Preheating-assisted solid-state friction stir repair of Al-Mg-Si alloy plate at different rotational speeds

Additive friction stir deposition(AFSD)is a novel structural repair and manufacturing technology has become a research hotspot at home and abroad in the past five years.In this work,the microstructural evolution and mechanical performance of the Al-Mg-Si alloy plate repaired by the preheating-assisted AFSD process were investigated.To evaluate the tool rotation speed and substrate preheating for repair quality,the AFSD technique was used to additively repair 5 mm depth blind holes on 6061 aluminum alloy substrates.The results showed that preheat-assisted AFSD repair significantly improved joint bonding and joint strength compared to the control non-preheat substrate condition.Moreover,increasing rotation speed was also beneficial to improve the metallurgical bonding of the interface and avoid volume defects.Under preheating conditions,the UTS and elongation were positively correlated with rotation speed.Under the process parameters of preheated substrate and tool rotation speed of 1000 r/min,defect-free specimens could be obtained accompanied by tensile fracture occurring in the substrate rather than the repaired zone.The UTS and elongation reached the maximum values of 164.2MPa and 13.4%,which are equivalent to 99.4%and 140%of the heated substrate,respectively.

Effects of rotating gas bubble stirring treatment on the microstructures of semi-solid AZ91-2Ca alloy

In this study,the effect of rotating gas bubble stirring treatment on the microstructures of semi-solid AZ91-2Ca alloy was investigated.The semi-solid slurry was produced by injecting fine gas bubbles into the melt through a rotating steel diffuser during solidification,and the samples of semi-solid slurry were taken by the rapid quenching method.The results show that fine and sphericalα-Mg particles can be obtained under rotating gas bubble stirring treatment.The process parameters such as gas flow rate,cooling rate and rotation speed have significant influence on the morphology of primary solid particles.After rotating gas bubble stirring treatment,the higher the particle density,the finer and rounder the primaryα-Mg particles.The formation of numerous solid particles is due to the combination mechanisms of copious nucleation and dendrite fragmentation.

Grain refinement and improved properties through electromagnetic stirring in Al alloy MIG welds

This paper described the effects of external excitatory parameters of current and frequency on the microstructure and mechanical properties of weld metal in MIG welding with longitudinal electromagnetic field. With a high speed video camera capturing the images of arc shape, the mechanism of arc rotation and how the periodic contraction and expansion of arc affected the movement of molten pool were investigated. The technique resulted in fine equiaxed grains in weld metal and optimum parameters of electromagnetic stirring were suggested based on the extent of refinement. Fine-grained weld metal exhibited better yield strength and significant improvement in elongation.

Effect of pin rotating speed on lap shear strength of stationary shoulder friction stir lap welded 6005A-T6 aluminum alloy

Stationary shoulder friction stir lap welding （SSFSLW） was successfully used to weld 6005A-T6 aluminum alloy in this paper. Effect of pin rotating speed on cross section morphologies and lap shear strength of the SSFSLW joints were mainly discussed. Results show that joints without flash and shoulder marks can be obtained by the stationary shoulder. Cross section of the SSFSLW joint presents a basin-like morphology and little material loss. By increasing the rotating speed from 1 000 rpm to 1 600 rpm, both effective sheet thickness and lap width increase, while lap shear failure load firstly decreases and then increases. The maximum failure load of 14. 05 kN /s attained when 1 000 rpm is used. All SSFSLW joints present shear fracture mode.

Friction-stir-welded overaged 7020-T6 alloy joint: an investigation on the effect of rotational speed on the microstructure and mechanical properties

Commercial A7020-T6 plates in the overaged state were subjected to friction stir welding with four different tool rotational speeds of 500, 710, 1000, and 1400 r/min and a single traverse feed rate of 40 mm/min. The resultant changes in the welding heat input, microstructure, and the mechanical properties of the joints were investigated. The changes were related to the processes of growth, dissolution, and re-formation of precipitates. The precipitate evolution was examined by differential scanning calorimetry, and the microstructural analysis was conducted using optical, scanning, and transmission electron microscopes. The results showed that the grain size in the stirred zone(SZ) decreased substantially compared with the base metal, but increased with tool rotational speed because of the rise in temperature. We found that the width of the heat-affected zone increased with tool rotational speed. The hardness and the tensile strength in the SZ increased with increasing heat input compared with the base metal in the overaged condition. This recovery in mechanical properties of the joints can be attributed to the dissolution and re-formation of precipitates in the SZ and the thermomechanically affected zone. This process is referred to as an "auto-aging treatment."

