Effects of heat treatment on the intermetallic compounds and mechanical properties of the stainless steel 321–aluminum 1230 explosive-welding interface

The effects of heat treatment on the microstructure and mechanical properties of intermetallic compounds in the interface of stainless steel 321 explosively bonded to aluminum 1230 were investigated in this study. Experimental investigations were performed by optical microscopy, scanning electron microscopy, and microhardness and shear tensile strength testing. Prior to heat treatment, increasing the stand-off distance between samples from 1 to 2.5 mm caused their interface to become wavy and the thickness of intermetallic layers to increase from 3.5 to 102.3 μm. The microhardness increased from HV 766 in the sample prepared at a stand-off distance of 1 mm to HV 927 in the sample prepared at a stand-off distance of 2.5 mm; in addition, the sample strength increased from 103.2 to 214.5 MPa. Heat treatment at 450°C for 6 h increased the thickness of intermetallic compound layers to 4.4 and 118.5 μm in the samples prepared at stand-off distances of 1 and 2.5 mm, respectively. These results indicated that increasing the duration and temperature of heat treatment decreased the microhardness and strength of the interface of explosively welded stainless steel 321-Al 1230 and increased the thickness of the intermetallic region.

Microstructural characterization and mechanical properties of aluminum 6061-T6 plates welded with copper insert plate(Al/Cu/Al) using friction stir welding

Friction stir welding was used to join two aluminum 6061-T6 plates with an insert of a pure copper plate(Al/Cu/Al),and then the influence of the copper insert on the joint performance was studied.The dissimilar welding results were also compared with AA 6061 friction stir welds produced without copper insert(Al/Al).Optical and scanning electron microscopes were used for the microstructural observations of the welded samples.X-ray diffraction analysis was used to analyze phase component of the Al/Cu/Al specimen.A defect-free joint was observed for the Al/Cu/Al joint at a rotational speed of 950 r/min and a welding speed of 50 mm/min.Microstructural observation of the weld nugget zone(WNZ)demonstrates the formation of composite-like structure which promotes metallurgical bonding of aluminum and copper.XRD results show the formation of intermetallic compounds(IMCs),such as Al4Cu9 and Al2Cu.Furthermore,it was observed that the hardness of the weld with the Cu insert plate is higher than that of other samples due to more dislocation density and a distinct rise in hardness values was observed due to the presence of IMCs.The ultimate tensile strength of the joint with copper insert plate is higher than that of the other sample due to the strong metallurgical bonding between Al and Cu.

Effect of process parameters on interfacial microstructure and mechanical properties of Al/Cu friction stir lap welding joints

In this study,friction stir lap welding(FSLW)was performed for the welding test of 6061 aluminium alloy and T2 pure copper.The effect of process parameters containing rotation rate and travel speed on interfacial microstructure evolution and mechanical properties of Al/Cu dissimilar joints were explored.The experiments were carried out under the rotation rates of 600,900 and 1200 r/min and with the travel speeds of 30,70 and 100 mm/min.The characteristic of interface transition zones(ITZs)and the species of intermetallic compounds(IMCs)were investigated.The Al/Cu interface showed a layered structure composed of Al-Cu IMCs,which will affect the mechanical property.The layer consisting of Al2Cu was formed at lower heat input,and as heat input increased the Al4Cu9 phase started to form.Excessive heat input will increase the thickness of the interface and raise the brittleness of the joints.The thickness of the IMCs layers changed from0.89μm to 3.96μm as the heat input increased.The maximum value of tensile shear loading of 4.65 kN was obtained at the rotation rate of900 r/min and travel speed of 100 mm/min with the interface thickness of 2.89μm.The fracture mode of the joints was a mix of ductile and brittle fracture.

