Effect of Processing Parameters on the Mechanical Properties of Interstitial Free Steel Subjected to Friction Stir Processing

In the present work, the effect of friction stir processing parameters on the mechanical properties of an interstitial free steel was studied. Four rotating speeds (800, 1250, 1600, 2000 rpm) and two traverse speeds (31.5 and 63 mm/min) were employed. On both sides of specimens, a nanograin layer with the thickness and nanograins of 150 μm and 50-100 nm were formed, respectively. For the specimen processed at rotating speed of 1600 rpm and the traverse speed of 31.5 mm/min, the maximum strength was achieved, which was about 80% increase in the strength comparing to that of base material. For constant traverse speed, the increase in the rotation speed from 800 to 1600 rpm led to a decrease in uniform and total elongation of friction stir processed samples. By contrast, when the rotating speed exceeded 1600 rpm, the uniform and total elongation was increased again, while there was a drop in strength. The results of microhardness indicate more than threefold increase in the hardness of the stirred zone comparing to that of base material.     

Effect of Intermetallic Compound Phases on the Mechanical Properties of the Dissimilar Al/Cu Friction Stir Welded Joints

Types and distribution of intermetallic compound phases and their effects on the mechanical properties of dissimilar Al/Cu friction stir welded joints were investigated. Three different rotation speeds of 1000, 1200 and 1400 rpm were used with two welding speeds of 20 and 50 mm/min. The results show that the microstructures inside the stir zone were greatly affected by the rotation speed. Complex layered structures that containing intermetallic compound phases such as CuAl₂, Al₄Cu₉ were formed in the stir zone. Their amount found to be increased with increasing rotation speed. However, the increasing of the rotation speed slightly lowered the hardness of the stir zone. Many sharp hardness peaks in the stir zones were found as a result of the intermetallic compounds formed, and the highest peaks of 420 Hv were observed at a rotation speed of 1400 rpm. The joints ultimate tensile strength reached a maximum value of 105 MPa at the rotation speed of 1200 rpm and travel speed of 20 mm/min with the joint efficiency ranged between 88 and 96% of the aluminum base metal. At the travel speed of 50 mm/min, the maximum value of the ultimate tensile strength was 96 MPa at rotation speed of 1400 rpm with the joint efficiency ranged between 79 and 90%. The fracture surfaces of tensile test specimens showed no evidence for the effect of the brittle intermetallic compounds in the stir zones on the tensile strength of the joints.     

Effect of Temperature on Microstructure and Fracture Mechanisms in Friction Stir Welded Al6061 Joints

Aluminum and its alloys are widely used in different industries due to such attractive properties as adequate strength, ductility, and low density. It is desirable to characterize welds of aluminum alloys obtained using “friction stir welding” at high temperatures. Al-to-Al (both 6061-T6) butt joints are produced by friction stir welding at tool rotation speed of 1600 rpm and four levels of tool advancing speeds: 250, 500, 750, and 1000 mm/min. Microstructural properties of the different welds are investigated. Observed are noticeable differences in microstructure characteristics between the various weld zones. Mechanical properties of these welded joints are characterized under tensile tests at temperatures of 25, 100, 200, and 300 °C, at a constant strain rate of 10^?3/s. The optimum microstructural and mechanical properties were obtained for the samples FS welded with 1600 rpm tool rotation speed at 1000 mm/min tool advancing speed. The studied welds exhibited yield strength, ultimate tensile strength, and strain to failure with values inferior of those of the base material. Observations of postmortem samples revealed that in the temperature range of 25-200 °C the locus of failure originates at the region between the thermo-mechanically affected zone and the heat-affected zones. However, at higher temperatures (300 °C), the failure occurs in the stir zone. A change in the crack initiation mechanism with temperature is suggested to explain this observation.     

