Friction stir welding of aluminium hollow extrusion: weld formation and mechanical properties

Novel friction stir welding (FSW) technique, characterised by big concave upper and small convex lower shoulders, for aluminium hollow extrusion was studied. Assisted with the lower shoulder, root flaws due to the lack of tool penetration have been eliminated. The tensile strength increased with increasing welding speed. As the welding speed increases from 50 to 200 mm min^?1, the width of the welding nugget zone (WNZ) decreases, and the ductile fractured location occurred at WNZ instead of heat affected zone (HAZ) adjacent to thermomechanically affected zone (TMAZ). The interface between the TMAZ and HAZ exhibited the lowest microhardness. The results indicated that the novel FSW method has the potential to join tubular structures and hollow profiles widely used in transportation industries.     

Material flow during friction stir spot welding of dissimilar Al2024/Al materials

In the present paper, the material flow and intermixing during friction stir spot welding of dissimilar Al2024/Al materials were investigated. The dissimilar materials had quite different strength. The microstructural evolutions taking place during a series of lap and butt welds were observed. The effect of penetration depths, dwell time, rotational speed and tool geometry were systematically investigated. The material flow and formation of the intermixed region were explained by a modified model.     

Effects of welding parameters and post-heat treatment on mechanical properties of friction stir welded AA2195-T8 Al-Li alloy

In this study, the effects of main welding parameters(rotation speed(ω) and welding speed(v)) on the microstructure, micro-hardness distribution and tensile properties of friction stir welded(FSW)2195-T8 Al-Li alloy were investigated. The effects of T6 post-treatments at different solution and aging conditions on the mechanical properties and microstructure characteristics of the FSW joints were also investigated. The results show that with increasing and v, both strength and elongation of the joints increase first, and then decrease with further increase of and v. All the joints under varied welding parameters show significant strength loss, and the strength reaches only 65% of the base metal. The effect of T6 post-heat treatment on the mechanical properties of the joints depends on the solution and aging conditions. Two heat treatment processes(480℃× 0.5 h quenching + 180℃× 12 h,520℃× 0.5 h quenching + 180℃× 12 h aging) are found to increase the joint strength. Furthermore,low temperature quenching(480℃) is more beneficial to the joint strength. The joint strength can reach 85% of the base metal. Whereas both low temperature aging(140℃× 56 h) and stepped aging(100℃× 12 h + 180℃× 3 h) processes decrease the joint strength. After heat treatment all the joints show decreased ductility due to the obvious grain coarsening in the nugget zone(NZ) and thermo-mechanically affected zone(TMAZ).     

Effect of friction stir welding parameters on morphology and strength of acrylonitrile butadiene styrene plate welds

The aim of this study is to examine the effect of main friction stir welding (FSW) parameters on the quality of acrylonitrile butadiene styrene (ABS) plate welds. Welds were carried out in a FSW machine, using a tool with a stationary shoulder and no external heating system. The welding parameters studied were the tool rotational speed which varied between 1000 and 1500 (rpm); the traverse speed which varied between 50 and 200 (mm/min), and the axial force ranging from 0.75 to 4 (kN). The major novelty is to study the influence of the parameter axial force on FSW of polymers. Produced welds have always a tensile strength below the base material, reaching the maximum efficiencies of above 60 (%) for welds made with higher rotational speed and axial force. Good quality welds are achieved without using external heating, when the tool rotational speed and axial force are above a certain threshold. Above that threshold the formation of cavities and porosity in the retreating side of the stir zone is avoided and the weld region is very uniform and smooth. For low rotational speed and axial force welds have poor material mixing at the retreating side and voids at the nugget. For this reason the strain at break of these welded plates is low when compared with that of base material.     

Joining of metal to plastic using friction lap welding

Friction lap welding (FLW) is a new conception of joining method developed in Joining and Welding Research Institute (JWRI). The efficiency of joining metal and plastic using FLW was demonstrated through a case study on aluminium alloy AA6061 and MC Nylon-6. The lap joints with high shear strength were obtained over a wide range of welding parameters. A linear relationship was observed between FLW parameters (R/ν)^0.5 and the thickness of melted nylon (H). The influences of FLW parameters on bubbles and shear strength were investigated. The morphologies of the fractured surfaces of AA6061 alloy fell into seven types based on the scanning electron microscopy examination. Statistical analysis showed that the contribution to shear strength of these regions followed such an order: region II > region V > region VI > region VII > region IV > region I or III.     

