Hybrid laser-arc welding of aluminium alloys

Special features of laser welding of aluminium alloys with laser and arc heat sources are investigated. Advantages and shortcomings of these methods are noted. Experiments were carried out to combine laser and arc heat sources for welding aluminium alloys. Equipment for hybrid welding is described. The technological parameters influencing the external formation of the welded joints are determined. Specific conditions for welding 1424 aluminium alloys with a thickness of 4.0 mm are presented. High-quality welded joints were produced by hybrid laser-arc welding in 1424 alloy with a thickness of 4.0 mm.     

大厚度船用高强钢激光-电弧复合焊技术研究

为实现大厚度高强钢全熔透单道对接焊,针对厚度20mm的AH32船用高强钢,采用15kW大功率CO_2激光进行激光-电弧复合焊接.分析了工件坡口、焊接速度、送丝速度、离焦量、装配间隙等规范参数对焊缝成型影响;通过金相观察以及显微硬度测定分析了接头组织性能.结果表明:通过激光功率等焊接规范匹配,激光-电弧复合焊接能实现20mm厚板的全熔透单道对接;钝边为8mm的Y形坡口有助于提高厚板激光-电弧复合焊缝熔透能力;降低焊接速度有利于提高熔深能力;工件厚度较大时,装配间隙对焊缝熔深能力的影响较为显著;接头硬度表明厚板激光复合焊焊缝纵向热循环模式存在较大差异.     

Effect of Laser Welding Process Parameters on Microstructure and Mechanical Properties on Butt Joint of New Hot-Rolled Nano-scale Precipitation-Strengthened Steel

A 4 kW fiber laser was chosen to weld the new hot-rolled nano-scale precipitation-strengthened steel with a thickness of 4.5 mm. The effect of laser power, defocusing distance, and welding speed on the welded joint appearance was examined, and the microstructure and mechanical properties on the typical butt joints were investigated. Results showed that increasing laser welding power may cause faster downward flow of molten metal to produce greater root humping. With the welding speed increasing, the average welding seam （WS） width decreased, and the average WS and heat-affected zone （HAZ） hardness increased. The microstructures of WS, fusion line, and coarse grain heat-affected zone were lath martensite, but the growth direction of the original austenite grain boundaries was significantly different. The microstructures of fine grain heat-affected zone were ferrite and martensite, and the microstructure of mixed grain heat- affected zone contained ferrite, massive M/A island, and a small amount of martensite. The micro-hardness values of WS, HAZ, and base metal （BM） were 358, 302, and 265 HV, respectively. The butt joint fracture at the BM far from the WS and the welded joint tensile strength are observed to follow proportional relationship with hardness.     

Effect of plate thickness on very low‐cycle fatigue properties of butt welded joints containing weld defects. Study of acceptable defect size in girth welds of gas pipelines (Report 2)

Summary

To develop a joining technology for thick ceramics, the fundamental characteristics of high‐power CO₂ laser welding of 87% A1₂O₃ ceramics have been investigated. The results suggest that a penetration depth of 20 mm is possible at a welding speed of 6.5 mm/sec and laser power of 10 kW. The porosity ratio is lower at lower input powers, also tending to decrease with a decreasing welding speed at the same input power. The bending strength decreases with an increasing porosity ratio. Porosities, especially large sink mark porosities at the bead centre, strongly affect the bending strength of welded joints in alumina ceramics. The root bending strength of 4 mm thick butt‐welded plate has the same value as the base material.     

Process and joint characterizations of laser-MIG hybrid welding of AZ31 magnesium alloy

High power laser-metal inert gas (MIG) hybrid welding of AZ31 Mg alloys was studied. Microstructure and fracture surface of welded joints were observed by optical microscope and scanning electron microscope. The mechanical properties of welded joints were evaluated by tensile test. Under the optimal welding parameters, the stable process and sound joints were obtained. The tensile strength efficiency of welded joints recovered 84-98% of the substrate. It was found that the arc was compressed and stabilized by the laser beam during the hybrid welding. The compressed extent of arc column increased with laser power, and the process stability could be improved by increasing laser power and arc current or slowing welding speed. The arc stabilized mechanism in laser-MIG hybrid welding of Mg alloys was summarized in two factors. First, the laser keyhole fixes the arc root and improves the igniting ability of the arc. Second, the electromagnetic force is downward and increased by the laser-arc interaction, which prevents the overheating of the droplet and smoothes droplet transfer from the wire to the weld pool.     

