Dissimilar Friction Stir Welding Research Articles

Effect of position and force tool control in friction stir welding of dissimilar aluminum-steel lap joints for automotive applications

Widespread use of aluminum alloys for the fabrication of car body parts is conditional to the use of appropriate welding methods, especially if dissimilar welding must be performed with automotive steel grades. Friction stir welding (FSW) is considered to be a reasonable solution to obtain sound aluminum-steel joints. In this context, this work studies the effects of tool position and force control in dissimilar friction stir welding of AA6061 aluminum alloy on DC05 low carbon steel in lap joint configuration, also assessing proper welding parameter settings. Naked eye and scanning electron microscopy (SEM) have been used to detect macroscopic and microscopic defects in joints, as well as to determine the type of intermixture between aluminum and steel. The joint strength of sound joints has been assessed by shear tension test. Results point out that tool force control allows for obtaining joints with better quality and strength in a wider range of process parameters. A process window has been determined for tool force conditions to have joints with adequate strength for automotive purposes.

Simulation and experimental study of underwater dissimilar friction-stir welding between aluminium and steel

The volume of fluid (VOF) modeling method was implemented to simulate the underwater friction-stir welding (FSW) process for dissimilar joining between aluminum and steel. Temperature profile, materials flow, and intermixing during dissimilar bonding under the cooling medium were monitored via VOF modeling and verified according to experimental data. The effects of processing parameters on the formation of intermetallic compounds (IMCs) at the Al/St interface, microstructural characteristics, and mechanical property of dissimilar weldments were studied and addressed. By decreasing tool rotational speed (w), increasing traverse velocity (v), and employing cooling medium, peak temperature continuously reduced (down to ∼473 and 573 K for the aluminum and steel sides, respectively) led to substantial refining the grain structure and formation of a thinner IMC layer. The average grain size in the aluminum and steel sides of SZ is refined down to ∼4 and 12 µm, respectively. The thickness of the IMC layer varied depending on the processing parameters with the lowest value of ∼0.2 µm. The formation of a curved interface due to enhanced materials mixing at the advancing side is noted with a linear hardness gradient across the dissimilar weldment. Superior mechanical strength of ∼80 MPa attained at an optimized submerged condition of w = 1650 rpm/v = 40 mm/min showed combined ductile-brittle fractographic aspects on the fracture surface.

Improving performance of friction stir welded AZ31/AM60 dissimilar joint by adjusting texture distribution and microstructure

Inhomogeneous deformation, which was usually found during the deformation of friction stir welding (FSW) Mg alloys joints, could deteriorate the joint performance. This work aims to understand the effect of microstructure and texture distribution in joint on mechanical properties and deformation behavior of the FSW dissimilar Mg alloys joints. Two kinds of AZ31/AM60 dissimilar Mg alloys joints were obtained via FSW at two sets of welding parameters (higher rotation rate and welding speed (HRW), lower rotation rate and welding speed (LRW)). Electron backscatter diffraction measurements were conducted to examine the microstructure and texture distribution of these two joints. The results showed that the joint with finer grains, weaker texture and higher nugget zone (NZ) interface angle was obtained with HRW. The weaker texture and finer microstructure were beneficial to the homogeneous deformation of the joint. The larger angle between the NZ interface and the transverse direction (about 75°) made it away from the maximum shear force direction (45°) to avoid premature fracture. With these advantages, the mechanical properties of the joint with HRW were better than that with LRW. The yield strength, ultimate strength and elongation were improved 14.4%, 19.7% and 63.7%, respectively. In addition, the grain size of AZ31 of NZ in two joints was smaller than that of AM60. All the joints fractured at the AM60 side near the NZ boundary during the tension tests. This was mainly attributed to the larger grain size and higher Schmid factor of basal slip at the AM60 side near the NZ interface. This study provided some insights in understanding the improvement of the dissimilar FSW Mg joint performance by controlling texture distribution and microstructure.

