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.     

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%.     

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.     

中间层Ni对TC4/2A14异种金属搅拌摩擦焊接头组织和性能的影响

目的 添加0.05 mm厚的Ni箔作为中间层,对3 mm厚的TC4钛合金和2A14铝合金进行搅拌摩擦焊,分析Ni对接头力学性能的影响。方法 采用扫描电镜、EDS能谱及XRD衍射等微观表征分析方法,对焊接接头的断口形貌、成分进行分析,探究Ni箔对焊接接头力学性能的影响。结果 由于钛合金和铝合金存在较大的物理化学性能差异,Ti/Al异种金属焊接性较差,界面容易产生TiAl3、TiAl、Ti3Al等金属间化合物,其中脆性相TiAl3对接头性能的影响最大,会导致综合力学性能下降。当加入中间层材料Ni后,由于Ni与Al晶体结构均属于面心立方,因此Ni与Al的扩散系数大于Ti与Al的扩散系数,Ni和Al之间优先形成金属间化合物且弥散分布于焊缝中,从而缩短了Ti与Al之间的相互扩散时间,减少了TiAl3相的生成。结论 在未添加中间层材料时,接头平均抗拉强度为237.3 MPa,约为2A14铝合金母材抗拉强度的56.7%;当添加中间层Ni后,对焊缝中金属间化合物的种类和数量进行了调控,减少了对性能影响最大的TiAl3相的生成,接头平均抗拉强度达到285.3 MPa,为2A14铝合金母材抗拉强度的68%。     

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.     

钛网添加对镁/铝复合板微观组织和力学性能影响研究

目的 有效抑制镁/铝复合板界面处金属间化合物的形成。以钛网为中间金属夹层,研究它对镁/铝复合板微观组织和力学性能的影响。方法 利用复合轧制技术制备以钛网为中间金属夹层的镁/铝-钛复合板,采用扫描电子显微镜(SEM)、电子背散射衍射仪(EBSD)、万能试验机等对复合板退火前后的微观组织和力学性能进行表征和分析,系统研究中间层钛网对轧制态和退火态复合板微观组织、织构、拉伸性能、界面结合强度的影响规律。结果 中间层钛网均匀分布在镁/铝-钛复合板界面处,钛网的添加能有效抑制复合板退火过程中镁-铝金属间化合物的连续生长,减少金属间化合物的数量。与镁/铝复合板相比,钛网的添加对轧制态和退火态复合板中镁层和铝层的平均晶粒尺寸和织构类型的影响较小。与镁/铝复合板相比,钛网的添加降低了轧制态复合板的界面剪切强度和延伸率,但极大提升了退火态复合板的界面剪切强度、拉伸强度和延伸率。结论 中间层钛网的添加可有效减少复合板界面处金属间化合物的数量,提升退火态复合板的综合力学性能。     

Interfacial structure and strength on Ti(C,N) joint using liquid phase diffusion bonding with Ti/Ni interlayer

Abstract

Partial transient liquid phase diffusion bonding (PTLP-DB) on Ti(C,N) cermet was studied in the present paper using Ti/Ni/Ti foil sandwich structure as the interlayer. The interfacial structure and element distribution at the interface were observed using SEM, electron probe microanalysis and X-ray diffraction. The joint strength was measured using four-point bending test. The results showed that metallurgical bonding between Ti(C,N) cermet was achieved using PTLP-DB. Near Ti(C,N) cermet side, a strong chemical reaction occurred to produce an interfacial multilayer containing Ti–Al and Ti–Ni intermetallics. Different bonding times during PTLP-DB were also studied, and there was an optimum time during bonding. With a shorter bonding time, voids were observed at the interface, while with a prolonged time, the bending strength on the joints also decreased due to the overgrowth on intermetallic layer and the existence of high gradient residual stress at the interface.     