Microstructures and properties of welded joint of aluminum alloy to galvanized steel by Nd:YAG laser + MIG arc hybrid brazing-fusion welding

According to the differences in melting point between aluminum alloy and steel, 6013-T4 aluminum alloy was joined to galvanized steel by large spot Nd：YAG laser ＋ MIG arc hybrid brazing-fusion welding with ER4043（AlSi5） filler wire. The microstructures and mechanical properties of the brazed-fusion welded joint were investigated. The joint is divided into two parts of fusion weld and brazed seam. There is a zinc-rich zone at fusion weld toe, which consists of α（Al）-Zn solid solution and Al-Zn eutectic. The brazed seam is the Fe-Al intermetallic compounds （IMCs） layer of 2-4μm in thickness, and the IMCs include FeAl2, Fe2Al5 and Fe4Al13. FeAl2 and Fe2Al5 are located in the compact reaction layer near the steel side, and Fe4Al13 with tongue shape or sawtooth shape grows towards the fusion weld. The tensile strength of the joint firstly increases and then decreases as the welding current and laser power increase, the highest tensile strength can be up to 247.3 MPa, and the fracture usually occurs at fusion zone of the fusion weld. The hardness is the highest at the brazed seam because of hard Fe-Al IMCs, and gradually decreases along the fusion weld and galvanized steel, respectively.

Revealing microstructural evolution and mechanical properties of resistance spot welded NiTi-stainless steel with Ni or Nb interlayer

Dissimilar welding of NiTi and stainless steel(SS)for multifunctional device fabrication is challenging due to the brittle nature of intermetallic compounds(IMCs)that are formed in the weld zone.In this work,Ni and Nb interlayers were applied for the resistance spot welding(RSW)of NiTi and SS to replace the harmful Fe_(2)Ti phase and to restrict the mixing of dissimilar molten metals,respectively.Microstructural evolution and mechanical properties of the joints were investigated.It was shown that a conventional weld nugget was created in the absence of any interlayer in the welded joint suffering from traversed cracks due to the formation of brittle IMCs network in the fusion zone(FZ).By the addition of Ni from the interlayer,Fe_(2)Ti dominated weld nugget was efficaciously replaced by Ni_(3)Ti phase;however,the presence of the large pore and cracks reduced the effective joining area.The use of a Nb interlayer resulted in a fundamentally different joint,in which FZs at NiTi and SS sides separated by the unmolten Nb would suppress the mixing of dissimilar molten metals.Nb-containing eutectic structures with low brittleness formed at the interfaces,contributing to the enhancement of joint strength(increased by 38%on fracture load and 460%on energy absorption).A high-melting-point interlayer showed great potential to realize a reliable and high-performing RSWed NiTi-SS joint.

Geometrical, microstructural and mechanical characterization of pulse laser welded thin sheet 5052-H32 aluminium alloy for aerospace applications

Pulse laser welding of 0.6 mm-thick AA5052-H32 was performed to determine the optimum set of parameters including laser pulse current,pulse frequency and pulse duration that meets the AWS D17.1 specifications for aerospace industry.The microstructure and mechanical properties of the weldments were also investigated.Relationships between the parameters and weld bead geometry were found.High quality weld joints without solidification crack that met AWS D17.1 requirements were obtained at(I)high pulse energy(25 J)and high average peak power(4.2 kW)and(II)low pulse energy(17.6 J)and low average peak power(2.8 kW).The weld joint formed at lower heat energy input exhibited finer dendritic grain structure.Mg vapourisation and hard phase compound(Al0.5Fe3Si0.5)formation decreased in the weld joint formed at lower heat energy input.Consequently,the tensile strength of the weldment formed at lower heat energy input(168 MPa)is by a factor of 1.15 higher but showed^29%decrease in hardness(111 HV0.1)at the joint when being compared with the weldment formed at higher heat energy input.Appropriate parameters selection is critical to obtaining 0.6 mm-thick AA5052-H32 pulse laser weld joints that meet AWS D17.1 requirements for aircraft structures.

Intermetallic Compounds in the Banded Structure and Their Effect on Mechanical Properties of Al/Mg Dissimilar Friction Stir Welding Joints

Dissimilar friction stir welding（FSW） between aluminum and magnesium alloy was performed, using various tool rotational speed（TRS） at a ？xed travel speed, with tool offset to aluminum to investigate the formation of intermetallic compounds（IMCs） in the banded structure（BS） zone and their effect on mechanical properties. Large quantities of IMCs, in the form of alternating bands of particles or lamellae, were found in the BS zone, where drastic material intermixing occurred during FSW. The BS microstructural characters in terms of the morphology of the bands and the quantity and distribution of IMC particles varied with TRS. All welds exhibited brittle fracture mode with their fracture paths propagating mainly in/along the IMCs in the BS. It is shown that these BS microstructural characters have significant effect on the mechanical properties of the joints. Suggestions on tailoring the BS microstructure were proposed for improving the strength of the BS zone and the final mechanical properties of the Al/Mg FSW joints.

