Showing papers on "Filler metal published in 2011"

Microstructural and mechanical characterization of laser beam welded AA6056 Al-alloy

Abstract: Laser beam welding is considered to be a suitable joining process for high speed, low distortion, and high quality fabrication of aircraft structures manufactured from aluminum alloys, which are mainly preferred due to their favourable properties, such as high strength to weight ratio, ease of forming and high thermal and electrical conductivity. However, the laser beam welding of 6000 series aluminum alloys may exhibit a tendency to solidification cracking, and porosity may be a major problem unless appropriate welding parameters and filler metal are employed. In this study, the microstructural aspects and mechanical properties of laser beam welded new generation aluminum alloy, namely 6056, developed especially for aircraft structures, are investigated. A continuous wave CO 2 laser using AlSi12 filler wire was employed. A detailed microstructural examination of the weld region was carried out by Scanning Electron Microscopy (SEM). Standard tensile and microflat tensile specimens extracted from the welded plates were tested at room temperature for the determination of general and local mechanical properties of the welded joints. Extensive microhardness measurements were also conducted. Crack growth mechanisms of the joints produced were also determined by conducting fatigue tests under various stress ratios (i.e., 0.1 ≤ R ≤ 0.7).

Microstructure characteristics and mechanical property of aluminum alloy/stainless steel lap joints fabricated by MIG welding–brazing process

Abstract: Lap joints of aluminum alloy 2B50 and stainless steel 1Cr18Ni9Ti were welded by MIG welding–brazing method with 4043 Al–Si filler metal. The effect of aluminizing coating and galvanized zinc coating on fusion metal spreadability were studied. The aluminized coating had limited effect to promote weld surface appearance and obvious micro-cracks were found between the compound layer and the steel side. The fracture in tensile tests occurred at the interfacial layer of the weld with a low tensile strength about 60 MPa. Joints between aluminum alloy and galvanized steel had good surface appearances and the intermetallic compound in fusion zone region close to joint interface was Al 4.5 FeSi. The thickness of the intermetallic compound layer varied from about 5 μm to 15 μm depending on the heat input and the highest tensile strength of lap joint could reached 193.6 MPa when the heat input is 0.846 KJ/cm.

Spatter in laser welding

Abstract: Spatter, the ejection of melt from a weld pool, is a major problem whenever it occurs in a welding process. The ejection of droplets from the weld metal results in a weld with underfill, undercuts, craters, blowholes, or blowouts—all of which can have a detrimental effect on the mechanical properties of the weld. This paper presents a systematic description of the different types of spatter phenomena which occur during laser welding. A categorization system is proposed to facilitate the comparison and combination of research findings on spatter. This should allow researchers in this area to act as a more effective team in future.

Welding of thick stainless steel plates up to 50 mm with high brightness lasers

Abstract: Thick-section stainless steels are widely used in the components and structures for nuclear power plants. Laser welding is being considered as a high-efficiency method instead of arc welding for some components, so as to improve the production efficiency and reduce the residual stresses of the heat-affected zone. In this paper, multipasses narrow-gap welding of 50 mm thick Type 316L plates with an 8 kW disk laser was first investigated. The effect of welding conditions on the weld bead geometry and welding defects was studied. It shows that lack of fusion could be prevented by optimizing the relationship between laser power intensity and the deposited metal volume. Butt joint of 50 mm thick plates with narrow gap could be performed with eight-layers welding at laser power of 6 kW and welding speed of 0.4 m/min. In order to reduce the weld passes further, gas jet assisted laser welding was tried to weld thick Type 316L plates with a 10 kW fiber laser. The result shows that butt-joint welding of 40 mm plates without filler wire could be carried out at 0.3 m/min welding speed with no porosity or other welding defects. As for 50 mm thick plate, a good weld bead could be obtained with bead-on-plate welding from both sides at 0.2 m/min welding speed.

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

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

A comparative study of laser beam welding and laser–MIG hybrid welding of Ti–Al–Zr–Fe titanium alloy

Abstract: Ti–Al–Zr–Fe titanium alloy sheets with thickness of 4 mm were welded using laser beam welding (LBW) and laser-MIG hybrid welding (LAMIG) methods. To investigate the influence of the methods difference on the joint properties, optical microscope observation, microhardness measurement and mechanical tests were conducted. Experimental results show that the sheets can be welded at a high speed of 1.8 m/min and power of 8 kW, with no defects such as, surface oxidation, porosity, cracks and lack of penetration in the welding seam. In addition, all tensile test specimens fractured at the parent metal. Compared with the LBW, the LAMIG welding method can produce joints with higher ductility, due to the improvement of seam formation and lower microhardness by employing a low strength TA-10 welding wire. It can be concluded that LAMIG is much more feasible for welding the Ti–Al–Zr–Fe titanium alloy sheets.

