Microstructure characteristics and mechanical properties of stationary shoulder friction stir welded 2219-T6 aluminium alloy at high rotation speeds

Tool rotation speed is one of the most important processing parameters that govern the performance of the friction stir welds. In this study, a novel variant of friction stir welding for T-joints, which is termed as corner stationary shoulder friction stir welding (CSSFSW), is investigated regarding the effect of tool rotation speed on the microstructure and tensile strength of the T-joints. T-joints with 5 mm thickness for AA 6082-T6 plates were fabricated via a two-pass welding process by using different tool rotation speeds. The microstructure and tensile strength of the defect-free and defective T-joints were analyzed. It is found that void defects appear on the advancing side when the tool rotation speed was 1200 rpm; defect-free T-joints are obtained in the range of tool rotation speeds from 1500 to 2000 rpm. Generally, high tool rotation speed is favorable for eliminating weld defects. In the case of CSSFSW, the lower limit of the tool rotation speed for defect-free welds is higher than that in the conventional FSW, because the heat input is reduced as the stationary shoulder contributes little to the heat generation. The tensile strength of the defect-free joint made at the tool rotation speed of 1500 rpm reached a maximum in both skin and stiffener direction, while are measured to be 113 MPa in L direction and 170 MPa in T direction. The fracture morphologies of the T-joints welded at different tool rotation speeds in both skin and stiffener directions when subjected to tensile loads are documented. A conceptual model is proposed in order to discuss the weld formation in the CSSFSW configuration.

In robotic friction stir welding, high rotational speed is constantly employed to reduce both robot torque and the welding load. In this paper, a three-dimensional coupled thermo-mechanical model is developed. This model analyzes the multiphysics field in both friction stir welding and stationary shoulder friction stir welding at relatively high rotational speeds. Both experimental and numerical results indicate that the stationary shoulder friction stir welding joint has homogenous microstructure and temperature gradient distribution. Further research finds the peak temperature in the nugget zone of stationary shoulder friction stir welding and friction stir welding is 490° and 530°, respectively. Meanwhile, the effective strain of the stationary shoulder friction stir welding joint is lower when compared to the friction stir welding. However, the strain rate is higher. While being reduced along the thickness direction, the strongest material flow velocity is observed in the top surface of the workpiece. Stationary shoulder friction stir welding is shown as a favorable process for obtaining the homogeneity of the microstructure and reducing joint softening.

Friction Stir Incremental Forming of AA7075-O Sheets: Experimental Investigations on Performance Evaluation of Formed Parts

Elucidation of the factors controlling interface decohesion and particle fracture in a friction stir alloyed Al‒Fe alloy system

Experimental investigations on the single point incremental forming of a titanium alloy component combining static heating with high tool rotation speed

In this paper, the influence of process parameters (tool rotational speed, pin design, and configuration of joined alloys) on the macrostructure and mechanical properties of friction stir welded aluminum alloys 7075-T651 and 5083-H111 was characterized. The tool rotational speed and the alloy placement significantly influenced the formation of the weld (especially the stir zone). Superior mixing of materials was obtained at higher rotational speeds and in the configuration with 5083 on the advancing side and 7075 on the retreating side. However, under these conditions, more defects, such as porosity, voids, or wormholes, were found in the stir zone. Regardless of the pin design and weld configuration, with an increasing tool rotational speed, the mechanical properties decrease. Using the Triflute pin, however, guarantees higher tensile strength and weld efficiency (above 100%). The weld configuration did not influence the mechanical properties. The highest tensile strength (371 MPa) defect-free joint was obtained with 5083 on the advancing side, 7075 on the retreating side, a tool rotational speed of 280 rpm, and the Triflute pin.