Intermetallic Compounds Formation in Dissimilar Friction Stir Welding of Mg/Cu Alloys

Joining dissimilar Mg/Cu alloys was still an intractable problem because of the excessive intermetallic compounds(IMCs)and poor mechanical properties using conventional welding methods.In the present study,friction stir welding was employed for the butt joining of dissimilar AZ31B Mg-alloy and T2 pure Cu plates.Defect-free Mg/Cu joints were obtained with Mg-RS and Cu-AS configuration,at a welding speed of 50 mm/min and tool rotating speeds of 325 r/min,625 r/min and 925 r/min.At the joining interface,both Mg_(2)Cu and MgCu_(2) IMC phases were observed,with a clear,uniform and continuous IMCs layer composed of two sub-layers,layer-A of Mg+Mg_(2)Cu and layer-B of Mg_(2)Cu+MgCu_(2).The maximum ultimate tensile strength of the Mg/Cu friction stir welding joint reached 130 MPa at 925 r/min due to enhanced mechanical interlocking between Mg and Cu,as well as sufficient metallurgical bonding at the joining interface with an IMCs layer thickness in the range of 1.0-2.0μm.

Materials flow and phase transformation in friction stir welding of Al 6013/Mg

Material flow and phase transformation were studied at the interface of dissimilar joint between Al 6013 and Mg, produced by stir friction welding （FSW） experiments. Defect-free weld was obtained when aluminum and magnesium were placed in the advancing side and retreating side respectively and the tool was placed 1 mm off the weld centerline into the aluminum side. In order to understand the material flow during FSW, steel shots were implanted as indexes into the welding path. After welding, using X-ray images, secondary positions of the steel shots were evaluated. It was revealed that steel shots implanted in advancing side were penetrated from the advancing side into the retreating side, whereas the shots implanted in the retreating side remained in the retreating side, without penetrating into the advancing side. The welded specimens were also heat treated. The effects of heat treatment on the mechanical properties of the welds and the formation of new intermetallic layers were investigated. Two intermetallic compounds, Al3Mg2 and Al12Mg17, were formed sequentially at Al6013/Mg interface.

Friction stir welding of aluminum to copper—An overview

Components made by joining different materials are required in various engineering applications.Fabrication of suchcomponents is a challenging task due to the vast difference in mechanical,thermal and electrical properties of the materials beingused.Friction stir welding(FSW)is capable of joining dissimilar materials such as aluminum(Al)and copper(Cu)and thereforeresearchers have used this novel process for dissimilar joining.Consequently,several works pertaining to dissimilar joining,specifically Al?Cu,are available in the literature but they are scattered in different sources,which makes the task of gatheringinformation about dissimilar FSW of Al?Cu cumbersome.This work has been written with an aim to provide all pertinentinformation related to dissimilar FSW of Al?Cu at one place to ease the problems of researchers.It comprehensively covers andsummarizes the topics such as the effect of tool design and geometry,FSW process parameters,FSW strategies on mechanicalproperties,microstructure and formation of defects during dissimilar FSW of Al?Cu.In addition,it also presents and discussesseveral variants of dissimilar FSW of Al?Cu.Finally,this work not only puts forth major findings of the previous researchers but alsosuggests future recommendations for dissimilar FSW of Al?Cu.

Preparation of bimetallic nano-composite by dissimilar friction stir welding of copper to aluminum alloy

Butt friction stir welding between pure copper and AA5754 alloy was carried out.Reinforcing SiC nanoparticles were utilized in friction stir welded(FSW)joints to decline the harmful effects of intermetallic compounds.Tensile tests,micro-hardness experiments,scanning electron microscopy and X-ray diffraction analysis were applied to studying the properties of welded joints.The joints with a travel speed of 50 mm/min and a rotation speed of 1000 r/min showed the best results.The presence of nano-sized SiC particles reduced the grain size of aluminum and copper in the stir zone(SZ)from 38.3 and 12.4μm to 12.9 and 5.1μm,respectively.The tensile strength of the joint in the presence of reinforcing SiC nano-particles was~240 MPa,which is~90%of that for the aluminum base.Furthermore,the highest microhardness of the weld zone was significantly increased from HV 160 to HV 320 upon the addition of SiC nano-particles.The results also showed that raising the heat generation in FSW joints increased the amount of Al_(4)Cu_(9) and Al_(2)Cu intermetallic compounds.

