Friction Stir Welding Technology Research Articles

Innovate Method for Friction Stir Welding of Al-Mg-Si Alloy Thin Plate

Al-Mg-Si (6061-T6) alloy with 0.8 mm thick plate was welded successfully by use of high speed friction stir welding (FSW) technology. The microstructural characteristics and mechanical property of the butt joints prepared by high speed FSW were analyzed in detail, the influence of welding parameters, fixture condition and after welding heat treatment were also explored. The results shown that sound surface topography and defect-free bonding interface were observed in the nugget zone (NZ). The microhardness of the as-welded joint was lower than that of the base metal because of the welding heat effect. Compared with the conventional speed FSW, the number of β-Mg2Si, Al2CuMg and Al8Fe2Si precipitated phases existed in the high speed FSWed NZ increased, which made the microhardness in the NZ improved significantly. The rod-shaped precipitates (Mg2Si) have the greatest influence on the microhardness distributions. The maximum tensile strength of 301.8 MPa, which was 85.8% of the base metal, was obtained at high rotation speed of 8000 rpm and fast welding speed of 1500 mm/min. The tensile strength of the ultra-high speed FSWed butt joints were improved significantly by post-weld artificial aging, with a maximum joint efficiency of 90.4%.

Analiza procesu zużycia narzędzi wykonanych ze stali 1.2344 oraz stopu MP159 w procesie zgrzewania tarciowego z przemieszaniem (FSW) blach ze stopu Aluminium 7075 T6

The study presents an analysis of wear of tools made of 1.2344 steel and MP159 alloy for the process of obtaining an overlap joint in 1.0 mm and 0.8 mm sheet metal made of 7075 T6 aluminum alloy using friction stir welding (FSW) technology. Tool geometry was designed at the Czestochowa University of Technology. Evaluation of tool wear was conducted based on the measurements of geometry of working area of tools by means of a multisensory meter system and based on the assessment of the working area by means of a stereoscope after individual stages of wear tests. Furthermore, based on the results of a static tensile strength test and metallographic examinations of the specimens sampled from the joints obtained during tool wear tests, the effect of the degree of tool wear on joint quality was also evaluated. Analysis of the results revealed that both the tool made of 1.2344 steel and that made of MP159 alloy were substantially worn, increasing the risk of further use of the tools for the joint material (7075-T6) after obtaining the joint with length of 200m, which suggests their low durability. Furthermore, modification of tool geometry caused by wear led to insignificant improvements in joint strength. Therefore, the results of wear measurement set directions for further modification of tool geometry, also due to the fact that despite a substantial wear, the tools continued to yield high-quality joints without defects. As demonstrated in the study, the type of tool material does not only impact on tool life but also, as it was the case in their geometry, has a significant effect on the quality of obtained joints. Although the tool made of MP159 alloy was worn more than the tool made of 1.2344 steel, it allowed for obtaining the joints with substantially better strength parameters.

Fatigue of Friction Stir Welded Aluminum Alloy Joints: A Review

The application fields of friction stir welding technology, such as aerospace and transportation, has high safety requirements and fatigue is the dominant failure mode for weldments. It is of great significance to understand the fatigue properties of friction stir welded joints. This paper provides an overview of the fatigue mechanism, influencing factors, crack growth rate, and fatigue life assessment. It is found that the fatigue performance of friction stir welded joints can be affected by welding process parameters, test environment, stress ratio, residual stress, and weld defect. The optimized process parameters can produce high quality weld and increase the weld fatigue life. Laser peening is an effective post weld treatment to decrease fatigue crack growth rate and improve material fatigue life.

Special features of the weldability of a new wrought VMD16 magnesium alloy

ABSTRACTThe results of the investigation of the weldability of a new VMD16 magnesium alloy by automatic argon-shielded arc welding and friction stir welding are presented. The friction stir welding technology was investigated for the first time for the Russian magnesium wrought alloy. The data obtained in the studies of the phase composition and structure of the VMD16 alloy are presented. The experimental results show that the intermetallic phases (Mg, Zn)5REE (REE = rare-earth elements) and Zn2(Zr, REE)3 and the Laves phases ZrZn2, together with the fine-grained and equiaxed structure (the grain size 8–12 µm), result in a high level of the strength characteristics of the alloy and of welded joints in the alloy. It is also shown that the alloy is characterized by higher (two to six times) resistance to the formation of cracks in welding than the standard magnesium alloys MA2-1, MA2-1pch and MA20. The strength of the welded joints in the VMD16 alloy equals 0.85–0.88 of the strength of the parent material. Postweld heat treatment is not required.

