Microstructure and mechanical properties of Cu/Al joints brazed using (Cu,Ni, Zr,Er)-modified Al—Si filler alloys

To design a promising Al—Si filler alloy with a relatively low melting-point, good strength and plasticity for the Cu/Al joint, the Cu, Ni, Zr and Er elements were innovatively added to modify the traditional Al—Si eutectic filler. The microstructure and mechanical properties of filler alloys and Cu/Al joints were investigated. The result indicated that the Al—Si—Ni—Cu filler alloys mainly consisted of Al(s,s), Al₂(Cu,Ni) and Si(s,s). The Al—10Si—2Ni—6Cu filler alloy exhibited relatively low solidus (521 °C) and liquidus (577 °C) temperature, good tensile strength (305.8 MPa) and fracture elongation (8.5%). The corresponding Cu/Al joint brazed using Al—10Si—2Ni—6Cu filler was mainly composed of Al₈(Mn,Fe)₂Si, Al₂(Cu,Ni)₃, Al(Cu,Ni), Al₂(Cu,Ni) and Al(s,s), yielding a shear strength of (90.3±10.7) MPa. The joint strength was further improved to (94.6±2.5) MPa when the joint was brazed using the Al—10Si—2Ni—6Cu—0.2Er—0.2Zr filler alloy. Consequently, the (Cu, Ni, Zr, Er)-modified Al—Si filler alloy was suitable for obtaining high-quality Cu/Al brazed joints.     

Characterization of diffusion-bonded joint between Al and Mg using a Ni interlayer

Aluminum and magnesium were joined through diffusion bonding using Ni interlayer. The microstructure and mechanical performance of the Al/Ni/Mg joints at different temperatures was investigated by means of scanning electron microscope(SEM), electro-probe microanalyzer(EPMA), X-ray diffraction(XRD), Vickers hardness testing, and shear testing. The results show that the addition of Ni interlayer eliminates the formation of Mg–Al intermetallic compounds and improves the bonding strength of the Al/Mg joints. The Al/Ni/Mg joints are formed by the diffusion of Al, Ni and Mg, Ni. The microstructure at the joint interface from Al side to Mg side is Al substrate/Al–Ni reaction layer/Ni interlayer/Mg–Ni reaction layer/Mg substrate multilayer structure. The microhardness of the Mg–Ni reaction layer has the largest value of HV 255.0 owing to the existence of Mg_2Ni phase.With the increase of bonding temperature, the shear strength of the joints increases firstly and then decreases.The Al/Ni/Mg joint bonds at 713 K for 90 min, exhibiting the maximum shear strength of 20.5 MPa, which is greater than that of bonding joint bonded directly or with Ag interlayer. The fracture of the joints takes place at the Mg–Ni interface rather than the Al–Ni interface, and the fracture way of the joints is brittle fracture.     

铝基复合材料瞬间液相扩散连接接头的组织与力学性能

采用扫描电镜、能谱仪及电子拉伸试验机系统地研究了Cu,Ag作为中间层铝基复合材料瞬间液相扩散连接接头的组织与力学性能。根据组织结构特点接头可分为增强相偏聚区、增强相贫化区和母材区。增强相偏聚区的组织主要为Al2O3颗粒和铝合金基体，并含有汪量的MgAl2O4化合物，对于Cu中间层接头还含有少量的Al2Cu化合物。连接温度、连接时间和中间层厚度对接头抗剪强度具有较明显的影响。在一定条件下，Cu,Ag中间层接头的抗剪强度分别为82－99MPa和86－109MPa。增强相偏聚区是接头最薄弱的区域，减少增强相的偏聚是进一步改善接头力学性能的重要途径。     

