7075-O铝合金板料的摩擦搅拌渐进成形：成形零件性能的实验研究

本文中,用不同的主轴转速来成形两种典型零件,研究了摩擦搅拌渐进成形零件的综合性能：成形性,表面质量,拉伸性能,显微硬度和壁厚分布。试验结果表明,板料的成形性随着转速增加而呈现增强趋势;接触面的表面粗糙度在水平和竖直方向表现出不同的变化趋势;非接触面的表面质量几乎不受转速影响;相比原板料,成形零件的拉伸性能和显微硬度明显增强,但转转速超过3000 rpm后,硬度值开始逐步下降;在高转速下成形零件的壁厚分布略微优于低转速下的成形零件。总体上,除了力学性能,高转速下成形零件的综合性能比低转速下的成形零件好。     

Microstructural characteristics and mechanical properties of Al–Mg–Si alloy self-reacting friction stir welded joints

The 5?mm thick Al–Mg–Si alloy was self-reacting friction stir welded using the specially designed tool at a constant rotation speed of 400?rev?min^?1 with various welding speeds. Defect-free welds were successfully obtained with welding speeds ranging from 150 to 350?mm?min^?1, while pore defects were formed in the weld nugget zone (WNZ) at a welding speed of 450?mm?min^?1. Band patterns were observed at the advancing side of WNZ. Grain size and distribution of the precipitated phase in different regions of the joints varied depending on the welding speed. The hardness of the weld was obviously lower than that of the base metal, and the lowest hardness location was in the heat affected zone (HAZ). Results of transverse tensile tests indicated that the defective joint fractured in the WNZ with the lowest tensile strength, while the fracture location of the defect-free joints changed to the HAZ.     

Effect of rotation speed on microstructure and mechanical properties of bobbin tool friction stir welded AZ61 magnesium alloy

The 5-mm-thick AZ61 magnesium alloy was friction stir welded by using the specially designed bobbin tool with various rotation speeds. Defect-free welds were successfully obtained with rotation speed ranging from 550 to 600?rev?min^?1. Grain size in different regions of the joints varied depending on the rotation speed. The hardness value of the joint is uniform. The defective joint fractured in the weld nugget zone with the lowest tensile strength, while the fracture location of the defect-free joints changed to the heat affected zone. The impact energy of weld nugget zone is higher than that of the heat affected zone, and the impact energy of the two zones in defect-free joint both decreased with increasing rotation speed.     

Process–microstructure–property correlations in Al–Li AA2199 friction stir welds

Abstract

This paper examines the effect of three friction stir welding process parameters on the residual stresses, hardness and distortion for butt welded aluminium–lithium AA2199 alloy, a novel, low density high strength alloy with potential in the aerospace sector. A systematic set of nine trial welds is examined at different tool rotation and traverse speeds as well as tool downforces. The tensile residual stresses (～50% of parent material yield strength) and the hardness drop in the weld line varied little with any of the friction stir welding process parameters. However, their breadth increased with rotation speed and downforce and decreased with increasing translation speed, which is consistent with increasing heat input. Weld distortion took the form of a saddle with the longitudinal bending distortion correlating strongly with the width of the tensile zone consistent with it being driven by the magnitude of the tensile buckling forces in the weld region.     

Optimisation of friction stir welding process parameters to weld cast aluminium alloy A413 – an experimental approach

Abstract

A413 is a high strength eutectic aluminium silicon cast alloy used in the food, chemical, marine, electrical and automotive industries. Fusion welding of these cast alloys can lead to problems such as porosity, microfissuring and hot cracking, etc. However, friction stir welding can be used to weld these cast alloys effectively, without defects. In this investigation, an attempt was made to optimise the friction stir welding process parameters for joining the cast aluminium alloy A413. Joints were made using four levels each of tool rotation speed, welding speed and axial force. The quality of the weld zone was analysed using macrostructure and microstructure analysis. Tensile strength of the joints were evaluated and correlated with the weld zone hardness and microstructure. The joint fabricated using a tool rotation speed of 900 rev min^?1, a welding speed of 75 mm min^?1 and an axial force of 3 kN showed the best tensile strength.     