Effect of tool rotational speed on the particle distribution in friction stir welding of AA6092/17.5 SiCp-T6 composite plates and its consequences on the mechanical property of the joint

This study investigates the effect of tool rotational speed(TRS)on particle distribution in nugget zone(NZ)through quantitative approach and its consequences on the mechanical property of friction stir welded joints of AA6092/17.5 SiCp-T6 composite.6 mm thick plates are welded at a constant tool tilt angle of 2°and tool traverse speed of 1 mm/s by varying the TRS at 1000 rpm,1500 rpm and 2000 rpm with a taper pin profiled tool.Microstructure analysis shows large quantity of uniformly shaped smaller size SiC particle with lower average particle area which are homogeneously distributed in the NZ.The fragmentation of bigger size particles has been observed because of abrading action of the hard tool and resulting shearing effect and severe stress generation due to the rotation of tool.The particles occupy maximum area in the matrix compared to that of the base material(BM)due to the redistribution of broken particles as an effect of TRS.The migration of particles towards the TMAZ-NZ transition zone has been also encountered at higher TRS(2000 rpm).The microhardness analysis depicts variation in average hardness from top to bottom of the NZ,minimum for 1500 rpm and maximum for 2000 rpm.The impact strength at 1000 rpm and 1500 rpm remains close to that of BM(21.6 J)while 2000 rpm shows the accountable reduction.The maximum joint efficiency has been achieved at 1500 rpm(84%)and minimum at 1000 rpm(68%)under tensile loading.Fractographic analysis shows mixed mode of failure for BM,1000 rpm and 1500 rpm,whereas 2000 rpm shows the brittle mode of failure.

Numerical analysis of reverse dual-rotation friction stir welding process

A three-dimensional model of reverse dual-rotation friction stir welding （RDR-FSW） is developed to conduct the numerical simulation of heat generation and material flow during the process. The reverse rotation of the assisted shoulder and the tool pin is considered to model the heat generation rate. The predicted temperature difference between the advancing side and the retreating side in RDR-FSW is less than that in conventional FSW. There are two reverse flows during the RDR-FSW which is beneficial to the uniformity of the temperature profile. Due to the reverse rotation effects of the assisted shoulder, the predicted shape and size of thermal-mechanically affected zone （TMAZ） based on the iso-viscosity line are decreased greatly compared to the conventional FSW. It lays solid foundation for optimizing the process parameters in RDR-FSW.

Effect of Process Parameters on Tensile Strength of Friction Stir Welded Cast LM6 Aluminium Alloy Joints

This paper reports the effect of friction stir welding （FSW） process parameters on tensile strength of cast LM6 aluminium alloy. Joints were made by using different combinations of tool rotation speed, welding speed and axial force each at four levels. The quality of weld zone was investigated 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 rotational speed of 900 r/min, a welding speed of 75 mm/min and an axial force of 3 kN showed superior tensile strength compared with other joints. The tensile strength and microhardness of the welded joints for the optimum conditions were 166 MPa and 64.8 Hv respectively.

Simulation of Solid Suspension in a Stirred Tank Using CFD-DEM Coupled Approach＊

Computational fluid dynamics-discrete element method(CFD-DEM) coupled approach was employed to simulate the solid suspension behavior in a Rushton stirred tank with consideration of transitional and rotational motions of millions of particles with complex interactions with liquid and the rotating impeller. The simulations were satisfactorily validated with experimental data in literature in terms of measured particle velocities in the tank.Influences of operating conditions and physical properties of particles(i.e., particle diameter and density) on the two-phase flow field in the stirred tank involving particle distribution, particle velocity and vortex were studied.The wide distribution of particle angular velocity ranging from 0 to 105r·min 1is revealed. The Magnus force is comparable to the drag force during the particle movement in the tank. The strong particle rotation will generate extra shear force on the particles so that the particle morphology may be affected, especially in the bio-/polymer-product related processes. It can be concluded that the CFD-DEM coupled approach provides a theoretical way to understand the physics of particle movement in micro- to macro-scales in the solid suspension of a stirred tank.

Optimization of friction stir welding parameters for improved corrosion resistance of AA2219 aluminum alloy joints

The aluminium alloy AA2219(Al—Cu—Mg alloy) is widely used in the fabrication of lightweight structures with high strength-to-weight ratio and good corrosion resistance.Welding is main fabrication method of AA2219 alloy for manufacturing various engineering components.Friction stir welding(FSW) is a recently developed solid state welding process to overcome the problems encountered in fusion welding.This process uses a non-consumable tool to generate frictional heat on the abutting surfaces.The welding parameters,such as tool pin profile,rotational speed,welding speed and axial force,play major role in determining the microstructure and corrosion resistance of welded joint.The main objective of this work is to develop a mathematical model to predict the corrosion resistance of friction stir welded AA2219 aluminium alloy by incorporating FSW process parameters.In this work a central composite design with four factors and five levels has been used to minimize the experimental conditions.Dynamic polarization testing was carried out to determine critical pitting potential in millivolt,which is a criteria for measuring corrosion resistance and the data was used in model.Further the response surface method(RSM) was used to develop the model.The developed mathematical model was optimized using the simulated annealing algorithm optimizing technique to maximize the corrosion resistance of the friction stir welded AA2219 aluminium alloy joints.

