静轴肩辅助铝镁搅拌摩擦搭接接头的组织与性能

文中将静止轴肩技术应用到铝镁异种合金的搅拌摩擦搭接过程中,并分析了焊接速度对接头成形和力学性能的影响.结果表明,静止轴肩能够增强上下板之间的材料交换,焊后搅拌区呈较大的洋葱环形貌,其内部分布大量的金属间化合物;搭接面处发生良好的冶金结合.由于生成金属间化合物,洋葱环区域的显微硬度值明显高于接头其它区域.X射线衍射结果表明,金属间化合物的主要成分是Al₃Mg₂和Al₁₂Mg₁₇.接头的抗拉强度随着焊接速度的增加呈先上升后下降的趋势,最大值在焊接速度为40 mm/min时取得.     

Microstructure and mechanical properties of friction stir lap welded Mg/Al joint assisted by stationary shoulder

Using magnesium alloy as upper sheet, 3 mm-thick AZ31 magnesium alloy and 6061 aluminum alloy were joined using friction stir lap welding assisted by stationary shoulder. The effects of tool rotating speed on cross-sections, microstructure and mechanical properties of Mg/Al lap joints were mainly discussed. Results showed that stationary shoulder contributed to joint formation, by which stir zones (SZ) were characterized by big onion rings after welding. Because of the big forging force exerted by stationary shoulder, the upper region of hook was well bonded. SZ showed much higher hardness because of intermetallic compounds (IMCs). The bonding conditions at the base material (BM)/SZ interface at advancing side and the hook region played important roles on joint lap shear properties. The X-ray diffraction pattern analysis revealed that the main IMCs were Al₃Mg₂ and Al₁₂Mg₁₇.     

Cold metal transfer welding–brazing of magnesium to pure copper

Magnesium alloy AZ31B and pure copper T2 were lapped and joined by cold metal transfer (CMT) welding–brazing method by AZ61A magnesium alloy wire with a 1·2 mm diameter. Results indicated that a satisfied Mg/Cu CMT welding–brazing joint was obtained in the stable welding processes with no spatter. The joint was composed of Mg–Mg welding joint formed between the Mg weld metal and the Mg base metal, and Mg–Cu brazing joint formed between the Mg weld metal and the local molten Cu base metal. The microstructure and the intermetallic compound (IMC) distribution were inspected and analysed in detail. The interfacial reaction layers of the brazing joint consisted of Mg₂Cu, Al₆Cu₄Mg₅, MgCu₂ and Mg₁₇Al₁₂ IMCs. The tensile shear strength of the Mg/Cu CMT welding–brazing joint could reach 172·5 N mm^?1. In addition, two different fracture modes were observed: at the fusion zone and at the brazing interface.     

Microstructure and mechanical properties of dissimilar welded Mg–Al joints by ultrasonic spot welding technique

Abstract

Dissimilar spot welds of magnesium–aluminium alloy were produced via a solid state welding process, i.e. ultrasonic spot welding, and a sound joint was obtained under most of the welding conditions. It was observed that a layer of intermetallic compound (IMC) consisting of Al₁₂M₁₇ formed at the weld centre where the hardness became higher. The lap shear strength and failure energy of the welds first increased and then decreased with increasing welding energy, with the maximum lap shear strength and failure energy occurring at ～1250 J. This was a consequence of the competition between the increasing diffusion bonding arising from higher temperatures and the deterioration effect of the intermetallic layer of increasing thicknesses. Failure predominantly occurred in between the aluminium alloy and the intermetallic layer, which normally stayed at the magnesium side or from the cracks of the IMCs in the reaction layer.     

Improving weld strength of magnesium to aluminium dissimilar joints via tin interlayer during ultrasonic spot welding

Abstract

Welding of magnesium to aluminium alloys is enormously challenging due to the formation of brittle Al₁₂Mg₁₇ intermetallic compounds (IMCs). This study was aimed at improving the strength of dissimilar joints of AZ31B-H24 magnesium alloy to 5754-O aluminium alloy by using a tin interlayer inserted in between the faying surfaces during ultrasonic spot welding. The addition of tin interlayer was observed to successfully eliminate the brittle Al₁₂Mg₁₇ IMCs, which were replaced by a layer of composite-like tin and Mg₂Sn structure. Failure during the tensile lap shear tests occurred through the interior of the blended interlayer as revealed by X-ray diffraction and SEM observations. As a result, the addition of a tin interlayer resulted in a significant improvement in both joint strength and failure energy of magnesium to aluminium dissimilar joints and also led to an energy saving because the optimal welding energy required to achieve the highest strength decreased from ～1250 to ～1000 J.     