Welding and Joining of Magnesium Alloys

Abstract: Welding and joining of magnesium alloys exert a profound effect on magnesium application expansion, especially in ground and air transportations where large-size, complex components are required. This applies to joints between different grades of cast and wrought magnesium alloys and to dissimilar joints with other materials, most frequently with aluminum and steel. Due to specific physical properties of magnesium, its welding requires low and well controlled power input. Moreover, very high affinity of magnesium alloys to oxygen requires shielding gases which protect the liquid weld from an environment. To magnify complexity, also solid state reaction with oxygen, which forms a thermodynamically stable natural oxide layer on magnesium surface, is an inherent deficiency of joining (Czerwinski, 2008). Both the conventional and novel welding techniques were adapted to satisfy these requirements, including arc welding, resistance spot welding, electromagnetic welding, friction stir welding, electron beam and laser welding. Since fusion welding has a tendency to generate porosities and part distortion, many alternative joining practices were implemented. These include soldering, brazing, adhesive bonding and mechanical fastening. However, also the latter techniques have disadvantages associated, for example, with stress induced by drilling holes during mechanical fastening, preheating during clinching or extensive surface preparation in adhesive bonding. Hence, experiments are in progress with completely novel ideas of magnesium joining. An application of magnesium is often in multi-material structures, requiring dissimilar joints, involving magnesium alloys as one side where on another end there are alloys with drastically different properties. How to weld dissimilar materials is one of the most difficult problems in welding. A difference in physicochemical properties of dissimilar joint components creates challenges for mechanically bolted assemblies as well. Due to its very low electronegative potential, magnesium is susceptible to galvanic corrosion thus affecting performance of mechanical joints in conductive environments. This chapter covers key aspects of magnesium welding and joining along with engineering applications, challenges and still existing limitations. For each technique, the typical joint characteristics and possible defects are outlined with particular attention paid to weld metallurgy and its relationship with weld strength, ductility and corrosion resistance. Although fundamentals for each technique are provided, the primary focus is on recent global activities.

Effects of Zn-Based Alloys Coating on Mechanical Properties and Interfacial Microstructures of Steel/Aluminum Alloy Dissimilar Metals Joints Using Resistance Spot Welding

Abstract: The effects of Zn-based alloys coating (Zn, Al-Zn and Al-Mg-Zn) on the bondability of steel/aluminum alloy dissimilar metals joints were evaluated, in order to achieve strength in lower welding current. In the joint with Zn-based alloys insert, the oxide film on the aluminum alloy was sufficiently removed through eutectic reaction of Zn-based alloys and aluminum. In the joint with Zn-coated steel (GI), higher welding current is necessary to discharge the zinc coating and the oxide film from the bonding interface sufficiently. The thinner aluminum plate after welding and the thick reaction layer cause the decrease of cross tensile strength in the joints with no coating steel (SPCC) and Al-Zn-coated steel. Using Al-Mg-Zn-coated steel, higher strength was achieved in a lower welding current. This is because Al-Mg-Zn-coating melted at lower temperature than Zn and Al-Zn-coating, and the removal of the coating material and the oxide film on the aluminum alloy were sufficiently performed in the lower welding current.

Brazing C/SiC composites and Nb with TiNiNb active filler metal

Abstract: C/SiC composites and Nb were vacuum brazed with the Ti39·4Ni39·4Nb21·2 alloy being the active filler metal. The mechanical properties of the filler material, the microstructure and the strength of brazing joints were investigated. The results showed that the filler TiNiNb alloy has a tensile strength of 860 MPa, an elongation of 51% and an elastic modulus of 78 GPa. Both Ti and Nb elements in the filler reacted with C/SiC during the brazing process, and a well bonded C/SiC–Nb joint was obtained. The ductile filler metal released the thermal stress in the joint. When the brazing was performed at 1220°C for 20 min, the shear strength of brazed joints reached 149, 120 and 73 MPa at 20, 600 and 800°C respectively.

Welding behaviour of Duplex and Superduplex Stainless Steels using Laser and Plasma ARC Welding processes

Abstract: 14462 (UNS S31803) duplex stainless steel (DSS) and EN 14410 (UNS S32750) superduplex stainless steel (SDSS) have been welded by fibre laser welding and plasma arc welding (PAW) processes with-Cout filler metal Impact toughness testing at various temperatures from 20 °C down to −60 °C was carried out Microstructural examination included macro and microphotographs of the cross-sections, ferrite content measurements and hardness survey of the weld zones Weld metal impact toughness results on the order of 100 J were obtained while values between 30 J and 60 J were measured respectively for plasma arc and laser welds of the duplex and superduplex grades even at −60 °C test temperature Ferrite content of the welds varied generally in an acceptable range which affected the microstructure and the toughness properties Better toughness results of plasma arc welds of both duplex and superduplex material compared to the laser welds are attributed to the balanced microstructure of the weld metal having ferrite- austenite ratio close to 50:50 % obtained by controlled heat input

