Fatigue properties of friction stir welded particulate reinforced aluminium matrix composites

Few papers have discussed the friction stir welding (FSW) of particulate reinforced aluminium matrix composites and most of them focused on the set-up of the welding process parameters and their effect on microstructure, hardness and tensile behaviour. The aim of this study was to investigate the fatigue resistance of FSW joints on an as-cast particulate reinforced aluminium based composite (AA6061/22 vol.%/Al₂O_3p). The welding process was performed using different process parameters, also investigating their effect on joint microstructure. The mechanical properties of the FSW composites were compared with those of the base material and the results were correlated to the microstructural modifications induced by the FSW process on the aluminium alloy matrix and the ceramic reinforcement. FSW reduced the size of both particle reinforcement and aluminium grains, and also led to a significant increase in interparticle matrix microhardness, for all process parameters. The FSW specimens belonging to a different set of parameters, tested without any post-weld heat treatment, exhibited a very high joint efficiency (ranging from 90% to 99%) with respect to the ultimate tensile strength of the base material. The stress controlled fatigue test showed a high spread both for the base and FSW composites. Statistical analysis disclosed that all FSW specimens belonging to different process parameters showed apparently slightly worse fatigue behaviour than that of the base composite. Statistical processing applied to the different welding parameters revealed that all the welded specimens belonged to the same population. Therefore it can be concluded that the parameters used produced joints with similar microstructure and comparable fatigue behaviour. The slight difference in the fatigue behaviour of the FSW specimens whose process parameters differed form those of the unwelded composite was explained by the different microstructural homogeneity in the transition from the base to the FSW zone.     

Characterization of friction stir welded boron carbide particulate reinforced AA6061 aluminum alloy stir cast composite

Development of welding procedures to join aluminum matrix composite (AMCs) holds the key to replace conventional aluminum alloys in many applications. In this research work, AA6061/B₄C AMC was produced using stir casting route with the aid of K₂TiF₆ flux. Plates of 6 mm thickness were prepared from the castings and successfully butt joined using friction stir welding (FSW). The FSW was carried out using a tool rotational speed of 1000 rpm, welding speed of 80 mm/min and axial force of 10 kN. A tool made of high carbon high chromium steel with square pin profile was used. The microstructure of the welded joint was characterized using optical and scanning electron microscopy. The welded joint showed the presence of four zones typically observed in FSW of aluminum alloys. The weld zone showed fine grains and homogeneous distribution of B₄C particles. A joint efficiency of 93.4% was realized under the experimental conditions. But, FSW reduced the ductility of the composite.     

Predicting tensile strength,hardness and corrosion rate of friction stir welded AA6061-T6 aluminium alloy joints

AA6061-T₆ aluminium alloy (Al–Mg–Si alloy) has gathered wide acceptance in the fabrication of light weight structures requiring high strength-to-weight ratio and good corrosion resistance. The friction stir welding (FSW) process and tool parameters play major role in deciding the joint characteristics. In this research, the tensile strength and hardness along with the corrosion rate of friction-stir-butt welded joints of AA6061-T₆ aluminium alloy were investigated. The relationships between the FSW parameters (rotational speed, welding speed, axial force, shoulder diameter, pin diameter and tool hardness) and the responses (tensile strength, hardness and corrosion rate) were established. The optimal welding conditions to maximize the tensile strength and minimize the corrosion rate were identified and reported here.     

Microstructure and tensile strength of friction stir welded joints between interstitial free steel and commercially pure aluminium

In the present study, the joining of interstitial free steel and commercial pure aluminium was carried out by friction stir welding (FSW) technique using tool rotational speeds of 600, 900, 1200 rpm and traverse speed of 100 mm/min. The microstructure and micro-hardness of the weld interface have been investigated. Optical microscopy was used to characterize the microstructures of different regions of friction stir welding joints. The scanning electron microscopy-back scattered electron (SEM-BSE) images show the existence of the different reaction layers in the welded zone. The Al₃Fe intermetallic compound has been observed in the weld interface and their thickness increase with the increase in tool rotational speed. Tensile strength was also evaluated and maximum tensile strength of ∼123.2 MPa along with ∼4.5% elongation at fracture of the joint have been obtained when processed at 600 rpm tool rotational speed.     

