Improvement of Structural and Mechanical Properties of Al-1100 Alloy via Friction Stir Processing

In the present study, the relationship between structural and mechanical properties of friction stir processed Al-1100 alloy and process parameters (tool rotation rate: ω and traverse speed: ν) was studied to get an better understanding and optimizing the friction stir processing (FSP) condition of this alloy. Microstructural studies revealed that increasing of ω up to 720 rpm resulted in grain refinement in the stirred zone (SZ), but higher increasing of ω caused grain growth in this zone. These variations of SZ grain size illustrated that the prevailing factor that determined the SZ grain size was plastic deformation at first and thereafter, peak temperature in the SZ. Mechanical properties investigations were in accordance with microstructural findings and illustrated that optimized FSP condition for Al-1100 alloy was 720 rpm and 20 mm/min. Optimized FSP condition resulted in a significant improvement of tensile strength and elongation up to 22 and 8% of those of base metal, respectively.     

Mechanical and Damping Behavior of Age-Hardened and Non-age-hardened Al Alloys After Friction Stir Processing

This study investigated the microstructure, mechanical, and damping properties of a non-age-hardened Al alloy(5086) and an age-hardened Al alloy(7075) after friction stir processing(FSP). Microstructural analyses indicate that FSP led the grain refinement of samples, and the grains size decreased with the decrease in the tool rotation rate. Furthermore, FSP with low rotation rate promotes the η phase precipitation in the 7075 alloy, causing the micron-sized particles in the 5086 alloy to break up. After being subjected to FSP with low rotation rate, the 5086 and 7075 alloys exhibited excellent mechanical and damping properties. Such improved properties were ascribed to their equilibrium grain boundaries, fine grain, low density of dislocations, high fraction of high misorientation angle, and uniform particle distribution.     

The influence of multi-pass friction stir processing on the microstructural and mechanical properties of Aluminum Alloy 6082

Samples with one through three passes with 100% overlap were created using friction stir processing (FSP) in order to locally modify the microstructural and mechanical properties of 6082-T6 Aluminum Alloy. A constant rotational speed and three different traverse speeds were used for processing. In this article, the microstructural properties in terms of grain structure and second phase particles distribution, and also the mechanical properties in terms of hardness and tensile strength of the processed zone were addressed with respect to the number of passes and traverse speeds. The parameter combination which resulted in highest ultimate tensile strength was further compared with additional two rotation speeds. FSP caused dynamic recrystallization of the stir zone leading to equiaxed grains with high angle grain boundaries which increased with increasing the number of passes. The accumulated heat accompanying multiple passes resulted in increase in the grain size, dissolution of precipitates and fragmentation of second phase particles. Increasing the traverse speed on the other hand did not affect the grain size, yet reduced the particles size as well as increased the particle area fraction. Hardness and tensile test results of the stir zone were in good agreement where increasing the number of passes caused softening and reduction of the ultimate tensile strength, whereas, increasing the traverse speed increased the strength and hardness. Increasing the tool rotational speed did not have a significant influence on particle mean diameter, ultimate tensile strength and hardness values of the stir zone, whereas, it caused an increase in mean grain size as well as particle area fraction.     

Enhanced mechanical properties of Mg-Gd-Y-Zr casting via friction stir processing

Mg-10Gd-3Y-0.5Zr casting was subjected to friction stir processing (FSP) at a tool rotation rate of 800 rpm and a traverse speed of 50 mm/min. FSP resulted in the fundamental dissolution of the coarse network-like β-Mg₅(Gd,Y) phase and remarkable grain refinement (∼6.1 μm), thereby significantly improving the strength and ductility of the casting. Post-FSP aging resulted in the precipitation of fine β′′ and β′ particles in a fine-grained magnesium matrix, producing an ultimate tensile strength of 439 MPa and a yield strength of 330 MPa. FSP combined with aging is a simple and effective approach to enhancing the mechanical properties of Mg-Gd-Y-Zr casting.     