Experimental and numerical investigation on combined girth welding of API X80 pipeline steel

Abstract

API X80 pipeline steel is widely used in natural gas and oil transportation. In this study, X80 pipeline steels with 18.4?mm thickness and 1219?mm diameter, made in China, were welded by a combined girth welding technology. Experimental results showed that microstructures in weld metal and coarse grain heat affected zone are mainly composed of coarsening bainite grains with dimensions of 20–50?μm, and Vickers hardness in weld seam is lowered by the seven-pass welding process. Simulated results illustrated that repeatedly thermal cycles imposed by the combined multipass girth welding process easily result in softened weld joints. The predicted microstructures, phase compositions and hardness in weld metal are in agreement with the measured ones. The results could be applied to optimise this combined girth welding process and improve the weld quality of API X80 pipeline steel and even higher grade pipeline steels.     

Special features of laser welding using fibre and CO2 lasers

Investigations were carried out into the effect of different gas media on the process of welding in fibre lasers and comparison with CO₂ lasers using the method of smooth variation of the position of the focal spot in relation to the surface of the welded specimens. The penetrating capacity of the metal was determined. Special attention is given to the effect of the density of the laser radiation power on the behaviour of plasma and the processes taking place in the weld pool in the welding in fibre lasers with a power of 2.5 and 5 kW. The effect of the intensity of laser radiation on the formation of the welded joint is described.     

Investigation into properties of laser welded similar and dissimilar steel joints

Abstract

Laser beam welding is currently used in the welding of steels, aluminium alloys, thin sheets, and dissimilar materials. This high power density welding process has unique advantages of cost effectiveness, deep penetration, narrow bead and heat affected zone (HAZ) widths, and low distortion compared to other conventional welding processes. However, the metallurgical and mechanical properties of laser welds and the response of conventional materials to this new process are not yet fully established. The welding process may lead to drastic changes in the microstructure with accompanying effects on the mechanical properties and, hence, on the performance of the joint. The thermal cycles associated with laser beam welding are generally much faster than those involved in the conventional arc welding processes. This leads to the formation of a rather small weld zone that exhibits locally a high hardness in the case of C–Mn structural steels owing to the formation of martensite. It is currently difficult to determine the tensile properties (full stress–strain curves) of the laser welded joint area owing to the small size(～V 2·3 mm) of the fusion zone. Complete information on the tensile and fracture toughness properties of the fusion zone is essential for prequalification and complete understanding of the joint performance in service, as well as for conducting a defect assessment procedure on such welded joints. Therefore, an experimental investigation into the mechanical properties of laser welded joints was carried out to establish a testing procedure using fiat micro tensile specimens (0·5 mm in thickness, 2 mm in width) for determination of the tensile properties of the weld metal and H AZ of the laser beam welds. Three similar joints, namely St 37–St 37, St 52–St 52, and austenitic–austenitic, and two dissimilar ferritic–austenitic joints were produced by CO₂ laser, using 6 mm thickness plates. The mechanical properties have been examined by microhardness survey and testing of conventional transverse tensile, round tensile, and fiat microtensile specimens. The results for the micro tensile specimens were compared with those for standard round tensile specimens and this clearly showed the suitability of the microtensile specimen technique for such joints.     

激光-电弧复合焊技术在长输管道焊接中的研究进展

重点介绍了国内外管道激光焊接技术的发展,对不同类型激光器的激光-电弧复合焊技术在油气长输管道焊接上的研究进展和应用进行了详细回顾。结果表明,CO2激光器和闪光灯触发的Nd:YAG激光器由于传输方式和效能的不利因素,不适于油气管线长途作业,而高能Yb光纤激光技术推进了激光-电弧复合焊接技术在管道焊接现场应用的步伐;同时,对目前该技术在应用中存在的问题进行了总结分析;最后对激光-电弧复合焊技术在管道焊接上的应用前景进行了展望。激光-电弧复合焊技术已在试验室条件下成功焊接了管径1 219 mm、钝边高度8 mm的X80钢管,焊缝外观和焊缝力学性能均能满足长输管道焊缝合格标准要求,但后续为适用长输管道现场焊接,还需进行焊接工艺现场适应性试验。 创新点： 针对激光-电弧复合焊技术应用于管道焊接存在的共性问题进行分析总结,提出激光-电弧复合焊在现场应用的具体解决措施,为后续激光-电弧复合焊最终在现场应用提供可行的解决方案。     

