Interfacial structure of the joints between magnesium alloy and mild steel with nickel as interlayer by hybrid laser-TIG welding

The joint interface of Mg alloy to steel with Ni interlayer was investigated. Comparing with that without any interlayer, the joint shear strength was improved significantly. The characterization of interfaces in the joint with Ni interlayer was analyzed and discussed. The results show that the formation of intermetallic compound Mg₂Ni and solid solution of Ni in Fe at the interface altered the bonding mode of joints which contributed to the increase of the tensile shear strength in contrast to the direct joining of Mg alloy to steel. Owing to the addition of Ni interlayer, the conclusion is that the bonding mode of Mg alloy to steel from mechanical bonding to semi-metallurgical joining.     

Effects of copper addition on microstructure and strength of the hybrid laser-TIG welded joints between magnesium alloy and mild steel

Lap joint of magnesium alloy AZ31B to mild steel Q235 with the addition of copper interlayer by hybrid laser-TIG welding technique was investigated. The microstructure, element distribution at interfaces, and intermediate phases of joints were examined by scanning electron microscopy (SEM), electron probe micro-analyzer (EPMA), and X-ray diffraction (XRD), respectively. The results showed that intermetallic compounds Mg₂Cu with rod-like structure in the joint and equiaxed structure at interface were found, and the bonding between copper and steel was realized by mixing of copper and steel at upper margins of molten pool and a little solid solution of copper in iron at the bottom and side of molten pool. Besides, comparing with that without any interlayer, the wettability of molten magnesium alloy on steel was enhanced, which led to an intimate connection. In the end, the joining mechanism of magnesium–steel joints with copper interlayer was discussed.     

Strengthening effect of nickel and copper interlayers on hybrid laser-TIG welded joints between magnesium alloy and mild steel

AZ31B magnesium alloy and Q235 mild steel were lap joined with Ni and Cu interlayers using hybrid laser-TIG welding technique. Microstructure and mechanical properties of joints were examined. The results showed that the shear strength of Cu-added joint was a little higher than that of Ni-added joint, and the strength of both joints exceeded that of base material AZ31B Mg alloy. Microstructure in fusion zone of the both joints was in great difference and the comparison of microhardness profile in the fusion zone indicated that the morphology and distribution of intermediate phases played a vital role in strengthening the joints, and the strengthening effect of them on Cu-added joint was better than that on Ni-added joint.     

Study on laser‐tungsten inert gas hybrid welding of dissimilar Mg alloy and steel with Ni as interlayer

Dissimilar Mg alloy and Q235 steel lap joints are produced by Laser‐ tungsten inert gas (TIG) hybrid welding with Ni as an interlayer. Fe and Ni are joined together in the form of solid solution, while Mg alloy and Ni foil are joined together by intermetallic compound Mg₂Ni. During tensile testing, the joints fail at the interface between Ni foil and Mg alloy. The shear strength of the Mg/Steel joints with Ni as interlayer is 170 MPa, which is higher than that without interlayer 120MPa.     

Interface microstructure and mechanical properties of arc spot welding Mg–steel dissimilar joint with Cu interlayer

A novel technology was developed for the arc spot welding of AZ31 Mg alloy to Q235 steel with Cu as interlayer. The mechanisms of bonding dissimilar materials were investigated using mechanical and metallurgical examinations. Results show that the joining of Mg alloy to steel with Cu involved two bonding mechanisms: weld-brazing by the Cu transition layer at the interface edge and bonding by a micron-scale composite transition layer of Al₃Cu₄Fe₃ and Fe₄Cu₃ intermetallic phases at the interface center. The additional reaction of Cu increased the reaction temperature and composition ranges at the interface. It also elicited a bridge effect that improved the weldability of Mg alloy and steel by new formed phases.     