搅拌摩擦加工TA5钛合金的显微组织和力学性能

对TA5钛合金进行搅拌摩擦加工(FSP),获得超细晶组织.为了研究搅拌摩擦加工过程中的温度分布和材料流动情况,使用欧拉-拉格朗日耦合(CEL)方法对加工过程进行热力耦合模拟.采用光学显微镜、扫描电镜、硬度和拉伸测试技术对合金的显微组织和力学性能进行表征.由于在加工过程中材料发生动态再结晶,因此,加工后的合金由细小等轴晶...     

Microstructural modification of cast Mg alloys by friction stir processing

Abstract

Cast Mg alloys were processed using friction stir processing (FSP) to acquire a fine grained structure and high strength. Actually, FSP is a novel grain refinement method for light metal alloys. Using FSP, a cast microstructure with coarse grain size was refined to equiaxial fine grain through dynamic recrystallisation; second phase particles were finely dispersed by FSP. Moreover, FSP is effective to eliminate cast defects such as microshrinkages or porosities. Commercial die cast Mg alloy (AZ91D) and high strength Mg–Y–Zn alloy plates were prepared for FSP. Heat input using a rotational tool during FSP closely affected the microstructure in the stirred zone. Actually, FSP with lower heat input produced a finer grain size and higher hardness. Changes in the friction stir processed microstructures affecting mechanical properties were not only grain refinement, but also second phase particle distributions. Results show that alloys with high hardness by FSP have finely dispersed second phase particles without dissolution during FSP.     

Investigation of microstructure and mechanical properties of friction stir lap jointed Monel 400 and Inconel 600

This study was conducted to investigate the microstructure and mechanical properties of friction stir lap joints. Monel 400 and Inconel 600 were selected as the experimental materials, and friction stir welding was carried out at a tool rotation speed of 200 rpm and welding speed of 100 mm/min. The application of friction stir welding to Monel 400 effectively reduced the grain size in the stir zone; the average grain size of Monel 400 was reduced from 11.9 μm in the base material to 4.2 μm in the stir zone, which resulted in an improvement in the mechanical properties of the stir zone. The joint interface between Monel 400 and Inconel 600 showed a relatively sound weld without grooves or cracks, and only a small amount of voids with a size of 0.5 μm; however, no intermetallic compounds were observed in the lap jointed interface. Moreover, the hook on the advancing side of Monel 400 was formed from Inconel 600, which contributed to maintenance of the tensile strength. The evolution of microstructures and mechanical properties of friction stir lap jointed Monel 400 and Inconel 600 are also discussed herein.     

表面纳米化对镍基高温合金焊接液化裂纹的影响

采用搅拌摩擦处理对Waspaloy高温合金进行表面纳米化,并用激光对搅拌区域进行重熔,研究表面纳米化对液化裂纹的影响. 利用扫描电镜和电子背散射衍射,研究了搅拌区域和重熔区域的显微组织. 结果表明,搅拌摩擦处理在Waspaloy合金表面制备出200 ~ 700 nm的等轴纳米晶粒,细化机制为不连续动态再结晶;从搅拌区表层至底部,晶粒尺寸整体上逐渐增大;经激光重熔后,发现纳米晶层有效抑制了热影响区液化裂纹. 纳米化过程改变了碳化物的分布,避免液化相富集于晶界,晶粒尺寸减小则使晶界面积大大增加,从而减小了液膜厚度,抑制了裂纹的形成.     