Investigation of fracture for friction welded joint between pure nickel and pure aluminium with post-weld heat treatment

The present paper described the investigation of the fracture of friction welded joint between pure nickel (Ni) and pure aluminium (Al) with post-weld heat treatment (PWHT). Most of joints autogenously fractured from the adjacent portion of the intermediate layer (interlayer) consisting of intermetallic compound (IMC) on the weld interface due to growing of that after long heating time during the cooling process after PWHT. The IMC interlayer was composed with mainly NiAl, and that grew at the weld interface with PWHT. The joint fracture temperature increased with increasing width of the IMC interlayer in the axial direction of the joint. That is, the fracture of the joint occurred at the interface between NiAl layer and Al base metal. The fractured surface was covered with a little Ni₂Al₃ and/or NiAl₃, and that was like as disbonding. Furthermore, when the width of the IMC interlayer was smaller than approximately 40 μm, the joint fracture temperature of the joint was under about 470 K. However, when the width of the IMC interlayer exceeded 50 μm, the joint fracture temperature drastically increased up to about 800 K. Hence, it was able to be estimate that the joint fracture temperature increased with increasing width of the IMC interlayer. Therefore, one of the main reasons for the fracture of the joint could be concluded as remarkable decreasing of the bonding strength between NiAl layer and Al base metal, which was produced with PWHT.     

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.     

Effect of process parameters on semi-solid TLP bonding of Ti–6Al–4V to Mg–AZ31

The semi-solid transient liquid-phase bonding (Semi-solid TLP bonding) of titanium alloy Ti–6Al–4V to magnesium alloy Mg–AZ31 was performed using a eutectic forming nickel foil. The process parameters were optimized to achieve higher shear strength. The effect of temperature and pressure on microstructure evolution and mechanical characteristics were examined for bonding time between 5 and 60 min. Three reaction layers L1, L2 at Ni/Mg–AZ31 interface and L3 along the Ni/Ti–6Al–4V interface were determined within joint zone at a bonding temperature of 515 °C. The L1 and L2 reaction layers continued to be seen when the bonding temperature increased to 540 °C. When the bonding pressure increases from 0.2 to 0.7 MPa, a new reaction layer L4, at the Ni/Ti–6Al–4V interface was observed. The results showed that as the bonding time increased up to 60 min, the width of the joint decreased due to isothermal solidification. Maximum shear strength of 39 MPa was obtained for 540 °C and 0.2 MPa with a holding time of 20 min. However, further increase in bonding time to 60 min resulted in a decrease in shear strength to 8 MPa, and this decrease in strength was attributed to the increase in intermetallics forming within the joint zone.     

Formation of intermetallic compounds in Mg–Ag–Al joints during diffusion bonding

In this study, we conducted the diffusion bonding of Mg and Al alloys using a 30-μm-thick pure silver foil interlayer at median temperatures between 390 and 490 °C. We obtained a multilayered structure across the Mg–Ag–Al joint: Mg/Mg(ss, Ag)/Mg₃Ag/MgAg/Ag/Ag(ss, Al)/Ag₂Al/Al. The silver diffusion barrier prevented the formation of brittle intermetallics between Mg and Al. Intermetallics identified at the joint interface include the more ductile types between Mg and Ag, ε-Mg₃Ag and β′-MgAg, and Ag and Al, δ-Ag₂Al. As the bonding temperature increased, Ag₂Al, followed by MgAg, favored the growth of Mg₃Ag IMC layer. The shear strength of the joints increased with the rising bonding temperature to a maximum value of 11.8 MPa at 470 °C. Fracture failure in the joints mainly occurred in the Ag₂Al layer. The formation mechanism for interfacial layers in the joints is believed to consist of four stages: (1) solid-solution formation, (2) Mg–Ag IMC formation, (3) Ag–Al IMC formation, and (4) growth of Mg–Ag and Ag–Al IMCs.     

