Explosive welding: Mixing of metals without mutual solubility (iron-silver)

The results obtained for joints of dissimilar metals, iron-silver (earlier, copper-tantalum), which form immiscible liquid suspensions, explain why they are mixed in explosive welding. Inhomogeneities of the wavy interface, such as protrusions and zones of localized melting, were observed. The effect of granulating fragmentation, which is responsible for crushing initial materials into particles, was understood as one of the most efficient ways to dissipate the supplied energy. It is shown that, in the case of joints of metals without mutual solubility, zones of localized melting represent colloidal solutions, which form either emulsions or suspensions. At solidification, the emulsion represents a hazard for joint stability due to possible separation; on the contrary, suspension can enable the dispersion strengthening of the joint. The results can be used in the development of new metal joints without mutual solubility.     

Electron-microscopic examination of the transition zone of aluminum-tantalum bimetallic joints (explosion welding)

A study of the structure of an aluminum-tantalum joint and a comparison of this structure with the structures of iron-silver and copper-tantalum joints have revealed the following processes of the interpenetration of the materials that occur during explosion welding: the formation of protrusions, the injection of particles of one material into the other, and the formation of zones of local melting. Regardless of the mutual solubility of the metals being welded, two types of fragmentation occur, i.e., (1) a granulating fragmentation (GF), which includes the formation, explosion-governed (EG) dispersion, and partial consolidation of particles, and (2) the fragmentation that is usually observed during severe plastic deformation. It is important that this traditional fragmentation is not accompanied by the formation and EG dispersion of particles. This feature allows one to easily distinguish these types of fragmentation (traditional and GF fragmentation).     

The structure of molten zones in explosion welding (aluminium–tantalum,copper–titanium)

Investigations were carried out into the relief of the flat- and wave-shaped interfaces for explosion-welded aluminium–tantalum and copper–titanium welded joints. For these systems, characterized by a relatively high mutual solubility of the initial elements, the results show a typical set of the structures of the interfaces replacing each other with the intensification of the welding conditions. The unusual shape of the projections on the flat interfaces was found. They are similar to splashes, which form on the surface of the liquid, although they are solid-phase splashes. The vortex structure of the zones of local melting was also detected. The unusual shape of the waves was found: in the presence of mutual solubility they consist of the specially ordered set of projections. It may be assumed that this is caused by the formation of intermetallic compounds on the surface of the projections. The processes of self-organization, ensuring the evolution of the relief of the interface in the intensification of the welding conditions, have been investigated. The role of intermetallic compounds in these self-organization processes is clarified.     

碳钢-不锈钢爆炸焊接复合板界面的显微结构

通过力学性能测定、SEM检测以及EDS线扫描分析,分别观察了焊态及退火态碳钢-不锈钢爆炸焊接复合板结合界面的显微结构,研究了爆炸焊接形成的波状界面和界面间的过渡层.结果表明,该碳钢-不锈钢复合板的结合界面属于大波状结合界面,这种大波状界面并未使复合板的力学性能出现明显的降低,在爆炸焊接形成结合界面处出现了微观熔化现象,形成了一个宽度仅5μm左右的扩散过渡层.     

Interface Phenomena and Bonding Mechanism in Magnetic Pulse Welding

Magnetic pulse welding (MPW) is a solid-state impact welding technology that provides metallurgical joints while exhibiting a negligible heat-affected zone. The MPW process is a high speed single shot welding technique used mainly for joining tubular components in a lap configuration and characteristic length scales of few millimeters to centimeters. It is similar in operation to explosive welding and shares the same physical principles. The nature of bonding in MPW is not sufficiently understood yet and some controversial explanations are reported in the literature. The two major ideas are based on either solid state bonding or local melting and solidification. The present work summarizes our current understanding of the bonding mechanism and the structure in various similar and dissimilar metal pairs joined by MPW.     