Microstructure and mechanical behavior of similar and dissimilar AA2024 and AA7039 friction stir welds

In this work, similar and dissimilar friction stir welds of AA2024 and AA7039 were formed using optimized process parameters and truncated threaded tool. Characterization of weld joints for mechanical and microstructural properties was performed by tensile test, micro hardness test, optical microscopy, scanning electron microscopy, and energy dispersive spectrometry. The tensile strength of similar joints was higher than dissimilar joints despite lower microhardness of former. Fracture of FSW joints was found to be started by the fracture of strengthening precipitate θ or η or both in the region of tensile fracture. Dissimilar joints and similar joints of AA7039 exhibited ductile fracture mode while similar joints of AA2024 showed brittle fracture mode.

Effects of processing parameters on mechanical, material flow and wear behaviour of friction stir welded 6101-T6 and 7075-T651 aluminium alloys

Dissimilar friction stir welding (FSW) between 6101-T6 and 7075-T651 aluminium alloys was conducted. Three different parameters each were investigated for rotational speed and travel speed, and the effects of these parameters on the tensile behaviour, hardness and wear were evaluated. The results indicate that the ultimate tensile strength increases with an increase in the feed rate. However, the increase in rotational speed decreases the ultimate tensile values. The fractured analysis of the tensile samples shows similarities in the fractured pattern as all the samples failed at heat affected zone close to the 6101-T6 alloy. The hardness varies across the heat affected zones and nugget zone both at constant rotational speed and welding speeds. The highest resistance to wear occurred at 65 mm min−1 and 1850 rpm welding speed and rotational speed respectively while better material mixing was achieved at the nugget zone of the welds at 1250 rpm and 110 mm/min.

Machine Learning Approach for Defects Identification in Dissimilar Friction Stir Welded Aluminium Alloys AA 7075-AA 1100 Joints

Machine learning approaches are now applied in various manufacturing industries. Various machine learning algorithms can be implemented for prediction of the particular mechanical properties like Ultimate Tensile Strength (UTS), Elongation percentage and fracture strength of the given mechanical component and also image processing algorithms can be applied for defects detection in the mechanical components. In our recent work, we have used a novel machine learning approach for the detection of the surface defects in dissimilar Friction Stir Welded joints by using Local Binary Pattern (LBP) algorithm. The results obtained are satisfying and it is concluded that the LBP can be implemented in the detection of surface defects.

Effect of welding speeds on microstructure and mechanical properties of dissimilar friction stir welding of AA7075 and AA5083 alloy

Effect of welding speeds is studied in Friction stir welding (FSW) using cylindrical tool for the welding of Aluminum 7075 and 5083 alloys. Sound joint of similar and dissimilar FSW were obtained by use of 20 and 45 mm/min welding speed. The temperature distribution on entire weld zone influences the grain size of FSW. The grain size at different zones, affect the properties of FSW. This study, observed that the dissimilar joining of AA7075 and AA5083 exhibits better strength at the welding speed of 20 mm/min. Similar FSW achieved better strength at 45 mm/min welding speeds. Dissimilar welding required higher heat input as compare to similar welding.

Repairing of exit-hole in dissimilar Al-Mg friction stir welding: Process and microstructural pattern

The exit-hole is one major discontinuities in the friction based processes, where all the volume of the tool’s probe is missing with a depth that corresponds to the full thickness of the processed component. This letter presents a new technique to repair the exit-hole of an Al-Mg friction stir welding, without any third body material with inexpensive probeless tooling, inducing forging, stirring, and thermomechanical consolidation of the local spot joint. Intercalated banned type structures with interpenetrating features were achieved. Composite type mixed structure was obtained at repaired zone with a local tensile strength of 159 MPa.

Comparison of Strength in Dissimilar AA7204-5021 Using Friction Stir Welding by Varying Tool Pin Profile

Abstract Friction Stir Welding (FSW) of AA7204-5021 was performed with three different types of tool pin profile to analyze the strength of the materials. The fabricated welded materials undergone hardness testing for hardness of the material whereas tensile testing to identify the ductility of the work piece for the tool pin profile. By keeping the welding parameters like welding speed, traverse speed and tool rotational speed constant the work is performed for one tool profile. Furthermore investigation for the remaining two tool pin profile is performed for the selection of best tool pin profile. In this investigation the welding parameters are kept as high as possible for better results. By analyzing the stress strain ratio graphical results the better tool pin profile is selected for fixed parameters in the butt welded materials