Influences of welding parameters on mechanical properties of AZ31 friction stir spot welds

Abstract

In this study, the influence of welding parameters, including tool rotational speed, plunge rate and dwell time, on the overlap tensile shear properties of AZ31 friction stir spot welds was investigated. The microstructures in stir zones and fracture surfaces were observed using optical microscope and scanning electron microscope respectively. The bonded width and h value (the distance from the tip of the partially bonded region to the top of the weld surface) were measured. The results indicated that larger bonded width and higher h value of the AZ31 weld result in better mechanical property. It is proposed that high tensile shear loads are produced when the tool rotational speed range of 1500–2250 rev min^?1 and 1 s dwell time are applied during the friction stir spot welding of AZ31. The plunge rate range from 2·5 to 10 mm s^?1 has insignificant influence on the tensile shear load of AZ31 joints under the present conditions. The failure mode changes from interfacial to pullout when the tool rotational speed is >2250 rev min^?1. The fracture feature of AZ31 welds is brittle fracture.     

高强铝合金可变转速回填式搅拌摩擦点焊温度场及接头组织性能调控

针对7B04-T74铝合金,采用可变转速回填式搅拌摩擦点焊(variable rotation speed-refill friction stir spot welding, V-RFSSW)新方法开展了数值仿真及试验研究. 结果表明,V-RFSSW温度场围绕搅拌头轴线呈圆形对称分布,焊点高温区域集中在搅拌套空腔内部. 与扎入阶段转速相同的常规回填式搅拌摩擦点焊(refill friction stir spot welding, RFSSW)相比,V-RFSSW新方法既可在扎入阶段使材料充分塑化,以保证焊点成形,同时,通过降低回填阶段搅拌头转速降低焊接峰值温度及高温停留时间,抑制组分液化的发生,避免了共晶相的生成. V-RFSSW与常规RFSSW接头显微硬度均呈“W”形分布,且扎入阶段转速相同的情况下V-RFSSW接头搅拌区平均硬度更高. 在拉剪载荷下两种接头均以“纽扣”形式发生断裂,其中V-RFSSW接头拉剪失效载荷为8835 N,高于RFSSW接头的8162 N.     

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.     

The role of rotation speed on intermetallic compounds formation and mechanical behavior of friction stir welded brass/aluminum 1050 couple

In this paper, the intermetallic compounds formation during dissimilar friction stir welding of brass to aluminum 1050 and its effect on the mechanical behavior of joint were studied. Scanning Electron Microscopy (SEM), Energy dispersive spectroscopy analysis (EDS) and X-ray Diffraction analysis were used to characterize intermetallics. In addition, tensile tests and microhardness measurements were performed to evaluate mechanical properties. The results showed that utilizing rotation speeds higher than 400 rpm leads to gradual formation of intermetallic compounds in the stir zone and at the interface. CuAl₂ is the dominant compound in the composite structure of the stir zone, whereas four intermetallic bands are detected at the interface. From aluminum to brass, two middle layers were formed. Then, CuAl₂, Cu₉Al₄ and CuZn were detected. The increase in rotation speed is accompanied by thickening and development of interfacial intermetallic compounds. The optimum rotation speed of 450 rpm yielded a narrow interfacial intermetallic compound and a lamellar composite structure within the stir zone which enhances the tensile strength of the weld. On the other hand, further increase of rotation speed lowers the tensile strength of the weld which is accompanied by disappearance of lamellar composite structure, increment of weld defects and thickening of interfacial intermetallic layer.     

Texture development in near-α Ti friction stir welds

The microstructures and crystallographic textures produced during friction stir welding of the near-α Ti-5111 titanium alloy were characterized as a function of welding speed. The textures produced were compared with ideal hexagonal close packed (hcp) shear textures and with predicted textures of hcp Burgers variants of ideal body-centered cubic (bcc) shear textures, showing that the deposited welds are dominated by the hcp P₁ and bcc D₁ textures. The hcp P₁ shear texture was dominant at slow weld speeds, while the bcc D₁ shear texture was dominant at the fast weld speed. This variation appears to result from a poor transmission of the shear deformation from the rotating tool to the deposited weld that develops at faster welding speeds. These observations are compared to other studies of friction stir welds in hcp and bcc materials reported in the literature.     

