Analytical thermal model of conduction mode double sided arc welding

Abstract

An analytical thermal model of conduction mode double sided arc welding (DSAW) has been derived and used to predict the weld pool dimensions and shapes and temperatures within 2˙5 and 1˙15 mm thick AA5182 Al alloy sheets as functions of the primary DSAW parameters. Separate Gaussian distributed arc heat sources from a plasma arc welding and gas tungsten arc welding torch were assumed to act on the top and bottom surfaces of the sheets. There was excellent correlation between observed and predicted DSAW weld pool dimensions and shapes provided that suitable values for arc efficiencies and distribution coefficients for the two separate arcs were used in the model. The model is capable of predicting weld pool dimensions and shapes of both full and partial penetration conduction mode DSAW welds made in Al alloy sheet, the welding speed at which there is a transition from full to partial penetration welding and the speed above which no melting occurs.     

Comparison of formability of friction stir welded and laser welded dual phase 590 steel sheets

Abstract

The formability of welded dual phase 590 (DP 590) steel sheets was investigated, using both friction stir welding and laser welding. Similar and dissimilar gauge sheets were joined using both processes. The laser welded sheets were produced under process conditions typical of industrial production of tailor welded blanks. The friction stir welded specimens were produced in a lab, where different tool rotational speeds and translation speeds were investigated in order to obtain good weld properties. The formability of the welded sheets was evaluated using a series of mechanical tests, including transverse tension and plane strain formability testing. Friction stir welded specimens performed about the same as laser welded specimens in transverse tension testing; however, hardness profiles showed that the laser welds had greater peak hardness than the friction stir welds. Therefore plane strain formability tests were performed with the welds oriented along the major strain direction. When this type of weld stretching was performed the friction stir welded sheets were shown to be ～20% more formable than the laser welded sheets.     

Numerical analysis of heat transfer process for double sided tungsten inert gas – metal inert gas weld pool

Abstract

Double sided arc welding is a new type of technology developed in recent years. Many experiments show that this technology has great advantages over single arc welding for the joining of intermediate thickness stainless steel and aluminium alloy base metals. In the present work, a three-dimensional transient numerical model is created to reveal the heat transfer process for a double sided tungsten inert gas (TIG) - metal inert gas (MIG) weld pool from the viewpoint of heat transfer literature and hydrodynamics. Considering of the features of the model, effective calculation software using finite element technology is adopted. The temperature fields in the weld pool for double sided TIG - MIG welding are successfully calculated; in addition, the configuration of the weld pool is also calculated.Comparisons show that thecalculatedresults agree approximately with the experimentally measured results. STWJ/310     

Effect of Al coating conditions on laser weldability of Al coated steel sheet

Al coated steel sheets with excellent heat resistance, thermal reflection, and corrosion resistance are widely used in various applications. The laser weldability of the Al coated steel sheet for full penetration welding was reported. The phenomenon caused by intermixed aluminum and behavior of aluminum in the weld were investigated. Al coated steel sheets that have various thickness and coating mass were prepared for laser welding. The effects of parameters such as welding conditions and Al coating conditions were investigated. Al content mixed in the weld after laser welding was evaluated, and then a correlation between the mixed Al and mechanical properties was investigated. The results show that the Al-rich zones which have Fe-Al intermetallic compounds are found in the weld. The intermetallic compounds cause the decreased strength of the weld.     

Welding equipment for reinforcing the edges of corrugated walls of the casings of transformers of a new generation of TMG series

The application of aluminium alloy, which is a typical lightweight material, has been expected in the construction of transportation vehicles to achieve energy saving by reduction of weight. However, structures made of whole aluminium alloy have problems with low strength and high cost. Thus, hybrid structures made of Al alloy and steel are useful because of light weight and higher strength. To construct the hybrid structure, it is necessary to weld aluminium alloy and steel. However, conventional welding methods, like brazing and mechanical fastening, have problems such as low mechanical strength and low productivity. Also, it is difficult to weld Al alloy and steel by conventional fusion welding.

In this study, spot welding between aluminium alloy and low carbon steel by friction stirring was carried out. Especially, optimization in welding conditions was carried out. Moreover, the effect of welding conditions on the joint strength and weld interface was studied. As a result, relatively higher tensile shear strength of the weld, which was achieved at optimum welding conditions, was obtained. Temperature near weld interface measured by K-type thermocouple during welding was found to be lower than the melting point of A5052. From the observation results on microstructure of the weld interface, it was found that a Fe/Al intermetallic compound layer was formed.     

