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金属学报(英文版) , 2004,
Abstract: Friction stir welding achieves the weld in solid phase by locally introducing frictional heating and plastic flow arising from rotation of the welding tool, which results in changes in the local microstructure of magnesium alloy. The purpose in the paper is to study the microstructures of friction stir welded AZ31 magnesium alloy. Residual microstructures, including dynamic re-crystallization zone and nugget structures have been systematically investigated utilizing optical microscopy (OM), scanning electric microscopy (SEM), transmission electron microscopy (TEM) with energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and micro-hardness. AZ31 magnesium alloy has been successfully friction stir welded and exhibits the variations of microstructure including dynamically recrystallized, equaxied grains in the weld nugget. Residual hardness in the nugget was found slightly lower than the parent but not too obvious.
Effect of Microstructural changes on Mechanical properties of Friction stir welded Nano SiC reinforced AA6061composite
International Journal of Engineering Science and Technology , 2010,
Abstract: Aluminum alloys used in aircrafts generally exhibit low weldability on fusion welding techniques. Friction stir welding (FSW) has got a lot of attention as a solid state joining technique and provided an improved way of producing aluminum joints in a faster way. In the present work, nano Silicon carbide(SiC) particles reinforced aluminum AA6061metal matrix composites which find applications in aircrafts are casted and friction stir welded. FSW resulted in significant grain refinement and homogeneous distribution of nano SiC particles. The Microstructural analysis is carried out using optical microscopy(OM) and Scanning Electron Microscopy (SEM).The joint strength is increased compared to the conventional fusion welding techniques. The relationship between mechanical properties [hardness, UTS, Y.S] and microstructure of the welded region are studied.
An experimental study on the effect of welding parameters on mechanical and microstructural properties of AA 6082-T6 friction stir welded butt joints  [PDF]
G. Raghu Babu,K. G. K. Murti,G. Ranga Janardhana
Journal of Engineering and Applied Sciences , 2008,
Abstract: The effect of processing parameters on mechanical and microstructural properties of aluminium alloy 6082-T6 Friction stir-welded (FSW) joints were investigated in the present study. Different welded specimens were produced by employing variable rotating speeds and welding speeds. Tensile strength of the produced joints was tested at room temperature and the correlation with process parameter was assessed. Microstructures of various zones of FSW welds are presented and analyzed by means of optical microscopy and microhardness measurements. Several studies have been conducted to investigate the properties and microstructural changes in Friction Stir Welds in the aluminium alloy 6082-T6 in function of varying process parameters. The experimental results indicated that the process parameters have a significant effect on weld macrostructure and mechanical properties of joints.
Microstructural characteristics and mechanical properties of bobbin-tool friction stir welded 2024–T3 aluminum alloy  [PDF]
Ji-hong Dong,Chong Gao,Yao Lu,Jian Han,Xiang-dong Jiao,Zhi-xiong Zhu
- , 2017, DOI: https://doi.org/10.1007/s12613-017-1392-7
Abstract: Cold-rolled 2024–T3 sheet alloy was subjected to bobbin-tool friction stir welding (BTFSW). The microstructural characteristics and mechanical properties of the nugget zone in the as-welded state were investigated. The results show that the equiaxed grain size of BTFSW 2024–T3 alloy decreases from 7.6 to 2.8 μm as the welding speed is increased from 80 to 120 mm/min; in addition, fine grains are generated in the nugget zone and the size distribution is non-uniform. All Al2CuMg (S′) precipitates dissolve into the Al matrix, whereas Mn-rich phases confirmed as T phases (Al20Cu2Mn3, Al6Mn, or Al3Mn) remain unchanged. The optimized parameters for BTFSW are verified as the rotation speed of 350 r/min and the travel speed of 100 mm/min. The variations in precipitation and dislocation play more important roles than grain size in the nugget zone with respect to influencing the mechanical properties during the BTFSW process. After the BTFSW process, the fracture mode of base material 2024–T3 alloy transforms from ductile rupture to ductile-brittle mixed fracture.
