Joint under Different Friction Stir Welding Conditions

Abstract: In this work, similar butt joints of AA6061-T6 alloy prepared by underwater friction stir welding (UWFSW) and friction stir vibration welding (FSVW) processes were examined. The characteristics of joints were compared with the joints obtained by conventional friction stir welding (CFSW). The different kinds of microstructural modifications that occurred during CFSW, FSVW, and UWFSW processes were analyzed. The results are employed to analyze the different behaviors in strength, ductility, weldability, and hardness of the joints in different processes at different traverse speeds, rotational speeds, and vibration frequency. It was found that mechanical vibration decreases the grain size in the weld zone and hinders the coalescence and regrowth of the precipitates during FSVW. On the other hand, water significantly decreased the joint temperature during UWFSW and led to a refined microstructure in the stir zone, which substantially improved the mechanical properties of the welded joint. The synergetic effect of refined grains and lower dissolution of β″ precipitates (higher evolution of β″ to β′ and β-Mg2Si) due to fast cooling rate (intensified local deformation) led to higher hardness in UWFSW (FSVW) joint compared to CFSW joint. The small size with the uniform distribution of dimples indicated the combination of strength and ductility in FSVW-ed and UWFSW-ed joints. The simple and highly effective welding procedure, FSVW, can be readily scaled up for industrial welding applications.

Experimental Investigation of the Friction Stir Weldability of AA8006 with Zirconia Particle Reinforcement and Optimized Process Parameters.

Abstract: A lightweight, highly corrosive resistant, and high-strength wrought alloy in the aluminum family is the Aluminium 8006 alloy. The AA8006 alloy can be formed, welded, and adhesively bonded. However, the recommended welding methods such as laser, TIG (Tungsten Inert Gas welding), and ultrasonic are more costly. This investigation aims to reduce the cost of welding without compromising joint quality by means of friction stir welding. The aluminum alloy-friendly reinforcement agent zirconia is utilized as particles during the weld to improve the performance of the newly identified material AA8006 alloy in friction stir welding (FSW). The objectives of this research are to identify the level of process parameters for the friction stir welding of AA8006 to reduce the variability by the trial-and-error experimental method, thereby reducing the number of samples needing to be characterized to optimize the process parameters. To enhance the quality of the weld, the friction stir processing concept will be adapted with zirconia reinforcement during welding. The friction stir-processed samples were investigated regarding their mechanical properties such as tensile strength and Vickers microhardness. The welded samples were included in the corrosion testing to ensure that no foreign corrosive elements were included during the welding. The quality of the weld was investigated in terms of its surface morphology, including aspects such as the dispersion of reinforced particles on the welded area, the incorporation of foreign elements during the weld, micro defects or damage, and other notable changes through scanning electron microscopy analysis. The process of 3D profilometry was employed to perform optical microscopy investigation on the specimens inspected to ensure their surface quality and finish. Based on the outcomes, the optimal process parameters are suggested. Future directions for further investigation are highlighted.

Laser beam powder bed fusion of nitinol shape memory alloy (SMA)

Abstract: This study is focused on the 3D printing of NiTi shape memory alloy (SMA) in cuboidal shaped samples via the Laser Powder Bed Fusion (L-PBF) process using a dissimilar material build plate of 316L stainless steel. Four processing parameters were investigated at three levels for the optimization of the process. Those parameters were the laser beam power, scanning speed, laser beam spot size and hatch spacing. The produced samples exhibited varying levels of bonding with the substrate. Compression testing, Archimedes density measurement and EDX chemical composition were carried out. A design of experiment model was developed relating the input process parameters to the output properties. The effect of the calculated volumetric energy density and the sample melt-pool temperatures on the output measures were also investigated for the strong bonding and weldability with the substrate metal.