Joint strength and behaviour of coated aluminium in laser lap welding of steel sheets

When galvanized steel sheets are closely overlapped and welded by laser lap welding, a large amount of molten metal spatters, resulting in a poor surface appearance of the weld and weakened strength of the welded joint, as compared with that of cold-rolled steel sheets. Whereas in the case of aluminium-coated steel sheets, even when they are closely overlapped and welded by laser lap welding, no spattering occurs. Thus, a good surface appearance of the weld is obtained, but the welded joint has lower strength. In both the mentioned cases, it is known that if a clearance of about 0.1 mm is provided between the steel sheets, laser lap welding produces a good surface appearance of the weld and the welded joint strength equal to that of the cold-rolled steel sheets. This report discusses specifically how, in laser lap welding of overlapped Al-coated steel sheets, Al of the coated layer comes to enter the weld metal, also specifically how to reduce the joint strength, as well as what behaviours of Al are present when a clearance is provided between the steel sheets. When the steel sheets are closely overlapped and welded, Al becoming molten on the base metal side of the bond of the overlapped face becomes swallowed up by the bath streams of the molten pool, flowing into the molten pool, then forming the Fe–Al intermetallic compound, while not being sufficiently stirred. It is considered that when subjected to the tensile shear test, the Fe–Al intermetallic compound starts to fracture, thereby causing a partial loss of the weld metal and a reduction in the joint strength. On the other hand, when a clearance is provided between the steel sheets, it may be inferred that the fusion Al on the base metal side of the bond stays in place without flowing into the molten pool, consequently not forming the Fe–Al intermetallic compounds within the weld metal.     

Interface properties and thermodynamic analysis of laser–arc hybrid welded Al/steel joint

Abstract

Fibre laser–cold metal transfer hybrid welding was introduced to join AA 6061 aluminium alloy with AISI 304 stainless steel using Al–12Si filler wire. Interface properties and microstructure of welded joints were observed by optical microscope, scanning electron microscope, energy dispersive spectrometry and X-ray diffraction techniques. A serrated intermetallic compound (IMC) layer was found at the interface between fusion zone and stainless steel. The morphology of IMC layer was uniform from the top to the bottom, and its average thickness was 3 μm. The IMC layer consisted of two layers: Al₈(Fe,Cr)₂Si layer close to fusion zone and (Al,Si)₁₃Fe₄ layer close to stainless steel. The joint fractured at the IMC layer and presented a tensile strength of 165 MPa. The formation of the IMC layer was closely related with the thermodynamic and kinetic behaviours of the interface and fast cooling rate of hybrid welding.     

Effects of magnesium content on dual beam Nd : YAG laser welding of Al – Mg alloys

Abstract

The effects of Mg content on the weldability of aluminium alloy sheet using the dual-beam Nd:YAG laser welding process have been studied by making bead-on-plate welds on 1.6 mm thick AA 1100, AA 5754 (3.2 wt-%Mg) and AA 5182 (4.6 wt-%Mg) alloy sheets. Whereas all full-penetration laser welds made in 1100 aluminium were of excellent quality,many of the welds produced in the aluminium–magnesium alloys exhibited rough, spiky underbead surfaces with drop-through and undercut. A limited range of process variables was found, however, that allowed welds with acceptable weld bead quality to be produced in the 5754 and the 5182 alloy sheet. Goodwelds were only produced in these alloys if the lead/lag laser beam power ratio was ≥1. Weld penetration and the maximum welding speed allowing full penetration keyhole-mode welding were observed to increase with Mg content. This was attributed to the effect of Mg on the vapour pressure within the keyhole and the surface tension of the Al–Mg alloys. Significant occluded vapour porosity was seen in the 5754 and 5182 alloy welds with borderline penetration; however, there was no evidence of porosity in the acceptable full-penetration welds with smooth underbead surfaces. Hardness profiles in the 5754 and 5182 welds showed a gradual increase in hardness from the base metal values through the heat affected zone (HAZ) to a peak in hardness in the weld metal adjacent the fusion boundary. It is possible that this increase in hardness may be the result of the presence of Mg₂Al₃ or metastable Mg₂Al₃′ precipitates in this region of the weld and HAZ.     

5052铝合金/镀锌钢涂粉CO2激光熔钎焊工艺特性

以5052铝合金和热镀锌ST04Z钢为研究对象,采用预置涂粉CO₂激光搭接熔钎焊方法进行工艺试验.利用光学显微镜、扫描电镜和拉伸试验机对熔钎焊接头的微观组织和力学性能进行了研究.结果表明,涂助溶剂和粉末后,焊缝成形明显改善,镀锌层没有烧损;熔-钎焊接头过渡层最大厚度小于10 μm,针状Al-Fe金属间化合物没有向熔化的铝侧明显析出;接头具有较高的力学性能,最大机械抗载能力可达到208 MPa,约为5052铝合金母材抗拉强度的95.41%.     

