Developments of mathematical models for prediction of tensile properties of dissimilar AA6061-T6 to Cu welds prepared by friction stir welding process using Zn interlayer

Amount of intermetallics formed at the weld interface in dissimilar friction stir welding may be reduced by use of suitable interlayer materials such as Zn. In the present investigation, mathematical models have been developed for prediction of tensile properties of dissimilar AA6061-T6 to pure Cu welds prepared by friction stir welding process with Zn interlayer. Experiments were planned as per Box–Behnken design of response surface methodology. Three-factor, three-level Box–Behnken design with 15 runs was employed. Three process parameters: tool rotation speed (710, 1000 and 1400 rpm), tool travel speed (28, 56 and 80 mm/min) and tool pin offset (+0.5, +1.0 and +1.5 mm towards AA6061-T6 sheet) were considered. Lacks of fit for the developed models were assessed using analysis of variance (ANOVA). Validities of the developed models were checked by conducting confirmation runs. Predicted and experimental results of confirmation runs were found in reasonable agreements. Microstructural characterization revealed typical microstructure composed of intercalation of base metals. It was observed by X-ray diffraction analysis that use of Zn interlayer coupled with tool offset of +1.0 and +1.5 resulted in elimination of intermetallics of Al–Cu system at the weld interface, improving dissimilar weld quality.     

Material stirring during FSW of Al–Cu: Effect of pin profile

Friction stir welding (FSW) joins the material in solid state, and it gets evolved as a new and effective technique to join dissimilar materials such as aluminum and copper. FSW tool design and configuration critically affect the joint quality. This study has evaluated the effect of different pin profiles used during FSW of AA5754 Al alloy and commercially pure copper in a butt configuration on the microstructure, material movement, and microhardness for the different joints. The joining is performed through the different pin profiles of cylindrical, taper, cylindrical cam, taper cam, and square shape at the rotational and welding speed of 900?rpm and 40?mm/min respectively. Among all joints, the square pin profile provides good joining and microhardness. Square tool pin profile facilitates good amount of mixing at nugget zone, which consequently increases the hardness. The material movement in square tool pin profile joint is also studied on the longitudinal plane to understand the effect of pulsating and stirring action on the material mixing pattern in dissimilar FSW. It is evident that the softer material in the stir zone gets more stirring, and the flow lines are clearly visible for the stirred material.     

Friction stir welding of dissimilar aluminum alloys AA2219 to AA5083 – Optimization of process parameters using Taguchi technique

The joining of dissimilar Al–Cu alloy AA2219-T87 and Al–Mg alloy AA5083-H321 plates was carried out using friction stir welding (FSW) technique and the process parameters were optimized using Taguchi L₁₆ orthogonal design of experiments. The rotational speed, transverse speed, tool geometry and ratio between tool shoulder diameter and pin diameter were the parameters taken into consideration. The optimum process parameters were determined with reference to tensile strength of the joint. The predicted optimal value of tensile strength was confirmed by conducting the confirmation run using optimum parameters. This study shows that defect free, high efficiency welded joints can be produced using a wide range of process parameters and recommends parameters for producing best joint tensile properties. Analysis of variance showed that the ratio between tool shoulder diameter and pin diameter is the most dominant factor in deciding the joint soundness while pin geometry and welding speed also played significant roles. Microstructural studies revealed that the material placed on the advancing side dominates the nugget region. Hardness studies revealed that the lowest hardness in the weldment occurred in the heat-affected zone on alloy of 5083 side, where tensile failures were observed to take place.     