On the influence of build orientation on properties of friction stir welded Al–Si10Mg parts produced by selective laser melting

Abstract: Welding and joining of components processed by additive manufacturing (AM) to other AM as well as conventionally produced components is of high importance for industry as this allows to combine advantages of either technique and to produce large-scale structures, respectively. One of the key influencing factors with respect to weldability and mechanical properties of AM components was found to be the inherent microstructural anisotropy of these components. In present work, the precipitation-hardenable Al–Si10Mg was fabricated in different build orientations using selective laser melting (SLM) and subsequently joined by friction stir welding (FSW) in different combinations. Microstructural analysis showed considerable grain refinement in the friction stir zone, however, pronounced softening occurred in this area. The latter can be mainly attributed to changes in the morphology and size of Si particles. Upon combination of different build orientations a remarkable influence on the tensile strength of FSW joints was seen. Cyclic deformation responses of SLM and FSW samples were examined in depth. Fatigue properties of this alloy in the low-cycle fatigue (LCF) regime imply that SLM samples with the building direction parallel to the loading direction show superior performance under cyclic loading as compared to the other conditions and the FSW joints. From results presented solid process-microstructure-property relationships are drawn.

Microstructure and stress corrosion behaviour of CMT welded AA6061 T-6 aluminium alloy joints

Abstract: Superior properties of AA6061 grade aluminium alloys are finding greater use in automotive, marine and aircraft applications due to its strength, weldability and high corrosion resistance. But it is highly susceptible to stress corrosion cracking owing to alter the phase composition and microstructure during welding process. In the present work, an experimental study of stress corrosion cracking is conducted on Cold Metal Transfer welded aluminium alloy joints using various heat input under constant stress intensity to understand the susceptibility of various zones to Stress Corrosion Cracking and the performance has been analysed using Tafel electrochemical technique. The result shows that the mechanism of cracking is established to be anodic mode with transgranular nature of crack propagation. In addition, a linear relationship is also inferred to predict the time to failure by extrapolating the rate of steady state elongation. The integrity of the dissimilar joints are analysed with the help of Optical Microscopy, SEM, EDAX and XRD sophisticated analytical techniques.

Study on Microstructure and Mechanical Properties of Laser Welded Dissimilar Joint of P91 Steel and INCOLOY 800HT Nickel Alloy.

Abstract: This investigation attempts to explore the weld characteristics of a laser welded dissimilar joint of ferritic/martensitic 9Cr-1Mo-V-Nb (P91) steel and Incoloy 800HT austenitic nickel alloy. This dissimilar joint is essential in power generating nuclear and thermal plants operating at 600–650 °C. In such critical operating conditions, it is essential for a dissimilar joint to preserve its characteristics and be free from any kind of defect. The difference between the physical properties of P91 and Incoloy 800HT makes their weldability challenging. Thus, the need for detailed characterization of this dissimilar weld arises. The present work intends to explore the usage of an unconventional welding process (i.e., laser beam welding) and its effect on the joint’s characteristics. The single-pass laser welding technique was employed to obtain maximum penetration through the keyhole mode. The welded joint morphology and mechanical properties were studied in as-welded (AW) and post-weld heat treatment (PWHT) conditions. The macro-optical examination shows the complete penetrations with no inclusion and porosities in the weld. The microstructural study was done in order to observe the precipitation and segregation of elements in dendritic and interface regions. Solidification cracks were observed in the weld fusion zone, confirming the susceptibility of Incoloy 800HT to such cracks due to a mismatch between the melting point and thermal conductivity of the base metals. Failure from base metal was observed in tensile test results of standard AW specimen with a yield stress of 265 MPa, and after PWHT, the value increased to 297 MPa. The peak hardness of 391 HV was observed in the P91 coarse grain heat-affected zone (CGHAZ), and PWHT confirmed the reduction in hardness. The impact toughness results that were obtained were inadequate, as the maximum value of impact toughness was obtained for AW P91 heat-affected zone (HAZ) 108 J and the minimum for PWHT Incoloy 800HT HAZ 45 J. Thus, difficulty in obtaining a dissimilar joint with Incoloy 800HT using the laser beam welding technique was observed due to its susceptibility to solidification cracking.

Weldability Investigation and Optimization of Process Variables for TIG-Welded Aluminium Alloy (AA 8006)

Abstract: Aluminium and its alloys play a significant role in engineering material applications due to its low weight ratio and superior corrosion resistance. The welding of aluminium alloy is challenging for the normal conventional arc welding processes. This research tries to resolve those issues by the Tungsten Inert Gas welding process. The TIG welding method is an easy, friendly process to perform welding. The widely applicable wrought aluminium AA8006 alloy, which was not considered for TIG welding in earlier studies, is considered in this investigation. For optimizing the number of experiments, the Taguchi experimental design of L9 orthogonal array type experimental design/plan was employed by considering major influencing process parameters like welding speed, base current, and peak current at three levels. The welded samples are included to investigate mechanical characterizations like surface hardness and strengths for standing tensile and impact loading. The results of the investigation on mechanical characterization of permanent joint of aluminium AA8006 alloy TIG welding were statistically analyzed and discussed. The 3D profilometric images of tensile-tested specimens were investigated, and they suggested optimized process parameters based on the result investigations.