保温时间对瞬时液相扩散连接的Ti3Al /Ti2AlNb接头微观结构及力学性能的影响

采用Ni-Ti复合箔片作为中间层,在990 ℃、低连接压力（0.1 MPa）下,通过瞬时液相（TLP）扩散连接制备了Ti₃Al/Ti₂AlNb异种合金接头。分析了保温时间（10~90 min）对Ti₃Al/Ti₂AlNb接头微观结构及力学性能的影响,并研究了TLP扩散连接接头的界面演变和形成机制。结果表明,Ti₃Al/Ti₂AlNb接头具有典型的“Ti₃Al | Al_0.5Nb_0.5Ti₃ | 残余 Ni | NiTi | NiTi₂ | 残余 Ti | Al_0.5Nb_0.5Ti₃ | Ti₂AlNb”多层梯度结构。随着保温时间的延长,接头的抗剪切强度先增大后减小,当保温时间达到60 min时,Ti₃Al/Ti₂AlNb接头的抗剪切强度最大,达到167±12 MPa。另外,接头的断裂主要发生在Ti₂AlNb/Ti附近的NiTi₂层,并向Ti层延伸,呈现出脆性断裂的特征。     

Vacuum brazing of TiAl-based intermetallics with Ti–Zr–Cu–Ni–Co amorphous alloy as filler metal

An amorphous Ti41.7–Zr26.7–Cu14.7–Ni13.8–Co3.1 (wt%) ribbon fabricated by melt spinning was used as filler to vacuum braze Ti–48Al–2Nb–2Cr (at%) intermetallics. The influences of brazing temperature and time on the microstructure and strength of the joints were investigated. It is found that intermetallic phases of Ti₃Al and γ-Ti₂Cu/Ti₂Ni form in the brazed joints. The tensile strength of the joint first increases and then decreases with the increase of the brazing temperature in the range of 900–1050 °C and the brazing time varying from 3 to 15 min. The maximum tensile strength at room temperature is 316 MPa when the joint is brazed at 950 °C for 5 min. Cleavage facets are widely observed on all of the fracture surfaces of the brazed joints. The fracture path varies with the brazing condition and cracks prefer to initiate at locations with relatively high content of γ-Ti₂Cu/Ti₂Ni phases and propagate through them.     

Microstructure and properties of WC–Co/3Cr13 joints brazed using Ni electroplated interlayer

The brazed joints of WC–Co cemented carbide and 3Cr13 stainless steel using Ni electroplated on Cu–Zn alloy as interlayer were investigated. The shear strength of the WC–Co/interlayer/3Cr13 joints increased firstly and then decreased with the increase of brazing temperature or brazing time. The maximum shear strength value of the brazed joints was 154 MPa at 1100 °C for 10 min. The characterizations of the WC–Co/interlayer/3Cr13 joints were studied by SEM, EDS and XRD. The results showed that the brazed joints fractured in the bulk WC–Co substrates near the interlayer. The added Ni promoted the formation of interdiffusion zone, which possessed positive effects on the bond strength of the WC–Co/interlayer/3Cr13 joints. Austenite solid solution was formed in the WC–Co/interlayer/3Cr13 joint, and the majority of austenite solid solution presented as columnar crystal. The number of austenite crystals on the WC–Co/interlayer interface was tremendously more than that on the interlayer/3Cr13 interface.     

Improving the shear strength of Sn–Ag–Cu–Ni/Cu–Zn solder joints via modifying the microstructure and phase stability of Cu–Sn intermetallic compounds

This study focuses on the correlation between high-speed impact tests and the interfacial reaction in Sn-3.0Ag-0.5Cu-0.1Ni/Cu (wt%) and Sn-3.0Ag-0.5Cu-0.1Ni/Cu-15Zn solder joints. Adding Ni into the Sn–Ag–Cu solder alters the interfacial morphology from scallop type to layer type and exhibits high shear strength after reflow in both solder joints. However, the shear strength of Sn-3.0Ag-0.5Cu-0.1Ni/Cu solder joints degrades significantly after thermal aging at 150 °C for 500 h. It is notable that Sn-3.0Ag-0.5Cu-0.1Ni/Cu-15Zn solder joints still present higher shear strength after aging at 150 °C. The weakened shear strength in Sn-3.0Ag-0.5Cu-0.1Ni/Cu solder joints is due to stress accumulation in the interfacial (Cu,Ni)₆Sn₅ compound induced by the phase transformation from a high-temperature hexagonal structure (η-Cu₆Sn₅) to a low-temperature monoclinic structure (η'-Cu₆Sn₅). However, doping small amounts of Zn into (Cu,Ni)₆(Sn,Zn)₅ can inhibit the phase transformation during thermal aging and maintain strong shear strength. These experiments demonstrate that Sn-3.0Ag-0.5Cu-0.1Ni/Cu-15Zn solder joints can act as a stable connection in the micro-electronic packaging of most electronic products at their average working temperatures.     

