Control of weld composition when arc welding high strength aluminium alloys using multiple filler wires

Abstract

An experimental method of controlling weld composition when welding Al2024 has been explored. Utilising the tandem process and a cold wire feed unit, two and three commercially available filler wires were mixed in a single weld pool to control composition. Thermodynamic modelling was used to provide optimum weld compositions for the eradication of solidification cracking. Validation showed that by controlling the principal elements, not only was cracking eliminated, the mechanical properties of the weld could be varied. In particular, a composition was identified, which offered adequate joint strength and ductility. Exceeding this composition resulted in a corresponding increase in weld hardness at the expense of joint ductility.     

Research on Prediction Method of Liquation Cracking Susceptibility to Magnesium Alloy WeldsEI北大核心CSCD

Magnesium alloys has a wide application prospect due to their good properties, such as high specific strength and specific stiffness, but the susceptibility of liquation cracking is also pretty high. The liquation in partially melted zone of AZ-series magnesium alloys were investigated with circular-patch welding test. The AZ91, AZ31 base alloys were welded with AZ61 and AZ92 filler wires by using the cold metal transter metal inert-gas (CMT-MIG) welding. The results show that, the liquation occurred along the weld edge of AZ91 with the eutectic reaction occurring between gamma(Mg17Al12) phase and Mg-rich phase. The liquation susceptibility of AZ31 was pretty low as gamma(Mg17Al12) was not present in base metal of AZ31. Meanwhile, a new method for predicting liquation cracking based on binary phase diagram was proposed. When the initial solidification temperature of weld is higher and the solidification temperature range of weld is shorter than those of base metal, the liquation crack susceptibility of weld is mostly higher. When the initial solidification temperature of weld is close to or below that of base metal, and the solidification temperature range of weld is close to or longer than that of base metal, the liquation cracking susceptibility of weld is lower. This method worked well on predicting the effect of composition of base metal and filler wires on liquation cracking, and the predicting results are consistent with the experimental results. That is, the liquation cracking susceptibility is higher with AZ91 base metal used than that with AZ31 base metal. And, the liquation cracking susceptibility is lower with AZ92 filler wire than that with AZ61 filler wire.     

Measuring laser weldability of aluminium alloys using controlled restraint weldability test

Abstract

Al–Mg–Si alloys are known to be highly susceptible to solidification cracking. Weldability results of laminated AA6061-T6 plates are presented in this paper when welded in full penetration keyhole mode using a 1030 nm, 10 kW Yb:YAG disk laser welding source with different welding conditions. Making use of the controlled restraint weldability (CRW) cracking test, a boundary has been established between crack and no crack conditions for different preloads. The originality of the CRW test is the cross-shaped test coupon that partitions the pre-stress unequally along the welding path. The CRW is proven capable of ranking the solidification cracking behaviour of weld metals deposited under different welding conditions.     

Microcracking in multipass weld metal of alloy 690 Part 1 – Microcracking susceptibility in reheated weld metal

Abstract

Microcracking behaviour in the gas tungsten arc multipass weld metal of alloy 690 was investigated. The majority of microcracks occurred within about 300 μm from the fusion line of the subsequent weld bead and propagated along the solidification boundaries in the multipass weld metal. The morphology of the crack surface indicated the characteristic texture of ductility dip cracking. The microcracking susceptibility of the reheated weld metal was evaluated via the spot Varestraint test using three different filler metals having varying contents of impurity elements such as P and S. Microcracking occurring in the spot Varestraint tests consisted predominantly of ductility dip cracking, with a small amount of liquation cracking. The ductility dip cracking temperature range was about 1350–1600 K in the weld metal FF1, and narrowed in the order of weld metals FF1>FF3>FF5. The ductility dip cracking susceptibility was reduced with decreasing contents of impurity elements in the filler metal. It was concluded that the amount of (P + S) in the filler metal should be reduced as much as possible (to about 30 ppm in total) to suppress microcracking in the multipass weldment.     

Laser welding of high hardness armour steel

Abstract

A feasibility study of laser welding of high hardness steel (HHS) armours has been carried out at SMC DERA. The main issues investigated were weldability using different fillers and various combinations of beam power and travel speed; heat affected zone (HAZ) size and hardness; Charpy toughness; and ballistic behaviour. The best results in terms of a combination of cracking resistance and toughness were obtained in the autogenous weld, the filler wires tested clearly not being ideally suited to laser welding. A relationship emerged between the weld hardness profiles, in respect of both weld metal hardness and variable HAZ width and softening with beam travel speed, and their ballistic performance.     