Friction stir welding of aircraft wings

ABSTRACTTo reduce the weight of the wings of the TU-204SM aircraft, investigations were carried out to design the upper wing panel made of the V-1469 high-strength aluminium–lithium alloy of the third generation. The technology of friction stir welding was developed and fragments of the welded panel produced. The tests of the stability under compression showed that the application of the welded panels reduces the weight of the wing by up to ~10% and increases the stability and load carrying capacity by up to ~30%.

Microstructures evolution and localized properties variation of a thick friction stir welded CuCrZr alloy plate

The welding processing between large-dimension components is a big challenge for manufacturing in modern industry. In this work, a friction stir welding technology was employed to weld 30 mm thick CuCrZr alloy plates together with high strength and conductivity. The thermal histories and temperature distributions in the welded plate produced by friction stir welding (FSW) were simulated. The microstructural evolution and variation of properties in different regions around the weld line were investigated systematically. The results revealed that the large grains in the base material (BM) were transformed into a microstructure where the grains were completely equiaxed in the weld nugget zone (WNZ) induced by continuous dynamic recrystallization (CDRX), which can be attributed to the combination of severe deformation and high welding temperature. The significant changes to the heat gradient resulted in variations of prominent microstructures and properties in the structure from the top to the bottom layers in the WNZ. In the thickness direction, the exquiaxed grain size in the WNZ were decreased gradually while the hardness and strength were increased slightly. The large strength of the BM is due to the precipitation strengthening from the Cr precipitates even though the grain size is larger than that in the WNZ, while the large strength of the bottom layer is dominant because of the grain boundary strengthening.

Friction Stir Welding of AlSi10Mg Plates Produced by Selective Laser Melting

A preliminary research work is carried out to demonstrate the feasibility of friction stir welding of AlSi10Mg plates produced by selective laser melting. The metallurgical evolutions occurring have been studied and discussed on the basis of detailed microstructure observations. The FSW process enhances the structure of the parent material so that the weld presents an overall refinement of the microstructure and a decrease in microporosity in all its zones. Using the friction stir welding technology, sound welds harder than the parent material can be obtained.

Research of Urban Rail Transit Vehicle Aluminum Alloy Bolster FSW Welding Technology Based on Thermal-Mechanical Coupling

With the rapid development of urban rail transit and the increasing level of research and development, aluminum alloy materials feature excellent physical and mechanical properties, and thus an urban rail transit vehicle adopts aluminum alloy materials. Friction Stir Welding (FSW) technology is adopted in the production process of a bolster in this article and research of stress strain of friction stir welding parts plays an important role for engineering application of friction stir welding technology.

Modeling of friction-stir butt-welds and its application in automotive bumper impact performance Part 1. Thermo-mechanical weld process modeling

The demand for better structural performance in joining of components for road vehicles prompts the implementation of aluminum alloy friction stir welding technology in the automotive industry. The aim of current study is the creation of a 3-D finite element (FE) friction thermal model and stir welding (FSW) process of dissimilar aluminum alloy and for the estimation of crash worthiness performance of FSW fabricated shock absorber assembly. Thermo mechanical simulations and analysis are performed to understand the thermal behavior in the FSW weld zones. The developed models are correlated against published experimental results in terms of temperature profile of the weld zone. The developed models are then implemented for fabricating vehicle bumper parts to illustrate the performance of FSW welded components during an impact. Customary sled testing for low-speed guard necessities is performed utilizing a grating blend welded test apparatus at Wichita State University (WSU) at the National Institute for Aviation Research (NIAR). A few guard congregations are then appended to the test installation utilizing FSW and conventional Gas bend GMAW welding strategies. Numerical models are likewise created where limited component investigation is utilized to contrast the anticipated harm and the real harm maintained by both of the FSW and GMAW manufactured guards. During the research, a new FSW weld mold is created that allows for a better representation of the desired progressive crack propagation. The FSW fabricated bumper based on the Johnson-Cook failure model yields better failure prediction and is in good agreement to the test. The results from this study provide a guideline for an accurate finite element modeling of a FSW fabricated components and their application in the crashworthiness of such structural components.

The effect of changing chemical composition on dissimilar Mg/Al friction stir welded butt joints using zinc interlayer

In this study, solid state joining technology of friction stir welding (FSW) was carried out for Al and Mg butt joints. To improve the microstructural characteristics of the banded structure zone, before to the FSW process, a Zn interlayer was also inserted in the butt joints. Optimal conditions for friction stir welding were obtained using a combination of two travel speeds (25 and 35 mm/min) and three rotation speeds (550, 600 and 650 rpm). Mg-Zn and Mg-Al-Zn IMCs, Al solid solution and residual Zn were the most common phases in the stirred zone, eliminating Al-Mg intermetallic formation. The joint fabricated at 35 mm/min and 600 rpm, in which tensile strength of the weld improved from 141 to 175 MPa and an elongation from 0.7 to 1.9 was achieved, gave the maximum mechanical properties compared with the Zn free sample FSWed under identical conditions. The fracture micrographs were compatible with the corresponding ductility results and the fracture surfaces of Zn added samples possessed a fine texture combining brittle and ductile fracture features. Meanwhile, the hardness level was lower than that of the Zn free sample because of the change in the IMCs composition of the Zn added samples.