Effect of Tool Rotational Speed on the Tensile and Microstructural Properties of Friction Stir Welded Different Grades of Stainless Steel Joints

Friction stir welding is a relatively new solid state joining process, which is suitable for welding similar and dissimilar materials. The present research work concentrates on the effect of tool rotational speed on the tensile, microstructural properties and microhardness of the friction stir welded joints of different grades of austenitic stainless steel sheets. Four different tool rotational speeds are used in the experimentation while the other process parameters like traversing speed and the tool tilt angle are kept constant. The tensile testing, micrography and microhardness measurements were carried out in the welded samples. It is observed from the results of tensile testing that the joint made at the tool rotational speed of 1320 rpm has the maximum strength among the experimented speeds. The measured microhardness values at heat affected zone and parent metal zone have shown higher hardness than the weld zone. Fine and equi-axed grains are observed in the welded region at all experimented speeds with a negligible amount of transformation of austenite into martensite. These results have impact on the development of welding procedure for dissimilar stainless steel friction stir welding process.

Research Progress in Dissimilar Friction Stir Welding of Aluminium/Magnesium Alloys

Research Progress in Dissimilar Friction Stir Welding of Aluminium/Magnesium Alloys

Post corrosion tensile strength and failure of dissimilar friction stir welded aluminium alloys

The present study efforts towards appraising the effects of corrosion on the tensile and fracture behaviour of dissimilar friction stir welding (FSW) of aluminium alloys. Three different dissimilar FSW joints obtained between AA6061-T6 and AA7075-T651, AA6061-T6 and AA2014-T6, AA7075-T651 and AA2014-T6, using threaded pin profile with three flat faces (TIF) tool at rotational speed of 1200 rpm and welding speed of 98 mm/min. The maximum joint tensile strength was achieved for AA7075-AA2014 joints followed by AA6061-AA2014 and least recorded for AA6061-AA7075 for as obtained FSW joints (non-corroded). The joints are further immersed into a corrosive solution for 1, 2, 7 and 14 days duration. The corrosion occurred all over the joint but much accelerated rate of exfoliation corrosion exists away from stir zone near the confluence of heat affected zone and base material irrespective of the advancing or retreating side. With increase in corrosion time the location of tensile failure shifted towards corroded region (AA6061-T6) instead of stir zone in dissimilar weld joint AA6061-AA2014, whereas it remained unchanged for other two joints. The fractured surfaces of AA6061-AA2014 FSW joints reveals the articulated view of pits and fracture morphology advocating the loss in YS, UTS and % elongation with increases in immersion duration.

Local Binary Pattern for the Evaluation of Surface Quality of Dissimilar Friction Stir Welded Ultrafine Grained 1050 and 6061-T6 Aluminium Alloys

Friction Stir Welding process is an advanced solid-state joining process which finds application in various industries like automobiles, manufacturing, aerospace and railway firms. Input parameters like tool rotational speed, welding speed, axial force and tilt angle govern the quality of Friction Stir Welded joint. Improper selection of these parameters further leads to fabrication of the joint of bad quality resulting groove edges, flash formation and various other surface defects. In the present work, a texture based analytic machine learning algorithm known as Local Binary Pattern (LBP) is used for the extraction of texture features of the Friction Stir Welded joints which are welded at a different rotational speed. It was observed that LBP algorithm can accurately detect any irregularities present on the surface of Friction Stir Welded joint.

Recent Advances in Dissimilar Friction Stir Welding of Aluminum to Magnesium Alloys