Microcracking in multipass weld metal of alloy 690 Part 3 – Prevention of microcracking in reheated weld metal by addition of La to filler metal

Abstract

The effect of addition of La to a filler metal on microcracking (ductility dip cracking) in the multipass weld metal of alloy 690 was investigated with the aim of improving its microcracking susceptibility. The susceptibility to ductility dip cracking in the reheated weld metal could be greatly improved by adding 0·01–0·02 wt-%La to the weld metal. Conversely, excessive La addition to the weld metal led to liquation and solidification cracking in the weld metal. Hot ductility of the weld metal at the cracking temperature was greatly improved by adding 0·01–0·02 wt-%La to the weld metal, implying that the ductility dip cracking susceptibility was decreased as a result of the desegregation of impurity elements of P and S to grain boundaries due to the scavenging effect of La. The liquation and solidification cracking resulting from excessive addition of La to the weld metal is attributed to the formation of liquefiable Ni–La intermetallic compound. A multipass welding test confirmed that microcracks in the multipass weldment were completely prevented by using a filler metal containing an addition of 0·01 wt-%La.     

Characterisation of the cold metal transfer (CMT) process and its application for low dilution cladding

The process characteristics of the synergic cold metal transfer (CMT) process have been examined for welding aluminium alloy. Utilising a simple backlighting system and through the arc monitoring the droplet transfer modes were identified. Whilst the modified short circuit mode was evident for the lower parameter range, a two part transfer mode based upon a combination of spray and short circuit transfer was observed for the mid to upper parameter range. The technology was also explored as a cladding process for applying to ternary alloyed (Al-Cu-Mg) aluminium plate. This alloy system is known to be susceptible to solidification cracking when MIG welded using the binary Al-2319 (Al-Cu) filler wire, this being due to the wide element freezing range of the weld resulting from mixing with the base material. Utilising this filler, weld dilution ratios for both CMT and pulsed welding were identified across the examined parameter range. The CMT process exhibited greater control of dilution that enabled deposition of a quasi-binary (Al-Cu) layer exhibiting a less crack susceptible composition. Onto this layer conventional MIG welding could be applied which could potentially eradicate cracking using a binary filler wire.     

Study of all position electron beam welding process for pipeline joints

Abstract

For the purpose of applying the electron beam (EB) welding process to the site welding of natural gas pipelines, the authors investigated fundamental all position EB welding characteristics for 19 mm thick API 5L–X65 steel pipe. To establish appropriate welding conditions for satisfactory weld bead formation, the study was separated into two steps. First, appropriate welding parameter ranges were investigated in eight representative welding positions by rotating the test pipe in which the electron gun was fixed. Second, based on the investigation in the first step, all position continuous welding was carried out successfully by rotating the gun in a vertical plane. The influence of edge misalignment and mismatch on weld bead formation was investigated and the dimensional tolerances needed to obtain acceptable weld beads were clarified. Solidification cracking in the weld metal of a pipeline steel was investigated and it was determined that sulphur was the most harmful element in terms of promoting cracking. Some mechanical properties of the weld joint were also examined.     

254SMO/Q235B异种钢焊接接头显微组织

分别选用ERNiCrMo-2,ERNiCrMo-3,ERNiCrMo-10,ERNiCrMo-12,ERNiCrMo-13及ERNiCrMo-14 6种镍基合金焊丝,采用手工TIG焊对254SMO/Q235B异种钢板进行焊接试验解决254SMO波纹管与Q235B钢管焊接时出现的裂纹问题,.焊后利用光学显微镜、X射线衍射仪、扫描电子显微镜和能谱仪对焊接接头进行了分析研究.发现采用ERNiCrMo-2,ERNiCrMo-3和ERNiCrMo-14焊丝时,焊缝中有较多的微裂纹出现;选用另外3种焊丝进行焊接时,焊缝成形良好,未出现焊接裂纹.结果表明,该焊接裂纹为热裂纹,异种钢物理性能的差异及焊缝中杂质元素的偏析是造成焊接裂纹的关键因素.     

Microstructure,hardness and residual stress distribution in maraging steel gas tungsten arc weldments

Abstract

The distribution of residual stresses due to welding has been studied in maraging steel welds. Gas tungsten arc welding process was used and the effect of filler metal composition on the nature of residual stress distribution has been investigated using X-ray diffraction technique with Cr K_α radiation. Three types of filler materials were used, they include: maraging filler, austenitic stainless steel and medium alloy medium carbon steel filler metal. In the case of maraging steel weld, medium alloy medium carbon filler, the residual stress at the centre of the weld zone was more compressive while, less compressive stresses have been identified in the heat affected zone of the parent metal adjacent to the weld metal. But, in the case of austenitic stainless steel filler the residual stresses at the centre of the weld and heat affected zone were tensile. Post-weld aging treatment reduced the magnitude of stresses. The observed residual stress distribution across the weldments has been correlated with microstructure and hardness distribution across the weld.     