Microstructure and mechanical properties of diffusion bonded SiC/steel joint using W/Ni interlayer

This paper describes the design and examination of W/Ni double interlayer to produce a joint between SiC and ferritic stainless steel. Diffusion bonding was performed by a two steps solid state diffusion bonding process. Microstructural examination and mechanical properties evaluation of the joints show that bonding of SiC to steel was successful. EDS and XRD analysis revealed that W₅Si₃ and WC were formed at SiC/W interface. The diffusion products at W/Ni interface, Ni-rich solid solution Ni(W) or intermetallic compound Ni₄W, was found to be dependent on the second step joining temperature. Neither intermediate phases nor reaction products was observed at Ni/steel interface for the joints bonded at the temperature studied. The average tensile strength of 55 MPa which is insensitive to the second step process was measured for as-bonded SiC/steel joint and the failure occurred at SiC/W interface. The hardness near the various bonded interfaces was also evaluated.     

Effect of Ni interlayer on characteristics of diffusion bonded Mg/Al joints

Magnesium and aluminium were joined through diffusing bonding with a Ni interlayer prepared by plasma spraying for the first time. Examination of the microstructure and phase constitution of interfacial regions indicated that Mg–Al reaction was successfully prevented in the presence of the Ni interlayer. With the elevation of temperature, a reaction layer of Mg₂Ni intermetallic was formed at Mg/Ni interface but few Al–Ni intermetallic was generated at Al/Ni interface. The mechanical test results showed that the tensile strength of the Mg/Al joint was substantially improved compared to that of the direct joint of Mg and Al. A maximum value of 5.8?MPa was obtained at 420°C for the joint with Ni interlayer.     

5A06/TA2 diffusion bonding with Nb diffusion-retarding layers

The structure and performance of 5A06/TA2 diffusion bonding joints with or without Nb diffusion-retarding layers were studied by means of scanning electron microscopy (SEM), X-ray diffraction (XRD) and shear strength measurement. The results showed that a diffusion reaction occurred and Al₁₈Ti₂Mg₃ was formed, which markedly decreased the joint strength, and the highest shear strength of 5A06/TA2 joint in direct bonding was 83 MPa. The Nb interlayer impeded the diffusion of Mg atoms from the Al side to the Ti side and also retarded the diffusion of Ti atoms from the Ti side to the Al side, which was acting as a diffusion-retarding layer. The joint strengths were increased by the Nb diffusion-retarding layers, and the highest shear strength reached 105 MPa. When Ti diffused across the Nb layer and achieved saturation nearby the interface with Al alloy, the diffusion reaction of Ti, Al and Mg occurred and Al₁₈Ti₂Mg₃ appeared which decreased the joint strength.     

Microstructural characteristics of lap joint between magnesium alloy and mild steel with and without the addition of Sn element

Lap joint of AZ31B Mg alloy to Q235 steel by hybrid laser-TIG welding was studied. Microstructures of Sn-free and Sn-added joint were investigated, and the intermediate phase of Sn-added joints was also inspected. In contrast with the Sn-free joints, intermetallic compound Mg₂Sn with dendritic structure distributed in the grain boundaries of Mg alloy was identified; Gaps at the interfaces were vanished as the wettability of Mg alloy with the addition of Sn on steel was improved. Big particles in fusion zone became even smaller or disappeared in the Sn-added joints.     

化学镀锡层对镁铝异种金属超声波焊接的影响

为提高镁铝异种金属超声波焊接接头强度,预先在铝合金表面镀锡后进行镁铝异种金属超声波点焊,并对接头的微观组织和力学性能进行分析.研究表明:无镀锡层的镁铝超声波焊接接头界面出现了大量的Mg_3Al_2和Mg_(12)Al_(17)相,其接头的最大拉伸剪切强度为27.5 MPa;含镀锡层的铝镁超声波焊接结合区由镁锡反应扩散层、残余锡层和铝锡反应扩散层组成,其中,铝锡反应层是固溶体层,镁锡反应层主要是过饱和的固溶体基体及弥散析出的中间相Mg_2Sn,其接头的最大拉伸剪切强度为32.9 MPa.镀锡层的加入有效阻止了镁铝的相互扩散,抑制了硬脆的Mg-Al系金属间化合物的生成,提高了镁铝超声波焊接接头强度,与镁铝超声波焊接相比最大拉伸剪切强度提高了19.6%.     