Microstructure and mechanical properties of friction stir weld of dissimilar AZ31-O magnesium alloy to 6061-T6 aluminum alloy

Dissimilar friction stir welding between AZ31-O Mg and 6061-T6 Al alloys was investigated. 3 mm thick plates of aluminum and magnesium were used. Friction stir welding operations were performed at different rotation and travel speeds. The rotation speeds varied from 600 to 1400 r/min, and the travel speed varied from 20 to 60 mm/min. Defect-free weld was obtained with a rotation speed of 1000 r/min and travel speed of 40 mm/min. Metallographic studies showed that the grain size in the stir zone is much finer than that in the base metals. Complex flow pattern was formed in the stir zone. Microhardness measurement revealed an uneven distribution in the stir zone. Tensile test results indicated that the tensile strength of the welded specimen is about 76% of AZ31 Mg alloy and 60% of the 6061 Al alloy in tensile strength. SEM fracture surface image of the welded specimen indicated that the welded specimen failed through brittle-mode fracture.     

Influences of process parameters on tensile strength of friction stir welded cast A319 aluminium alloy joints

Fusion welding of cast A319 (Al-Si-Cu) alloy will lead to many problems including porosity, micro-fissuring, and hot cracking. Friction Stir Welding (FSW) can be used to weld A319 alloy without these defects. In this investigation, an attempt has been made to study the effect of FSW process parameters on the tensile strength of A319 alloy welded joints. Joints were made using different combinations of tool rotation speed, welding speed, and axial force, each at four levels. The quality of weld zone was analyzed using macrostructure and microstructure analysis. Tensile strength of the joints were evaluated and correlated with the weld zone microstructure. The joint fabricated with a 1200 rpm tool rotation speed, 40 mm/min welding speed, and 4 kN axial force showed superior tensile strength compared with the other joints.     

基于响应面法的不锈钢车体激光焊接工艺参数优化

为解决电阻点焊不锈钢车体表面质量差、密闭性差等问题,采用二次回归旋转设计试验方案,基于响应面法建立了不锈钢车体激光焊接工艺参数(激光功率、焊接速度、离焦量)与预测响应值(熔深、熔宽、接头剪切拉伸载荷)之间的数学模型,能够根据车体表面质量和接头强度的要求优选焊接工艺参数.并通过优化激光焊接工艺参数来预测激光搭接焊接头的熔深、熔宽以及接头的剪切拉伸载荷,实现焊缝成形与接头强度的最佳组合,为改善不锈钢车体焊接表面质量提供了新的工艺途径.     

7475铝合金回填式FSSW接头微观组织与力学性能研究

本文针对7475铝合金回填式搅拌摩擦点焊展开研究,首先采用不同工艺参数对2mm 7475铝合金进行焊接,然后对焊点表面和横截面进行观察,同时对试样进行硬度测量和拉伸剪切测试。结果表明,根据焊缝微观组织可以将焊点分为四个部分,不同部位的晶粒尺寸不同;并在微观组织中发现了Hook、孔洞和未连接等由于材料流动性不佳造成的微观组织缺陷;同时,母材区和搅拌区的硬度明显高于热影响区和热机影响区;另外,焊点的最高硬度和拉伸剪切强度随着焊具旋转速度、搅拌套下压深度的变化而呈现规律性变化,但是搅拌套运动速率对焊点力学性能的影响不明显。     

Effect of Tool Rotation Rate on Microstructure and Mechanical Behavior of Friction Stir Spot-Welded Al/Cu Composite

In this study, the friction stir spot welding of Al/Cu composite produced by accumulative roll-bonding process was performed using a triangular pin with no features. The influence of tool rotation rate on the microstructure, surface hardness, and tensile shear strength was examined. The results indicated that the weld made at lower tool rotation rate was not bonded because there was no intermixing between the upper and lower sheets. The maximum shear failure load increased with the increasing tool rotation rate, and reached a maximum value at 1400 rpm, which can be ascribed to the increasing area and effective length (d) of stir zone (SZ). The experimental observations showed the presence of the intermetallic compounds (Al₂Cu and AlCu₃) in the SZ. It was concluded that the intermetallic compounds, accompanied by the material crushing, increased the hardness of the SZ.     