Effects of torch configuration and welding current on weld bead formation in high speed tandem pulsed gas metal arc welding of steel sheets

Abstract

Undercut and humping bead are the common defects that limit the maximum welding speed of tandem pulsed gas metal arc (GMA) welding. In order to increase the maximum welding speed, effects of the inclination angle, interwire distance and welding current ratio between the leading wire and trailing wire on bead formation in high speed welding are investigated. The undercut and humping bead is attributed to the irregular flow of molten metal towards the rear part of the weld pool. This irregular flow can be prevented by the trailing wire with a push angle from 5° to 13° , which provides an appropriate component of arc force in the welding direction. The irregular flow is also related to the distance between the leading wire and the trailing wire, and the flow becomes regular when the distance is in the range 9–12 mm. Moreover, the stabilisation of the bulge of the weld pool between the two wires, the presence of enough molten metal below the trailing arc, and the reduced velocity of molten metal flow towards the rear part of the weld pool, are essential to increase the maximum welding speed. These conditions can be obtained by adjusting the ratio of the leading arc current to the trailing arc current. A maximum welding speed as high as 4–4·5 m min^?1 is achieved by setting the current ratio to a value ranging from 0·31 to 0·5.     

Effect of solidification velocity on weld solidification process of alloy tool steel

Abstract

In order to clarify the effect of solidification velocity on the weld solidification process of alloy tool steel during the welding, the information about microstructure evolution was obtained by the concurrent experiments of liquid tin quenching and time resolved X-ray diffraction technique using intense synchrotron radiation. It was found from the experiments that the solidification mode was transferred from an FA to an A mode at the high solidification velocity. The effect of solidification velocity on the phase selection during solidification between the primary δ-ferrite and γ-austenite was theoretically proved by the Kurz, Giovanola and Trivedi (KGT) model. It is thus explained that the solidification cracking susceptibility of the weld metal of alloy tool steel was enhanced due to the δ to γ transition of the primary phase.     

Experimental and numerical analysis of solidification cracking behaviour in fibre laser welding of 6013 aluminium alloy

Abstract

Experimental observation and numerical modelling were employed to investigate the solidification cracking behaviour during fibre laser welding of 6013 aluminium alloy. The solidification cracking initiation location and propagation path were studied using a high speed camera system and via metallurgical analysis. A three-dimensional thermomechanical finite element model of fibre laser welding of aluminium alloys was developed, which considered cylindrical volumetric heat source, temperature dependent material properties, solidification shrinkage and stress relaxation in the weld molten pool. The transient evolution and distribution of mechanical strain in the brittle temperature range (BTR) were analysed in detail to find the factors which drove the crack initiation and propagation. The results showed that the solidification cracking initiated near the fusion line and then propagated along the centreline of the weld, which was the result of the strain distribution characteristic in BTR.     

Chemical activity of a ceramic flux in surfacing with 15Kh18N12S4TYu strip

Abstract

The strength and notch impact toughness properties of pure weld metal and weld metal from welded joints deposited from the TGL 39 671 filler wires 10 MnSi 6, 10 MnSi 8 and similar welding wires are evaluated. The notch impact toughness is found to be determined in the main by the manganese content of the welding wires, lower manganese contents resulting in higher toughness values.     

Pulsed gas metal arc welding of Al–Cu–Li alloy

Abstract

An experimental Al–Cu–Li–Mg–Ag–Zr type alloy in the form of 13.7 mm thick plates was studied for its fusion characteristics using gas metal arc welding (GMAW) and pulsed gas metal arc welding (P-GMAW). High copper 2319 filler of 1.6 mm diameter was used. The burn-off characteristics of 2319 filler wire in GMAW and P-GMAW were experimentally determined, including the relation between pulse current and pulse duration for the desired one-drop detachment per pulse (ODPP) condition and feasible range of pulse parameters. The effect of welding parameters on bead geometry and shape relationships was investigated through beadon-plate experiments in the welding current range above the spray transition current. Reasonably good weld beads were obtained in P-GMAW at currents as low as 194 A and welding speeds of 45 cm min^–1. P-GMAW yielded significantly higher weld penetration compared to GMAW.     