Effect of post-weld aging on the mechanical and microstructural properties of friction stir welded aluminum alloy 7075  [PDF]
?. Yeni,S. Sayer,O. Ertu?rul,M. Pakdil
Archives of Materials Science and Engineering , 2008,
Abstract: Purpose: of this paper is to investigate the effect of post-weld artificial aging on the friction stir welding ofAluminum Alloy 7075 (AA 7075) for a welding condition of 1600 rpm and 100 mm/min using right and left helicalscrewed pins for two different shoulder diameters.Design/methodology/approach: The method followed is that first artificial aging has been carried out as24 hours at 125°C. Afterwards, in order to study the effect of post-weld aging on tool geometry, microstructuralexamination, hardness measurements and room temperature tensile tests have been carried out.Findings: The results show that left helical screw yields higher mechanical properties and hardness valuescompared to right helical screw when tested at the same shoulder diameter. It has been observed that post weldaging process compensates the hardness decrease observed in as-welded joints; no significant decrease in hardnessis obtained throughout the weld region.Research limitations/implications: For future work it can be suggested to vary the post weld aging condition,such as 12 hours at 125°C. Welding and rotation speeds are other parameters affecting the microstructural andmechanical properties; therefore the effect of varying these parameters should be considered.Practical implications: This study has practical implications and direct applicability. It indicates that helixangle rather than shoulder diameter directly affects the quality of the joint. At certain post weld aging conditions,for obtaining a sound welded joint the right tool selection will be of critical importance.Originality/value: The authors have examined the effect of post weld aging for different helix angles andshoulder diameters. It is believed that examination of the effect of the variation of these parameters on the jointquality provides originality to this study.
Effects of Microstructural Modification Using Friction Stir Processing on Fatigue Strength of Butt-Welded Joints for High-Strength Steels  [PDF]
Hajime Yamamoto, Kazuhiro Ito
Materials Sciences and Applications (MSA) , 2018, DOI: 10.4236/msa.2018.97045
Abstract: Friction stir processing (FSP) is an effective surface-microstructure modification technique using a rotational tool to refine and homogenize microstructure of metallic materials. In this study, FSP was conducted on the surface of the heat-affected zone (HAZ), which is a region exhibiting degraded mechanical properties and shown to have microstructural changes, of butt-welded joints for two high-strength steels with tensile strength grades of 490 MPa and 780 MPa (hereafter HT490 and HT780, respectively). Inhomogeneous mixing of materials derived from weld metals and base metals (BMs) in a stir zone (SZ) produced inhomogeneous distribution of elements and microstructure depending on the set of the advancing side and retreating side in the SZs. The welded joints with FSP for HT490 exhibited higher hardness than that of the BM through whole of the SZ surface (fine polygonal ferrite grains and bainite structure with laths at the Mn-rich and Mn-poor regions, respectively). On the other hand, those for HT780 exhibited the minimum hardness value similar to that of the BM at the SZ surface (a few polygonal ferrite grains in the matrix of martensite laths). Fatigue strength increased by about 35 MPa and 15 MPa in stress amplitude at 107 cycles as fatigue limit due to FSP. Fatigue failure occurred at the BM and the SZ, respectively, in the welded joints modified by FSP for HT490 and HT780, in comparison with the HAZs in the as-welded joints for both grade steels. The difference in fatigue strength increase due to FSP and failure location between the welded joints for HT490 and HT780 can be attributed to the topmost SZ microstructures and their distribution.