NEW ACHIEVEMENTS ON THE THEORY AND TECHNOLOGY OF EXPLOSIVE WELDING

There are four new achievements of this work on the theory and technology of explosive welding.(1) It has been found and defined three kinds of bonding interfaces: big wavy, small wavy and micro wavy, and the micro wavy interface is the best. In a cladding plate, it is for the first time to find that the form of interface presents regular distribution.(2) Although the interface has the features of melt, diffusion and pressure welding in the mean time, the seam and "hole" brought by the melt weaken the bonding strength of interface greatly, and the effect of melt on interface must be eliminated in explosive welding, so explosive welding is not a melt weld. The diffusion welding is a kind of form of pressure welding, and the diffusion is not the reason of the bonding of interface but the result of interface high pressure. So the diffusion welding cannot also explain the bonding mechanism of it. The experiment and theory make clear that explosive welding is a special pressure one.(3) To get good interface     

Numerical study on mechanism of explosive welding

Abstract

Explosive welding technology has been widely used in industrial production. However, there is always a controversy on the mechanism of explosive bonding, whether explosive welding should belong to a kind of mature welding such as a fusion welding or a solid phase welding. Based on the observation and analysis of the metallographs at interfaces, various opinions are proposed by different authors. This paper investigated the various mechanisms of the wavy interface formation in explosive welding and tried to determine a more reasonable one by using smoothed particle hydrodynamics method. The numerical analysis results show that explosive welding is a unique and complex kind of welding. In general cases, high pressure and melted particles can be found in the collision area at the interface. A version, in which explosive welding is a combination of diffusion bonding, fusion bonding and pressure welding, is considered as a more reasonable one.     

Structural Transformations Occurring upon Explosive Welding of Alloy Steel and High-Strength Titanium

Features of the structure of a layered material welded by explosion of high-strength titanium alloy and tool roller steel with an intermediate layer of the structural low-carbon steel have been studied. The structural transformations occurring in materials upon their dynamic interaction have been analyzed. Particular attention is paid to the structure of vortex zones formed at the interfaces of billets of various steels, as well as structural steel and titanium-based alloy. The structural analysis methods made it possible to fix stable and metastable joints appearing upon the explosive welding of various metals. To reveal features of structural transformations caused by prolonged heating, billets of titanium alloy and structural steel were also joined by diffusion welding. It has been shown that, in the course of the diffusion welding process, a continuous layer of stable brittle intermetallic compounds is formed along the entire interface of the welded materials. In the explosively welded materials, the intermetallic phases are distributed locally and, thus, they have a weaker embrittlement effect.     

Application of high velocity impact welding at varied different length scales

Three complementary impact welding technologies are described in this paper. They are explosive welding, magnetic pulse welding, and laser impact welding, which have been used to provide metallurgical bonds between both similar and dissimilar metal pairs. They share the physical principle that general impact-driven welding can be carried out by oblique impact but are used at different length scales from meters to sub-millimeter. The different length scales require different kinds of systems to drive the process, and the scales themselves can give different weld morphologies. Metallographic analysis on cross-sections shows a wavy interface morphology which is likely the result of an instability associated with jetting, which scours the surfaces clean during impact. The normalized period and amplitude of the undulations increase with increasing impact energy density. Microhardness testing results show the impact welded interface has a much greater hardness than the base metals. This can lead to weldments that have strengths equal to or greater than that of the weakest base material.     

Behavior and mechanism of the bonding interface of 0Cr18Ni9/16MnR by explosive welding

In order to investigate the bonding behavior and mechanism of the interface prepared by explosive welding,the bonding interfaces of OCr18Ni9/16MnR were observed and analyzed by means of optical microscope(OM),scanning electron microscope(SEM)and electron probe microanalysis(EPMA).It is found that the welding interfaces are wavy due to the wavy explosive loading.There are three kinds of bonding interfaces i.e.big wave,small wave and micro wave.There are a few seam defects and all elements contents are less than both of the base and flyer plate in the transition zone of big wavy interface.Moreover,some"holes"result in the lowest bonding strength of big wavy interface nearby the interface in the base plate.All elements contents of the small wavy interface are between two metals,and there are few seam and hole defects,so it is the higher for the bonding strength of small wavy interface.There is no transition zone and defects in the micro wavy interface,so the interface is the best.To gain the high quality small and micro wavy bonding interface the explosive charge should be controlled.     