Mechanical and microstructural properties of submerged arc weldments with high heat input

The purpose of this work is to present a study of the mechanical and microstructural properties of welded joints in carbon steel obtained by the automated submerged arc process with high heat input, with the aim of increasing productivity in the fabrication of pipes for mooring equipment. Joints were welded in ASTM A-572 Gr.50 steel with thickness of 25 mm by the single-pass submerged arc process, with heat input varying from 7.8 to 14.0 kJ/mm. The joints were assessed by Charpy-V impact testing at a temperature of 0 °C, Vickers microhardness with 1-kgf load, and metallography of test specimens taken from the weld metal and the heat-affected zone. The results showed that the welded joints had impact toughness above the minima required for use in the welding of C-Mn and low-alloy steels with impact requirements of 34 J at 0 °C. A significant increase in productivity was observed, without impairing the mechanical properties, allowing fabrication of pipes for oil equipment with a significant reduction in fabrication time.     

HC340/590DP钢板激光焊可行性分析

HC340/590DP双相钢在氧化性介质中具有优良的耐蚀性能和高温力学性能,其塑性和韧性较高,且不可淬硬,焊接性能较好。通过分析其化学成分、力学性能和焊接性,利用激光焊技术的1k W激光发生器、激光头、光学系统、机器人、控制系统、夹具系统和外围周边集成等组成的系统进行大量试验、检测及焊接过程控制,确定焊接参数为:焊接速度40 mm/s、功率1 k W、光斑直径0.6~0.8 mm,获得的焊接接头既能焊透又不塌陷,表面成形较好,熔宽合适,确保试件的焊接接头性能满足实际需要,达到生产化的目的。     

镁合金激光氩弧复合热源冷填丝焊接工艺

研究了镁合金的低功率激光-氩弧复合热源冷填丝焊接工艺.通过5 mm厚镁合金板材的堆焊试验,研究了焊接电流、焊接速度、钨极高度和热源距离等参数对焊缝成形和焊接熔深的影响,确定了钨极高度为0.75 mm,热源间距DLA为1.2 mm左右的焊接参数范围;在堆焊基础上,进行了2.5 mm厚镁合金板材的对焊试验,实现了单面焊双面成形,焊接速度达1 200 mm/min,焊接接头熔深为单TIG冷填丝接头熔深的两倍,抗拉强度达到母材的95%左右,实现了高速、优质的镁合金冷填丝焊接.另外,简要分析了激光的加入对焊接过程的影响.     

Development of electrodes for welding transmission pipelines and marine equipment made of high-strength low-alloy cold-resistant steels

The problems of production of welding electrodes with basic coatings in Russia is associated with the changes in the raw materials base used as components for electrode coatings, in particular, the electrodes of the UONII-13 series used extensively in industry in welding important structures made of cold-resistant low-alloy steels of different strength categories are examined. A promising composition of the electrode coating with a new deoxidation alloying system is proposed. The system results in high welding and technological characteristics of the electrodes and stable mechanical properties of the metal of welded joints in low-alloy steels with a strength of up to 560 MPa. The high-quality parameters are achieved as a result of using Minal (mineral alloy) in the electrode coating for adding through this coating the mineral and rare-earth components. The compositions of the coatings of the developed electrodes are calculated using the phase equilibrium diagrams of non-metallic systems.     