Effect of brazing temperature and brazing time on the microstructure and tensile strength of TiAl-based alloy joints with Ti-Zr-Cu-Ni amorphous alloy as filler metal

An amorphous Ti-37.5Zr-15Cu-15Ni (wt.%) ribbon fabricated by vacuum arc remelting and rapid solidification was used as filler metal to vacuum braze TiAl alloy (Ti-45Al-2Mn-2Nb-1B (at.%)). The effects of brazing temperature and time on the microstructure and strength of the joints were investigated in details. The typical brazed joint major consisted of three zones and the brazed joints mainly consisted of α_2-Ti₃Al phase, α-Ti phase and (Ti, Zr)₂(Cu, Ni) phase. When the brazing temperature varied from 910 °C to 1010 °C for 30 min, the tensile strength of the joint first increased and then decreased. With increasing the brazing time, the tensile strength of the joint increased. The maximum room temperature tensile strength was 468 MPa when the specimen was brazed at 930 °C for 60 min. All the fracture surfaces assumed typical brittle cleavage fracture characteristic. The fracture path varied with the brazing parameter and cracks preferred to initiate at (Ti, Zr)₂(Cu, Ni) phase and propagation path were mainly determined by the content and distribution of α-Ti phase and (Ti, Zr)₂(Cu, Ni) phase.     

Friction welding of pure titanium and pure nickel

Abstract

The joint tensile strength and metallurgical properties of a friction welded joint of commercially pure Ti and pure Ni has been investigated in as welded and post-weld heat treated conditions. While friction pressure did not significantly impinge on joint tensile strength, joint tensile strength was affected by friction time. A 1–1·5 μm thick interlayer is essential to join pure Ti and pure Ni using friction welding. A maximum joint tensile strength of 450 MPa was achieved and the joint fractured in the Ti original (not heat affected zone) substrate, i.e. the joint efficiency was approximately 112% relative to Ti substrate and 94·5% relative to Ni substrate. The joint tensile strength abruptly decreased as heating temperature was increased to 873 K and/or the Larson-Miller parameter was increased to approximately 19–20 × 10³. The joint tensile strength rapidly decreased with increasing interlayer thickness up to approximately 10 μm, and then remained constant for further increase in interlayer thickness. Four layers occurred at the interface of joints heated to more than 873 K, namely Ti₂Ni, TiNi, TiNi₂, TiNi₃. The fracture of heated joints propagated mainly in the Ti₂Ni layer and/or at the interface between the TiNi and TiNi₃ layers.     

Microstructure and shear strength of γ-TiAl/GH536 joints brazed with Ti−Zr−Cu−Ni−Fe−Co−Mo filler alloy

The influence of brazing temperature and brazing time on the microstructure and shear strength of γ-TiAl/GH536 joints brazed with Ti−Zr−Cu−Ni−Fe−Co−Mo filler was investigated using SEM, EDS, XRD and universal testing machine. Results show that all the brazed joints mainly consist of four reaction layers regardless of the brazing temperature and brazing time. The thickness of the brazed seam and the average shear strength of the joint increase firstly and then decrease with brazing temperature in the range of 1090−1170 °C and brazing time varying from 0 to 20 min. The maximum shear strength of 262 MPa is obtained at 1150 °C for 10 min. The brittle Al₃NiTi₂ and TiNi₃ intermetallics are the main controlling factors for the crack generation and deterioration of joint strength. The fracture surface is characterized as typical cleavage fracture and it mainly consists of massive brittle Al₃NiTi₂ intermetallics.     