Effect of adding Nb foil on joint properties of laser fusion welding for TC4 titanium and 7075 aluminum alloy

It is difficult to gain effective Ti-Al fusion welding joints due to their differences in thermal properties and the appearance of brittle Ti-Al Intermetallic Compounds(IMCs).The experiments of laser fusion welding for TC4 titanium and 7075 aluminum alloy were carried out,temperature field and ductility/brittleness,as well as chemical potential of elements,were calculated,and the effect of adding Nb foil on mechanical properties of the weld was also investigated.The results suggested that Nb atoms tend to diffuse toward Al side,which is conducive to the participation of Nb in the metallurgical reaction and contributes to forming the Ti-Nb-Al IMC layer at the interface.As the thickness of Nb foil increases,the tensile-shear force of joint climbs first but then declines,and reaches the highest value of 1663 N with 0.10 mm-thickness Nb foil,representing 58.38%enhancement compared with the non-added one.Adding Nb foil slows down the heat transfer as a blocker,and thus both the melting amount of Al and the mixing area of Ti and Al decrease.In addition,Nb alloying reduces the brittleness of the Ti-Al compound.Hence,the joint properties of titanium/aluminum are improved with the addition of Nb foil.

铝/钢异种金属旋转摩擦焊接技术研究进展

铝/钢异种金属结构以其质量轻、设计柔性大的特点在航空航天领域尤其是大推力液体运载火箭输送管路中有着重要应用。相比于熔焊、钎焊等其他焊接方法,旋转摩擦焊可以实现铝/钢异种金属高质、高强、高可靠连接。本文基于对铝/钢异种金属焊接性分析,从工艺参数优化、界面显微组织分析、界面不均匀性调控和添加中间层金属冶金调控等方面综述了铝/钢异种金属旋转摩擦焊接技术研究进展,并对铝/钢异种金属旋转摩擦焊接技术发展趋势及亟须解决的科学问题进行了总结。

Microstructure and Mechanical Properties of Dissimilar Double-Side Friction Stir Welds Between Medium-Thick 6061-T6 Aluminum and Pure Copper Plates

It is difficult to achieve Al/Cu dissimilar welds with good mechanical properties for medium-thick plates due to the inherent high heat generation rate at the shoulder-workpiece contact interface in conventional friction stir welding.Thus,doubleside friction stir welding is innovatively applied to join 12-mm medium-thick 6061-T6 aluminum alloy and pure copper dissimilar plates,and the effect of welding speeds on the joint microstructure and mechanical properties of Al/Cu welds is systematically analyzed.It reveals that a sound Al/Cu joint without macroscopic defects can be achieved when the welding speed is lower than 180 mm/min,while a nonuniform relatively thick intermetallic compound(IMC)layer is formed at the Al/Cu interface,resulting in lots of local microcracks within the first-pass weld under the plunging force of the tool during friction stir welding of the second-pass,and seriously deteriorates the mechanical properties of the joint.With the increase of welding speed to more than 300 mm/min void defects appear in the joint,but the joint properties are still better than the welds performed at low welding speed conditions since a continuous uniform thin IMCs layer is formed at the Al/Cu interface.The maximum tensile strength and elongation of Al/Cu weld are,respectively,135.11 MPa and 6.06%,which is achieved at the welding speed of 400 mm/min.In addition,due to the influence of welding distortion of the first-pass weld,the secondpass weld is more prone to form void defects than the first-pass weld when the same plunge depth is applied on both sides.The double-side friction stir welding is proved to be a good method for dissimilar welding of medium-thick Al/Cu plates.

送丝速度对铝/钢激光熔钎焊接头组织与性能的影响

采用ER2319焊丝进行了6061-T6铝合金/Q235镀锌钢光纤激光熔钎焊接,分析了送丝速度对接头成型、显微组织与力学性能的影响。结果表明:当激光功率为1.2 kW,焊接速度为1.2 m/min时,送丝速度在1.2~3.0 m/min范围内均可获得有效接头。接头的抗拉强度随着送丝速度的增加呈现先上升后减小的趋势,当送丝速度为2.4 m/min时平均抗拉强度达到最大值,为116.15 MPa。当送丝速度为1.8、2.4 m/min时,接头的上下表面的金属间化合物层可控制在10μm以内,而对接界面处的金属间化合物层厚度随着送丝速度的改变变化不明显,对接界面的IMC层主要由FeAl、FeAl_(2)、Fe_(4)Al_(13)相组成。接头的断裂形式为典型的解理断裂模式,而位于润湿铺展在钢表面的铝合金处则为韧性断裂。