铝合金激光-MIG双面焊接接头组织和性能研究

针对16mm厚1561铝合金(俄罗斯牌号),采用不开坡口无间隙的双面激光-MIG复合焊接工艺,并研究焊接接头的拉伸性能、显微硬度和微观组织。结果表明,采用较大的激光功率使双面焊道交叉面积增大,有利于减少焊道根部缺陷,提高拉伸性能;接头中存在着基体相α-Al和第二相Fe(Mn Al)6,第二相经焊接热循环重熔后弥散分布,其中单独激光作用区弥散度最高;焊缝硬度在激光单独作用区相对于母材升高,而在激光-电弧复合作用区相对于母材降低,这与焊缝显微组织中的第二相数量和形态密切相关。     

基于自动脉冲TIG焊的核级阀门管道焊接工艺

针对核电厂运行期间核一级手动截止阀唇边焊易发生泄露的风险,要求阀门需要进行整体更换,分别对核级阀门两种规格的接头开展自动脉冲TIG焊接工艺研究,并对焊后的试件进行渗透、X射线探伤等无损检验和拉伸、弯曲、金相、化学分析和晶间腐蚀等破坏性检验。试验结果表明,壁厚2.77 mm的焊接接头拉伸力平均值为564 MPa,断后伸长率平均值为39.25%;壁厚8.7 mm的焊接接头拉伸力平均值为612 MPa,断后伸长率平均值为46.75%,两种壁厚的焊接接头均具有良好的力学性能,面弯试验和背弯试验均未发现裂纹,弯曲性能良好;壁厚2.77 mm接头的金相组织主要是板条状铁素体,壁厚8.7 mm接头的金相组织主要以树枝状铁素体为主;两种壁厚的焊接接头中熔敷金属的化学成分经检验均满足技术条件的规定;采用弯曲法进行晶间腐蚀试验,经检验两种规格的接头均无晶间腐蚀倾向。     

Welding experiments of aluminium pipe by space GHTA welding in aircraft-borne simulated space environment

The gas hollow tungsten arc (GHTA) welding experiments on aluminum pipe were carried out in a simulated space environment using an aircraft. A vacuum chamber and welding machine for GHTA welding test were placed in the cabin of the aircraft and the 10^? 2 G gravity environment was produced by a parabolic flight of the aircraft. The square butt welding joints with non root gap on aluminum pipe were made by orbital welding in the vacuum chamber without wire filler metal using DC or DC-pulsed power supply under the 10^? 2 and 1 G gravity conditions. The welding phenomenon during the aluminum GHTA welding recorded in the high-speed video image was analysed and also the macrostructure and mechanical properties of butt weld joints were investigated. The welding experiments under simulated space environment showed that the DC-pulsed GHTA process could make the welding joints without the weld defects such as a lack of fusion, oxide film inclusion and spattering, though throat thickness decreased by the impulsive arc pressure of pulsed current. It was also clarified that the arc discharge phenomenon and melting characteristic at the molten pool surface during the DC-pulsed GHTA welding were insensitive to the gravity condition. However, the sagging weld metal made at 1 G gravity condition increases a little more than that welded under the 10^? 2 G gravity condition.     

Influence of interpass temperature on the properties of duplex stainless steel during welding by submerged arc welding process

Duplex stainless steels are materials that present high corrosion resistance with high values of mechanical strength, therefore motivating their use in various components in the offshore industry. However, there are major challenges in the welding of these materials in terms of the productivity and quality of the joint produced, considering its extensive use for components of small thickness, such as umbilicals, to those of large thickness, such as salt water injection pipelines. In relation to pipes of small thickness, the gas tungsten arc welding process is successfully used. In thick-walled pipes, the automatic process of submerged arc welding (SAW) has been recently implemented in lines of pre-assembled piping, and this has considerably increased the productivity of the joints produced, though, a great deal of time is required to perform a new weld pass, due to the fact that the maximum interpass temperature needs to be lower than 150 °C. This work presents the results of characterization and the evaluation of corrosion resistance of a welded joint corresponding to DSS UNS S31803, with a wall thickness of 21.4 mm, welded by the gas metal arc welding process in the root and SAW process in the filling and cap passes, employing an interpass temperature between 150 and 290 °C. The results of the characterization of the mechanical properties, chemical composition and corrosion resistance in different regions of the welded joint were compared with those obtained for the base metal of the pipe, as well as with the minimum values required by the project standards. Therefore, this study has made an evaluation of the influence of the interpass temperature in the properties of the joints produced, motivated by a possible increase in productivity in pipe welding.     