Brazing of TiBw/TC4 composite and Ti60 alloy using TiZrNiCu amorphous filler alloy

TiB_w/TC4 composite was brazed to Ti60 alloy successfully using TiZrNiCu amorphous filler alloy, and the interfacial microstructures and mechanical properties were characterized by SEM, EDX, XRD and universal tensile testing machine. The typical interfacial microstructure was TiB_w/TC4 composite/β-Ti + TiB whiskers/(Ti, Zr)₂(Ni, Cu) intermetallic layer/β-Ti/Ti60 alloy when being brazed at 940 °C for 10 min. The interfacial microstructure evolution was influenced strongly by the diffusion and reaction between molten fillers and the substrates. Increasing brazing temperature decreased the thickness of brittle (Ti, Zr)₂(Ni, Cu) intermetallic layer, which disappeared finally when the brazing temperature exceeded 1020 °C. Fracture analyses indicated that cracks were initialized in the brittle intermetallic layer when (Ti, Zr)₂(Ni, Cu) phase existed in the brazing seam. The maximum average shear strength of joints reached 368.6 MPa when brazing was conducted at 1020 °C. Further increasing brazing temperature to 1060 °C, the shear strength was decreased due to the formation of coarse lamellar (α+β)-Ti structure.     

Interlayer growth at interfaces of Ti/Al–1%Mn,Ti/Al–4·6%Mg and Ti/pure Al friction weld joints by post-weld heat treatment

Abstract

The interlayer growth at interfaces of Ti/Al–1%Mn and Ti/Al–4·6%Mg weld joints was studied by postweld heat treatment. The heating temperatures ranged from 676 to 873 K (400–600°C) and maximum heating time was 360 ks (100 h). The basic mechanism of interlayer growth for pure Ti/pure Al friction weld joint was also estimated. The interlayer growth rate of Ti/Al–4·6%Mg joint was much faster than for the Ti/ Al–1%Mn joint. The interlayer mainly consisted of (Al,Si)₃Ti for the Ti/Al–1%Mn joint, and Al₁₈Mg₃Ti₂ for the Ti/Al–4·6%Mg joint. While the interlayer grew from Al alloy substrate to the Ti side for the Ti/Al–1%Mn joint, it grew from the Ti substrate to the Al alloy side for the Ti/Al–4·6%Mg joint. The interlayer growth stopped for several hours on heating for 36 ks (10 h). Neither linear nor parabolic time-dependence relations could be exactly fit to the interlayer growth rate for both joints. The interlayer growth of Ti/Al–1%Mn was proportional to heating time raised to approximately 0·85. The crystal direction of Al₃Ti interlayer growth of the Ti/Al joint was close to 〈001〉 and 〈111〉 directions obtained by OIM method. Nucleation and nuclei growth were observed at the interface of the Ti/Al joint. The nucleation and the nuclei growth are the reason for the phenomena (time dependence) described above.     

Microstructure and bond strength of diffusion-bonded nickel aluminide–titanium joints

Diffusion bonding of Ni₇₅Al₂₅ alloy to commercially pure titanium was carried out at 900 °C for different times under 2 MPa in vacuum. The microstructure of transition joints was revealed by scanning electron microscopy (SEM). Good bonding was observed on all the samples. Chemical compositions of the interface of the bonded samples were identified by energy dispersive spectroscopy. EDS results indicated the formation of the different compositions at the interface of the bonded samples. X-ray diffraction studies showed the presence of TiNi, Ti₂Ni, Ni₃Al, Ni4.22Al0.9 and Ti phases on the fractured surfaces of bonded samples. It was observed that the shear strengths of joints increased with increasing of bonding time. The maximum shear strength was found as 205 MPa for the bonded couple treated for 2 h.     