Structure of boundaries in composite materials obtained using explosive loading

We have presented the results of studying the fine structure of interphase boundaries for a number of composite materials obtained by methods of explosive welding and explosive compacting of powder mixtures. Joints of different metals (titanium-low-carbon steel, copper-tantalum) and metals with refractory carbides (chromium carbide-titanium) have been investigated. Under welding, pairs differed from each other by the type of interaction. It has been found that, in these composites, interphase boundaries exhibit a final thickness on the order of 200 nm, throughout which the composition of the material changes gradually from a composition that corresponds to one of the components of the composite to a composition that corresponds to the second component. It has been shown that the structure of interphase boundaries is complex. With the limited solubility of components along boundaries, two fairly thick crystalline interlayers are detected, the total thickness of which is equal to the total thickness of the boundary; between the interlayers, there is a thin (to 5–7 nm in thickness) interlayer with a crystalline or amorphous structure.     

水下爆炸焊接制备NiTi合金与铜箔复合板

应用水下爆炸焊方法进行了NiTi形状记忆合金与铜箔的爆炸焊研究．利用大型有限元软件ANASYS／LS-DYNA对水下爆炸冲击波驱动飞板的飞行过程进行了数值模拟．飞板的飞行速度与爆炸焊产生射流的最小碰撞速度对比表明,可以实现焊接．通过分析微观组织和断裂机理,评估复合板焊接效果．结果表明,微观组织观察显示界面为连续均匀的波纹形态,界面结合处无裂纹,焊接性能良好．断口形貌分析显示断裂主要表现为解理和准解理断裂,界面处端口形貌与微观组织形态观察一致．水下爆炸焊方法将解决脆性、薄板金属用传统爆炸焊方法难以焊接的问题．     

Laser welding of components of different thickness made of dissimilar metals

The results of investigations into laser welding of components of different thicknesses produced from dissimilar metals are presented. The experimental results show that uniform heating of the weld edges is achieved by producing welded joints with a bead on the thin wall component, with the height of the bead 3–4 times greater than the thickness of the component. Experiments were carried out to investigate pulsed laser welding of components of different thicknesses made of dissimilar metals. The experimental results confirm that the mutual melting of the beads takes place without lack of fusion defects and burning in the welded joints only when the optimum dimensions of the beads are adhered to.     

Interfacial surface relief in explosive welding of homogeneous materials

ABSTRACT

Changes of the microstructure of the interface in intensification of the explosion welding conditions for the copper – cupronickel alloy, simulating the copper–copper homogeneous pair are investigated. Typical wavy structures were produced at the interface. The results were compared with the special features of the relief of joints such as Cu–Ta, Cu–Ti and titanium–orthorhombic titanium aluminide. Heterogeneities were found at the interface: projections, local melting zones, groups of projections, leading to imperfect interfaces, branching of the interface, intersection and convergence of the bands. A quasi-wave surface was found in the vicinity of the flat interface (slightly above it) which contains sections of bands and almost circular islands, away from the bands. Large unfinished rotated areas (macro-rotations) were found in the solid phase.     

碳钢爆炸焊界面形貌预测及影响因素分析

为完善爆炸焊波状界面形成机理和特性,并探究界面形貌的量化预测分析方法,文中以流体弹塑性模型为基础,结合多组钢/钢、钛/钢爆炸焊试验结果,定性地分析了基板材料强度与飞板冲击强度对爆炸焊界面形貌的影响,并定量推导了界面形貌的量化计算方法。结果表明,在相同的爆炸焊条件下,界面的波纹形貌受基板材料强度及飞板冲击强度的影响十分明显,且界面比波长随比强度的变化趋势存在明显的流动限拐点;拐点前比波长随比强度的增大而迅速上升,拐点后比波长受比强度的影响较小并随比强度的增大而逐渐平稳。以比强度为主要变量,结合流体弹塑性模型及可焊窗口理论构建的界面形貌预测计算公式在钢/钢、钛/钢材料的爆炸焊试验中均呈现了较好的定性分析效果;以比强度作为分析爆炸焊界面形貌主要特征变量之一的方法在性能与碳钢接近的金属中具有一定的参考价值。创新点： (1)完善了爆炸焊波状界面发展特性,并提出了界面比波长随比强度发展的过程中存在流动限拐点。(2)以流体弹塑形模型及可焊窗口理论为基础构造了爆炸焊界面比波长关于比强度的定量分析公式。     