Influence of Annealing on the Properties of Explosively Welded Titanium Grade 1—AW7075 Aluminum Alloy Bimetals

Explosive welding of titanium Grade 1 to AW7075 aluminum alloy arranged in parallel setup was performed. The annealing of produced bimetals at the temperatures of 450, 500 and 550 °C for times ranging from 20 to 100 h was carried out after explosive welding. The produced bimetal was characteristic by its wavy interface typical for that bonding process. Increase in the microhardness at the interface was recorded due to work hardening. Delamination of titanium Grade 1 flyer sheet was firstly observed when annealing temperature of 500 °C for 40 h was carried out. Annealing at 550 °C also resulted in delamination of upper sheet. The intermetallic compound (IMC) layer was observed at the interface after annealing of bimetals. The higher the annealing temperature and time, the higher the thickness of continuous IMC layer. The maximum measured thickness of IMC layer averaged 13 µm. Energy dispersive x-ray spectroscopy (EDS) and x-ray diffraction (XRD) analyses revealed that the interface layer is consisted of Al₁₈Ti₂Mg₃ IMC. Microhardness at the interface increased dramatically up to 439 HV0.1 after annealing of bimetal due to the presence of above-mentioned IMC.     

Microstructure evolution and mechanical properties of Cu–Al joints by ultrasonic welding

Dissimilar joints of copper to aluminium were produced by high power ultrasonic welding (USW). The interfacial reaction between copper and 6061 aluminium alloy as a function of welding time was studied. The intermetallic compound (IMC) layer is mainly composed of CuAl₂ and Cu₉Al₄. The thickness of the IMC layer increases with the welding time. For a relatively long welding time (0·7 s) in USW, the dendritic solidification microstructure was observed in local regions, owing to the occurrence of the eutectic reaction, α-Al+θ→L, in the welding process. The lap shear load (or strength) of the joints first increases and then decreases with increasing welding time, and the failure of the joints occurred dominantly at the interface. This is mainly attributed to the development of IMC layer at the interface.     

带状组织对铝/镁异种金属搅拌摩擦焊接头力学性能的影响

采用搅拌摩擦焊(FSW)对厚度为4 mm的6061铝合金与AZ31B镁合金进行不同工艺的平板对接试验. 采用光学显微镜(OM)、扫描电镜(SEM)、X射线衍射仪(XRD)及能谱仪(EDS)对接头进行微观组织观察,采用电子万能试验机对接头力学性能进行测试. 结果表明,在接头焊核区(WNZ)中存在着明显的带状组织,带状组织是由插入镁基体中的铝合金条以及弥散分布在条带上的金属间化合物(IMCs)组成;IMCs主要为Al₁₂Mg₁₇和Al₃Mg₂;铝/镁异种金属FSW接头裂纹形核和扩展均发生在带状组织内;焊接工艺影响带状组织形态和IMCs尺寸及数量;随着转速(n)的增加或焊接速度(v)的降低,带状组织呈弯曲状,长度相对较短且呈不连续分布;当转速(n)过高或焊接速度(v)过低时,带状组织变细,但IMCs数量增多且尺寸变大;铝/镁异种金属FSW接头强度主要取决于带状组织形态和IMCs尺寸及数量.     

Effect of Intermetallic Compound Phases on the Mechanical Properties of the Dissimilar Al/Cu Friction Stir Welded Joints

Types and distribution of intermetallic compound phases and their effects on the mechanical properties of dissimilar Al/Cu friction stir welded joints were investigated. Three different rotation speeds of 1000, 1200 and 1400 rpm were used with two welding speeds of 20 and 50 mm/min. The results show that the microstructures inside the stir zone were greatly affected by the rotation speed. Complex layered structures that containing intermetallic compound phases such as CuAl₂, Al₄Cu₉ were formed in the stir zone. Their amount found to be increased with increasing rotation speed. However, the increasing of the rotation speed slightly lowered the hardness of the stir zone. Many sharp hardness peaks in the stir zones were found as a result of the intermetallic compounds formed, and the highest peaks of 420 Hv were observed at a rotation speed of 1400 rpm. The joints ultimate tensile strength reached a maximum value of 105 MPa at the rotation speed of 1200 rpm and travel speed of 20 mm/min with the joint efficiency ranged between 88 and 96% of the aluminum base metal. At the travel speed of 50 mm/min, the maximum value of the ultimate tensile strength was 96 MPa at rotation speed of 1400 rpm with the joint efficiency ranged between 79 and 90%. The fracture surfaces of tensile test specimens showed no evidence for the effect of the brittle intermetallic compounds in the stir zones on the tensile strength of the joints.     