Effects of Al-Ni powder addition on dissimilar friction stir welding between AA7075-T6 and 304 L

Friction stir welding between AA7075-T6 aluminum alloy and 304 L stainless steel sheet metal was performed with the addition of Al−Ni powder between the joining interfaces to increase the joining performance. The welding tool was rotated at 200 min⁻¹ to 800 min⁻¹ with the constant traverse speed of 25 mm/min. The resulting joint interfaces were analyzed using a field emission-scanning electron microscope and energy-dispersive x-ray spectroscopy analysis. The tensile strength was greater for the Al−Ni powder added specimens at the lower tool rotational speeds. The tensile strength of 360 MPa was obtained for the ‘with-powder’ specimen as compared to 220 MPa for the ‘without-powder’ specimen at the 200 min⁻¹ tool speed. Electron microscope images of the stir zone showed a significant mixing of the Al−Ni powder with the base materials, increased contact at the interface, which resulted in increased joining strength at the lower tool rotational speeds. However, based on the images, intermetallic compound that may contribute to the joining strength in the vicinity of the interfacial region was not detected.     

工艺参数和搅拌头尺寸对2024铝合金和AZ31镁合金异种金属搅拌摩擦连接接头性能的影响

研究了2024铝合金与AZ31镁合金的异种搅拌摩擦连接工艺,并获得了良好的3mm板材对接接头。采用5种不同的工艺参数和两种不同尺寸的搅拌头进行加工。研究了不同工艺参数对接头微观组织、拉伸强度和硬度分布的影响。结果表明,使用15mm轴肩的搅拌头能够获得无缺陷的接头,在转速500r/min、连接速度500mm/min的工艺参数下,显微硬度分布均匀,材料边界明显,异种材料间的机械锁和结构增大了接头强度。在转速300r/min、连接速度30mm/min的工艺参数下,拉伸断裂位置位于铝合金一侧的热机影响区和材料混合区的交界处,虽然接头存在金属间化合物,但充分的材料混合使接头拉伸强度与前者相当。     

Study of the Linear Friction Welding Process of Dissimilar Ti-6Al-4V–Stainless Steel Joints

Linear friction welding (LFW) is an innovative joining method that can be used to obtain high-strength joints between dissimilar materials. A key factor that influences the joint's performances are the intermetallic compounds that could be formed during the welding process. These intermetallics are brittle and could compromise the mechanical performances of the joint. This article deals with the analysis of the LFW process of dissimilar titanium–stainless steel joints. Two different types of joints were studied: AISI 304–Ti6Al4V and AISI 316–Ti6Al4V. Particular attention was paid to characterizing the intermetallic compounds using scanning electron microscopy, Electron probe microanalysis and X-ray diffractometry. Zones with different microstructure were observed. Due to the diffusive phenomena occurring during the welding, Kirkendall effect and occurrence of several intermetallics were observed. Moreover, it was found that the joint with AISI 316 formed brittle intermetallic compounds, which led to crack formation close to the weld line.     

Microstructure and interface characterization of dissimilar friction stir welded lap joints between Ti–6Al–4V and AISI 304

The feasibility of dissimilar friction stir welding (FSW) in overlap configuration between Ti–6Al–4V alloy (Ti64) and AISI 304 austenitic stainless steels (304SS) was investigated. Sound joints were achieved when placing titanium as the upper workpiece. Joints were successfully produced by employing a welding speed of 1 mm/s and rotational speeds of 300 and 500 rpm. A lamellar microstructure was formed in the stir zone of Ti64, where grain size was found to increase with increasing rotational speed, and austenitic equiaxed grains were obtained near the interface of 304SS coupon. Energy dispersive X-ray spectroscopy (SEM-EDS) of the interface revealed a thin intermixed region and suggested intermetallic compound formation. Microhardness data in the titanium weld zone for both rotational speeds exhibited slightly lower values than the base material, with the lowest values in the heat affected zone, whereas the microhardness values in the stainless steel side around the weld center were found to be higher than those obtained for the base material.     

Interface microstructure evolution of dissimilar friction stir butt welded F82H steel and SUS304

The dissimilar butt welded joint of reduced-activation ferritic/martensitic steel (RAF/M) F82H and austenite stainless steel (AISI304 (SUS304)) were studied by friction stir welding. The effect of the position of the steels and tool plunging was considered in order to prohibit the mixing of the F82H and SUS304. When the dissimilar butt welding was performed such that the F82H plate was on the advancing side and the tool was plunged on the F82H side, defect-free joints could be successfully fabricated. Optical microscopy and EDX analysis were used to characterize the dissimilar joint microstructures and the interface. It was confirmed that the dissimilar joint formed no mixed structure and inter-metallic compounds.     