Barium titanate reinforced nickel aluminium bronze surface composite by friction stir processing

Friction stir processing (FSP) is a surface modification technique, which can be used for the fabrication of surface composites. In the present work, a surface composite was prepared by introducing a piezoelectric ceramic powder (PZT; BaTiO₃) to a nickel aluminium bronze (NAB) metal matrix using FSP. BaTiO₃ powder was placed in holes drilled at the centre of a NAB plate and FSP was carried out. Microstructural characterisation of the surface composite was carried out using optical microscopy and scanning electron microscopy. The microhardness and tensile behaviour of the surface composite were investigated, together with the cavitation erosion behaviour. The results are discussed in light of the microstructural modification.     

Microstructures and wear property of friction stir welded AZ91 Mg/SiC particle reinforced composite

The microstructures and wear property of friction stir welded AZ91 Mg alloy/SiC particle reinforced composite (AZ91/SiC/10p) were investigated. The initial microstructures of the AZ91/SiC/10p were composed of irregularly distributed β-phases (Al₁₂Mg₁₇) and agglomerated SiC particles, while the friction stir weld zone was characterized by the homogeneous distribution of SiC particles, the recrystallized grain structure and the dissolution of β-phase. Thank to the microstructural modification, an improvement in the hardness and wear property of the weld zone were observed as compared to those of the base metal. The hardness near the weld zone was a higher and more homogeneously distributed and the wear resistance within the weld zone, as evaluated by the specific wear loss, was superior, as compared with the base metal.     

Analysis of residual stresses in particulate reinforced aluminium matrix composite after EDM

This paper reports the effect of properties of three types of particulate reinforced metal matrix composite materials (65?vol.-%SiC/A356·2, 10?vol.-%-SiC–5?vol.-% quartz/Al, 30?vol.-%SiC/A359) and machining parameters on residual stresses induced in the machined surface during powder mixed electric discharge machining. Three electrode materials (Cu, Gr and Cu–Gr) and three machining parameters, namely, peak current and pulse (on/off) duration, are varied to determine the magnitude of induced residual stresses. The result shows that the workpiece, electrode material properties, and pulse off time significantly contribute in the formation of residual stresses. Concentration of reinforced particulates and matrix conductivity also play a vital role in the development of residual stresses. The deposition of disintegrated particles of composite electrode (Cu–Gr) results in high magnitude of residual stresses.     

亚麻落麻纤维增强可降解复合材料的拉伸强度预测

采用非织造结合热压成型工艺制备了亚麻落麻纤维增强聚乳酸(PLA)基可降解复合材料(亚麻落麻/PLA),研究了纤维体积分数对材料拉伸强度的影响,并利用 Kelly-Tyson拉伸强度预测模型及相关修正理论,提出了非连续植物纤维增强可降解复合材料(D-NFRBC)强度预测模型,该模型考虑了纤维长度、取向角、直径、强度概率分布及材料界面剪切强度与材料中纤维临界长度、纤维极限拉伸强度三者间制约关系对复合材料强度的影响。结果表明;亚麻落麻/PLA拉伸强度在纤维体积分数为39.6%时达到最大,应用本文建立的强度预测模型所得亚麻落麻/PLA拉伸强度预测值与实验值吻合良好。     

Optimization of friction stir welding process parameters to maximize tensile strength of stir cast AA6061-T6/AlNp composite

Aluminium Matrix Composites (AMCs) reinforced with particulate form of reinforcement has replaced monolithic alloys in many engineering industries due to its superior mechanical properties and tailorable thermal and electrical properties. As aluminium nitride (AlN) has high specific strength, high thermal conductivity, high electrical resistivity, low dielectric constant, low coefficient of thermal expansion and good compatibility with aluminium alloy, Al/AlN composite is extensively used in electronic packaging industries. Joining of AMCs is unavoidable in many engineering applications. Friction Stir Welding (FSW) is one of the most suitable welding process to weld the AMCs reinforced with particulate form of ceramics without deteriorating its superior mechanical properties. An attempt has been made to develop regression models to predict the Ultimate Tensile Strength (UTS) and Percent Elongation (PE) of the friction stir welded AA6061 matrix composite reinforced with aluminium nitride particles (AlN_p) by correlating the significant parameters such as tool rotational speed, welding speed, axial force and percentage of AlN_p reinforcement in the AA6061 matrix. Statistical software SYSTAT 12 and statistical tools such as analysis of variance (ANOVA) and student’s t test, have been used to validate the developed models. It was observed from the investigation that these factors independently influenced the UTS and PE of the friction stir welded composite joints. The developed regression models were optimized to maximize UTS of friction stir welded AA6061/AlN_p composite joints.     