Effect of Rotating Electromagnetic Stirring on Solidification Structure of Incoloy 800H

In this work,the solidification structure of Incoloy 800H with rotating electromagnetic stirring(R-EMS)and without R-EMS were investigated.Comparing the structure without R-EMS,structure with R-EMS is greatly affected by the R-EMS.From the point of view of dendrites,we studied the evolution of solidification structure of Incoloy 800H with R-EMS,consisting of the fine equiaxed dendrites,the long unidirectional dendrites,cross dendrites and equiaxed dendrites.According to the evolution,dendrite fragment dissociation was presented and proved by acquiring the main element composition variation of dendrite trunk in the different zone.As a result,element segregation of the ingot is improved and the grains are refined.

Tool-workpiece interaction and shear layer flow during friction stir welding of aluminium alloys

Material flow phenomena during friction stir welding(FSW) and the forming mechanism of "onion rings" are complicated and currently not fully understood. In the present FSW study aluminium alloys 5083 and A356,with the latter more readily welded than the former,were used. The experiments were conducted to obtain samples of tool and workpiece "frozen" together during FSW for analysis. Two deposition modes for forming the weld nugget zone were observed,one for each alloy with the present FSW parameters. The first is the deposition of shear layers forming the "onion rings" in 5083 alloy nugget. The tool-workpiece interaction leading to the layer thickness being equal to the ratio of welding speed and tool rotation speed is suggested. The second mode is the combination of depositing the rotational shear material in the lower part on the advancing side and the drag flow of material from the retreating site forming the rest of the A356 nugget. The latter mode resulted in the absence of a clear ring structure.

降低石墨微细鳞片含量的再磨工艺优化研究

对黑龙江某石墨粗精矿进行了立式搅拌磨机再磨试验。以陶瓷球为磨矿介质,研究了磨机转速、介质球直径、磨矿时间等工艺参数对石墨磨矿-浮选效果的影响。结果表明,石墨磨矿的优化工艺参数为:采用慢-快-慢交替的磨机转速,陶瓷介质球直径8~10 mm,磨矿时间5 min,在该优化条件下进行磨矿-浮选开路试验,获得了固定碳含量95.83%、-0.045 mm粒级含量24.51%、大鳞片(+0.15 mm)含量14.27%的石墨精矿。

双层三窄叶旋桨搅拌槽内流场特性研究

以甘油-水溶液为流动介质,采用计算流体动力学和粒子图像测速技术相结合的方法,针对双层三窄叶旋桨搅拌槽,研究了旋桨参数离底距C_(1)、桨间距C_(2)及转速N对槽内流场特性的影响。结果表明,随着C_(1)的增大,下层桨叶的推动作用先增强后减弱,在C_(1)=0.25h(h为槽内液位高度)时槽底流体混合状态最佳。在C_(2)=0.24h时,上层旋桨影响区域形成高速涡旋,槽内两层旋桨桨叶间的流体流动状态最佳。在N=120 r/min时,槽内流体的湍动能及流速分布均较均匀,能耗较低。

旋转速度对静止轴肩搅拌摩擦焊温度场和应力场的影响

针对3 mm厚的2024-T4铝合金,采用ABAQUS软件建立静止轴肩搅拌摩擦焊热源三维模型,分析2024-T4铝合金静止轴肩搅拌摩擦焊温度场和应力场的有限元模拟,研究了恒定150 mm/min焊接速度下,旋转速度从800 mm/min到1 200 mm/min对焊接接头残余应力的影响。结果表明:常规搅拌摩擦焊焊缝横截面高温区域呈现碗状分布,而静止轴肩搅拌摩擦焊呈类似于搅拌针形貌分布。相比于常规搅拌摩擦焊,静止轴肩可以获得更窄的搅拌区宽度,并且有效降低焊缝中心的峰值温度。焊后垂直于焊缝区域的纵向残余应力呈现“M”形分布,随着搅拌头旋转速度的增大,两种工艺下的焊后残余应力均增大。此外,静止轴肩在焊接过程中对焊缝区域持续碾压,使得焊后试样的纵向残余应力峰值相比较于传统搅拌摩擦焊能降低45.6%。