Friction Stir Welding of Low-Carbon AISI 1006 Steel: Room and High-Temperature Mechanical Properties

Friction stir welding (FSW) is an ecologically benign solid-state joining process. In this work, FSW of low-carbon AISI 1006 steel was carried out to study the microstructure and mechanical properties of the resulting joints at both room temperature (RT) and 200 °C. In the parameter space investigated here, a rotational tool speed and translation feed combination of 1200 rpm and 60 mm/min produced a defect-free weld with balanced mechanical properties and a superior Vickers microhardness profile compared to all other conditions and to base metal (BM). At faster translation feeds (100 and 150 mm/min), wormhole defects were observed in the weld microstructure and were attributed to higher strain rate experienced by the weld zone. Under tensile loading, welded material exhibited yield strength that was up to 86 and 91% of the BM at RT and 200 °C, respectively. On the other hand, tensile strength of welded material was nearly similar to that of the base metal at both RT and 200 °C. However, at both temperatures the tensile ductility of the welded joints was observed to be significantly lower than the BM. Annealing of the 1200 rpm and 60 mm/min FSW specimen resulted in tensile strength of 102% compared to base material and 47% increase in the strain at failure compared to the as-welded specimen. The Charpy impact values revealed up to 62 and 53% increase in the specific impact energy for the 1200 rpm and 60 mm/min welded joints as compared with the BM.     

An Investigation into the Microstructure of Friction-Stir Welded and Artificially Aged AA2017

Microstructural changes in friction-stir welding (FSW) of artificially aged AA2017 were investigated. First, FSW was performed with rotational and linear speeds of 800 rpm and 40 mm/min, respectively. Then, microstructural studies by means of optical metallography and electron microscopy were conducted in different regions of the welded plates. Hardness testing was also employed to determine local strength and subsequent natural aging progress after welding. The results indicate that the considerable hardness degradation occurs in the thermo-mechanically affected zone owing to coarsening of semi-coherent precipitates. Grain refinement also takes place in the weld nugget as a result of dynamic recrystallization and it results in a fine-grained structure with the mean grain size to 5 μm. On the other hand, the initial precipitate distribution is completely vanished in the weld nugget and instead, spherical-shaped particles are formed. Moreover, natural aging after FSW occurs in the welded sample and leads to considerable increase in the hardness of the weld nugget zone.     

Influence of Rotation Rate on Microstructure and Comprehensive Performance of FSWed Mg Alloy

Die-casting AZ31 Mg alloys were successfully friction stir welded at a constant welding speed and different rotation rates. More uniform and fine grains were obtained at the rotation rate of 1400 rpm due to more suitable temperature for dynamic recrystallization in this welding condition. In addition, the intensity of (0001) texture in stir zone increased with the increasing rotation rate. The results of mechanical property test indicated joint with rotation rate of 1400 rpm had better tensile property, which was associated with fine grains, uniform transition in the interface between thermo-mechanically affected zone and stir zone as well as more favorable Schmidt factor for basal slip and twinning. The corrosion resistance of joints increased with the increasing rotation rate, which is significantly related to the (0001) texture with basal plane parallel to the corroded surfaces.     

Microstructure and mechanical properties of Al-6061-T6 alloy welded by a new hybrid FSW/SSW joining process

In this study for the first time, the effects of decrease in heat inflow to the weld metal in friction stir process by utilising semisolid processing and decreasing the pin rotational speed as well as increasing the pin transverse speed were examined. As a result, the characteristic loss of hardness and strength in the weld zone were eliminated. The results showed that by approaching the ultrafine microstructure in the weld zone through the hybrid FSW/SSW process, the hardness and elongation values reached to 90?Hv and 8.88%, respectively. These are only slightly different from those of the base metal of the welded samples. Furthermore, the ultimate tensile strength of the samples welded by the hybrid technique was found to be about 167?MPa that was higher than those of the samples welded by friction stir welding (151?MPa) and semisolid welding (114?MPa) techniques.     