Effect of Ni interlayer on partial transient liquid phase bonding of Zr–Sn–Nb alloy and 304 stainless steel

Zr–Sn–Nb alloy and 304 stainless steel were joined by means of partial transient liquid phase bonding. The effects of Ni interlayer on the microstructure and properties of the joints were investigated. The reaction layers are formed in both joints and which are mainly composed of σ-FeCr layer, Zr(Cr, Fe)₂ + α-Zr layer and α-Zr + Zr₂(Ni, Fe) layer. The intermetallic compounds are compact relatively and cracks are formed in the reaction layer of the direct bonded joint. In the joint with Ni interlayer, many α-Zr phases dispersedly exist in the reaction layer and the thickness of the reaction layer is distinctly larger than that without Ni interlayer. As a result of lower residual stresses and wider crack-free reaction layer, the bonding strength of the joint increases by using Ni interlayer.     

Ni–Cu alloy for diffusion bonding cermet/steel in air

Microstructural and mechanical evaluation for joints obtained by static and dynamic diffusion bonding of a 90MnCrV8 high strength steel coated with WC–Co, using a Ni–Cu alloy as interlayer, are shown in the present work. In all joints different reacted zones generated during the bonding process can be distinguished by means of scanning electron microscopy and dispersive X-ray spectrometry. The maximum tensile strength obtained using dynamic diffusion bonding process confirms a very promising technology for industrial applications.     

Effect of gradient thermal distribution on butt joining of magnesium alloy to steel with Cu–Zn alloy interlayer by hybrid laser–tungsten inert gas welding

Experimental investigations on butt welding of magnesium alloy to steel by hybrid laser–tungsten inert gas (TIG) welding with Cu–Zn alloy interlayer are carried out. The results show that the gradient thermal distribution of hybrid laser–TIG welding, controlled by offset adjustment, has a noticeable effect on mechanical properties and microstructure of the joints. Particularly, at the offset of 0.2 mm, defect-free joints are obtained, and the tensile strength could attain a maximum value of 203 MPa. Moreover, the fracture of the joint with the 0.2 mm offset happens in the weld seam of Mg alloy instead of the Mg/Fe interface. Owning to the addition of the Cu–Zn alloy interlayer, a metallurgical bonding between Mg alloy and steel is achieved based on the formation of intermetallic compounds of CuMgZn and solid solutions of Cu and Al in Fe. Meanwhile, the same element distribution tendency of Fe and Al indicates the intimate interaction between Fe and Al in current experimental conditions.     

Application of Ni and Cu nanoparticles in transient liquid phase (TLP) bonding of Ti-6Al-4V and Mg-AZ31 alloys

The transient liquid phase (TLP) bonding of Ti-6Al-4V alloy to a Mg-AZ31 alloy was performed using an electrodeposited Ni coating containing a dispersion of Ni and Cu nanoparticles. Bond formation was attributed to two mechanisms; first, solid-state diffusion of Ni and Mg, followed by liquid eutectic formation at the Mg-AZ31 interface. Second, the solid-state diffusion of Ni and Ti at the Ti-6Al-4V interface resulted in a metallurgical joint. The joint interface was characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction analysis. Microhardness and shear strength tests were used to investigate the mechanical properties of the bonds. The use of Cu nanoparticles as a dispersion produced the maximum joint shear strength of 69 MPa. This shear strength value corresponded to a 15 % enhancement in joint strength compared to TLP bonds made without the use of nanoparticles dispersion.     

Microstructure and mechanical properties of diffusion bonded W/steel joint using V/Ni composite interlayer

Diffusion bonding between W and steel using V/Ni composite interlayer was carried out in vacuum at 1050 °C and 10 MPa for 1 h. The microstructural examination and mechanical property evaluation of the joints show that the bonding of W to steel was successful. No intermetallic compound was observed at the steel/Ni and V/W interfaces for the joints bonded. The electron probe microanalysis and X-ray diffraction analysis revealed that Ni₃V, Ni₂V, Ni₂V₃ and NiV₃ were formed at the Ni/V interface. The tensile strength of about 362 MPa was obtained for as-bonded W/steel joint and the failure occurred at W near the V/W interface. The nano-indentation test across the joining interfaces demonstrated the effect of solid solution strengthening and intermetallic compound formation in the diffusion zone.     