Influence of process variables on weld bead quality in two wire tandem submerged arc welding of HSLA steel

Two-wire tandem submerged arc welding process involves simultaneous depositions from two electrode wires with the leading wire usually connected to a DC power source and the trailing wire connected to a pulsed AC power source. The weld bead profile and mechanical properties in the tandem submerged welding are significantly affected by the leading and trailing wire current transients and the welding speed. We present here a detailed experimental study on the influence of leading wire current, trailing wire current pulses, and welding speed on the weld bead dimensions and mechanical properties in single-pass tandem submerged welding of a typical HSLA steel. It is realized that the weld bead penetration is primarily influenced by the leading wire current while the weld bead width and the reinforcement height are sensitive to the trailing wire current pulses. Greater magnitude of trailing wire current pulses and shorter negative pulse duration increase the weld pool volume leading to reduced cooling rate and poor mechanical properties as the formation of the strengthening phases like acicular ferrite is inhibited. In contrast, increase in welding speed reduces the rate of heat input thereby enhancing the cooling rate and the weld bead mechanical properties. A set of empirical relations are developed to estimate the weld bead dimensions and mechanical properties as function of the welding conditions. The predictions from the empirical relations and the corresponding measured results are observed to be in fair agreement.     

Mitigation of hot cracking of alloy 52M overlay on cast stainless steel CF8A

Abstract

Effects of ER308L buffer layer and welding parameter slope down time on the hot cracking susceptibility of alloy 52M overlay on CF8A base metal were studied. The results indicated that Si segregation was a critical factor affecting Alloy 52M hot cracking. Applying ER308L buffer layers between CF8A and Alloy 52M can reduce the dilution of Alloy 52M weld beads and minimise the contribution of Si from CF8A into Alloy 52M, thereby alleviating Si segregation and the hot cracking susceptibility of Alloy 52M. When the Si content in the grain boundary region was lower than 0·81 wt-%, the hot cracking in the weld bead could be mitigated completely. In many cases, crater cracks occurred in the end crater of the weld bead. Increasing the number of ER308L buffer layers and extending the slope down time could reduce crater crack susceptibility. However, the Si content in the grain boundary region should be controlled to be lower than 0·63 wt-% to prevent crater cracking.     

Solidification and microstructure modelling of welds in aluminium alloys 5754 and 6111

Abstract

A solidification and microstructure modelling approach has been developed to predict weld metal and heat affected zone (HAZ) characteristics. The freezing range and phase evolution in the weld metal region were predicted using thermodynamic and diffusion controlled growth calculations. The calculated freezing range was correlated with the weld solidification cracking tendency. A simplified analytical model was suggested to describe thermal cycles that are experienced by the HAZ. This analytical model was coupled with a published microstructure model for age hardenable alloys to predict the hardness variations across the HAZ. The above integrated approach was evaluated using experimental welds made on non­age hardenable 5754 (Al–Mg) and age hardenable 6111 (Al–Mg–Si) alloys using gas tungsten arc, electron beam, and gas metal arc welding processes.     

Laser beam welding of wrought aluminium alloys

Abstract

Laser beam welding is now a common manufacturing method for a wide range of steel products from automobiles to razor blades. However, the process has only recently been approved for critical applications involving aluminium alloys, notably in the aerospace and automotive industries. The properties of aluminium alloys influence the interaction between the beam and the material to a far greater extent than for steels. The challenge of developing industrial welding procedures has therefore been considerable. The present review describes the effects of CO₂ and Nd–YAG laser beam processing parameters and the properties of the most common wrought aluminium alloys on the characteristics of welded joints. Porosity, solidification cracking, and poor weld bead geometry are shown to be the most frequently encountered imperfections. These can be eliminated through the use of appropriate filler materials, process gases, material preparation, and in some instances, adaptive control systems. Very little work has been reported on the corrosion properties of laser welded aluminium alloys. Experimental processing parameters are presented and compared using an analytical model, which can also be employed for predictive purposes. A number of industrial applications are described. These demonstrate that, for specific alloys, the process is now sufficiently well understood to be approved for high volume production, particularly in the transport industries.     

Simulation of hydrogen induced cold cracking using electrolytic precharging procedure

Abstract

A simple electrolytic cell can be used to charge hydrogen into steel samples. The present paper investigates the validity of this procedure for simulating hydrogen induced cold cracking in steel weld metal, as compared with weld metal containing hydrogen originating from the welding process. The simulation procedure has been investigated since a potential advantage is its ability to provide improved understanding of the quantitative relationships between hydrogen, microstructure, and cracking susceptibility when applied to mechanical test specimens. The intention of the present study was to verify that the distribution of hydrogen was uniform in test samples. Various experiments were therefore carried out which showed how, with care, the hydrogen concentration could be controlled to simulate that expected during welding. This has been further verified using a simple model of diffusion. In addition, it has been shown that the procedure can simulate the same microstructural mechanisms of crack initiation and propagation that are observed in welds containing hydrogen originating from the welding process.