Tensile behavior of dissimilar friction stir welded joints of aluminium alloys

The heat treatable aluminium alloy AA2024 is used extensively in the aircraft industry because of its high strength to weight ratio and good ductility. The non-heat treatable aluminium alloy AA5083 possesses medium strength and high ductility and used typically in structural applications, marine, and automotive industries. When compared to fusion welding processes, friction stir welding (FSW) process is an emerging solid state joining process which is best suitable for joining these alloys. The friction stir welding parameters such as tool pin profile, tool rotational speed, welding speed, and tool axial force influence the mechanical properties of the FS welded joints significantly. Dissimilar FS welded joints are fabricated using five different tool pin profiles. Central composite design with four parameters, five levels, and 31 runs is used to conduct the experiments and response surface method (RSM) is employed to develop the model. Mathematical regression models are developed to predict the ultimate tensile strength (UTS) and tensile elongation (TE) of the dissimilar friction stir welded joints of aluminium alloys 2024-T6 and 5083-H321, and they are validated. The effects of the above process parameters and tool pin profile on tensile strength and tensile elongation of dissimilar friction stir welded joints are analysed in detail. Joints fabricated using Tapered Hexagon tool pin profile have the highest tensile strength and tensile elongation, whereas the Straight Cylinder tool pin profile have the lowest tensile strength and tensile elongation. The results are useful to have a better understanding of the effects of process parameters, to fabricate the joints with desired tensile properties, and to automate the FS welding process.     

Effect of heat treatment on tensile properties of friction stir welded joints of 2219-T6 aluminium alloy

Abstract

The effect of post-weld heat treatment (PWHT) on the tensile properties of friction stir welded (FSW) joints of 2219-T6 aluminium alloy was investigated. The PWHT was carried out at aging temperature of 165°C for 18 h. The mechanical properties of the joints were evaluated using tensile tests. The experimental results indicate that the PWHT significantly influences the tensile properties of the FSW joints. After the heat treatment, the tensile strength of the joints increases and the elongation at fracture of the joints decreases. The maximum tensile strength of the joints is equivalent to 89% of that of the base material. The fracture location characteristics of the heat treated joints are similar to those of the as welded joints. The defect free joints fracture in the heat affected zone on the retreating side and the joints with a void defect fracture in the weld zone on the advancing side. All of the experimental results can be explained by the hardness profiles and welding defects in the joints.     

Microstructure and microtextural studies of friction stir welded aluminium alloy 5052

The present investigation presents a composite picture of the microstructural developments in a friction stir welded (FSW) AA5052. Optimized, defect free and chemically homogeneous, FS weld was generalized in four regions – base material (BM), nugget, advancing side (AS) and retreating side (RS), using standard nomenclatures. Each region had its signature of microstructural features. AS had clear indications of shear and of grain fragmentation. The nugget region, on the other hand, had nearly equiaxed grains, with strong in-grain misorientation and presence of grain-interior dislocation structure ruling out contributions from static recrystallization. Equiaxed grains of the nugget region had typical onion ring structure – each ring did approximately correspond to one dominant family of orientation. Microstructural developments, as obtained from relative grain refinement, in-grain misorientation development, relative banding, etc., were most significant in nugget followed by AS and then by RS. Heterogeneous plastic deformation and thermal activation through localized heating/friction were the apparent causes. Most of the friction stir welded specimen fractured away from the nugget and showed ductile mode of failure.     

Microstructure and mechanical properties of friction stir welded Al/Mg2Si metal matrix cast composite

In this research, friction stir weldability of 15 wt.% Mg₂Si particulate aluminum matrix cast composite and effects of tool rotation speed and number of welding passes on microstructure and mechanical properties of the joints were investigated. Microstructural observations were carried out by employing optical and scanning electron microscopy of the cross sections perpendicular to the tool traverse direction. Mechanical properties including microhardness and tensile strength were evaluated in detail. The results showed fragmentation of Mg₂Si particles and Mg₂Si needles existing in eutectic structure in stir zone. Also, homogeneous distribution of Mg₂Si particles was observed in the stir zone as a result of stirring with high plastic strains. Tension test results indicated that tensile strength of the joint had an optimum at 1120 rpm tool rotation speed and decreased with increasing of the number of welding passes. Hardness of the joint increased due to modification of solidification microstructure of the base composite. This research indicates that friction stir welding is a good candidate for joining of 15 wt.% Mg₂Si aluminum matrix composite castings.     