Diffusion bonding of titanium alloy to stainless steel wire mesh

Abstract

The feasibility and appropriate processing parameters of diffusion bonding of titanium alloy to stainless steel wire mesh directly and with a nickel interlayer have been investigated. The microstructures of the diffusion bonded joints were observed by optical microscopy, scanning electron microscopy, X-ray diffraction, and electron probe microanalysis and the main factors affecting diffusion bonding were analysed. The maximum shear strengths of the joints were 72 and 148 MPa for direct bonding and indirect bonding using a nickel interlayer respectively. Atomic diffusion and migration between titanium and iron are effectively prevented by adding pure nickel as the interlayer metal, and a firm joint is obtained.     

Comparative study on microstructure and mechanical properties of laser welded–brazed Mg/mild steel and Mg/stainless steel joints

A laser welding–brazing (LWB) technology using Mg based filler has been developed for joining Mg alloy to mild steel and Mg alloy to stainless steel in a lap configuration. Microstructure and mechanical properties of laser welded–brazed lap joints in both cases were comparatively studied. The results indicated that no distinct reaction layer was observed at the interface of Mg/mild steel and subsequently the interface was confirmed as mechanical bonding, whereas an ultra thin reaction layer with a continuous and uniform morphology was evidenced at the Mg/stainless steel interface, which was indicative of metallurgical bonding. The newly formed interfacial layer was indexed as FeAl phase by transmission electron microscopy (TEM) combined with energy dispersive spectroscopy (EDS). The average tensile–shear strength of Mg/mild steel joint was only 142 N/mm with typical interfacial failure, while that of Mg/stainless steel joint could reach 270 N/mm, representing 82.4% joint efficiency relative to the Mg alloy base metal. The fracture location of Mg/stainless steel joint was at Mg fusion welding side, suggesting the interface was not weak point due to the formation of ultra thin interfacial layer. The role of alloying elements in base metal and bonding mechanism of the interfacial layer were discussed, respectively.     

Effect of Ni interlayer on strength and microstructure of diffusion-bonded Mo/Cu joints

Mo and Cu were bonded successfully by means of diffusion bonding using a Ni interlayer. The tensile strength of the joint increases firstly and then decreases with the bonding temperature or holding time increases. Compared with 79 MPa which was the maximum value of Mo/Cu joint, the maximum tensile strength of joint with Ni interlayer was 97 MPa. The interfacial structure of the joints was studied by SEM, EPMA, EDS and XRD, the results showed that the different atoms diffused to each other in the bonding process and no intermetallic compound appeared. MoNi and NiCu solid solutions formed in the joint. The fracture of the joint had taken place in the Mo/Ni interface rather than in the Ni/Cu interface and the fracture way of the joints was brittle fracture.     

Mg/Zn/Al瞬间液相过冷连接界面的组织与性能研究

采用瞬间液相过冷连接方法对AZ31镁合金/锌中间层/5083铝合金进行连接,利用SEM、XRD、拉伸实验机和微观硬度计对结合界面的微观组织、力学性能进行了表征。结果表明,以锌作中间层,采用瞬间液相过冷连接可以实现AZ31镁合金与5083铝合金的有效连接,接头的最高抗拉强度可以达到38.5MPa,随着低温扩散保温时间的延长,扩散层厚度随之增加,接头的抗拉强度也随之升高;接头的拉伸断口属于脆性断裂,结合界面形成了MgZn2和少量的Mg17Al12金属间化合物;结合界面的微观硬度最高达170。     

XRD and SEM analysis near the diffusion bonding interface of Mg/Al dissimilar materials

The microstructure and phase constitution near the diffusion bonding interface of Mg/Al dissimilar materials are studied using a scanning electron microscope (SEM), X-ray diffraction (XRD) and transmission electron microscope (TEM). The test results indicated that an obvious diffusion zone was formed near the Mg/Al interface during the vacuum diffusion bonding. The diffusion transition zone near the interface consists of various Mg_xAl_y phases. The transition region on the Mg side mainly consists of Mg crystals, and the new phase formed was the Mg₃Al₂ phase having a face-centred cubic lattice. This is favorable for improving the combined strength of Mg substrate and diffusion transition zone.