Mechanisms of joining aluminium A6061-T6 and titanium Ti–6Al–4V alloys by cold metal transfer technology

Abstract

Cold metal transfer (CMT) welding–brazing joining of Ti6Al4V and Al A6061-T6 was carried out using AlSi₅ wire. The joining mechanisms and mechanical properties of the joints were identified and characterised by scanning electron microscope, energy dispersive spectroscopy and tensile–shear tests. Desired CMT joints with satisfied weld appearances and mechanical properties were achieved by overlapping Ti on the top of Al. The joints had dual characteristics of a welding joint on the aluminium side and a brazing joint on the titanium side. Three brazing interfaces were formed for the joint, which increased the strength of the joint. An intermetallic compound layer was formed at the brazing interface, which included Ti₃Al, TiAl and TiAl₃. Two different fracture modes were also observed: one fractured at the welding/brazing interface and weld metal and the other at the Al heat affected zone (HAZ). Clearly, the joints fractured at the Al HAZ had higher tensile strength than those fractured at the welding/brazing interface and weld metal.     

工业纯钛TA2/紫铜T2异种金属CMT焊接接头的微观组织和腐蚀性能

采用冷金属过渡技术(CMT)对工业纯钛TA2和紫铜T2异种金属薄板进行对接焊.焊接过程中,使焊丝偏向铜的一侧,铜母材和焊丝熔化形成熔焊接头,熔化的填充材料润湿钛母材,形成钎焊界面,实现钛和铜的熔钎焊连接.使用扫描电镜(SEM)、能谱分析(EDS)和力学试验研究焊接接头的组织以及连接机理.在室温下10%HCl溶液中,研究钛/铜异种金属CMT焊接接头的腐蚀行为.结果表明,钎焊界面由TiCu,Ti₂Cu,AlCu₂Ti等多种金属间化合物组成;焊缝区由铜基固溶体和Ti-Cu-Al-Ni-Fe五元素析出相组成;接头的抗拉强度达到205 MPa;焊接接头在室温10%HCl溶液中腐蚀7天后,钎焊界面出现腐蚀沟槽,14天后自行断裂.     

Interface structure and strength of brazed joints between TiC ceramic and iron

Abstract

The brazing of TiC ceramic to iron was carried out at 1123–1273 K for 5–20 min using Ag–Cu–Zn filler metal. Interface structure and shear strength of joints were investigated, the former via electron probe microanalysis, scanning electron microscopy, and X-ray diffraction, and the latter via the shearing method. The results show the formation of three phases in the TiC ceramic–iron joint, namely, copper base solid solution, FeNi, and silver base solid solution. The highest joint shear strength of 256.5 MPa is obtained for a brazing temperature of 1173 K and brazing time of 5 min.     

CuSnTiNi钎料真空钎焊金刚石

采用两种不同比例CuSnTiNi混合单质金属粉,对金刚石在1 040℃保温5 min进行了真空钎焊试验.利用SEM,EDS及XRD对金刚石焊后界面微结构和钎料的微观组织进行了测试分析.结果表明,适合钎焊金刚石的活性成分为BCu70Sn15Ti10Ni5（质量分数,%）,该钎料能够在钎焊时首先合金化,在金刚石表面形成了断续的TiC,实现了金刚石的高强度连接,金刚石的热损伤较小,钎料组织由α-Cu固溶体、δ-Cu₃₁Sn₈等相组成,该钎料显微硬度为130~180 HV0.1,比CuSnTi有较高的硬度.     

Cold metal transfer welding–brazing of magnesium to pure copper

Magnesium alloy AZ31B and pure copper T2 were lapped and joined by cold metal transfer (CMT) welding–brazing method by AZ61A magnesium alloy wire with a 1·2 mm diameter. Results indicated that a satisfied Mg/Cu CMT welding–brazing joint was obtained in the stable welding processes with no spatter. The joint was composed of Mg–Mg welding joint formed between the Mg weld metal and the Mg base metal, and Mg–Cu brazing joint formed between the Mg weld metal and the local molten Cu base metal. The microstructure and the intermetallic compound (IMC) distribution were inspected and analysed in detail. The interfacial reaction layers of the brazing joint consisted of Mg₂Cu, Al₆Cu₄Mg₅, MgCu₂ and Mg₁₇Al₁₂ IMCs. The tensile shear strength of the Mg/Cu CMT welding–brazing joint could reach 172·5 N mm^?1. In addition, two different fracture modes were observed: at the fusion zone and at the brazing interface.     