Microstructure and mechanical properties of tungsten inert gas welded–brazed Mg/Ti lap joints

The tungsten inert gas (TIG) welding–brazing technology using Mg based filler was developed to join AZ31B Mg alloy to TA2 pure Ti in a lap configuration. The results indicate that robust joints can be obtained with welding current in the range of 60–70 A and welding speed of 0·2 m min^?1. The joints were found to be composed of the coarse grained fusion zone accompanied with the precipitated phase of Mg₁₇Al₁₂, and a distributed Mg–Ti solid solution zone at the interface of Mg/Ti, indicating that metallurgical bonding was achieved. The maximum tensile–shear strength of 193·5 N mm^?1, representing 82·3% joint efficiency relative to the Mg alloy base metal, was attained. The optimised Mg/Ti joint fractured at Mg fusion zone upon tensile–shear loading, mainly caused by grain coarsening. Moreover, the fracture surface practically consisted of scraggly areas, which was characterised by equiaxed dimple patterns accompanied with a few lamellar tearing.     

Effect of pin rotating speed on lap shear strength of stationary shoulder friction stir lap welded 6005A-T6 aluminum alloy

Stationary shoulder friction stir lap welding (SSFSLW) was successfully used to weld 6005A-T6 aluminum alloy in this paper.Effect of pin rotating speed on cross section morphologies and lap shear strength of the SSFSLW joints were mainly discussed.Results show that joints without flash and shoulder marks can be obtained by the stationary shoulder.Cross section of the SSFSLW joint presents a basin-like morphology and little material loss.By increasing the rotating speed from 1 000 rpm to 1 600 rpm,both effective sheet thickness and lap width increase,while lap shear failure load firstly decreases and then increases.The maximum failure load of 14.05 kN is attained when 1 000 rpm is used.All SSFSLW joints present shear fracture mode.     

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.     

Friction stir welding of aluminium lap joint by tool without probe

A friction stir welding process, with a rotating tool without a probe, was employed and applied to a lap joint of aluminium plate. The thickness of the aluminium plates was 0.5 mm. New tool shapes were developed. The tops of the tool were dome shaped. In this process, the rotating tool was plunged into the aluminium plate. The tool-rotating axis was vertical to the specimen surface, and then moved in the welding direction at a speed of 20 mm/s. Tool rotation speed was 18,000 rpm.

At tool plunge depths of 0.1 mm or over, it was possible to weld the two plates. At tool plunge depth of 0.1 mm, its joint was fractured at the weld interface. At tool plunge depth of 0.2 mm or over, the joints were fractured at the stir zone of the upper plate or the heat affected zone of the lower plate. Based on observation of the hardness profiles and the thickness change of the weld area, controlling factors of the joint strength are discussed.     

Modelling intermetallic phase formation in dissimilar metal ultrasonic welding of aluminium and magnesium alloys

Abstract

Intermetallic compound (IMC) formation at the joint line usually has strongly detrimental effect on the performance of dissimilar metal welds. To understand the formation of IMC interlayers, and explore strategies to control their growth, a model has been developed and applied to the case of dissimilar joining of aluminium and magnesium alloys using ultrasonic welding. The model accounts for microbond formation during welding, diffusion across the joint line, as well as nucleation, spreading and thickening of the first IMC layer (Mg₁₇Al₁₂ phase) and the formation and simultaneous thickening of the second (Al₃Mg₂) layer. The model predictions match measurements reasonably well and the model has been used to predict the sensitivity of IMC layer thickness to weld temperature and time.     

铝/黄铜异种金属TIG填丝熔钎焊工艺

采用TIG熔钎焊进行5052铝合金和H62黄铜搭接,选用Al-12% Si药芯焊丝作为填充材料,并对接头微观组织和力学性能进行分析.结果表明,Al-12% Si药芯焊丝在黄铜母材表面润湿性较差,较难获得优质的熔钎焊接头.焊缝中黄铜侧界面层附近过渡区内铝含量较高,与部分熔化和溶解的黄铜母材形成了尺寸较大的条状AlCu金属间化合物相,严重影响接头力学性能.黄铜母材侧界面层由两层不同的金属间化合物相组成,从焊缝到黄铜母材分别为Cu₉Al₄和CuZn.拉伸试验中,试样断裂于黄铜侧过渡区或界面层,断口呈现解理断裂的特征.     