High cycle fatigue and fatigue crack propagation design curves for 5754-H22 and 6082-T6 aluminium alloys and their friction stir welded joints

Friction stir welding (FSW) is a dynamically developing version of pressure welding processes. Nowadays, learning the properties and behaviour of the welded joints is an important direction of investigation, especially under cyclic loading. The research work aimed (i) to demonstrate the behaviour of FS welded joints under cyclic loading conditions and (ii) to determine fatigue design curves for two aluminium alloys and their welded joints made by the FSW process. Experiments were performed on 5754-H22 and 6082-T6 aluminium alloys and their welded joints; high cycle fatigue (HCF) and fatigue crack propagation (FCG) tests were performed. Statistical approaches were applied during the experiments and the evaluation process. HCF design curves were determined based on the staircase method and FCG design curves were determined by our own previously developed six-step method. The results of the HCF and FCG tests on FS welded joints confirm the applicability of the applied FSW technology and show good correspondence with results of the comparative base materials and welded joints that can be found in the literature. Based on our experimental results and the evaluation methods used, statistically established parameters of HCF and FCG design curves were calculated.

Microstructure evolution and fracture behaviour of friction stir welded 6061-T6 thin plate joints under high rotational speed

ABSTRACT6061-T6 sheets with 0.8 mm thickness were successfully welded using high-speed friction stir welding (FSW) technology. The microstructural evolution and fracture behaviour of the joints were studied. The results show that sound joints could be obtained at the investigated high rotational speed of 8000 rev min−1 and welding speeds of 300–1200 mm min−1. Compared with conventional rotational speed, the grain size in the nugget zone (NZ) is obviously refined under high rotational speed. The Mg2Si, Al8Fe2Si and Al2CuMg precipitates reprecipitated adequately in the NZ during high-speed FSW, resulting in the number of the precipitates increased significantly, and further alleviating the weld softening. The difference in weld softening leads to different fracture characteristics during the tensile process. After artificial aging, the maximum welding softening in all joints is located in the heat affected zone, and the fracture is characterised by brittle fracture.

Recent progress in friction stir welding tools used for steels

Friction stir welding (FSW) technology is being increasingly attractive in welding steels on account of the high-quality weld formation and excellent weld properties. The feasibility of FSW of steels has been convinced for nearly 20 years. However, the application progress for FSW of steels is slower than that of aluminum alloys owing to the high cost and poor usability of tools. The FSW tools are called as the heart of FSW process which is critical for welding quality control and the weld microstructure and properties. The recent progresses in research and development of FSW tools for welding steels have been reviewed. Material selections, geometry parameters, wear behavior and use life of the tools are summarized from the available literatures.

EFFECT OF PROCESS PARAMETERS ON MICROSTRUCTURE AND MECHANICAL PROPERTIES OF RFSSW LAP JOINTS OF THIN AL7075-T6 SHEETS

1. Financial support of The National Centre for Research and Development, European Union, PZL Mielec A Sikorsky Company in the framework of European Regional Development Fund Project “Advanced techniques for the fabrication of airframe structures using innovative friction stir welding (FSW) technology”, Nr INNOLOT/I/4/NCBR/2013 is gratefully acknowledged.

Ultrasonic testing of thin walled components made of aluminum based laminates

The goal of this paper is to evaluate the feasibility of testing thin walled components made of aluminum based laminates using ultrasonic waves. Aluminum alloys are applied in aviation, maritime and railway industries. The advantages of aluminum alloys include high specific strength, good machinability, and formability. In recent years, the position of aluminum as preferred material in transportation has been challenged by composites. The share of composites in the structure of aircraft such as AirBus A350XWB and Boeing 787 Dreamliner exceeds 50%. The application of composites allow weight to be reduced by 10 ÷ 20%. In response to the proliferation of composite structures aluminum industry started developing the next generation of aluminum lithium alloys allowing a reduction in aircraft structure weight by 8 ÷ 15%. In Bombardier CSeries aircraft the fuselage was made of aluminum lithium alloy, while the wings were made of composites. In the near future, both aluminum and composites will be used in aviation. There is a need for the development of technology for testing of thin walled components made of aluminum based sheets. In this work, ultrasonic testing of the aluminum based laminate having section thickness of 1.5 mm is presented. The laminate comprised two aluminum sheets with and without the polyimide interlayer which were joined using friction stir welding technology. The suggested ultrasonic method allowed material discontinuities having a width greater than 0.4 mm to be detected.