Methods for electromagnetic pressure seam welding of Al/Fe sheets

Aluminium (Al), despite its low melting point, has a high electric conductivity and thermal conductivity but poor heating efficiency, ranking as a hard-to-weld material. It is routinely necessary to weld aluminium sheets to sheets made of a dissimilar metal, such as steel sheets (Fe). In this case, it is advisable to use seam welding than spot welding in order to ensure good weld strength and joint tightness. However, seam welding of Al/Fe sheets is difficult and little reported in literature.     

Quantitative characterization of porosity in Fe–Al dissimilar materials lap joint made by gas metal arc welding with different current modes

5052 Al alloy sheets and galvanized mild steel sheets were joined by gas metal arc welding with three different current modes, including direct-current pulse gas metal arc welding (DPG), alternate-current pulse gas metal arc welding (APG) and alternate-current double pulse gas metal arc welding (ADG). The effect of current mode on size, distribution and volume fraction of pores generated in Fe–Al dissimilar materials lap joint was quantitatively studied. EDS result showed that pores in Fe–Al joint were mainly caused by trapped zinc metal vapor from galvanized steel. Volume fraction of pores in joints made by APG and ADG processes was larger than that in joint resulted from DPG process. Moreover, pores in joints made by APG and ADG processes had smaller diameter, and tended to distribute in the middle of the weld seam. On the contrary, pores with large diameter were inclined to distribute close to upper weld surface of the joint resulted from DPG process. These results are attributed to the difference of arc stirring force and linear heat input in these three processes caused by different current modes.     

Special features of the winding bend test

Summary

This paper deals with the resistance spot weldability of steel to aluminium alloy using an intermediate layer of aluminium clad steel. Five types of clad sheet with various steel/aluminium thickness ratios were produced by hot rolling. The mechanical properties of the clad sheet changed with the thickness ratio and ranged between those of steel and:those of aluminium sheet. The peel strength of the steel/aluminium interfaces was greater than 25 N/mm.

Materials used in spot welding were 0.8 mm thick EDDQ steel sheet, three types of 1.0 mm thick aluminium alloy sheet and the clad sheet mentioned above. Spot‐weldability, including suitable welding current, nugget diameter, tensile shear strength and thickness of the intermetallic compound layer formed at the interface of the clad sheets, changed with the thickness ratio of the clad sheet. From these results, it was concluded that spot‐weldability was affected by the thickness ratio of the clad sheets.

Spot‐weldability was also affected by the alloying elements in the aluminium alloy sheet. Tensile shear strength and nugget diameter varied in various types of aluminium alloy sheet.     

Comparative study of fatigue behaviour in dissimilar Al alloy/steel and Mg alloy/steel friction stir spot welds fabricated by scroll grooved tool without probe

Abstract

Aluminium alloy A6061-T6 or magnesium alloy AZ31 sheet was welded to steel sheet by a friction stir spot welding technique using a scroll grooved tool without a probe. The material flow in the nugget of the Mg/steel weld was less than that in the Al/steel one. The Al/steel weld exhibited higher static tensile–shear strength than the Al/Al weld, while the strengths of Mg/steel and Mg/Mg welds were comparable. Tensile–shear fatigue tests were performed using lap shear specimens of both dissimilar and similar welds. The dissimilar welds exhibited nearly the same fatigue strengths as the similar ones. The effective nugget size in the dissimilar welds was defined as the area where Al or Mg alloy remained on the steel side after static fracture. When the fatigue strengths of dissimilar welds were evaluated based on the effective nugget size, the normalised fatigue strengths of Al/steel and Mg/steel welds were comparable.     

Welding of titanium alloys with activating flux

Abstract

In the present paper, the effects of an activating flux on Ti–6Al–4V alloy welding were investigated. Tungsten inert gas welding was used to weld 8.0 mm thickness Ti–6Al–4V alloy plates. Results show that applying the activating flux on the Ti–6Al–4V alloy surface leads to an increase in weld penetration depth, whereas the corresponding weld bead width is reduced. It was also found that various welding conditions, particularly flux thickness, influence the effectiveness of the activating flux. Furthermore, a data acquisition system was used to monitor the current and voltage signals during welding. Results from monitoring of the welding current and voltage signals reveal that there is a clear correlation between the signals and the weld penetration when the welding arc is steady. Analysis of the acquired signals can be used to identify inconsistencies in weld penetration. In summary, to take advantage of the use of activating flux in Ti alloy welding, it is important that a uniform flux layer is present at the alloy plate surface and suitable welding parameters are selected.     