Abstract Welding of dissimilar magnesium alloys and aluminum alloys is a critical issue because of their worldwide increasing applications. Dissimilar welding technology has touched new frontiers to take up the benefits of both metals simultaneously through their local demands. Friction Stir Welding (TWI, 1991) is rapidly blooming in the contemporary fields of aerospace, defence, marine, automotive, and railway industries as proven approach of solid state joining. Owing to its versatility, affability to environment and energy efficiency, it is widely getting acceptance as “green technology” in modern industries. FSW has facilitated joining of high-strength, lightweight aluminum and magnesium alloys which were earlier treated as unweldable by conventional fusion welding. Present article significantly appraises the review of growth of research towards joining of dissimilar aluminium–magnesium alloys by friction stir Processing (FSP). The investigative approach is addressed through the description of joining mechanism and hurdle faced in unification of Al-Mg. Formation of intermetallic compounds (IMCs) are inevitable during joining of such heterogeneous alloys (Al-Mg) irrespective of joining methods. So it becomes challenging to impede formation and growth of IMCs, hence research community always looks for novel techniques, a few of which are covered in this piece of writing. Present review also addresses responsible theories for IMCs and its correlation with process parameters through (categorized A, B, C) evolution of microstructures. Unlike fusion welding different sorts of defects have also been reported in literature originating through FSP. Moreover, influence and correlation of process variants have been covered through study of mechanical and metallurgical characterization mentioned in literature. Mainly literature advocates research involving optimization of process parameters and their compounding effects that eventually govern quality of weld and joint efficiency during FSP of Al-Mg. Finally, article throws light on summary of FSW developments by novel techniques and untouched future endeavours being potential area of research for Al-Mg

Submerged friction stir welding of dissimilar joints between an Al-Mg alloy and low carbon steel: Thermo-mechanical modeling, microstructural features, and mechanical properties

Underwater dissimilar friction stir welding of an Al-Mg alloy (AA5005) and low carbon steel (ASTM A283) in butt joint configuration was studied. The effect of submerged temperature at three levels of 273, 298 and 333 K on the mechanical and metallurgical properties of the joints was investigated. An improvement in the properties of the submerged dissimilar joints as compared with air-processed specimens is shown. It is demonstrated that this improvement is due to the reduced peak temperature and finer grain structure caused by the cooling effect of the medium. However, the surface flow of the materials is smoother in the air-processed specimens, although processing at heated water yields better surface quality. The thickness of the interface is also reduced by the submerge friction stir welding. The strength of the dissimilar joints varies between 62–72% and 19–23% of the aluminum alloy and the steel, respectively. A lower hardness is attained in the submerged welding that can be improved by processing in warm water. The results of this study may pave a way for robust friction stir welding of dissimilar joints through controlling the temperature of the processing environment.

Optimizing the mechanical properties of friction stir welded dissimilar joint of AM60 and AZ31 alloys by controlling deformation behavior

The special microstructure distribution of the friction stir welded (FSW) Mg alloys joints is usually responsible for the non-uniform deformation and poor mechanical properties. Hence, it was possible to improve the joint mechanical properties by modifying the microstructure. In the present study, two kinds of AM60/AZ31 Mg alloys dissimilar FSW joints with different microstructure were obtained using different rotation rates (800 rpm and 1600 rpm). The results of mechanical tests showed that the tensile strength and elongation of the joint at 1600 rpm were 13.5% and 115% higher than those at 800 rpm, respectively. The microstructure observation indicated that the grain size of various zones in the joint at 1600 rpm was obviously larger than that at 800 rpm, especially at the AM60 side. However, there was no obvious difference in the texture distribution of the two welds. In addition, microstructure observation after fracture showed that there were more twins in AM60 side of the joint with coarse grains. These coarse grains promoted the activation of basal slip and twinning in the regions far away from the nugget zone (NZ) interface. This weakened the strain localization of the joint to some extent. Meanwhile, the coarse grain joint had lower concentration degree of the strain and dislocation near the NZ boundary compared with the fine grain joint. These factors led to better mechanical properties of the joint with coarse grains. This work could provide some guidelines for improving the inhomogeneous deformation behavior of dissimilar Mg alloys FSW joints.

Investigation of the Hydrogen Embrittlement Susceptibility of AA5083-H111 and AA6082-T6 Dissimilar Friction Stir Welds

The present study focused on the evaluation of the hydrogen embrittlement susceptibility of dissimilar friction stir welds of AA5083-H111 and AA6082-T6 aluminum alloys. Electrochemical cathodic charging and slow strain rate tensile method were performed to investigate the embrittlement effect of diffused hydrogen cations into the polycrystalline matrices. The main embrittlement mechanisms were studied for applied current densities of 20, 50 and 80 mA/cm2 and duration of cathodic charging effect for 2 and 4 h. The slow strain rate tensile tests were performed with a strain rate of 2.4 × 10–4 s−1 in order to promote hydrogen migration effect to critical sites (deep traps). With the increment in applied current density from 20 to 80 mA/cm2, a severe reduction in ductility and a lower decrease in yield stress and ultimate tensile strength were observed. The fractured surfaces were characterized by increased volume fraction of embrittling features such as river patterns, quasi-cleavage facets and teardrop ridges.