Lapped friction stir welding between ductile cast irons and stainless steels

This study investigated the influence of preheating temperature and welding speed on the microstructure of dissimilar lapped friction stir welding (FSW) of ductile cast iron FCD450 and 304 stainless steel. The stainless steel was placed on FCD450, and then FSW was carried out at a tool rotational speed of 200, 400, and 600 rpm and welding speed between 1 and 10 mm/s. Preheating was conducted at 573 and 773 K. Martensitic structure was formed in HAZ of FCD450 without the preheating, while the preheating resulted in the formation of a pearlite structure. Even when the preheating was employed, however, stir zone (SZ) of FCD450 had the chill structure at a lower welding speed, because the SZ temperature exceeded the eutectic temperature. Formation of the chill structure in the SZ could be prevented at a higher welding speed. This study showed that FSW would be available as a dissimilar welding method between ductile cast iron and stainless steel.     

Friction stir welding of dissimilar A319 and A356 aluminium cast alloys

Abstract

In the present investigation, the microstructure and mechanical characteristics of dissimilar A319 and A356 cast Al alloys plates joined by friction stir welding (FSW) were evaluated. The effect of tool rotational and welding speeds as well as the post-weld heat treatment (PWHT) on such properties was investigated. Post-weld heat treatment was carried out at a solutionising temperature of 540°C for 12 h followed by aging at 155°C for 6 h. For the as welded specimens, the welded zone (WZ) exhibited higher hardness values when compared with the A319 and A356 parent alloys. The peak hardness at the WZ was found to increase by increasing the tool rotational speed and/or reducing the welding speed. In contrast, the post-weld heat treated (PWHTed) specimens exhibited lower hardness values at the WZ than the parent alloys. For PWHTed specimens, the peak hardness at the WZ was found to decrease by increasing the tool rotational speed and/or reducing the welding speed. Tensile tests results demonstrate that, for the as welded specimens, the tensile fracture took place on A356 side where the hardness was minimal. While for PWHTed specimens, the fracture took place at the WZ. Increasing the tool rotational speed reducing both tensile and yield strengths, but increases the ductility of the joint.     

铁素体不锈钢搅拌摩擦焊工艺及缺陷形成机理

采用钨铼合金搅拌工具对T4003铁素体不锈钢进行搅拌摩擦焊接工艺试验,研究搅拌摩擦焊缝成形、接头组织特征及缺陷形成机理.结果表明,不同旋转速度下随焊接速度增加,轴向压力呈单调增加趋势;当转速为150,250 r/min时,可获得无缺陷致密焊缝;当转速为350 r/min时,靠近前进侧的焊缝区出现孔洞缺陷,随着焊接速度和轴向压力不断增加,焊接缺陷有减少趋势.焊接接头焊核区发生了相变和明显淬硬现象,组织为细小等轴铁素体和低碳马氏体,焊缝具有明显不均匀硬度分布.提出了一种焊缝热塑性金属平衡流动模型分析其缺陷形成机理.     

Friction stir welding of aluminium lap joint by tool without probe

A friction stir welding process, with a rotating tool without a probe, was employed and applied to a lap joint of aluminium plate. The thickness of the aluminium plates was 0.5 mm. New tool shapes were developed. The tops of the tool were dome shaped. In this process, the rotating tool was plunged into the aluminium plate. The tool-rotating axis was vertical to the specimen surface, and then moved in the welding direction at a speed of 20 mm/s. Tool rotation speed was 18,000 rpm.

At tool plunge depths of 0.1 mm or over, it was possible to weld the two plates. At tool plunge depth of 0.1 mm, its joint was fractured at the weld interface. At tool plunge depth of 0.2 mm or over, the joints were fractured at the stir zone of the upper plate or the heat affected zone of the lower plate. Based on observation of the hardness profiles and the thickness change of the weld area, controlling factors of the joint strength are discussed.     

Microstructure and Mechanical Properties of Friction Stir Welded 1.5 GPa Martensitic High-Strength Steel Plates

In this study, 2.4 mm thick high-strength martensitic steel plates with a tensile strength of 1500 MPa were friction stir welded at various welding speeds of 40, 60, 80, 100, 120 mm/min and a constant rotation speed of 300 rpm. Sound joints could be obtained when the welding speed was 40, 60 and 80 mm/min, while a kissing bond was found in the joint welded at 100 and 120 mm/min. It was revealed that the peak temperature exceeded A_C3 (the end temperature at which all ferrite transformed to austenite when the steel was heated) for all the welding conditions and martensitic structures were finally formed in the stir zone of the joints. A significant decrease in hardness was located in the heat-affected zone, which had a transitional microstructure from tempered martensite near base metal to a mixed structure containing hard martensite, soft ferrite and bainite near stir zone. For the sound joints, the specimen was fractured in the heat-affected zone during tensile tests and the highest tensile strength could reach about 1058 MPa.     