The optimisation of process parameters for friction stir spot-welded AA3003-H12 aluminium alloy using a Taguchi orthogonal array

The aim of the present work is to optimise the welding parameters for friction stir spot welded non-heat-treatable AA3003-H12 aluminium alloy sheets using a Taguchi orthogonal array. The welding parameters, such as the tool rotational speed, tool plunge depth and dwell time, were determined according to the Taguchi orthogonal table L9 using a randomised approach. The optimum welding parameters for the peak tensile shear load of the joints were predicted, and the individual importance of each parameter on the tensile shear load of the friction stir spot weld was evaluated by examining the signal-to-noise ratio and analysis of variance (ANOVA) results. The optimum levels of the plunge depth, dwell time and tool rotational speed were found to be 4.8 mm, 2 s and 1500 rpm, respectively. The ANOVA results indicated that the tool plunge depth has the higher statistical effect with 69.26% on the tensile shear load, followed by the dwell time and rotational speed. The tensile shear load of the friction stir spot welding (FSSW) joints increased with increasing plunge depth. Additionally, examination of the weld cross-sections, microhardness tests and fracture characterisation of the selected friction spot welded joints were conducted to understand the better performance of the joints. All the fractures of the joints during tensile testing occurred at stir zone (SZ), where the bonded section was minimum. The tensile shear load and tensile deformation of the FSSW joints increased linearly with increasing the bonded size. The finer grain size in the SZ led to the higher hardness, which resulted in higher fracture strength. When the tensile shear load of the joints increased approximately 3-fold, the failure energy absorption of the joints increased approximately 15-fold.     

Flow patterns in friction stir welds of AA5083 and AA6082 alloys

The flow patterns in dissimilar friction stir welds of AA5083-O and AA6082-T6 alloys have been studied. It was observed that material flows (pushes but does not mix) more from the advancing side into the retreating side. Material flow from the retreating side to the advancing side only occurs in the tool shoulder domain, and the pull is greatest at the transition region between the tool shoulder domain and the tool pin domain. It was also observed that materials tend to extrude out only in the thermomechanically affected zone of the retreating side, which was influenced by rotation of both the tool shoulder and the tool pin. The finest grains were present in the regions closest to the tool edge in the retreating side. The volume fraction of recrystallized grains increases down into the deeper part of the nugget from the flow arm region. Microhardness measurements revealed that regions of lowest hardness values were the nugget and the heat affected zone of the AA6082-T6 alloy side. The welding speeds had no influence on the microhardness values per se, but affected the mixing proportions in the flow arm and in the nugget stem.     

Analysis of process parameters effects on friction stir welding of dissimilar aluminum alloy to advanced high strength steel

Thin sheets of aluminum alloy 6061-T6 and one type of Advanced high strength steel, transformation induced plasticity (TRIP) steel have been successfully butt joined using friction stir welding (FSW) technique. The maximum ultimate tensile strength can reach 85% of the base aluminum alloy. Intermetallic compound (IMC) layer of FeAl or Fe₃Al with thickness of less than 1 μm was formed at the Al–Fe interface in the advancing side, which can actually contribute to the joint strength. Tensile tests and scanning electron microscopy (SEM) results indicate that the weld nugget can be considered as aluminum matrix composite, which is enhanced by dispersed sheared-off steel fragments encompassed by a thin intermetallic layer or simply intermetallic particles. Effects of process parameters on the joint microstructure evolution were analyzed based on mechanical welding force and temperature that have been measured during the welding process.     

搅拌摩擦焊镁合金隔声性能的研究

伴随搅拌摩擦焊在镁合金上的广泛应用,对其隔声特性研究尤为重要,基于自适应网格技术,对搅拌摩擦焊过程进行数值模拟,为后续声学计算提供约束模态,解决了材料属性难以确定的问题,一定程度上实现了焊接与声学的结合。自行设计和制造了混响箱,用以测量焊接镁合金板的隔声量,弥补了混响室测试小试件的不足。进而使用finite element-statistical energy analysis(FE-SEA)混合法计算焊接件的隔声量,与试验结果进行对比,吻合良好,表明此方法行之有效。通过对比焊接前后镁合金板件的隔声量,发现在吻合低谷区,焊接后板件的隔声有所降低。为了研究焊接参数对隔声的影响,分别改变焊接速度和搅拌头旋转速度,观察隔声量的变化,结果表明,这些参数都需要合理的设置,并非越大或者越小越好。     