Welding of high-entropy alloys and compositionally complex alloys—an overview

Abstract: High-entropy alloys (HEAs) and compositionally complex alloys (CCAs) represent new classes of materials containing five or more alloying elements (concentration of each element ranging from 5 to 35 at. %). In the present study, HEAs are defined as single-phase solid solutions; CCAs contain at least two phases. The alloy concept of HEAs/CCAs is fundamentally different from most conventional alloys and promises interesting properties for industrial applications (e.g., to overcome the strength-ductility trade-off). To date, little attention has been paid to the weldability of HEAs/CCAs encompassing effects on the welding metallurgy. It remains open whether welding of HEAs/CCAs may lead to the formation of brittle intermetallics and promote elemental segregation at crystalline defects. The effect on the weld joint properties (strength, corrosion resistance) must be investigated. The weld metal and heat-affected zone in conventional alloys are characterized by non-equilibrium microstructural evolutions that most probably occur in HEAs/CCAs. The corresponding weldability has not yet been studied in detail in the literature, and the existing information is not documented in a comprehensive way. Therefore, this study summarizes the most important results on the welding of HEAs/CCAs and their weld joint properties, classified by HEA/CCA type (focused on CoCrFeMnNi and AlxCoCrCuyFeNi system) and welding process.

Calculating the Susceptibility of Carbon Steels to Solidification Cracking During Welding

Abstract: Existing experimental results of weldability tests show the susceptibility of carbon steels to solidification cracking varies significantly with the C content. To analyze the effect of the C content on the susceptibility, equilibrium solidification of binary Fe-C alloys was assumed as an approximation in view of the rapid diffusion of the interstitial solute C in Fe. First, the curve of the equilibrium freezing temperature range vs. the C content was plotted and compared with the experimental results, but the agreement was not good. Then, the susceptibility index, i.e., |dT/d(fS)1/2| near (fS)1/2 = 1 (T: temperature; fS: fraction solid) recently proposed for Al alloys was tried. The curve of the susceptibility index vs. the C content was calculated. The curve agreed well with the experimental results of crack susceptibility tests of carbon steels in welding.

Development and Application Prospects of Aluminum–Lithium Alloys in Aircraft and Space Technology

Abstract: New models of competitive aviation and space technology cannot be created without contemporary materials. The development of aluminum–lithium alloys was mainly determined by the fact that the addition of lithium to aluminum alloys decreases their density and increases the modulus of elasticity, thereby providing a significant structural weight reduction compared to traditional aluminum alloys. Along with a reduced density, aluminum–lithium alloys have high strength, good corrosion resistance, and good weldability; therefore, they represent a strategically crucial material for aviation and space technology products. This article presents the history of the development of aluminum–lithium alloys and their application.

Effect of laser welding heat input on fatigue crack growth and CTOD fracture toughness of HSLA steel joints

Abstract: High strength low alloy steels are employed in structural elements and, despite presenting good weldability, the welded joint is always a critical issue and its evaluation is fundamental in guaranteeing structural integrity. The mechanical properties of weld beads can be significantly different from the base material's properties due to metallurgical alterations caused by the welding process. One of the factors leading to significant impact is the heat input. This paper evaluates the hardness, fracture toughness and fatigue crack growth in weld beads obtained via a Laser process with two different heat inputs, which resulted in weld beads with distinct microstructures: one composed of ferrite presenting different morphologies and the other composed of martensite and bainite. The aims of this work are evaluating the effect of Laser welding heat input on microstructures in the weld beads, and the correlation of the microstructure with fatigue crack growth and crack-tip opening displacement fracture toughness. Fracture toughness presented itself to be more sensitive to the microstructural alterations caused by the heat input than hardness and fatigue crack growth. Weld beads showed higher resistance to fatigue crack growth when compared to the base metal, even though there were no significant differences between them.