Influence of copper on amorphous nickel based brazing alloy

Abstract

Brazing of stainless steel using nickel based alloys has sometimes been avoided, in spite of its various advantages, because it is a somewhat unreliable process in terms of the mechanical characteristics and corrosion resistance of the brazed joints. Addition of copper to amorphous Ni–Cr–B–Si brazing alloys has been shown to be a promising method of improving the performance of joints. Because copper can form a solid solution with nickel at any concentration, addition of copper has a great effect on the microstructures of the nickel based filler metal and braze seam, by improving the volume ratio of nickel based solid solution to the embrittled intermetallic compounds. As a result, a significant increase in the critical brazing clearance (CBC) was obtained in the present work. Furthermore, copper might increase the electrode potential of nickel based solid solution, so that addition of copper could improve the corrosion resistance of the brazed joints. The results show that an appropriate copper addition to the present Ni–Cr–B–Si group amorphous brazing foil provides an effective method of overcoming the weaknesses of joints brazed using conventional nickel based filler metals, such as low value of CBC and low corrosion resistance.     

水下湿法手工自蔓延焊接技术

基于自蔓延高温合成技术（SHS技术）和湿法电弧焊原理,研究了一种用于水下金属结构应急维修的新型焊接方法—水下湿法手工自蔓延焊接技术.通过焊条结构设计、焊药设计等,研制了水下燃烧型焊条,进行了焊接试验,对接头组织和性能进行了分析.结果表明,该技术可在无电、无气、无其它设备的条件下实现水下金属构件的湿法焊接,单面焊双面成形,接头抗拉强度达267 MPa,冲击吸收能量13.8 J;SEM和EDS分析表明,焊缝金属为以α-Cu固溶体为基体、有大量块状富铁第二相析出的高铁铜合金,熔合区的成分和组织与焊缝第二相基本相同,焊缝合金与熔融母材交互结晶,形成了梯度熔焊连接;拉伸断裂发生在焊缝或熔合区,断口有大量韧窝,属韧性断裂.     

Brazing of A5056 aluminium alloy with the aid of ultrasonic vibration using Ag filler metal

In order to produce a high strength brazed joint of A5056 aluminium alloy containing magnesium of about 5 mass%, the authors applied a flux-free brazing method with the aid of ultrasonic vibration to the aluminium alloy by selecting pure Ag foil as brazing filler metal and examined the effect of brazing conditions on the joint properties. The main results obtained in this study are as follows.

At a brazing temperature of 570°C, just above the eutectic point of Al–Ag binary system, application of ultrasonic vibration for 4.0 s provided the brazed joint with the maximum tensile strength and the strength decreased with the application time. When the brazing temperature was varied from 550 to 580°C and the application time of ultrasonic vibration was kept constant at 4.0 s, the joint brazed at 560°C attained the maximum tensile strength and fractured in the base metal. It was found that using a pure Ag foil as brazing filler metal successfully brazed A5056 aluminium alloy and the joint strength was equivalent to that of the base metal. Fracture of the joint was prone to occur along the (Al₃Mg₂ + Al solid solution) phase with high hardness formed at the grain boundary of the base metal. The amount of the hard (Al₃Mg₂ + Al solid solution) phase increased with the ultrasonic application time and the brazing temperature. It seemed that the increase of the hard (Al₃Mg₂ + Al solid solution) phase mainly caused the brazed joint strength to decrease.     

核电站高温用电气贯穿件馈通线钎焊密封技术

对陶瓷表面先进行金属化处理,再使用常规钎料钎焊陶瓷与金属,利用无氧铜环作为过渡层来缓解钎焊过程中产生的残余应力,可获得无焊接缺陷、气密性良好的电气贯穿件馈通线。SEM和EDS分析结果表明,无氧铜棒与无氧铜环钎焊接头主要由灰色的Cu基固溶体、白色的Ag基固溶体及Ag-Cu共晶组织组成。陶瓷与无氧铜环钎焊接头、陶瓷与可伐合金钎焊接头主要由Cu基固溶体、Ag-Cu共晶组织、Cu-Ni固溶体组成。     

Effect of hot dip aluminising on interfacial microstructure and mechanical properties of Ti/Al joint by TIG arc welding brazing

Abstract

The joint of Al 5A06 and aluminised Ti–6Al–4V dissimilar alloys was achieved by means of tungsten inert gas arc welding brazing. The effect of aluminized coating on the spreading behaviour of filler metal on Ti substrate was studied. The spreadability of liquid filler metal on the Ti substrate was enhanced obviously due to the presence of aluminised coating. The interfacial reaction layer was characterised by a uniform lamellar layer of TiAl₃ intermetallic, with a thickness of 1 μm. Sound joints with well appearance were obtained, and the optimised tensile strength of the joint reached 216 MPa. The failure initiated from the interfacial layer at the root face and then propagated within the weld seam at the upper part of the joint. Capable welding parameters were broadened by the presence of aluminised coating for dissimilar metal joining of Ti/Al.     