Characterization of ultrasonic spot welded joints of Mg-to-galvanized and ungalvanized steel with a tin interlayer

Ultrasonic spot welded (USWed) Mg-to-bare steel, Mg-to-galvanized steel and Mg-to-bare steel with Sn interlayer (placed in-between Mg and bare steel) were studied. Weak joining occurred in the USWed Mg-to-bare steel, since Mg and Fe do not react with each other. The intermetallic compounds (IMCs) of Mg₇Zn₃ and Mg₂Zn₁₁, which led to the failure of the joint, were largely present in the USWed Mg-to-galvanized steel joint. The introduction of a Sn interlayer in the USWed Mg-to-bare steel actively worked as an intermediate medium to join Mg to Fe, and led to the presence of a distinctive composite-like Sn and Mg₂Sn eutectic structure. The lap shear strength of Mg-to-bare steel with Sn interlayer joint was significantly higher than that of the Mg-to-bare steel and Mg-to-galvanized steel joints. Failure during the tensile lap shear tests occurred mainly in the partial nugget pull-out mode in the dissimilar joints of Mg-to-bare steel with Sn interlayer. All the joints of Mg-to-galvanized steel failed from the interface (cohesive failure). The addition of Sn interlayer resulted in energy saving since the welding energy required to achieve the maximum strength decreased from 1750 to 1500 J in the Mg-to-steel joints.     

Microstructural characterization of Al/Mg alloy interdiffusion mechanism during Accumulative Roll Bonding

In this study, the Accumulative Roll Bonding (ARB) process was used with a snap-stack procedure to reduplicate an Al (1100)/Mg (AZ31) alloy. Samples underwent four rolling and stacking cycles four times, which produced a 24-layer structure. The ARB process creates a multilayer compound between Al/Mg layers with excellent bonding characteristics. The excellent bonding characteristics were due to atomic diffusion. Diffusion couples between Al and Mg were investigated to study the composition of the formation in the Al−Mg system. Layers of intermetallic compound (IMC) Al₃Mg₂ and Al₁₂Mg₁₇ were observed. The composition-depth curves of the diffusion zone were determined by electron microprobe analyses of the IMCs.     

Interface morphology and microstructure of high-power ultrasonic spot welded Mg/Al dissimilar joint

High-power ultrasonic welding technology, which has the excellent characteristics of low-energy input and high efficiency, can effectively shorten the welding time, reduce the formation of intermetallic compounds (IMCs), and improve the strength of Mg/Al dissimilar welded joints in the future manufacturing industry. Mg/Al dissimilar metal ultrasonic welded joints with favourable mechanical properties were obtained through reasonable selection of sonotrode patterns and optimisation of welding parameters. The connection mechanisms of joints were discussed based on the analysis of weld interface morphology, microstructure evolution, and the composition and distribution of Mg–Al IMCs that varied with welding energy. The mechanical interlocking phenomenon and discontinuously distributed Mg₁₇Al₁₂ with low thickness were observed at the weld interface, which helped to improve the joint performance.     

冷金属过渡搭接焊镁铝异种金属接头组织及性能

采用冷金属过渡（CMT）焊接工艺,以HS201铜焊丝作为焊缝填充金属对AZ3l镁合金和6061铝合金进行搭接焊接．测试了接头的抗剪强度和显微硬度,并利用光学显微镜（OM）、扫描电镜（SEM）、能谱（EDS）对接头的组织成分及断口形貌进行了分析．结果表明,当焊接电流为109A,电弧电压10．9V,送丝速度4．9mm／s,...     

Tensile resistance,microstructures of intermetallic compounds,and fracture modes of welded steel/aluminum joints produced using laser lap welding

The joining of DP780 steel to Al5052 was conducted by laser lap welding, in which the metal vapor and spatters were monitored by a high-speed camera. A universal testing machine was used to test the mechanical properties of the welded joints, and the changing law of lap tensile resistance with the laser welding parameters was analyzed. Optical microscope and scanning electron microscope were used to observe the macro-structure and micro-structure, respectively. Three different intermetallic compounds (IMCs) phases, i.e. banded Fe₂Al₅, FeAl₂ and needle-like FeAl₃ were generated at the steel/Al interface on microscopic observation. The aim of this research is to investigate the relationship among the lap tensile resistance, the welding parameters and the failure mode under different energy densities. Experimental results showed that the steel/Al joints have two different fracture modes at low heat input and high heat input. The failures happened along the heat-affected zone of the weld and along the steel/Al joint interface, respectively. And both of the two failure modes are brittle fractures. Additionally, cracks appeared at the fracture interface, and needle-like particle clusters were found in the fracture microstructure.