Laser beam processing of a SiC particulate reinforced 6061 aluminium metal matrix composite

SiC particulate reinforced 6061 Al metal matrix composites were laser beam cut using a 3kW continuous wave CO2 laser. The influence of laser processing parameters such as cutting speed, laser power, and shielding gas on the quality of the cuts were investigated. Optical microscopy, scanning electron microscopy and X-ray diffraction were used to analyse the laser treated zone. Experimental results show that 6061 Al metal matrix composites can cut be successfully using laser. A number of Al4C3/Al4SiC4 plates were formed in the heat affected zones due to a chemical reaction between Si and Al that occurred during the laser processing. This revised version was published online in November 2006 with corrections to the Cover Date.     

A review of friction stir welding of aluminium matrix composites

As a solid state joining process, friction stir welding (FSW) has proven to be a promising approach for joining aluminium matrix composites (AMCs). However, challenges still remain in using FSW to join AMCs even with considerable progress having been made in recent years. This review paper provides an overview of the state-of-the-art of FSW of AMC materials. Specific attention and critical assessment have been given to: (a) the macrostructure and microstructure of AMC joints, (b) the evaluation of mechanical properties of joints, and (c) the wear of FSW tools due to the presence of reinforcement materials in aluminium matrices. This review concludes with recommendations for future research directions.     

Warm and room temperature deformation of friction stir welded thin aluminium sheets

Friction stir welding is a welding solid state process of large potential advantages for aerospace and automotive industries dealing with light alloys. The metal to be welded is not melted and this avoids welding defects such as cracks and porosity. Moreover, there is no significant deterioration in mechanical properties due to phase transformations in the joint and low-cost and high-quality joints can be produced even from heat-treatable aluminium alloys, notably difficult to weld. In this study, very thin rolled sheets (0.8 mm in thickness) of 2024T3 and 6082T6 were friction stir welded, parallel to the rolling directions, obtaining similar joints (2024T3–2024T3 and 6082T6–6082T6) and dissimilar joints (6082T6–2024T3). Tensile tests at temperatures and strain rates of 170–230 °C and 10⁻³–10⁻⁵ s⁻¹ respectively were performed on the thin joints. The flow stress decreased with increasing temperature and decreasing strain rate. The ductility was quite independent from temperature and strain rate. The tensile stress–strain curves of the thin dissimilar joints placed at an intermediate level between the high strength 2024T3–2024T3 and low strength 6082T6–6082T6 flow curves. The fracture occurred in the middle of the stir zone for all the investigated joints and was of ductile type. Microhardness profiles were slightly modified by straining.     

An assessment of microstructure,hardness, tensile and impact strength of friction stir welded ferritic stainless steel joints

Microstructure and mechanical characterization of friction stir welded 409M ferritic stainless steel joint were carried out. Single pass welds free of volumetric defects were produced at a welding speed of 50 mm/min and rotation speed of 1000 rpm. Optical microscopy, microhardness testing, transverse tensile, impact and bend tests were performed. The coarse ferrite grains in the base material are changed to very fine grains consisting duplex structure of ferrite and martensite due to the rapid cooling rate and high strain induced by severe plastic deformation caused by frictional stirring. Tensile testing indicates overmatching of the weld metal relative to the base metal. The joints are also exhibited acceptable ductility and impact toughness.     

Fracture of alumina particulate reinforced aluminium alloy matrix composites

Fracture toughness tests were performed on two aluminium alloy matrices, 2014-0 and 2024-0 reinforced with alumina particulates of different volume fractions and particulate sizes so as to investigate the fracture mechanisms operative in such composites and to determine how microstructural parameters such as volume fraction, particulate size and interparticle spacing affect the fracture toughness. The results indicate that fracture occurred by a locally ductile mechanism. The fracture toughness increased with increasing particle spacing provided that the particle size was less than a limiting value, above which unstable crack growth occurred and the toughness lowered.     

厚板7022铝合金搅拌摩擦焊接实验研究

对10mm厚度的7022铝合金进行了搅拌摩擦焊接,获得表面光滑的焊接接头,并通过X射线检测焊缝无裂纹和气孔。研究该搅拌摩擦焊接头不同区域的显微组织特征,并通过拉伸、冲击和硬度试验分析了焊接接头的力学性能。结果表明,焊缝处组织为细小均匀的等轴晶粒;在搅拌头转速为400r/min,焊接速度为100mm/min时焊接接头的抗拉强度、屈服强度均比母材高;焊接接头的冲击韧性比母材高;焊接接头显微硬度比母材稍低,焊接接头具有良好的力学性能。