Tuning process parameters to optimize microstructure and mechanical properties of novel maraging steel fabricated by selective laser melting

Abstract: Maraging steel is a promising material for additive manufacturing due to its ultrahigh yield strength, reasonable ductility and good weldability. However, the ductility of the fabricated part will be degraded after aging treatment. In this regard, we firstly designed a new composition of maraging steel Fe-18.3Ni-9Co-4.84Mo-0.92Ti-0.27Al-0.13Cr-0.01C (wt.%), whose strength and ductility can be simultaneously improved by selective laser melting. The relationship between laser process parameters and forming defects has been studied. Using single-track and single-layer experiments, fully dense parts were fabricated with a certain range of process parameters, corresponding to the 30–50% lap rate in the X–Y plane and 70% remelted rate along Z-axis. Besides, we found film-like reverted austenite along the martensite lath boundaries in the as-fabricated part. The effects of heat treatment processes on the reverted austenite and mechanical properties of the fabricated parts were also studied; the strength-ductility trade-off of maraging steel after heat treatment can be alleviated. The tensile strength and elongation of printed samples after direct aging treatment can respectively reach 2037 MPa and 6.4%, and 2182 MPa, 4.8% after solution and aging treatment.

Fabrication and characterization of the Mo/cu bimetal with thick Mo layer and high interfacial strength

Abstract: Due to the brittleness of molybdenum (Mo) and high difference in melting point, it is still a challenge to clad thick Mo onto copper (Cu) with high quality bonding. In this study, a 5 mm thick Mo plate was successfully welded with Cu plate by hot explosive welding, without any cracks being formed. The maximum shear strength of the interface exceeded 295 MPa. The calculated weldability window indicated that the welding was achieved with the parameters close to the lower boundary, and successfully predicted the wavy interfaces. The interfacial microstructures were investigated by scanning electron microscope, electron backscatter diffraction and transmission electron microscopy, the results showed that the dislocations in Cu were higher than the Mo side and the evolutions of interfacial structure due to severe deformation, such as misorientation angle, recrystallization and texture, were quite different for Mo and Cu.

Friction Stir Spot Welding of 5052 Aluminum Alloy to Carbon Fiber Reinforced Polyether Ether Ketone Composites

Abstract: The hybrid structure composed of aluminum alloy and carbon fiber reinforced plastics could combine their advantages. In order to investigate the weldability of these two lightweight materials, the hybrid joints of 5052 aluminum alloy (AA5052) and carbon fiber reinforced polyether ether ketone composites (CF-PEEK) were fabricated by friction stir spot welding. The variance analysis revealed that the dwell time and plunge speed were the most significant factors. By optimizing the welding parameters, the ultimate tensile shear load reached 2690±64 N (the dwell time: 8 s, the plunge speed: 10 mm/min). The interface could be divided into pin-affected zone, shoulder-affected zone, resin adhesive zone and resin concentrated zone. Since resin concentrated zone could not provide interfacial bonding due to delamination, the shoulder-affected zone and pin-affected zone were decisive regions for mechanical properties. The bonding mechanism included three parts: adhesive bonding provided by re-solidified resin, macro-mechanical interlocking of aluminum alloy that entered aluminum alloys and CFRP.

Solid-state joining of aluminum to titanium: A review:

Abstract: The dissimilar material joining of aluminum and titanium alloys is recognized as a challenge due to the significant differences in the physical, chemical, and metallurgical properties of these allo...

Weldability of Underwater Wet-Welded HSLA Steel: Effects of Electrode Hydrophobic Coatings.

Abstract: The paper presents the effects of waterproof coatings use to cover electrodes on the weldability of high-strength, low-alloy (HSLA) steel in water. With the aim of improving the weldability of S460N HSLA steel in water, modifications of welding filler material were chosen. The surfaces of electrodes were covered by different hydrophobic substances. The aim of the controlled thermal severity (CTS) test was to check the influence of these substances on the HSLA steel weldability in the wet welding conditions. The visual test, metallographic tests, and hardness Vickers HV10 measurements were performed during investigations. The results proved that hydrophobic coatings can reduce the hardness of welded joints in the heat-affected zone by 40–50 HV10. Additionally, the number of cold cracks can be significantly reduced by application of waterproof coatings on the filler material. The obtained results showed that electrode hydrophobic coatings can be used to improve the weldability of HSLA steel in underwater conditions.