AZ31/LA141搅拌摩擦搭接焊工艺及性能研究

借助体视镜、光学显微镜、万能试验机和维氏显微硬度计探究不同旋转速度对AZ31/LA141异种材料搅拌摩擦搭接焊接头组织、显微硬度和剪切性能的影响。结果表明:当焊接速度为0.1 m/min,旋转速度为1400~1800 r/min时,焊缝质量良好,无明显缺陷。同一焊接参数下,上层AZ31和下层LA141的前进侧热影响区晶粒尺寸均大于后退侧,而前进侧热机影响区晶粒尺寸的变化趋势小于后退侧。前进侧热机影响区晶粒尺寸随旋转速度的增加而增加。当旋转速度增大时,上层AZ31和下层LA141的显微硬度均增大,焊核区的显微硬度最大值为68.2HV。搅拌摩擦搭接焊接头的拉剪力先增后减,当焊接速度为0.1 m/min,旋转速度为1600 r/min时,拉剪力达到最大值2313.5 N。

Effect of some parameters on the performance of anchor impellers for stirring shear-thinning fluids in a cylindrical vessel

The 3-D hydrodynamics of shear thinning fluids in a stirred tank with an anchor impeller were numerically simulated.By using a computational fluid dynamics code（CFX 13.0）,the obtained results give a good prediction of the hydrodynamics such as the velocity fields and cavern size.The multiple reference frames（MRF） technique was employed to model the rotation of the impellers.The rheology of the fluid was approximated using the Ostwald model.To validate the CFD model,some predicted results were compared with the experimental data and a satisfactory agreement was found.The effects of impeller speed,fluid rheology,and some design parameters on the flow pattern,cavern size and power consumption were explored.

Effects of the Reversely Rotating Assisted Shoulder on Microstructures During the Reverse Dual-rotation Friction Stir Welding

The reverse dual-rotation friction stir welding(RDR-FSW) has the capability to adjust the heat generation because of the separately designed tool shoulder and tool pin.The welding torque exerted on the workpiece by the reversely rotating shoulder is opposite to that exerted by the rotating tool pin,so the total welding torque is reduced,which is beneficial to reducing the clamping requirement of workpieces.In the present paper,a RDR-FSW joint was welded in a condition similar to the optimal welding condition of conventional FSW,and microstructures in various zones were investigated by comparison,aiming to highlight effects of the reversely rotating assisted shoulder.Due to the heat conduction of the middle cylinder and the bottom end cover on which the assisted shoulder was machined,the thermal effect of RDR-FSW was smaller than that of the conventional FSW.Moreover,the effect of assisted shoulder on the plastic flow or deformation of material or was constrained in a thin layer near the weld top surface,and thus the flow of material especially along the thickness direction was clearly decreased in the RDR-FSW.In the heat-affected zone(HAZ),the precipitate coarsening was the main evolution and was completed through the dissolution of small precipitates and the continuous growth of large precipitates.By contrast,the dissolution degree of precipitates increased significantly in the thermomechanically affected zone(TMAZ),and a small amount of original meta-stable precipitates transformed to block-shaped stable precipitates.Precipitate evolutions in the shoulder affected zone(SAZ)and the weld nugget zone were similar,i.e.the majority of original meta-stable precipitates dissolved into the matrix and the remainder transformed to stable precipitates,though the dissolution degree was greater in the SAZ.Compared with the conventional FSW joint,the coarsening degrees of precipitates in the HAZ and TMAZ of RDR-FSW joint were much smaller,as well as the dissolution degrees of precipitates in all four specified zones.

基于EDEM的板材制备立轴行星式搅拌机特性

以木屑、氯化镁、氧化镁、卤水为搅拌原料,以聚氯乙烯树脂粉、尿素为添加剂,研究立轴行星式搅拌机叶片安装角度、搅拌轴转速对搅拌效果的影响,采用离散元分析软件模拟仿真混合物料搅拌过程,研究叶片不同安装角度、搅拌轴不同转速情况下的物料混合效果;对比分析同等情况下氯化镁颗粒的离散系数大小,确定搅拌的最优参数;对生产的木质板材进行力学性能验证。结果表明:立轴行星式搅拌机叶片的安装角度为45°、搅拌轴转速为30 r/min时搅拌效果最佳。

主轴转向对再生Al-Si-Fe-Mg合金多道次搅拌摩擦加工区组织和性能的影响

对4.5 mm厚的再生Al-7.0Si-0.85Fe-0.30Mg合金板进行相同主轴转向1~3道次和改变第2道次主轴转向2,3道次的搅拌摩擦加工,研究了主轴转向对搅拌摩擦加工区组织和力学性能的影响。结果表明:随着加工道次的增加,加工区的面积以及前进侧热机影响区的宽度增大,加工核心区的富铁相、共晶硅等第二相颗粒长度减小,圆整度提高,强度和硬度无显著改变,断后伸长率显著提高。改变第2道次主轴转向后加工区面积较相同主轴转向时减小,但组织对称性提高,前进侧热机影响区宽度减小;改变主轴转向后,第二相颗粒尺寸变化不明显,但圆整度显著降低,强度和硬度的变化也不明显,断后伸长率略有提高。