搅拌摩擦加工改性冷喷涂Al-12Si合金涂层的组织和性能

采用冷喷涂在碳钢基体上沉积制备了Al-12Si合金涂层,分别采用平端面和渐开线端面的无针搅拌头以950r/min转速对涂层表面进行搅拌摩擦加工(FSP)改性。采用光镜和扫描电镜对喷涂态和FSP改性后涂层的组织结构进行了表征。结果表明:采用两种搅拌头获得了不同形貌的组织,随着渐开线端面搅拌头的移动,提高了热输入,涂层中组织出现了过热造成的气孔缺陷。Si颗粒在FSP的塑性变形过程中得到了充分的混合,均匀地分散在了涂层中,分析表明沉积粒子的再分布和晶粒的细化能显著提高涂层的表面性能,此外,两种FSP搅拌头改性后涂层表面的硬度分别为113.8HV0.5和125.1HV0.5。     

Effects of Tool Rotation Rates on Superplastic Deformation Behavior of Friction Stir Processed Mg-Zn-Y-Zr AlloyEI北大核心CSCD

Compared to conventional Mg-Al and Mg-Zn system magnesium alloys, the Mg-Zn-Y-Zr heat-resistant alloy exhibits high thermal stability due to the addition of Y earth element, which is an ideal candidate for producing high strain rate superplasticity (HSRS, strain rate >= 1 x 10(-2) s(-1)). Recently, the HSRS of Mg-Zn-Y-Zr alloy was achieved by friction stir processing (FSP), because the FSP resulted in the generation of fine and equiaxed recrystallized grains and fine and homogeneous second phase particles. However, the study on superplastic deformation mechanism of FSP Mg-Zn-Y-Zr alloy at various parameters is limited relatively. Therefore, at the present work, six millimeters thick as-extruded Mg-Zn-Y-Zr plates were subjected to FSP at relatively wide heat input range of rotation rates of 800 r/min to 1600 r/min with a constant traverse speed of 100 mm/min, obtaining FSP samples consisting of homogeneous, fine and equiaxed dynamically recrystallized grains and fine and uniform Mg-Zn-Y ternary phase (W-phase) particles. With increasing rotation rate, within the FSP samples the W-phase particles were broken up and dispersed significantly and the recrystallized grains were refined slightly, while the fraction ratio of the high angle grain boundaries (grain boundaries misorientation angle >= 15 degrees) was increased obviously. Increasing rotation rate resulted in an increase in both optimum strain rate and superplastic elongation. For the FSP sample obtained at 1600 r/min, a maximum elongation of 1200% was achieved at a high-strain rate of 1x10(-2) s(-1) and 450 degrees C. Grain boundary sliding was identified to be the primary deformation mechanism in the FSP samples at various rotation rates by superplastic data analyses and surfacial morphology observations. Furthermore, the increase in rotation rate accelerated superplastic deformation kinetics remarkably. For the FSP sample at 1600 r/min, superplastic deformation kinetics is in good agreement with the prediction by the superplastic constitutive equation for fine-grained magnesium alloys governed by grain boundary sliding mechanism.     

慢速搅拌摩擦加工对工业纯钛摩擦磨损性能的影响

目的利用慢速搅拌摩擦加工,获得工业纯钛细晶组织,提高其耐磨性能。方法采用慢速搅拌摩擦加工对TA2工业纯钛退火板材进行表面处理,获得细晶结构。使用EBSD技术和显微硬度检测仪对表面微观结构及力学性能进行表征。采用球盘式摩擦磨损试验仪对搅拌摩擦加工前后的样品进行摩擦磨损性能测试,计算磨损率,并使用SEM及EDS分析磨痕特征。结果搅拌摩擦加工处理后,工业纯钛晶粒尺寸显著细化,小角度晶界比例较高,加工硬化程度高。搅拌摩擦加工样品氧化磨损较为严重,粘着磨损程度减小。搅拌摩擦加工后,样品主要磨损方式由粘着磨损和二体磨损转变为氧化磨损和三体磨损。经过180 r/min、25 mm/min处理的工业纯钛磨损率仅为未加工样品的1/4左右。结论慢速搅拌摩擦加工可同时提高工业纯钛表面硬度及耐磨损性能,较小的晶粒尺寸及合适的加工硬化程度可减轻粘着磨损和磨粒磨损。     

搅拌摩擦加工对铸态7075铝合金显微组织的影响

采用搅拌摩擦加工对变形能力差的铸态7075铝合金进行改性加工,探讨了加工工艺对加工区显微组织的影响.加工工艺优化实验表明,在同样的工具设计和加工参数下,通过两道次重叠加工可在搅拌区获得均匀的细小等轴晶组织;此外,减小加工工具尺寸并提高旋转速度也可明显提高搅拌区显微观组织的均匀性.     