Force response characteristics and mechanical properties of friction stir welded AA2024 sheets

Process force and tensile properties in friction stir welding of AA2024 sheets were studied. Results show that the forces present a periodic variation with the same periodicity which is nearly equal to the time of one tool rotation, and thus it only depends on rotation speed. With increasing welding speed the forces increase gradually, while with increasing rotation speed the forces first decrease and then increase. Joints with superior strength-ductility synergy are produced at 900?rev?min^?1–300?mm?min^?1 and 1000?rev?min^?1–350?mm?min^?1. These joints experience nearly the same peak temperature and axial force. As heat input increases the failure initiates from the interface between nugget zone (NZ) and thermo-mechanically affected zone to heat-affected zone continuing to NZ.     

Mechanical properties of friction stir butt‐welded Al‐5086 H32 plate

Al‐5086 H32 plates with a thickness of 3 mm were friction stir butt‐welded using different welding speeds at a tool rotational speed of 1600 rpm. The effect of welding speed on the weld performance of the joints was investigated by conducting optical microscopy, microhardness measurements and mechanical tests (i.e. tensile and bend tests). The effect of heat input during friction stir welding on the microstructure, and thus mechanical properties, of cold‐rolled Al‐ 5086 plates was also determined. The experimental results indicated that the maximum tensile strength of the joints, which is about 75 % that of the base plate, was obtained with a traverse speed of 200 mm/min at the tool rotational speed used, e.g. 1600 rpm, and the maximum bending angle of the joints can reach 180^o. The maximum ductility performance of the joints was, on the other hand, relatively low, e.g. about 20 %. These results are not unexpected due to the loss of the cold‐work strengthening in the weld region as a result of the heat input during welding, and thus the confined plasticity within the stirred zone owing to strength undermatching. Higher joint performances can also be achieved by increasing the penetration depth of the stirring probe in butt‐friction stir welding of Al‐5086 H32 plates.     

Taguchi optimization and ultrasonic measurement of residual stresses in the friction stir welding

The main goal of this study is optimization of residual stresses produced by friction stir welding (FSW) of 5086 aluminum plates. Taguchi method is employed as statistical design of experiment (DOE) to optimize welding parameters including feed rate, rotational speed, pin diameter and shoulder diameter. The optimization process depends on effect of the welding parameters on longitudinal residual stress, which is measured by employing ultrasonic technique. The ultrasonic measurement method is based on acoustoelasticity law, which describes the relation between acoustic waves and internal stresses of the material. In this study, the ultrasonic stress measurement is fulfilled by using longitudinal critically refracted (L_CR) waves which are longitudinal ultrasonic waves propagated parallel to the surface within an effective depth. The ultrasonic stress measurement results are also verified by employing the hole-drilling standard technique. By using statistical analysis of variance (ANOVA), it has been concluded that the most significant effect on the longitudinal residual stress peak is related to the feed rate while the pin and shoulder diameter have no dominant effect. The rotational speed variation leads to changing the welding heat input which affects on the residual stress considerably.     

Fabrication of large-bulk ultrafine grained 6061 aluminum alloy by rolling and low-heat-input friction stir welding

In this study, the ultrafine grained (UFG) 6061 Al alloys fabricated by cold rolling were friction stir welded (FSW) with different rotation rates under both air cooling and rapid cooling in water. Low-heat-input parameters of 400 rpm rotation rate in water (400-Water) could effectively inhibit the coarsening of recrystallized grains, reduce the precipitation rate, and retain more dislocations of the UFG 6061 Al parent metal. 400-Water joint showed high lowest-hardness value, narrow low-hardness zone, and high tensile strength, attributing to the effect of dislocation, grain boundary, solid-solution, and precipitation hardening. This work provides an effective strategy to fabricate large-sized bulk UFG Al alloy by cold rolling with large deformation and low-heat-input FSW.     

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.     