Effects of processing parameters on the characteristics of dissimilar friction-stir-welded joints between AA5058 aluminum alloy and PMMA polymer

In this research, newly modified solid-state friction-stir welding (FSW) technology was employed to bond the sheets of an aluminum-magnesium alloy (AA5058) and poly-methyl-methacrylate (PMMA) in a lap-joint design. Effects of processing parameters including tool rotational speed (w), traverse velocity (v), tilt angle and plunge depth on the surface morphology, materials flow pattern, microstructural characteristics, and mechanical properties of the dissimilar FSWed joints were studied. The geometry of U-antler macro-mechanical interlocking and interfacial micro- and nano-scale chemical bonding was mainly controlled by the tool tilting angle. A sound dissimilar weld with the highest tensile strength of around 45 MPa was attained at an optimum working window containing w = 1600 rpm, v = 25 mm/min, tool tilt angle of 2°, and plunge depth of 0.2 mm. Fracture of dissimilar lap joints occurred during transverse tensile-shear testing from the weld-polymer interface with a maximum strength ratio of ~ 60% by detachment of aluminum U-antler from the solidified polymer.

Effect of pin tool design on the material flow of dissimilar AA7075-AA6061 friction stir welds

Tool design is the most influential aspect in the friction stir welding (FSW) technology. Influence of pin tool geometry on material flow pattern are studied in this work during the FSW of dissimilar AA7075 and AA6061 aluminium alloys. Three truncated pin tool profiles (threaded, threaded with single flat, and unthreaded with single flat) were used to prepare the weldments. The workpieces were joined using a custom-made clamping system under 1100 rpm of spindle speed, 300 mm/min of traverse rate and 3° of tilt angle. The metallographic analysis showed that defect-free welds can be produced using the three pin tools with significant changes in the mixing stir zone structure. The results declared that the introducing of the flat on the cone of the probe deviates the pattern of the onion rings without changing the chemical composition of the created layers. This in turn improves the hardness distribution and tensile strength of the welded joint. It was also noted that both heat affected zone (HAZ) and thermal-mechanical affected zone (TMAZ) are similar in composition to their corresponding base materials (BM).

Residual Stress Measurement in Innovative Friction Stir Welding Processes

In recent years, important innovations have been introduced in Friction Stir Welding (FSW) technology such as, for example, the Laser assisted Friction Stir Welding (LFSW) and in-process Cooled Friction Stir Welding (CFSW). Residual stresses have a fundamental role in welded structures because they affect the way to design the structures, fatigue life, corrosion resistance and many other material properties. Consequently, it is important to investigate the residual stress distribution in FSW where, though the heat input is lower compared to traditional welding techniques, the constraints applied to the parts to weld are more severe. The aim of the present work is to verify the capabilities of both FSW techniques in reduction of the residual stress in aluminium butt joints.

Alternative friction stir welding technology for titanium–6Al–4V propellant tanks within the space industry

ABSTRACTFriction stir welding (FSW) offers an appealing solid state joining alternative to traditional fusion welding techniques for titanium alloys because it reduces problems associated with high temperature processing. Propellant tanks are a critical component of every spacecraft and contain several weld seams and a prime candidate for this innovative technology. This paper reviews the current technological maturity of FSW relative to titanium alloys and considers the application with respect to a pressure vessel. FSW is currently in a period of significant investment by large engineering companies and international research institutions. The technology is advancing and evolving to cater for high temperature alloys. Stationary shoulder FSW and hybrid techniques show promising potential with respect to Ti–6Al–4V. The tool material and limited process window for this material are restrictive factors at present but can be overcome with future development.

Parameter optimisation of friction stir welded dissimilar polymers joints

There has been a significant increase in the use of polymeric materials in various areas of industry and engineering, which were previously dominated by metallic components. Recently, the possibility of implementing friction stir welding (FSW) technology for welding polymer-polymer and polymer-metal has come under investigation. Polymeric materials behave differently from metallic ones, and there is still a limited number of research works in the literature concerning this specific topic. In this study, a stationary shoulder made of Teflon was used to weld thin plates of polypropylene and polyethylene together in the lap-joint configuration without external heating. Using a stationary shoulder, the probe generates all the frictional heat and stirs the nearly molten material under an axial force. This article is focused on parameter optimisation for friction stir welded lap joints of dissimilar polymers using a new tool concept. It was concluded that the tool design has the most effective role regarding the lap-shear strength of joints. Welds fabricated with the optimised welding parameters present good surface quality and strength. Moreover, for welding polymeric materials with this method, the main defects have been found on the retreating side of the welds. This behaviour can be explained by insufficient heat generation on the retreating side as well as poor thermal conductivity of polymeric materials.