Microstructure evolution and microhardness of friction stir welded cast aluminum bronze

Microstructural characteristics and mechanical properties of a friction stir welded cast aluminum bronze (Cu–9Al–1Fe), produced by a sand casting method, have been investigated at tool rotation of 850–1500 rpm and traverse speed of 50–100 mm/min. Refinement of the primary coarse cast microstructure in the base metal was seen after friction stir welding. Microstructure of the stir zone was characterized in four distinct areas of non-isometric fine grains while a significant grain growth was noticed in some of the areas. Conditions of grain growth are defined with high heat input intensity and low heat transfer capability. The grain size was observed to decrease after FSW, resulting in a greater microhardness across the welded region from about 100 HV in the base metal to about 150 HV at the center of the stir zone. The increased hardness in the stir zone may have stemmed from the locally refined grain size according to Hall–Petch relation.     

The Effect of Friction Stir Welding on Corrosion Behavior of Ti-6Al-4V

Fusion welding can deteriorate corrosion behavior of Ti-6Al-4V alloy. However, the use of friction stir welding leads to a more appropriate corrosion resistance. In this study, the corrosion resistance of welded zones of Ti-6Al-4V alloy using friction stir welding technique is evaluated. For these purposes, the study of structural characteristics using SEM and FESEM equipped with EDS micro-analyses was conducted. Micro-hardness test was also employed to estimate the hardness of welded zones. Corrosion behavior was investigated by a potentiostat instrument. SEM micrographs, EDS and XRD analyses confirmed non-uniformity of chemical composition within the welded zones. The results reveal that the stir zone contains typical alpha and prior beta phases. Nevertheless, thermomechanical zone included equiaxed and bimodal lamellae structure. Furthermore, the presence of different types of phases and microstructure in the thermomechanical zone led to reduced corrosion resistance. The corresponding values of corrosion current density in the stir zone, thermomechanical zone and base metal were 0.048, 0.55 and 0.032 µA, respectively. Corresponding corrosion potential for these zones was estimated as ?207, ?110 and ?157 mV. Evidently, the results show that corrosion resistance of thermomechanical zone is less than that of the stir zone and both zones have lower value than the base metal.     

An Investigation into Microstructures and Mechanical Properties of AA7075-T6 during Friction Stir Welding at Relatively High Rotational Speeds

In this study, microstructural changes and mechanical properties during friction stir welding of AA7075-T6 have been investigated. Friction stir welding at relatively high rotational speeds ranging from 1000 to 1400 rpm and longitudinal speeds in the range of 40 to 80 mm/min have been performed and then microstructures and mechanical properties of the weldments have been studied. The results show that the rotational and longitudinal speeds have a significant effect on the microstructures as well as the mechanical behavior of the welded material while a fine grain structure is produced at higher ratio of rotational speed to longitudinal speed. On the other hand, for a given longitudinal speed, it is revealed that there is an optimum rotational speed which gives the highest tensile strength and elongation for the stirred zone.     

Influence of Processing Parameters on Induced Energy, Mechanical and Corrosion Properties of FSW Butt Joint of 7475 AA

Friction stir welding (FSW), a promising solid state joining process invented at TWI in 1991, was used to join 9?mm thick 7475 aluminum alloy which is considered essentially unweldable by fusion processes. In the present work, the process parameters such as tool rotational speed were varied from 300 to 1000?rpm for a travel speed of 50?mm/min and the influence of process parameters in terms of energy input on microstructure, hardness, tensile strength, and the corrosion property of 7475 aluminum joints was evaluated and analyzed. The maximum tensile strength of FSW joints was obtained at rotational speed of 400?rpm and traverse speed of 50?mm/min (59.2?kJ) which attributed maximum stirred zone area and maximum hardness. The maximum corrosion resistance properties of weld in 3.5% NaCl solution, however, were obtained at rotational speed of 1000?rpm and traverse speed of 50?mm/min. Furthermore, for a given weld, stirred zone showed improved corrosion properties than TMAZ.     