Microstructures and mechanical properties of TC4/AZ91D bimetal prepared by solid–liquid compound casting combined with Zn/Al composite interlayer

To achieve Ti/Mg bimetallic composite with high strength and metallurgical bonding interface, Al interlayer and Zn/Al composite interlayer were used to prepare TC4/AZ91D bimetal composite with metallurgical bonding interface by solid–liquid compound casting, respectively. Al interlayer was prepared on the surface of TC4 alloy by hot dipping, and Zn/Al composite interlayer was prepared by electroplating process. The results suggested that the phases across the interface were AlTi and α(Al) + Mg₂₁(Al, Zn)₁₇ when Zn/Al composite interlayer was used. When Al interlayer was used as interlayer, AlMgTi ternary structure and Al₁₂Mg₁₇ + δ-Mg eutectic structure were the main phases at the interface. The shear strength of TC4/AZ91D bimetal with Zn/Al composite interlayer was much higher than that with pure Al interlayer, and the value of the shear strength was increased from 48.5 to 67.4 MPa. Thermodynamic models based on different compositions of the interface were established to explain the microstructure evolution of the interfacial zone.     

Properties of as welded and heat treated pure titanium–7075 Al–Zn–Mg alloy friction weld joints

Abstract

The effects of joining conditions and an age hardening post­weld heat treatment (PWHT) at 120°C for 24 h on the tensile strength and metallurgical properties of dissimilar friction joints between pure titanium and age strengthened 7075 Al–Zn–Mg alloy were investigated. Highest strength was achieved using intermediate friction pressure (150 MPa), short friction time (0.5 s), and high upsetting (forging) pressure (400 MPa). The joint tensile strength decreased when the joint diameter was increased from 8 to 16 mm. The joint tensile strength of as welded (AW) dissimilar joints was similar to that of PWHT joints with diameters of 8, 12, and 16 mm. Detailed TEM confirmed that there was a negligible difference in the thickness of the intermetallic layer formed at the dissimilar joint interface for AW and PWHT joints. While the intermetallic phases formed at the joint interface comprised Al₃Ti, τ (Ti₂Mg₃Al₁₈), and Al in AW joints, they consisted of Al+τ or Mg₂Al₃+τ+Al in PWHT joints. Softened regions were generated in 7075 base material immediately next to the interface in AW joints. Post­weld heat treatment increased the hardness of the softened region almost to that of as received 7075–T6 base material in 12 and 16 mm diameter joints. In contrast, the hardness of the softened region in 8 mm diameter joints could not be recovered to that of the as received material. This was a result of overaging and coarse precipitates in the softened region produced during the friction welding operation.     

Effect of HEA/Al composite interlayer on microstructure and mechanical property of Ti/Mg bimetal composite by solid-liquid compound casting

In this study,HEA/AI composite interlayer was used to fabricate Ti/Mg bimetal composites by solidliquid compound casting process.The Al layer was prepared on the surface of TC4 alloy by hot dipping,and the FeCoNiCr HEA layer was prepared by magnetron sputtering onto the Al layer.The influence of the HEA layer thickness and pouring temperature on interface evolution was investigated based on SEM observation and thermodynamic analysis.Results indicate that the sluggish diffusion effect of HEA can ...     

TLP bonding of Ti−6Al−4V to Al 2024 using thermal spray Babbitt alloy interlayer

Thermal spray assisted transient liquid phase (TLP) bonding of Ti−6Al−4V to Al2024 alloys was investigated, where the interlayer was 80 µm Babbitt thermal spray coat on Al substrate. Thermal spray creates a rough and clean surface which leads to establishing a joint with higher strength. The optimized parameters were bonding temperature of 580 °C and bonding time of 30 and 60 min. Microstructural observation together with XRD patterns confirmed the existence of Al₂Cu, Al₂CuMg, Cu₃Ti, TiAl₃, TiAl and Mg₂Sn intermetallic compounds formed in Al weld side. On the other hand, Ti₃Al, Sn₃Ti₅ and Ti₃Sn intermetallic compounds formed in Ti side. With increasing bonding time from 30 to 60 min, although the interlayer was not completely consumed, the thickness of remained Babbitt interlayer decreased to approximately 15 µm. The study showed that shear strength of the joint reaches the high value of 57 MPa obtained at larger bonding time of 60 min.     