Optimization of Bead Geometry in CO2 Laser Welding of Ti 6Al 4V Using Response Surface Methodology  [PDF]
Ali Khorram, Majid Ghoreishi, Mohammad Reza Soleymani Yazdi, Mahmood Moradi
Engineering (ENG) , 2011, DOI: 10.4236/eng.2011.37084
Abstract: In the presented study, the laser butt-welding of Ti 6Al 4V is investigated using 2.2 kw CO2 laser. Ti 6Al 4V alloy has widespread application in various fields of industries including the medical, nuclear and aerospace. In this study, Response Surface Methodology (RSM) is employed to establish the design of experiments and to optimize the bead geometry. The relationships between the input laser-welding parameters (i.e. laser power, welding speed and focal point position) and the process responses (i.e. welded zone width, heat affected zone width, welded zone area, heat affected zone area and penetration depth) are investigated. The multi-response optimizations are used to optimize the welding process. The optimum welding conditions are identified in order to increase the productivity and minimize the total operating cost. The validation results demonstrate that the developed models are accurate with low percentages of error (less than 12.5%).
Microstructural evolution and mechanical properties of friction stir-welded C71000 copper–nickel alloy and 304 austenitic stainless steel  [PDF]
Hamed Jamshidi Aval
- , 2018, DOI: https://doi.org/10.1007/s12613-018-1682-8
Abstract: Dissimilar joints comprised of copper–nickel and steel alloys are a challenge for manufacturers in modern industries, as these metals are not thermomechanically or chemically well matched. The present study investigated the effects of tool rotational speed and linear speed on the microstructure and mechanical properties of friction stir-welded C71000 copper–nickel and 340 stainless steel alloys using a tungsten carbide tool with a cylindrical pin. The results indicated that a rotational-to-linear speed ratio of 12.5 r/mm did not cause any macro defects, whereas some tunneling defects and longitudinal cracks were found at other ratios that were lower and higher. Furthermore, chromium carbide was formed on the grain boundaries of the 304 stainless steel near the shoulder zone and inside the joint zone, directing carbon and chromium penetration toward the grain boundaries. Tensile strength and elongation percentages were 84% and 65% of the corresponding values in the copper–nickel base metal, respectively.
钛合金Ti??6Al??4V车削加工表面硬化实验  [PDF]
哈尔滨工程大学学报 , 2013, DOI: 10.3969/j.issn.1006??7043. 201211021
Abstract: 针对钛合金Ti??6Al??4V加工表面硬化问题,通过不同切削参数下钛合金Ti??6Al??4V切削加工表面的显微硬度与微观结构检测实验研究,探索钛合金Ti??6Al??4V车削加工的表面硬化机理,分析切削参数对加工硬化与表面变质层影响规律.结果表明:进行钛合金Ti??6Al??4V车削加工时,表面层微观组织发生显著变化,但表面硬化程度不高,切削速度提高不会使表面硬化程度加剧,并有利于减少表面变质层的厚度;切削热对加工表面硬化的影响显著,切削温度升高将减弱表面层材料变形产生的应变硬化作用,表面变质层的显微硬度值低于亚表层的显微硬度值,但高于基体的显微硬度值.
Microstructure and Mechanical Behavior of Porous Ti–6Al–4V Processed by Spherical Powder Sintering  [PDF]
Lucía Reig,Concepción Tojal,David J. Busquets,Vicente Amigó
Materials , 2013, DOI: 10.3390/ma6104868
Abstract: Reducing the stiffness of titanium is an important issue to improve the behavior of this material when working together with bone, which can be achieved by generating a porous structure. The aim of this research was to analyze the porosity and mechanical behavior of Ti–6Al–4V porous samples developed by spherical powder sintering. Four different microsphere sizes were sintered at temperatures ranging from 1300 to 1400 °C for 2, 4 and 8 h. An open, interconnected porosity was obtained, with mean pore sizes ranging from 54.6 to 140 μm. The stiffness of the samples diminished by as much as 40% when compared to that of solid material and the mechanical properties were affected mainly by powder particles size. Bending strengths ranging from 48 to 320 MPa and compressive strengths from 51 to 255 MPa were obtained.
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