Global and local mechanical properties and microstructure of Bobbin tool friction-stir-welded Al–Li alloy

AA2198–T851 sheets were welded by bobbin tool friction stir welding using a rotational speed of 800?rpm and welding speed of 42?mm?min^?1. The microstructure and precipitates within the joint were characterised by transmission electron microscopy. The global and local mechanical behaviour was determined using a digital image correlation system. Specific attention was given to the relationship between the local microstructure and properties across the joint, which govern the global strength and ductility of the welds. A lower global elongation of the joint is caused by the premature strain localisation in the softened zone.     

Effect of Welding Parameters on the Microstructure and Strength of Friction Stir Weld Joints in Twin Roll Cast EN AW Al-Mn1Cu Plates

Twin roll cast EN AW Al-Mn1Cu plates were butt welded with the friction stir welding process which employed a non-consumable tool, tilted by 1.5° and 3° with respect to the plate normal, rotated in a clockwise direction at 400 and 800 rpm, while traversing at a fixed rate of 80 mm/min along the weld line. Microstructural observations and microhardness tests were performed on sections perpendicular to the tool traverse direction. Tensile tests were carried out at room temperature on samples cut perpendicular to the weld line. The ultimate tensile strength of the welded EN AW Al-Mn1Cu plates improved with increasing tool rotation speed and decreasing tool tilt angle. This marked improvement in ultimate tensile strength is attributed to the increase in the heat input owing to an increased frictional heat generation. There appears to be a perfect correlation between the ultimate tensile strength and the size of the weld zone. The fracture surfaces of the base plate and the welded plates are distinctly different. The former is dominated by dimples typical of ductile fractures. A vast majority of the intermetallic particles inside the weld zones are too small to generate dimples during a tensile test. The fracture surface of the welded plates is thus characterized by occasional dimples that are elongated in the same direction suggesting a tensile tearing mechanism.     

Al-Mg合金填充式搅拌摩擦点焊性能

为了确定Al-Mg铝合金填充式搅拌摩擦点焊性能,以Al-Mg铝合金中2 mm的5A06为研究对象,对填充式搅拌摩擦点焊接头进行了剪切拉伸、十字形拉伸、显微组织和疲劳性能等测试,并建立了焊点组织区模型.结果表明,接头显微组织可以分为焊核区、热影响区、热力影响区和母材区部分;旋转频率为2000 r/min时,剪切载荷均值7865 MPa,十字形拉伸载荷均值3480 N;通过SEM和OM分析,点焊接头疲劳裂纹均起始于上下板结合面的焊点边缘,该区域的环沟槽、孔洞及包铝层等缺陷和应力集中是造成疲劳破坏的主要原因.     

Effect of Travel Speed on the Stress Corrosion Behavior of Friction Stir Welded 2024-T4 Aluminum Alloy

The effect of travel speed on stress corrosion cracking (SCC) behavior of friction stir welded 2024-T4 aluminum alloy was investigated by slow strain rate tensile test. Microstructure and microhardness of the welded joint were studied. The results showed that the size of second phase particles increased with increasing travel speed, and the distribution of second phase particles was much more homogeneous at lower travel speed. The minimum microhardness was located at the boundary of nugget zone and thermomechanically affected zone. In addition, the SCC susceptibility of the friction stir welded joint increased with the increase of travel speed, owing to the size and distribution of second phase particles in the welds. The anodic applied potentials of ?700, ?650, ?600 mV, and cathodic applied potential of ?1200 mV facilitated SCC while the cathodic applied potential of ?1000 mV improved the SCC resistance. The SCC behavior was mainly controlled by the metal anodic dissolution at the open circuit potential, and hydrogen accelerated metal embrittlement.