Effect of tool geometry on microstructure and static strength in friction stir spot welded aluminium alloys

The effect of tool geometry on microstructure and static strength in friction stir spot welds of 6061 aluminium alloy sheets was studied. Tools with three different probe lengths were used to join the aluminium sheet with different tool rotational speeds and tool holding times. The weld microstructures varied significantly depending on probe length, tool rotational speed and tool holding time. Two particular aspects were identified: the thickness of the upper sheet under the shoulder indentation and the nugget size. The former decreased with increasing probe length at the shortest tool holding time and the slowest tool rotational speed, but there were no discernible differences in other welding conditions, while the latter increased with increasing probe length, tool rotational speed and tool holding time. The tensile shear strength increased with increasing probe length, while the cross-tension strength was not affected significantly by probe length. Two fracture modes were observed: shear fracture of the nugget and mixed mode fracture under tensile shear loading, and nugget debonding and pull-out under cross-tension loading. Based on experimental observation of the microstructures, the effect of probe length on static strength and the fracture mechanisms were discussed.     

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.     

Friction stir welding of co-cast aluminium clad sheet

The effects of welding parameters on material consolidation are examined during friction stir butt welding of 2 mm Al 5083 alloy aluminium sheet with a surface cladding of Al 3025 alloy, which was co-cast from the melt. The influence of welding parameters on joint consolidation is investigated when tool revolutions per minute, travel speed and penetration depth were varied. It was found that modifying the pin of the welding tool to have a two-flat profile improves material consolidation and avoids defect formation during welding, and optimum welding parameters involve a combination of high tool rotation speed and travel speed. Optical and electron microscopy revealed that the integrity of the surface cladding layer could be maintained during friction stir welding while avoiding defect formation within the stir zone of the weld. The tensile strength of the joint was ～58% of the base material due to softening within the stir zone.     

旋转速度对镁/铜异种金属搅拌摩擦焊接头成形及拉伸性能的影响

保持95 mm/min焊接速度不变的条件下,通过改变旋转速度研究其对镁/铜异种金属搅拌摩擦焊接头成形和力学性能的影响。结果表明:采用750 r/min搅拌头旋转速度焊接时,焊缝表面出现起皮现象;焊核区底部形成明显的隧道槽缺陷。适当增加搅拌头旋转速度至950 r/min时,焊缝表面变得更光滑;混合区尺寸增大;内部隧道槽缺陷消失;该混合区主要由被搅碎的Mg、Cu合金和少量新生成的Mg₂Cu金属间化合物组成;接头的抗拉性能最好,抗拉强度达81.7 MPa;但是,继续增大搅拌头旋转速度至1180 r/min时,不利于接头成形,混合区底部有细小的孔洞缺陷产生。     

铝合金搅拌摩擦焊接头焊核区等轴再结晶组织的形成机制

建立了搅拌摩擦焊铝合金接头焊核区等轴再结晶组织形成过程的物理模型，详细阐述了焊核区的组织形成过程。试验结果表明，热循环的作用导致搅拌头附近的母材发生软化，形成软化层；软化层在搅拌头的机械搅拌作用下发生塑性流动，软化层内不同的流层间流速不同，存在速度梯度。在流层间的界面处产生粘性摩擦剪应力。在粘性剪应力的作用下，母材轧制态下的板条状组织被拉长，并发生强烈的弯曲变形，当弯曲程度超过了其晶界所能承受的上限时，原有的板条状组织晶界被破坏而逐渐消失，板条内的等轴再结晶组织按能量最小原理重新排列，形成焊态下无序、无方向性的等轴再结晶组织排列。