Diffusional bonds in laminated composites produced by ECAP

The microstructure, diffusional and mechanical bonding behavior and microhardness distribution of laminated composites fabricated by ECAP process were investigated. Al-Cu and Cu-Ni laminated composites were produced by ECAP process up to 4 passes at room temperature and high temperature (300 °C). The results of microstructure characterization by SEM and shear strength test revealed that the joints between the layers of 4-pass ECAPed samples were considerably stronger than those of 1-pass ECAPed samples due to tolerating higher values of plastic deformations during ECAP. Furthermore, shear strength data showed that increasing ECAP temperature caused a notable increase in shear strength of the specimens. The reason lies in the formation of diffusional joint between the interface of both Al/Cu and Cu/Ni layers at high temperature. The shear bonding strength of ECAPed Cu/Ni/Cu composite at high temperature was remarkably higher than that of ECAPed Cu/Al/Cu composite.     

Effects of Insert Metal Type on Interfacial Microstructure During Dissimilar Joining of TiAl Alloy to SCM440 by Friction Welding

Although the welding zone of direct bonding between a TiAl alloy and SCM440 can be obtained by friction welding, martensitic transformation and the formation of intermetallic compounds (IMCs) and cracks result in a lower tensile strength of the joints relative to those of other welding techniques. Insert metals were used as a buffer layer to relieve stress while increasing the bond strength. In this study, the microstructure and mechanical properties on welded joints of a TiAl alloy and SCM440 with various insert metals, were investigated. The TiAl/Cu/SCM440 and TiAl/Ni/SCM440 joints were fabricated using a servo-motor-type friction welding machine. As a result, it was confirmed that the formation of a welding flash was dependent on the insert metal type, and the strength of the base metal. At the TiAl/Cu/SCM440 interface, the formation of IMCs CuTiAl and Cu₂TiAl was observed at TiAl/Cu, while no IMC formation was observed at Cu/SCM440. On the other hand, at the TiAl/Ni/SCM440 interface, several IMCs with more than 100 μm thickness were found, and roughly two compositions, viz., Ti₂NiAl₃ and TiNi₂Al, were observed at the TiAl/Ni interface. At the Ni/SCM440 interface, 10 μm-thick FeNi and others were found.     

Ti活度对Al2O3/AgCuTi/Fe-Ni-Co钎焊接头机械性能和微观组织结构的影响

采用AgCuTi钎料实现了Al₂O₃陶瓷与Fe-Co-Ni合金的钎焊连接,并调查了不同钛含量的钎料对Al₂O₃/AgCuTi/Fe-Ni-Co钎焊接头机械性能和微观组织结构的影响。扫描电子显微镜(SEM), X射线能量色散光谱仪(EDS), X射线衍射仪(XRD)及电子万能试验机用于分析钎焊接头的机械性能和微观组织结构,结果表明:钛含量的增加明显提高AgCuTi钎料与Al₂O₃陶瓷的相互作用,在Al₂O₃/Ag-Cu-Ti界面生成一层由Ti-Al 和 Ti-O化合物组成的反应层。Al₂O₃/AgCuTi/Fe-Ni-Co钎焊接头的抗拉强度随钛含量的增加而增加,当钛含量提高到8wt.%时,抗拉强度达到最大值78Mpa。通过微观组织结构分析发现,采用AgCu4Ti在890℃保温5min的条件下可以获得较好的钎焊接头,典型接头的微观组织结构为Al₂O₃/TiAl+Ti₃O₅/NiTi+Cu₃Ti+Ag(s,s)/Ag(s,s)+Cu(s,s)+(Cu,Ni)/Fe-Ni-Co。采用AgCu8Ti获得的钎焊接头的界面反应层与AgCu4Ti差异不大,但反应层稍微增厚,并伴有TiO和Ti3Al在Al₂O₃/Ag-Cu-Ti界面生成。