Effect of solid solution phase constitution on dissimilar Al/Cu FSW using Zn as an alloying element at the joint interface

The effect of Al/Zn/Cu binary and ternary solid solution phase constituents on metallurgical and mechanical properties of Al/Cu dissimilar friction stir welding using Zn as an alloying element was investigated. Because of Zn interlayer material binary intermetallic compounds (IMCs) such as AlCu, Al2Cu, Al.71Zn.29, CuZn5 and ternary IMCs such as Al4.2Cu3.2Zn.7 are formed. These solid solution alloying phase constituents improved the weld properties of the joint. The tensile strength was enhanced by 13% for Zn alloying specimens compared with non-alloyed weld specimen and 104% of the Al base material due to the formation of thin and controlled IMCs and solid solution phase constitution strengthening as well as Orowan strengthening. The fractured surface with Zn alloying element suggested combination of ductile–brittle fracture and indicated transgranular failure. Micro-hardness with Zn alloying specimen is higher compared to the non-alloyed specimen for the existence of different IMCs at the stir-zone. The mapping analysis indicated that the thickness of the IMCs with Zn alloying was at micro-meter level. Phase constituent revealed that thin continuous and uniformly distributed binary and ternary phases are beneficial for the enhancement of mechanical and metallurgical qualities. Macrostructural views revealed variation in IMCs flows at non-alloyed and Zn alloying cases. Different weld zone reflected grain variations and finer grain at the weld nugget due to the nucleating effect of Zn interlayer.

Dissimilar friction stir welding of AA6061 and Ti6Al4V alloys: A study on microstructure and mechanical properties

Intact Al/Ti joints were fabricated using W-Re pin tool at various welding speeds when the rotating speed was 1000 rpm. The temperature histories were recorded and tool wear was measured, in order to study the welding processes. The microstructure of the welds had a smaller grain size as the welding speed increased. The base materials were intermixed at a welding speed of 40 mm/min, forming the Al/Ti mechanical mixture and hook structure at/beside the interface. However, no obvious Al/Ti intermixing could be found in joints welded at 80 mm/min or more. Distinguishable amount of intermetallic compound (IMC) were depicted from the Al/Ti mixture in light of the SEM and EDS results. TiAl3 was further identified from the interface by TEM. The lowest hardness was tested at the boundary between HAZ and TMAZ, and the highest hardness was found at interface, due to the excessive IMCs in the Al/Ti mixture. The joints reached the maximum shear load of 4206 N at 80 mm/min. The specimens all failed along the interface with the characteristics of both brittle and plastic fracture.

Investigation of Heat-Assisted Dissimilar Friction Stir Welding of AA7075-T6 Aluminum and AZ31B Magnesium Alloys

This study investigates the successful joining methods of dissimilar metals of AZ31B Mg and AA7075-T6 Al alloys. The specimens were joined by using open-flame heating system and investigated the effect of the friction stir welding (FSW) process parameters on the welding quality, transverse rupture strength (TRS), tensile strength, microhardness, and microstructure of the resulting specimens. The welding experiments were conducted based on the Taguchi mixed-orthogonal-array for tests, L16 (42 × 22), at a constant spindle speed of 500 rpm using a K10 grade carbide mixing tool with two different tilt angles (0° and 3°), and two tool tip geometries (square and triangle). The specimens were successfully welded, and the test results revealed that the welding temperatures and forces had the strongest effect on the welding quality. The achieved maximum tensile strength and TRS were approximately 122.1 MPa and 712.1 MPa, respectively, at a tool travel speed of 20 mm/min, tool offset value of 0.75 mm, tool tilt angle of 3°, and using a triangle tool tip. The microstructural analysis indicated that a dynamically recrystallized and grain refinement structure formed in the welded zone depending on the temperature and on the excessive deformation. The increase in the microhardness values depends on the intermetallic compounds ratio and fine-grained structure in the welded zone.