Development of high strength stainless steel brazed joints using rapidly solidified filler alloys

Abstract

Two types of rapidly solidified filler alloys of nominal composition Cu–40Mn–10Ni (C50) and Ni–7Cr–3·2B–4·5Si–3Fe (N82) were used for stainless steel (SS304) brazing joints. The C50 foil is crystalline in nature, whereas N82 foil shows amorphous structure. The SS304/C50/SS304 joint shows solid solution phases at interfacial area, with maximum bond strength of 500 MPa, which qualifies to 80% of base metal strength. Conversely, the SS304/N82/SS304 joint develops brittle Cr_xB_y intermetallic phases, which lowers bond strength to 330 MPa.     

Glow discharge plasma brazing of Fe–Ni alloy in vacuum

Abstract

A novel vacuum brazing technique, termed glow discharge plasma brazing, is investigated. During the brazing process, the heating temperature of base metals is proportional to the square of the operating barometric pressure and the operating voltage, and the temperature distribution of the base metals is easily regulated by means of suitable measures. The ion beam from the glow discharge anode can efficiently sputterclean the surface of the base metals and the filler metal, which improves the wetting and spreading properties of the filler metal. Unlike the traditional vacuum brazing process, a high quality braze of Fe–Ni alloy is achieved at lower vacuum (a pressure of 5– 30 Pa or higher) by using the glow discharge brazing method. The brazing technique has a promising application in industry.     

Hydrogen effusion from high strength weld metal

Abstract

Constant heating rate hydrogen thermal analyses were carried out for weld metals with tensile strengths in the range 490–1000 MPa. It was found that the hydrogen diffusion rate in the highest strength weld metal is lower by a factor of five than that in a lower strength variant. The hydrogen diffusion behaviour varied greatly between weld metal and wrought steel. Finite difference analyses indicated that this difference can be attributed to the changes in the interaction energy between a trap site and hydrogen. Using the analysis it was possible to determine apparent diffusion rates at temperatures from 20 to 300°C and explain satisfactorily the effect of plastic deformation on hydrogen diffusion in a steel.     

Microstructure characteristics and acoustic properties of laser repaired Chinese bronze bells 2300 years ago

Six broken Chinese bronze bells, unearthed from Jiu-Lian-Dun tomb of the warring states period 2300 years ago, are repaired successfully in shapes and acoustic properties by laser welding. The tone pitches of repaired bells are harmonious and well coherent with those of nearby bells. The investigation shows the weld metal has a good consistency with base metals in both microstructure and chemical components, which is the main mechanism to recover the bell's acoustic property. Besides, both the microstructure of weld and base metal are dendrites consisting of pro-eutectoid α-Cu and the eutectoid (α-Cu + δ-Cu₆Sn₅) between the dendrite arms.     

Development of Ag based brazing filler metal with low melting point

Abstract

This study was carried out to develop cadmium free silver based brazing filler metals that meet the following requirements. First, they have to have a melting point lower than that of BAg-1 brazing filler metal. Second, they have to have not only good wetting characteristics and the ability to produce a sound joint with excellent mechanical properties but also plastic formability. Using the calculated phase diagrams on Ag–Cu–Zn–Sn quaternary system alloys, the authors selected several alloys with a possibility of meeting the above requirements. The melting point and other properties, such as hardness and brazeability of the selected alloys, were evaluated. As a result, the authors successfully developed silver based brazing filler metals that have a low melting point below ～600°C and meet the above requirements by adding a small amount of indium as an alloying element into the Ag–Cu–Zn–Sn quaternary system alloy. The newly developed brazing filler metals are slightly inferior in wetting characteristics to BAg-1; however, the brazing filler metal containing ～3 mass-% indium element showed wetting characteristics comparable to those of BAg-1. Furthermore, the new brazing filler metals could produce joints with a high tensile strength equivalent to ～83% of that of a joint brazed using BAg-1.     