Microstructure and mechanical properties in nano and microscale SiC-included dissimilar friction stir welding of AA6061-AA2024

This work investigates the effect of SiC particles on the microstructure and mechanical properties of dissimilar friction stir welding between AA6061-T6 and AA2024-T351. Two variations in the size of SiC particles, along the joint line, various groove width, and tool offset, were used for the welding. It was found that the joints made by rotational speed of 800?rev?min^?1, travelling speed of 31.5?mm?min^?1, groove width of 0.3?mm, and tool offset of 0.5?mm exhibited the most uniform distribution of particles for both micro- and nano-scale SiC particles. Additionally, the smaller and rounded equiaxed particles result in easier material flow, a more uniform metal matrix composite, the smallest grain size in the stir zone and the highest tensile strength.     

Influence of probe offset distance on interfacial microstructure and mechanical properties of friction stir butt welded joint of Ti6Al4V and A6061 dissimilar alloys

Friction stir butt welding of titanium alloy Ti6Al4V and aluminum alloy A6061-T6 with 2 mm thickness was conducted by offsetting probe edge into the titanium alloy at rotation speed of 750 rpm and 1000 rpm and welding speed of 120 mm/min. The effect of probe offset distance on the interfacial microstructure and mechanical properties of the butt joint was investigated. When the probe offset distance is not sufficient, the two alloys cannot be completely joined together, i.e. there exists no bonding or kissing bonding at the root part of joint interface. However, when the probe offset distance is too large, a great amount of intermetallic compounds are formed at the joint interface and its adjacency, leading to fracturing roughly along the joint interface during a tensile test. In a proper range of probe offset distance, sound dissimilar butt joints are produced, which have comparatively high tensile strength and fracture in heat affected zone of the aluminum alloy during a tensile test.     

Stop drilling procedure for fatigue life improvement

This paper investigated how the stop drilling procedure improved the crack initiation life and the total fatigue life in specimens of 6061-T651 aluminium alloy and AISI 304 stainless steel. The crack initiation life was the number of fatigue cycles initiating a 0.2 mm crack at a stophole edge. The larger the stophole diameter, the longer the crack initiation and total fatigue lives. The 2, 2.5, and 3 mm diameter stopholes improved the nonstop-drilled total fatigue life of the 6061-T651 specimen by 187%, 321%, and 443% and that of the AISI 304 specimen by 72%, 121%, and 174%. At each stophole diameter, the 6061-T651 crack initiation life improved over the AISI 304 counterpart because of lower values of the K_f factor and the ΔJ/ρ_c ratio.     

Microstructure-property characterization of a friction-stir welded joint between AA5059 aluminum alloy and high density polyethylene

Aluminum alloys and high density polyethylene are utilized in a wide variety of industrial applications. In the present work the feasibility of friction stir butt welding between AA5059 alloy and high density polyethylene sheets is examined. The bonding mechanism, joint strength, and microhardness are considered in this study. Various welding parameters and tool alignment were investigated until sound joints were achieved by positioning approximately 85% of the rotating tool in the aluminum material on the advancing side (1.4 mm offset) at constant spindle speed and traverse speed of 710 rpm and 63 mm/min, respectively. The results indicate that AA5059 aluminum and high density polyethylene sheets can be successfully joined with a combination of secondary bonding and mechanical interlocking of the materials, which provides a potential alternative to adhesive bonding or mechanical fastening.     