Influence of the parameters of a high-frequency acoustic wave on the structure,properties, and plastic flow of metal in the zone of a joint of materials welded by ultrasound-assisted explosive welding

The results of an investigation of the influence of the parameters of high-frequency acoustic wave on the structure and properties of the zone of joint of homogeneous metals bonded by explosive welding under the action of ultrasound have been presented. The influence of the frequency and amplitude of ultrasonic vibrations on the structure and properties of the explosively welded joints compared with the samples welded without the application of ultrasound has been established. The action of high-frequency acoustic waves on the metal leads to a reduction in the dynamic yield stress, which changes the properties of the surface layers of the metal and the conditions of the formation of the joint of the colliding plates upon the explosive welding. It has been shown that the changes in the length and amplitude of waves that arise in the weld joint upon the explosive welding with the simultaneous action of ultrasonic vibrations are connected with a decrease in the magnitude of the deforming pulse and time of action of the compressive stresses that exceed the dynamic yield stress beyond the point of contact.     

Structure formation and properties of a copper–aluminum joint produced by ultrasound-assisted explosive welding

The effect of ultrasound-assisted explosive welding on the structure formation and the properties of copper–aluminum joints is studied. Ultrasound-assisted explosive welding improves the quality of formed copper–aluminum joints, i.e., enhances their strength and significantly reduces the amount of fused metal over the entire weldability range. It is shown that ultrasound-assisted explosive welding can noticeably extend the weldability range of the copper–aluminum pair to obtain equal-in-strength joints with minimum structural heterogeneity in the wide welding range.     

铝/钛复合管爆炸焊接三维数值模拟

复合管爆炸焊接在工艺上的差异性决定了其焊接过程与复合板焊接过程不同,而复合管爆炸焊接作用空间的相对密闭导致观察和分析其焊接过程的困难,通过软件AUTODYN模拟出了复合管爆炸焊接过程,在验证模型正确有效的基础上,分析了复合管射流产生以及结合界面波形结构的独特性,发现射流产生波状结合满足侵彻机理假说.对比爆炸焊接试验结果表明,模拟结果与试验结果具有良好的一致性,这为研究复合管波形结构以及射流形成机理等提供了重要手段.     

爆炸焊接铝/不锈钢薄壁复合管界面的微观分析

采用扫描电镜、能谱仪和显微硬度计对爆炸焊接铝，不锈钢薄壁双金属复合管界面的显微组织、成分和硬度梯度进行了分析研究。结果表明，结合良好的薄壁铝，不锈钢复合管的结合区界面，是平直界面和平直至波形过渡的非稳态波形界面二者混合出现；元素在界面扩散主要是Fe，Cr，Ni元素向Al层内进行扩散，Al元素向不锈钢层内扩散量极少，界面附近不锈钢侧有明显硬化现象；由于热影响消除了铝层硬化现象。在Al侧出现的由超塑流变造成的组织变化，并没有从硬度分布表现出来；需要严格控制爆炸焊接静态参数，尽量减少Al-Fe化合物脆性相生成量。     

Study on weldability window and interface morphology of steel tube and tungsten alloy rod welded by explosive welding

The explosive welding of the axisymmetric 30CrMnSi tube and tungsten alloy rod was studied. Through theoretical analysis, the weldability window of these two metals was obtained, which could enable the prediction of the welding interface morphology under different explosive conditions. The explosive welding tests under different explosive loading conditions were carried out and 30CrMnSi/tungsten alloy composite rods were obtained. Analytical investigations of the microstructure, hardness, and composition of the samples were performed. The results showed that 30CrMnSi steel tubes and tungsten alloy rods could be successfully welded together. The welding interfaces of composite rods obtained under different explosive loads had different morphological characteristics. With the increase in the explosive load, the welding interface transforms from a straight interface to a corrugated one and even forms a melting transition zone at the interface. The chemical compositions of the transition zone showed that the region consists of two kinds of welded materials. It indicated that the temperature at the interface during the welding process exceeded the melting temperature of the tungsten alloy, and both of the welded materials generated melting phenomena.