Join Al–steel dissimilar metal by novel high frequency electric cooperated arc welding

ABSTRACT

A novel high frequency electric cooperated arc welding method (HFAW) was developed to join aluminium and steel of 3.0?mm thickness without groove. Owing to the skin effect and proximity effect of high frequency current, a part of welding heat was directly distributed all over weld side wall. Consequently, sound double-sided weld formation was achieved under a low MIG heat input and high welding speed. The average thickness of interfacial layer was limited to 2.3?µm. Benefitted from the balanced heat input and thin interfacial layer, the failure mode of the HFAW joint was necking at Al base metal. For traditional MIG joint, however, poor back weld formation and thick interfacial layer resulted in spontaneous fracture at interface.     

Resistance spot welding of steel and aluminium sheet using insert metal sheet

Abstract

The present paper reports the resistance spot welding of steel and aluminium sheets using aluminium clad steel sheets as insert metals. Intermetallic compound layers were formed in the weld zones in direct spot welding of steel sheets to aluminium sheets. Thus, the strength of these joints was lower than that of aluminium to aluminium joints. Intermetallic compound layers were also formed at the steel/aluminium interfaces of the insert metal in welding of steel to aluminium using an insert metal sheet. However, the strength of these joints was of the same order as that of the aluminium joints. The fracture mode of these joints varied with the welding current. The suitable welding current for steel to aluminium joints varied between the values suitable for steel to steel and aluminium to aluminium joints. The fatigue strength of joints using insert metals was somewhat lower than that of the aluminium joints.     

Effect of alloying elements of steel wire on the structure and properties of coatings in electric arc spraying

This paper reports the results of a comparison between the mechanical characteristics of butt joints in 3.0 mm thick Ti6Al4V titanium alloy sheets, made by laser welding with no filler material and by laser–arc hybrid welding. Vickers hardness tests have been performed on cross-sections of the beads obtained. In particular, the influence of the gap between the sheets in test welds performed using CO₂ laser–MIG hybrid welding has been analysed. Cross-sections of the weld beads obtained with several different gap sizes have been analysed morphologically. The welded joints have been subjected to draw testing, and joint deformation behaviour has been analysed using an optical deformation measurement system based on stereoscopic image capture (ARAMIS 3D analysis system).     

铝合金/镀锌钢异种材料薄板的超声波点焊

为了实现铝合金和钢板的高效连接,对3003铝合金和镀锌钢板进行了超声波点焊. 研究了接头的显微组织特征、焊接参数对接头性能的影响以及焊缝区的温度变化过程. 结果表明,超声波焊接可以对3003铝合金与镀锌钢板进行有效连接;镀锌层被不规则挤出,铝合金与钢直接接触区形成了FeAl₃和Fe₂Al₅相;在一定范围内,随着焊接时间的增加,接头抗拉强度先增加后减小,其减小的原因是过长的焊接时间诱导显微组织演变;当焊接时间为240 ms,焊接压力为0.4 MPa时,获得接头的最大抗拉力为673.05 N;在文中试验条件下,焊接区最高温度达到390 ℃.     

Optimization of Ti6Al4V titanium alloy laser–arc hybrid weld parameters

This article reports the results of a study aimed at using statistical methods to optimize the parameters for laser–arc hybrid butt welding of Ti6Al4V titanium alloy sheets with a thickness of 3.0 mm. The study has examined the effects of the hybrid welding process parameters, such as laser beam power, arc pulse frequency, arc length, arc current, wire speed, laser and arc relative positions, and weld speed. Microstructure has been studied using light microscopy and morphological analysis of weld bead cross sections. This article reports the results of energy and morphological tests.     

Effect of welding speed on microstructural and mechanical properties of laser lap weld joints in dissimilar Al and Cu sheets

Conventional fusion welding of aluminium and copper dissimilar materials is difficult because of poor weldability arising from the formation of brittle intermetallic compounds on the weld zone as well as different chemical, mechanical and thermal properties of welded joints. Joining of Al and Cu plates or sheets offers a metallurgical challenge due to unavoidable formation of brittle intermetallic compounds. Therefore, it is necessary to effectively suppress the formation and growth of Al–Cu intermetallic compounds. For welding of dissimilar Al and Cu sheets, no systematic work has been conducted to reduce these defects. Thus, this paper focuses on the effect of welding speed on the quality of a lap weld joint in the Al and Cu sheets with a single mode fibre laser. It was found that consequently sound strong weld joints could be produced by suppressing the formation of intermetallic compounds in the interface zone at extremely high speeds.