Effect of tool rotational speed and pin profile on microstructure and tensile strength of dissimilar friction stir welded AA5083-H111 and AA6351-T6 aluminum alloys

The relatively new welding process friction stir welding (FSW) was applied in this research work to join 6 mm thick dissimilar aluminum alloys AA5083-H111 and AA6351-T6. The effect of tool rotational speed and pin profile on the microstructure and tensile strength of the joints were studied. Dissimilar joints were made using three different tool rotational speeds of 600 rpm, 950 rpm and 1300 rpm and five different tool pin profiles of straight square (SS), straight hexagon (SH), straight octagon (SO), tapered square (TS), and tapered octagon (TO). Three different regions namely unmixed region, mechanically mixed region and mixed flow region were observed in the weld zone. The tool rotational speed and pin profile considerably influenced the microstructure and tensile strength of the joints. The joint which was fabricated using tool rotational speed of 950 rpm and straight square pin profile yielded highest tensile strength of 273 MPa. The two process parameters affected the joint strength due to variations in material flow behavior, loss of cold work in the HAZ of AA5083 side, dissolution and over aging of precipitates of AA6351 side and formation of macroscopic defects in the weld zone.     

Softened zone formation and joint strength properties in dissimilar friction welds

The mechanical properties of dissimilar MMC/AISI 304 stainless steel friction welds with and without silver interlayers were examined. The notch tensile strengths of MMC/AISI 304 stainless steel and MMC/Ag/AISI 304 stainless steel friction welds increased when high friction pressures were applied during the joining operation. The higher notch tensile strengths of dissimilar MMC/AISI and MMC/Ag/AISI 304 stainless steel friction welds resulted from the formation of narrow softened zones in MMC material immediately adjacent to the bondline. The influence of softened zone width and hardness (yield strength) on the notch tensile strengths of dissimilar welds was analysed using finite element modelling (FEM). FEM in combination with the assumption of a ductile failure criterion was used to calculate the notch tensile strengths of dissimilar joints. The key assumption in this work is that dissimilar weld failure wholly depended on the characteristics (mechanical properties and dimensions) of the softened zone formed in MMC material immediately adjacent to the bondline. The modelling results produced based on this assumption closely correspond with the actual notch tensile strengths of dissimilar MMC/Ag/AISI 304 stainless steel and MMC/Ag/AISI 304 stainless steel friction welds.     

Role of plunge depth on the joint formation and mechanical behavior of Al6063-AZ91 dissimilar lap joint produced by friction stir welding

Dissimilar lap joint of Al6063 aluminium and AZ91 magnesium alloys was successfully produced by friction stir welding. Three different plunge depths (3.2 mm, 3.25 mm, and 3.3 mm) were adopted during welding. Similar Al6063–Al6063 lap joints were also produced along with the dissimilar Al6063–AZ91 joints for the purpose of comparing the joint formation. With the increased plunge depth, the width of the similar Al6063 - Al6063 lap joint was increased. On the contrary, joint width was decreased for the dissimilar joint with increased plunge depths. The dissimilar joint was formed with a strong metallurgical bonding between the Al6063 and AZ91 alloys, which is attributed to the mechanical mixing of these alloys in the nugget zone. Additionally, the formation of intermetallics was also observed from the x-ray diffraction analysis. The variations within the measured hardness values were higher at the joint interface due to the mixing of aluminium and magnesium alloys in the nugget zone. From the tensile shear tests, increased strength and decreased elongation were measured with the increased plunge depth. The results demonstrate the importance of the plunge depth on the lap joint formation between dissimilar Al6063–AZ91 alloys during friction stir welding.     

A Review on Dissimilar Friction Stir Welding of Copper to Aluminum: Process,Properties, and Variants

Copper and aluminum materials are extensively used in different industries because of its great conductivities and corrosion resistant nature. It is important to join dissimilar materials such as copper and aluminum to permit maximum use of the special properties of both the materials. The joining of dissimilar materials is one of the most advanced topics, which researchers have found from last few years. Friction stir welding (FSW) technology is feasible to join dissimilar materials because of its solid state nature. Present article provides a comprehensive insight on dissimilar copper to aluminum materials joined by FSW technology. FSW parameters such as tool design, tool pin offset, rotational speed, welding speed, tool tilt angle, and position of workpiece material in fixture for dissimilar Cu–Al system are summarized in the present review article. Additionally, welding defects, microstructure, and intermetallic compound generation for Cu–Al FSW system have been also discussed in this article. Furthermore, the new developments and future scope of dissimilar Cu–Al FSW system have been addressed.     