Twinning-induced mechanical properties’ modification of CP-Ti by friction stir welding associated with simultaneous backward cooling

Commercial pure Ti (CP-Ti) plates with 2?mm in thickness were successfully joined by friction stir welding (FSW) associated with simultaneous backward cooling. The measured processing temperatures were strictly controlled below the α/β phase transformation point. The microstructural characterisation showed that the stir zone has an ultra-refined grain structure with abundant twin boundaries by decreasing processing temperature. The geometric dynamic recrystallisation and twinning-induced dynamic recrystallisation were the main mechanisms of the grain refinement process. The resulting tensile properties of the stir zone illustrate that both the strength and ductility enhanced due to the appearance of abundant twin boundaries. This work also provides an effective strategy to enhance the strength of the stir zone of FSW CP-Ti joint without ductility loss.     

Friction stir welding of twin-roll cast EN AW 3003 plates

Twin-roll cast EN AW 3003 plates were butt-welded with friction stir welding and their structural features were identified. Sound welds were obtained in twin-roll cast EN AW 3003 plates at tool rotation speeds higher than 500 rpm. The ultimate tensile strength of the welded plates was 134 ± 3 MPa, comparable to the ultimate tensile strength of the original plate, at 146 MPa. The stirring action of the pin fractured the interdendritic network and coarse eutectic cells, replacing the dendritic features of the base plate with a uniform dispersion of very fine intermetallic particles across the stir zone. The thermal and mechanical cycles introduced during FSW relaxed the supersaturation of the cast plate, leading to the precipitation of intermetallic particles. This precipitation activity produced a particle population gradient that peaks inside the stir zone and dictates the etching response across the plate section. The material in direct contact with the rotating pin is severely deformed and is exposed to frictional heating and inevitably undergoes dynamic recrystallization. The very fine grain structure thus obtained suffers abnormal grain growth when annealed at high temperatures due to the effective pinning of the grain boundaries by the fine particles.     

Microstructure Distribution and Tensile Anisotropy of Dissimilar Friction Stir Welded AM60 and AZ31 Magnesium Alloys

The microstructure distribution, tensile anisotropy and fracture behaviors in the dissimilar friction stir welded joint of AM60/AZ31 alloys were investigated. Experimental results showed that a significant grain refinement and an orientation fluctuation occurred in the weld. The grain size of AZ31 side in joint was obviously smaller than that of AM60 side. There was a higher percentage of low angle grain boundaries (LAGBs) and a lower degree of recrystallization in AZ31 side compared with those in AM60 side, especially for the thermo-mechanically affected zone in AZ31 side. The discrepancies of grain size distribution, recrystallization behavior and LAGBs in joint depended on the different initial state of two metals and the inhomogeneous temperature distribution in joint. In addition, the (0001) basal plane in weld was roughly parallel to the surface of the pin, showing the symmetrically distributed texture characteristics. The joint showed an obvious tensile anisotropy due to the special texture distribution. The comprehensive tensile properties of joint along the three directions decreased in the order: welding direction, 45° direction and transverse direction. The maximum ultimate tensile strength, yield strength and elongation of the joint were 242 MPa, 116 MPa and 21.2%, respectively. The fluctuations of grain size and texture in joint affected the fracture behavior of samples in the three directions.     