Welding of high thicknesses using a fibre optic laser up to 30 kW

The industrial applications of high-power fibre optic lasers include welding, 2D and 3D cutting, remote cutting and welding, brazing and surface treatments. The availability of fibre optic lasers with power outputs in excess of 10 kW might allow the development of novel fields of application in the welding of high thickness pieces: shipbuilding and offshore industries, pipe and cable manufacture and other heavy industry sectors. Carrying the beam by fibre optics allows high flexibility, even for the production of very large pieces, such as in the shipbuilding sector. This study describes the laser welding of high thickness pieces using a 30 kW laser and a 200 μm diameter fibre. On the one hand, such lasers allow a weld penetration depth of over 30 mm in a single pass, and very high process speeds for thinner materials on the other. Combining lasers with conventional arc welding techniques (hybrid welding) allows further optimization of weld quality and makes it possible to weld butt joints with a ‘gap’ of up to 1 mm. This paper presents the most recent results from very high-power fibre optic laser welding along with new applications in the manufacturing sector.     

Research on laser-arc hybrid welding of lap fillet joints of thin sheet

ABSTRACT

Laser welding is capable of welding at high speeds by high-density energy, while arc welding is an effective construction method from the viewpoint of tolerance of the gap and welding position. Laser-arc hybrid welding has both these features. The authors have researched suitable welding parameters and consumables for this hybrid welding process that couples laser beam with MAG arc for lap fillet weld joining of thin steel sheets. As a result, the following welding parameters have been proven to be the most appropriate for better bead shapes and root-gap tolerance, i.e. laser leading (kept at a right angle) and MAG trailing (kept at a push angle); the laser-arc distance was 3 mm and the laser beam focus size was 2 mm. In addition, it was proven that HT490-class welding wire of Si-Mn-Ti type (JIS YGW11) was the most appropriate for better bead shapes and root-gap tolerance. The bead shape was apt to be better in cases of higher surface tension of welding wire. The result of the tensile shear test of the joint by welding with HT490-class welding wire of Si-Mn-Ti type (JIS YGW11) under selected welding condition demonstrated that the value of the tensile strength of parent material was equal to that of lab fillet joints.     

The synchronized tandem wire welding process applied to the welding of structural plates*

As part of a European research project, partially funded by the Steel Research Fund (RFS-CR-03049), the potential benefits derived from the use of synchronized tandem wire welding (STW) technology applied to structural plates, in place of the currently used arc techniques, have been evaluated.

In particular, two welded joint types have been investigated: T joints and butt joints in S355 grade structural plate, 6 and 12 mm thick. Considering the variables that characterize the process, also depending on the type of tandem torch, i.e. variable or fixed electrode configuration, the influence of the distance between the electrodes, stick-out, the type of arc and weld speed on the process characteristics have been examined.

The joints obtained have been compared with those produced using traditional technology in terms of overall joint deformation, structural integrity, microstructural analysis and mechanical performance (toughness and fatigue strength).

The results have demonstrated that the STW process is an effective technology for increasing both the weld speed, at the same penetration and the quantity of metal deposited, by about 50% compared to GMAW welding, with only slightly higher but relatively modest heat input (1 kJ/mm). These operating conditions have allowed the preservation of a level of joint quality (EN ISO 5817 quality level B) and structural integrity, comparable with those of GMAW and SAW welded joints, in addition to significant reductions in distortion. Furthermore, the fatigue strength of STW joints has also been in compliance with the reference class (butt joint, FAT class 100).

The objective of the project (RFS-CR-03049), partially supported by the Research Fund for Coal and Steel, was to explore and quantify the benefits of STW applied to structural steels as an alternative technology to established arc welding technologies.

T joints and butt joints of 6 and 12 mm steel grade S355 plates have been investigated using two different types of welding gun configuration, i.e. fixed electrodes and variable electrodes configuration. The influence of electrodes distance, stick-out, arc types and welding speed have been examined. The optimized joints have been characterized in terms of structural integrity, microstructure, mechanical performance (impact fracture toughness and fatigue resistance), total deformation and compared to traditional arc welding joints.

STW technology allowed an increase of about 50% in both the welding speed, at the same penetration and deposited metal compared to GMAW with a not much greater heat input (1 kJ/mm) maintaining the same level of joint quality (EN ISO 5817 quality level B) and structural integrity with a reduction of joint distortion. In addition, fatigue resistance of STW joints was in compliance with the requirement (FAT Class 100 MPa).