Dissimilar friction stir lap welding of AA 5754-H22/AA 6082-T6 aluminium alloys: Influence of material properties and tool geometry on weld strength

Dissimilar friction stir welding (FSW) of heat (AA 6082-T6) and non-heat (AA 5754-H22) treatable aluminium alloys, in lap joint configuration, was performed in this work. The base material plates were 1 mm thick. Welds were performed combining different plates positioning, relative to the tool shoulder, in order to assess the influence of base materials properties on welds strength. Three different tools were tested, one cylindrical and two conical, with different taper angles. Welds strength was characterized by performing transverse and tensile–shear tests. Strain data acquisition by Digital Image Correlation (DIC) was used to determine local weld properties. The results obtained enabled to conclude that the dissimilar welds strength is strongly dependent on the presence of the well-known hooking defect and that the hooking characteristics are strongly conditioned by base materials properties/positioning. By placing the AA 6082-T6 alloy, as top plate, in contact with the tool shoulder, superior weld properties are achieved independently of the tool geometry. It is also concluded that the use of unthreaded conical pin tools, with a low shoulder/pin diameter relation, is the most suitable solution for the production of welds with similar strengths for advancing and retreating sides.     

Impact performance of friction welded butt joints between 6061-T6 aluminium alloy and type 304 stainless steel

Abstract

The tensile strength and energy absorption for dissimilar metal friction welds between 6061-T6 Al alloy and type 304 stainless steel at high rates of loading were determined using the split Hopkinson bar. Cylindrical tensile specimens machined from as welded butt joints of 13 mm in diameter were used in both static and impact tests. Friction welding was conducted using a brake type friction welding machine under two different welding conditions. The effects of welding conditions and loading rate on the joint tensile properties were examined. Results show that the joint tensile properties were greatly affected by the welding parameters, and were slightly enhanced with increased loading rate. Scanning electron microscope observations revealed that the tensile fracture modes in the butt joint specimens varied with loading rate and depend on welding conditions. Microhardness profiles across the weld interface were measured to investigate the extent of the heat affected zone. The slight enhancement of the joint tensile properties with increasing loading rate is primarily attributed to the strain rate dependence of the thermally softened 6061-T6 Al alloy base material.     

ENVIRONMENTAL FATIGUE CRACK PROPAGATION IN METAL/COMPOSITE LAMINATES

Abstract— Flight simulation fatigue crack propagation tests with gust spectrum loading were carried out on laminates of (i) aluminium alloy 2024-T3/carbon epoxy, (ii) aluminium alloy 7475-T761/carbon-epoxy and (iii) titanium alloy Ti–6Al–4V/carbon-epoxy, each with a nominal weight saving of 30% as compared to equivalent 2024-T3 panels. The performance of the 2024-T3/carbon-epoxy laminates was much superior to those of the other material combinations. Overall, there was a fairly strong effect of changing from an environment of normal air to an air plus water spray environment. Probable reasons for this strong effect are discussed.     

Chemical and Mechanical Characterization of AISI 304 and AISI 1010 Laser Welding

This paper addresses to the dissimilar laser welding of AISI 304 and AISI 1010 steel thin sheets. Cracks-free dissimilar edge fillet welds have been conducted using a Nd:YAG laser. Geometrical, microstructural, chemical, and mechanical proprieties of the welds were investigated using electron microscopy, EDS and tensile test assisted by digital image correlating. The proper results were achieved at an energy density of 88 J/mm² using a 0.4 mm laser spot diameter. An austenite-ferrite structure characterizes the weld bead and the precipitation of the chromium carbide at the grain limits was observed in the heat affected zone. Good tensile behavior was obtained; dissimilar joint was fractured on the carbon steel side at 482 MPa and 0.35 stain.