Effect of microstructural feature on the tensile properties and vibration fracture resistance of friction stirred 5083 Alloy

In this study, 5083 Al-Mg plates were friction stirred at optimal rotation speeds to investigate the tensile properties and vibration fracture resistance. As a result, grain refinement could be observed at the stir zone with 7 μm average grain size and fine particles could be observed as well. The tensile strain-elongation curves reveal that the tensile strength and elongation tended to increase as the microstructure was refined in the friction stirred sample. The D-N curves of the specimens recorded under an identical initial deflection show that there was a slight difference between the parent metal and the friction stirred sample. A refined grain size is partially responsible for an improvement in vibration fracture resistance; however there is another factor which plays a role too. It should be noted that the deterioration of vibration fracture resistance is a consequence of fine particles stirred into a softened matrix. From the crack propagation results, an intergranular crack propagation feature can be recognized in the friction stirred specimen, and it is reasonable to suggest that the fine particles played an important role in the deterioration of the vibration fracture resistance.     

Achieving a High-Strength CoCrFeNiCu High-Entropy Alloy with an Ultrafine-Grained Structure via Friction Stir Processing

High-entropy alloys(HEAs) are a new class of materials with a potential engineering application,but how to obtain ultrafine or nano-sized crystal structures of HEAs has been a challenge.Here,we first presented an equiatomic CoCrFeNiCu HEA with excellent mechanical properties obtained via friction stir processing(FSP).After FSP,the Cu element segregation in the cast CoCrFeNiCu HEA was almost eliminated,and the cast coarse two-phase structure(several micrometers) was changed into an ultrafine-grained single-phase structure(150 nm) with a large fraction of high-angle grain boundaries and nanoscale deformation twins.This unique microstructure was mainly attributed to the severe plastic deformation during FSP,and the sluggish diffusion effect in dynamics and the lattice distortion effect in crystallography for HEAs.Furthermore,FSP largely improved the hardness and yield strength of the CoCrFeNiCu HEA with a value of 380 HV and more than 1150 MPa,respectively,which were 1.5 times higher than those of the base material.The great strengthening after FSP was mainly attributed to the significant grain refinement with large lattice distortion and nano-twins.This study provides a new method to largely refine the microstructure and improve the strength of cast CoCrFeNiCu HEAs.     

Influence of multi-pass friction stir processing on microstructure and mechanical properties of 7B04-O Al alloy

Three-pass friction stir processing (FSP) with different moving distances of the stirring tool between the two successive passes, 50% diameter of the pin (traditional way) and 50% diameter of the shoulder (novel way), was conducted on 7B04-O Al alloy. The result shows that an improvement in the mechanical properties of the processed zone is accomplished due to grain and second phase particles refinement. The hardness of the multi-pass FSP (M-FSP) sample is about HV 40 higher than that of the base metal. And the tensile strength of the M-FSP specimens is also significantly increased to about 1.4 times that of the base metal. Besides, the weak region of the processed zone is mainly dependent on the moving distance, where it is the previous pass stir zone in the traditional way and the transitional zone in the novel way. Increasing the rotational speed narrows the weak region in the novel way, while it does not in the traditional way.     

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.     

On the Al5083–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–TiO<Subscript>2</Subscript> Hybrid Surface Nanocomposite Produced by Friction Stir Processing

In this study Al5083–Al₂O₃–TiO₂ hybrid surface nanocomposite was successfully prepared by friction stir processing (FSP). The effects of different combination of rotational and travel speed of tool were investigated. The samples were characterized by optical and scanning electron microscopy (SEM), microhardness and undergone tensile and wear tests. Based on the maximum tensile strength and hardness value, optimum rotational speed of 710 rpm and travel speed of 20 mm/min was achieved. The microhardness and tensile strength of the as-received alloy and specimens having optimum surface nanocomposite were about 80 Hv, 285 MPa, 140 Hv and 375 MPa, respectively. Surface nanocomposites showed significantly lower friction coefficients and wear rates than those obtained for substrate. Based on scanning electron microscopy tests, abrasive wear as dominant wear mechanism was detected.