Effect of welding parameters on microstructure in the stir zone of FSW joints of aluminum die casting alloy

The effect of the welding speed and the rotation speed on the microstructure in the stir zone has been investigated by measuring the Si particle distribution in the ADC12 alloy. The stir zone has fine recrystallized grains without dendritic structures, and the eutectic Si was uniformly dispersed in the stir zone. The size of the Si particles was statistically determined in the stir zone using image processing. The number of finer Si particles, which is formed by stirring of the tool probe, increases during the FSW. Finer Si particles are distributed more in the bottom than in the other regions, though the size of the Si particles in the base metal is the same in all the regions. The size of the Si particles decreases with increasing welding speed. However, it is not significantly affected by the rotation speed.     

A review of numerical analysis of friction stir welding

Friction stir welding is a relatively new solid-state joining technique which is widely adopted in different industry fields to join different metallic alloys that are hard to weld by conventional fusion welding. Friction stir welding is a highly complex process comprising several highly coupled physical phenomena. The complex geometry of some kinds of joints and their three dimensional nature make it difficult to develop an overall system of governing equations for theoretical analyzing the behavior of the friction stir welded joints. The experiments are often time consuming and costly. To overcome these problems, numerical analysis has frequently been used since the 2000s. This paper reviews the latest developments in the numerical analysis of friction stir welding processes, microstructures of friction stir welded joints and the properties of friction stir welded structures. Some important numerical issues such as materials flow modeling, meshing procedure and failure criteria are discussed. Numerical analysis of friction stir welding will allow many different welding processes to be simulated in order to understand the effects of changes in different system parameters before physical testing, which would be time-consuming or prohibitively expensive in practice. The main methods used in numerical analysis of friction stir welding are discussed and illustrated with brief case studies. In addition, several important key problems and issues remain to be addressed about the numerical analysis of friction stir welding and opportunities for further research are identified.     

The effect of weld parameters on friction stir welding of brass plates

More successful results have been obtained in butt‐ and overlap‐joining of Al‐alloy plates by a recently developed solid state joining technique, namely friction stir welding (FSW), than in more conventional fusion welding processes. In this joining technique, no fusion takes place in the joint area of the plates welded. This novel joining method also offers the potential to weld some other materials rather than Al‐alloys, such as Mg‐alloys, brasses and low strength steels. In this study, the applicability of friction stir welding to brasses, namely 90 %Cu‐10 %Zn and 70 %Cu‐30 %Zn alloys, has been investigated. The joint performance was determined by conducting optical microscopy, microhardness mesurements and mechanical testing (e.g. tensile and bend tests). The effect of welding speed on the joint quality at a given rotational speed of the stirring pin (i.e. 1600 rpm) was also determined for both alloys. The highest joint performances were obtained at a welding speed of 210 mm/min for both alloys.     

Defects and tensile properties of 6013 aluminum alloy T-joints by friction stir welding

In this paper, 6013-T4 T-joints were successfully fabricated with different welding parameters by friction stir welding in two different combination modes of skins and stringers. The distribution features and formation mechanisms of defects in T-joints were observed and analyzed. The effect of defects and welding parameters on tensile properties of T-joints was investigated. The result shows that the T-joint without tunnel defect only can be obtained with the traverse speed of 100 mm/min in this experiment, and the welding parameters influence the features and sizes of kissing bond defects. The fracture of T-joints along the shin is attributed to the kissing bond defect and the tunnel defect is the main factor affecting the tensile properties along the stringer.     

Friction stir based welding and processing technologies - processes,parameters, microstructures and applications: A review

Friction stir welding (FSW) has achieved remarkable success in the joining and processing of aluminium alloys and other softer structural alloys. Conventional FSW, however, has not been entirely successful in the joining, processing and manufacturing of different desired materials essential to meet the sophisticated green globe requirements. Through the efforts of improving the process and transferring the existing friction stir knowledge base to other advanced applications, several friction stir based daughter technologies have emerged over the timeline. A few among these technologies are well developed while others are under the process of emergence. Beginning with a broad classification of the scattered frictions stir based technologies into two categories, welding and processing, it appears now time to know, compile and review these to enable their rapid access for reference and academia. In this review article, the friction stir based technologies classified under the category of welding are those applied for joining of materials while the remnant are labeled as friction stir processing (FSP) technologies. This review article presents an overview of four general aspects of both the developed and the developing friction stir based technologies, their associated process parameters, metallurgical features of their products and their feasibility and application to various materials. The lesser known and emerging technologies have been emphasized.