AZ91D镁合金电火花堆焊组织及腐蚀性能

采用与母材同质的电极材料,在AZ91D镁合金母材上进行电火花堆焊,研究了焊缝的组织、界面特征及腐蚀性能.结果表明,通过优化的工艺参数可以获得组织均匀、致密的电火花堆焊焊缝.焊缝组织晶粒尺寸在1~5μm之间,由过饱和的α-Mg相、Mg₁₇Al₁₂相以及亚稳态Al Mg相所组成;焊缝与母材之间为冶金结合,形成超薄层熔化互扩散结晶型结合界面,母材一侧没有形成明显热影响区,焊缝保持电极原有的成分;焊缝耐蚀性能优于母材,细化的晶粒组织提高腐蚀的均匀性,过饱和的α-Mg相和晶界上网状连续分布的β相降低腐蚀速率,是其耐蚀性能提高的主要因素.     

Laser brazing of alloy 600 with precious filler metals

Abstract

The diode laser brazing of Ni base heat resistant alloy with precious filler metals has been conducted using the tandem beam for preheating and brazing. A couple of 1 mm thick plates of alloy 600 (Inconel 600) were butt brazed using Au–18Ni, Ag–10Pd and Ag–21Cu–25Pd filler metals of 0·5 mm diameter with a brazing flux. Sound butt joints which were free from brazing defects such as porosity and lack of penetration could be obtained at brazing clearances of 0·1–1·5 mm. The tensile strength of the braze joint produced using Ag–Pd filler metal increased with decreasing brazing clearance and reached ～70% of the base metal strength at a brazing clearance of 0·1 mm while those obtained by using Au–Ni and Ag–Cu–Pd filler metals were comparable with the base metal strength at any clearances between 0·1 and 1·5 mm. The laser brazing technique could be successfully applied to the brazing of Ni base superalloy to attain a joint with high performance and reliability.     

钢/铝管磁脉冲辅助半固态钎焊界面行为

结合电磁成形技术和半固态钎焊技术,提出了一种钢/铝管磁脉冲辅助半固态钎焊工艺,利用电磁脉冲产生的洛伦兹力使铝外管高速碰撞半固态钎料,通过半固态钎料中固相颗粒对母材表面径向压缩和轴向剪切作用去除母材表面氧化膜,实现钢铝异种管材的无钎剂钎焊. 在不同工艺参数下进行了钢/铝管磁脉冲半固态钎焊试验,研究了钎焊接头界面元素的扩散行为和金属间化合物的生长机理. 结果表明,焊缝组织主要为α-Al以及富锌相,铝侧界面处的Al₂O₃氧化膜破碎与去除情况良好,钢侧界面处有薄层FeAl₃金属间化合物形成,各部位均获得较好的冶金结合.     

Effect of cathodic protection on ductility of X65 linepipe steel weldments

Abstract

The combined effects of strain rate, monotonic loading, and cathodic protection and overprotection on the mechanical properties of X65 linepipe steel parent plate and gas metal arc weld metal have been investigated in NaCl solution. The results obtained on longitudinal all parent plate and all weld metal specimens indicate that the latter material, having a higher hardness and strength level, is more susceptible to environmental cracking due to cathodically evolved hydrogen entering the steel. However, with transverse specimens, taken perpendicular to the weld, the gauge length contains parent plate, heat affected zone material, and weld metal. In this case, irrespective of the greater inherent susceptibility of the weld metal, environmental cracking and failure always occur in the parent plate. This result is attributed to the ultimate tensile strength of the lower strength parent plate being exceeded at stress levels significantly lower than the yield strength of the higher strength weld metal. The practical implications of these results are discussed. In addition, the results are presented of a fractographic analysis which relates the morphology of the environmentally induced fracture surfaces to microstructural features in the weld metal and the parent plate.     

Measurement of surface temperature of weld pools by infrared two colour pyrometry

Abstract

In this research, two colour pyrometry was conducted to obtain the surface temperature of weld pools, in which the weld pool was photographed by a high speed camera during arc welding. Two wavelengths (950 and 980 nm) of light in the infrared range were selected from the thermal radiation light emitted from the weld pool at the instant when the arc was extinguished, using an imaging spectroscope. Consequently, in gas tungsten arc welding, it was shown that the surface temperature distribution of a weld pool is affected by the sulphur content in the base metal. It is thought that this temperature distribution is determined by the balance between the driving forces of viscous drag from the cathode jet of plasma and Marangoni surface tension. In gas metal arc welding, it was seen that the surface temperature distribution becomes uniform and the temperature is 1715–1845 K, which is obviously lower than that of the metal droplet.