Brazing of WC–8Co cemented carbide to steel using Cu–Ni–Al alloys as filler metal: Microstructures and joint mechanical behavior

Three novel Cu–Ni–Al brazing filler alloys with Cu/Ni weight ratio of 4:1 and 2.5–10 wt% Al were developed and characterized, and the wetting of three Cu–Ni–Al alloys on WC–8 Co cemented carbide were investigated at 1190–1210?C by the sessile drop technique. Vacuum brazing of the WC–8 Co cemented carbide to SAE1045 steel using the three Cu–Ni–Al alloys as filler metal was further carried out based on the wetting test results. The interfacial interactions and joint mechanical behaviors involving microhardness, shear strength and fracture were analyzed and discussed. The experimental results show that all the three wetting systems present excellent wettability with final contact angles of less than 5?and fast spreading. An obvious degeneration layer with continuous thin strip forms in the cemented carbide adjacent to the Cu–Ni–Al/WC–8 Co interface. The variation of microhardness in the joint cross-section is closely related to the interactions(such as diffusion and solid solution) of WC–8 Co/Cu–Ni–Al/steel system. Compared with the other two brazed joints, the WC–8 Co/Cu–19 Ni–5 Al/steel brazed joint presents more reliable interlayer microstructure and mechanical property while brazing at the corresponding wetting temperatures for 5 min, and its average shear strength is over 200 MPa after further optimizing the brazing temperature and holding time. The joint shear fracture path passes along the degeneration layer, Cu–Ni–Al/WC–8 Co interface and brazing interlayer, showing a mixed ductile-brittle fracture.     

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.     

Reactive brazing of Al alloy to Mg alloy using zinc-based brazing alloy

According to the feature of Mg–Zn eutectic reaction, Al alloy was bonded to Mg alloy by contact reaction brazing using a zinc-based brazing alloy successfully. The experimental observations showed that Mg–Al intermetallic compounds were avoided for the addition of the zinc-based brazing alloy. The Mg substrate and the remanent brazing alloy were bonded with the reaction zone that formed along the zinc rich and magnesium poor interface. Only a few Mg–Zn intermetallic compounds (MgZn2) existed homogeneously in the reaction zone. The substrate and the remanent brazing alloy were bonded with a thin Al–Zn solution. The average tensile-shear strength of the final joints was a little lower than that of the zinc-based brazing alloy owning to some pores at the interface between the reaction zone and the remanent brazing alloy layer.     

Comparative study on characteristics of hybrid laser-TIG welded AZ61/Q235 lap joints with and without interlayers

AZ61 Mg alloy to Q235 mild steel were lap joined using hybrid laser-TIG welding technique. At the joint interface and fusion zone (FZ), microstructure was revealed by scanning electron microscopy equipped with energy dispersive X-ray spectroscopy; element distribution was analyzed by electron probe micro-analyzer; intermediate phases were identified using X-ray diffraction test. Comparing with interlayer-free joints, the new intermediate phases Mg₂Ni and Mg₂Cu were generated in the FZ and at the Mg alloy/interlayer interface, and the solid solution of Ni or Cu in Fe was found along the edge of weld pool on steel side. It was found that direct joint without any interlayer was mechanical bonding, while Ni- and Cu-added joints were semi-metallurgical bonding. The joint shear strength was not only related to the penetration depth, but also related to the bonding mode. The strengthening effect on Cu-added joint was higher than that on Ni-added joint.     

Microstructure characteristics and mechanical properties of cold metal transfer welding Mg/Al dissimilar metals

AZ31B Mg alloy and 6061 Al alloy were joined by using cold metal transfer (CMT) welding with pure copper (HS201) as the filler metal. The microstructure of Mg/Al CMT weld joint was studied by means of Optical Microscopy, Scanning Electron Microscope (SEM), Energy Dispersive X-ray (EDX), X-ray Diffraction (XRD). Results showed that dissimilar metals of Mg/Al could be successfully joined by CMT under proper processing parameters. The bonding strength of the joint was 34.7 MPa. A variety of Al–Cu intermetallic compounds, i.e. AlCu, CuAl₂, Cu₉Al₄, presented in the fusion zone of Al side, and Cu based solid solution was generated in weld zone, while Cu₂Mg and Al–Cu–Mg ternary eutectic structure was formed in the fusion zone of Mg side. The micro-hardness in the both sides of fusion zones increased sharply, which were 362 HV in Mg side and 260 HV in Al side. The joint was brittle fractured in the intermetallic compound layer of the fusion zone of Mg side, where plenty of Cu₂Mg intermetallic compounds were distributed continuously.     