Effect of Al coating conditions on laser weldability of Al coated steel sheet

Al coated steel sheets with excellent heat resistance,thermal reflection,and corrosion resistance are widely used in various applications.The laser weldability of the Al coated steel sheet for full penetration welding was reported.The phenomenon caused by intermixed aluminum and behavior of aluminum in the weld were investigated.Al coated steel sheets that have various thickness and coating mass were prepared for laser welding.The effects of parameters such as welding conditions and Al coating conditions were investigated.Al content mixed in the weld after laser welding was evaluated,and then a correlation between the mixed Al and mechanical properties was investigated.The results show that the Al-rich zones which have Fe-Al intermetallic compounds are found in the weld.The intermetallic compounds cause the decreased strength of the weld.

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0.05mm厚的Ni箔作为中间层,对3mm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TiAl_(3)、TiAl、Ti_(3)Al等金属间化合物,其中脆性相TiAl_(3)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TiAl_(3)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TiAl_(3)相的生成,接头平均抗拉强度达到285.3MPa,为2A14铝合金母材抗拉强度的68%。

铝/钢异种材料电阻点焊研究进展

铝/钢电阻点焊技术是促进铝/钢混合轻量化技术在汽车产业应用的关键技术之一,但铝合金与钢材的传热性、导电性和热膨胀性的差异较大,且电阻点焊接头界面会生成脆性的金属间化合物(IMC)层,因此难以形成良好焊接。近年来,改进设计后的电极提高了铝/钢电阻点焊的焊接性能,并且由于焊接工艺的优化,实现了铝/钢电阻点焊的高质量连接。学者们探究了铝/钢接头界面IMC的生长机理和接头的断裂失效机理,也研究了IMC厚度、熔核直径、钢涂层类型、焊接工况和腐蚀对点焊接头性能的影响,并通过优化焊接参数、引入垫片或中间层及复合焊接等方式来提高焊接质量,以最终指导铝/钢电阻点焊焊接工艺设计并推动其工程应用。本文主要从IMC的生长机理、接头断裂失效行为、焊接质量的影响因素、工艺优化方法和焊接仿真分析等方面综述铝/钢异种材料电阻点焊的研究进展。

镁/铝层状复合板材搅拌摩擦焊焊接行为

采用搅拌摩擦焊(FSW)方法对爆炸焊方法制备的镁/铝层状复合板进行焊接,对不同焊接速度条件下焊接接头的微观组织、物相以及力学性能进行分析。结果表明:镁/铝层状复合板的搅拌摩擦焊焊接接头界面连接效果良好,热机械影响区和热影响区界线不明显,搅拌区内镁、铝交替分布呈条带状,在搅拌区、热机械影响区和热影响区形成了Al_(3)Mg_(2)和Mg_(17)Al_(12)金属间化合物,焊接缺陷主要为界面处金属没有及时填充形成的隧道孔洞;焊接接头横截面硬度呈“W”形分布,搅拌区的硬度从铝侧→界面→镁侧逐渐降低;FSW焊接接头的抗拉强度最大可达94.5 MPa,伸长率为6.7%,断裂机理为金属间化合物的脆性断裂和金属基体镁/铝的韧性断裂。

夹层辅助激光焊接镁/钢异种金属的显微组织与性能

采用镁合金在上、钢板在下且添加中间夹层辅助的激光焊接技术,对AZ31B镁合金和DP590双相钢平板试件进行焊接,基于热力学性能和本征力学性质的计算来选择夹层元素,分析添加夹层前后镁/钢接头显微组织和性能的变化。结果表明:添加Sn和Al夹层,接头最大载荷分别为730和590 N,与没有添加夹层相比,分别提高2.04倍和1.46倍;添加Al夹层,接头界面生成脆性较大的Mg_(17)Al_(12)化合物,其限制了镁/钢接头性能提升;而添加Sn夹层,界面生成脆性相对较低的Mg_(2)Sn化合物以及延性Fe_(3)Sn化合物,这是添加Sn夹层镁/钢接头性能高于添加Al夹层的重要原因。