Wetting and Soldering Behavior of Eutectic Au-Ge Alloy on Cu and Ni Substrates

Abstract: Au-Ge-based alloys are interesting as novel high-temperature lead-free solders because of their low melting point, good thermal and electrical conductivity, and high corrosion resistance. In the present work, the wetting and soldering behavior of the eutectic Au-28Ge (at.%) alloy on Cu and Ni substrates have been investigated. Good wetting on both substrates with final contact angles of 13° to 14° was observed. In addition, solder joints with bond shear strength of 30 MPa to 35 MPa could be produced under controlled conditions. Cu substrates exhibit pronounced dissolution into the Au-Ge filler metal. On Ni substrates, the NiGe intermetallic compound was formed at the filler/substrate interface, which prevents dissolution of Ni into the solder. Using thin filler metal foils (25 μm), complete consumption of Ge in the reaction at the Ni interface was observed, leading to the formation of an almost pure Au layer in the soldering zone.

Influence of Ti on microstructure and strength of c-BN/ Cu–Ni–Sn–Ti composites

Abstract: The c-BN grain has been brazed with Cu–Ni–Sn–Ti filler metal in vacuum at 1373 K holding for 600 s. The microstructure of the interface between c-BN grain and Cu–Ni–Sn–Ti filler metal has been studied using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS). The composition of the interface has been analyzed by X-ray diffraction analyzer (XRD). Experimental results showed that the reaction layer appeared at the interface between the c-BN grain and the filler metal. The reaction layer mainly consisted of TiN, TiB and TiB2. And the thickness of the reaction layer increases with the increase of Ti content in the filler metal. When Ti content in the filler metal exceeds 15 wt.%, microcracks form at c-BN side of the interface because of the increase of TiN, CuTi and Cu3Ti2 brittle phases and residual stresses, leading to a decrease of the tensile strength of c-BN/Cu–Ni–Sn–Ti composites. Ti content in the filler metal had obvious influence on microstructure and strength of c-BN/ Cu–Ni–Sn–Ti composites. The maximum tensile strength reached 105.1 MPa with 10 wt.% Ti content in the filler metal.

Single-Pass Laser-Gma Hybrid Welding of 13.5 mm thick duplex stainless steel

Abstract: Single-pass solid-state laser welding of plates in the thickness range of 10 to 20 mm became possible with the invention of the fibre laser. This new technique provides excellent beam quality at powers as high as 20 kW or more, and has proved applicable in several industrial applications. By replacing conventional methods with the fibre laser, it is possible to avoid multiple-pass welding that requires time-consuming bevelling. The high energy density of the fibre laser beam also reduces the heat input and consequently the distortion. However, the rapid solidification and cooling associated with laser welding can cause imbalance of the microstructure of duplex stainless steel weldments, where excessively high ferrite contents may reduce the corrosion resistance and the ductility of the material. The solution is normally to add nickel-based filler wire and to increase the heat input. By using a hybrid welding process where the laser beam and the gas metal arc (GMA) process act in a common process zone, filler metal can be added to the molten pool at higher heat input and at the same time, higher welding speed and deeper penetration can be achieved. In this work, 13.5 mm thick 2205 (EN 1.4462, UNS S31803) was fibre laser-GMA hybrid welded in a single-pass using 14 kW of laser power and ISO 22 9 3 N L as filler wire for the GMA process. The resulting welds were free from defects, with smooth surfaces and full penetration. The investigation examines the weld metal microstructure and the effect on corrosion resistance and mechanical properties. The option to add nickel foil, when hybrid welding, was also investigated, as comparison, and the effect on austenite formation was evaluated.

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

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

Effects of Welding Processes and Post-Weld Aging Treatment on Fatigue Behavior of AA2219 Aluminium Alloy Joints

Abstract: AA2219 aluminium alloy square butt joints without filler metal addition were fabricated using gas tungsten arc welding (GTAW), electron beam welding (EBW), and friction stir welding (FSW) processes. The fabricated joints were post-weld aged at 175 °C for 12 h. The effect of three welding processes and post-weld aging (PWA) treatment on the fatigue properties is reported. Transverse tensile properties of the welded joints were evaluated. Microstructure analysis was also carried out using optical and electron microscopes. It was found that the post-weld aged FSW joints showed superior fatigue performance compared to EBW and GTAW joints. This was mainly due to the formation of very fine, dynamically recrystallized grains and uniform distribution of fine precipitates in the weld region.