Laser-tungsten inert gas hybrid welding of dissimilar metals AZ31B Mg alloys to Zn coated steel

Laser-tungsten inert gas (TIG) hybrid welding has been developed for joining Mg alloys to Zn coated steel in a lap joint configuration. The joint could not be produced in laser or arc welding only, while acceptable joints without obvious defects were obtained with a relatively wide processing window in the hybrid process. Two reaction layers were observed to form at the interface and were identified as Mg–Zn eutectic structure (α-Mg + MgZn) and Fe₃Al phase by TEM analysis. In some cases, Al₆Mn phase also formed adjacent to the Fe–Al reaction layer. The tensile-shear strength attained the maximum value of 68 MPa, representing 52.3% joint efficiency relative to Mg base metal. The element Al from AZ31B Mg alloys diffused to the liquid/solid interface and then reacted with the elements from steel, such as Fe and Mn, contributing to the metallurgical bonding at the interface. The weak bonding between Mg–Zn reaction layer and newly formed Fe–Al layer resulted in the interfacial failure.     

MB2-LY12扩散焊接头界面组织结构及其形成机制

采用真空扩散焊接技术进行镁合金（MB2）与铝合金（LY12）的焊接,采用超声波无损检测,电子探针、X射线衍射和扫描电镜等手段研究了焊接温度对焊接接头界面附近组织结构的影响,分析了界面反应物的生成机理。结果表明,随着焊接温度的升高,焊接界面的焊合率提高,在焊接压力为3 MPa、保温时间为100 min的条件下,温度升高到480℃完全焊合,在Al侧和Mg侧分别形成了A1（ss,Mg）和Mg（ss,A1）固溶体,焊接界面形成了Al₁₂Mg₁₇、AlMg、Al₃Mg₂三种金属间化合物层,其厚度随着焊接温度的升高而增加,其中AlMg层厚度增长得最快,接头断裂发生在金属间化合物层且呈阶梯状断裂。界面扩散区的形成主要由有效物理接触阶段、固溶体形成阶段、金属间化合物相形成阶段以及金属间化合物增长阶段组成。     

搅拌摩擦焊辅助Al/Zn/Mg接头扩散连接

对2mm厚的AZ31B镁合金和6061铝合金平板进行添加夹层Zn的搅拌摩擦诱导扩散连接实验。通过SEM,EPMA,XRD,拉伸实验和维氏硬度测试研究Al/Zn/Mg搭接接头显微组织和力学性能。结果表明:当旋转速率合适时,扩散层存在Al富集区,Al5Mg11Zn4层及Mg-Zn共晶区;而旋转速率较低时,扩散层存在残留的Zn层;旋转速率过大时,扩散层出现Al-Mg系金属间化合物。由于扩散层主要为金属间化合物,其显微硬度明显高于母材。Zn箔的加入提高了Al/Mg搭接接头的力学性能。断口观察分析表明,接头失效发生在靠近Al侧的扩散层上。     

Characterization of Al/Ni multilayers and their application in diffusion bonding of TiAl to TiC cermet

The Al/Ni multilayers were characterized and diffusion bonding of TiAl intermetallics to TiC cermets was carried out using the multilayers. The microstructure of Al/Ni multilayers and TiAl/TiC cermet joint was investigated. The layered structures consisting of a Ni₃(AlTi) layer, a Ni₂AlTi layer, a (Ni,Al,Ti) layer and a Ni diffusion layer were observed from the interlayer to the TiAl substrate. Only one AlNi₃ layer formed at the multilayer/TiC cermet interface. The reaction behaviour of Al/Ni multilayers was characterized by means of differential scanning calorimeter (DSC) and X-ray diffraction. The initial exothermic peak of the DSC curve was formed due to the formation of Al₃Ni and Al₃Ni₂ phases. The reaction sequence of the Al/Ni multilayers was Al₃Ni → Al₃Ni₂ → AlNi → AlNi₃ and the final products were AlNi and AlNi₃ phases. The shear strength of the joint was tested and the experimental results suggested that the application of Al/Ni multilayers improved the joining quality.