In the last decade there has been significant research into joining steel alloys using the Friction Stir Welding technique due to its ability to carry out welding below the melting point of the parent material and without using fillers such as in fusion welding techniques. This coincided with the increased use of DH36 and EH46 steel grades for ship building. The main reason for joining these steel grades by the friction stir welding technique is to reduce the weight of the vessel, as well as, the high welded joint quality especially mechanical properties such as fatigue and impact resistance. Other improved physical characteristics include increased tensile strength, microhardness and surface finish. This research project has attempted to model friction stir welding using Computational Fluid Dynamics (CFD). Three different approaches have been used when considering the interface between the tool and the workpiece; these are torque, sticking/slipping and fully sticking. The project also investigates the mechanical properties of the welded joints including tensile, fatigue and microhardness. The microstructural evolution of welded joints carried out using different welding parameters is also investigated. The phenomenon of elemental precipitation/segregation during the friction stir welding process has been investigated and the limit of tool rotational speed at which the segregation occurs has been determined by modelling and also by heat treatment to simulate FSW. The purpose of the heat treatment trials was to attempt to replicate the temperature and time that the parent materials experiences during the FSW process. Defects in the weld joints associated with unsuitable friction stir welding parameters were also investigated and two new types of defect have been identified for the first time. Finally, tool wear has been investigated in the different weld joints in order to understand the suitable welding parameters that can prolong tool life. The results from the mathematical modelling of FSW using CFD showed that the fully sticking assumption is the most effective approach for modelling friction stir welding of steel. The model also revealed that local melting at the advancing-trailing side of the tool is likely to occur at high tool rotational speeds. The experimental findings were in agreement with the results from the CFD model as the high tool rotational speed welded joints showed elemental segregation of Mn, Si, Al and O which only occurs when the peak temperature during welding approaches the melting point of steel. Experimental work has also shown significant improvement in the mechanical properties of the welded joints in terms of fatigue and tensile strength after friction stir welding compared to the parent metal. However, the joints welded at high tool rotational/traverse speeds have shown lower mechanical properties as a result of defects such as weld root defect and microcrackes which have been introduced. Tool wear was found to increase with the increasing tool rotational speed as a result of the tools W-Re binder softening. Tool wear was also found to increase with increasing plunge depth as a result of the high shear stress originating from the high thermo-mechanical action at the FSW tool surface. The current project has contributed to knowledge in the friction stir welding of steel by revealing the limits of tool speed that causes elemental segregation. The new technique for estimating the peak temperature and cooling rate using TiN precipitates can also be an alternative to thermocouple measurements which can significantly underestimate the tool-workpiece interface temperature.

With the continuous development of milling technology and the increasing number of slim hole plugging removal operations worldwide, how to guide operators to select reasonable working parameters to achieve efficient plugging removal has become a problem worth paying attention to. At present, the research on the optimization of working parameters based on the characteristics of plugging material is not complete. In order to explore the feasibility of efficient unplugging operation with low weight on bit and high rotational speed in slim hole, this paper chooses cement plug as plugging material, and uses Mechanical Specific Energy (MSE) and Rate of Penetration (ROP) as the evaluation index of plugging efficiency. A test bench was established and a low WOB milling test was designed. Meanwhile, a 3D simulation model of full-size PDC bit milling cement plug was established. Through the test and numerical simulation analysis, it is found that when the bit weight is enough to destroy the blockage, efficient operation can be realized under the working condition of low WOB and high rotational speed. A working parameter optimization method is proposed, and the recommended working interval is 3 kN WOB and 1500 ~ 2000 r/min rotational speed; 5 kN WOB, 1000 r/min rotational speed. The results show that the increase of WOB and rotational speed can improve the ROP of the bit, and it is feasible to use rotational speed to compensate the WOB to increase the ROP. In simulation and test, the efficiency of milling plugs is not good when the WOB is lower than 3 kN. To achieve high efficiency milling plugs, the priority should be to ensure that the WOB is enough to allow the cutter to normally break the plug. When analyzed with power drilling tools in conjunction with downhole motors, the ROP obtained by PDC bit with turbodrill under the condition of low WOB and high rotational speed is better than that obtained by a positive displacement motor with high WOB and low rotational speed, the results highlight the advantages of low WOB and high rotational speed milling cement plug. This paper provides a new idea for the optimization of working parameters of coiled tubing during plugging removal in slim holes.

High rotational speed friction stir welding (FSW) was successfully employed to weld 6061-T6 aluminum alloy thin plates. The effect of high rotational speed and fast transverse speed on temperature distribution, microstructure evolution, and tensile properties of friction stir welded 6061-T6 joints was investigated in detail. The high rotational speed with fast transverse speed had a significant influence on the peak temperature in the nugget zone (NZ). Increasing the rotational speed and decreasing the transverse speed could obviously improve the peak temperature in the NZ, but exhibit little effect on the heat-affected zone under high rotational speed FSW. The NZ was characterized as a significant refinement of the equiaxed grain. The number of precipitates, subgrains, and low angle grain boundaries in the NZ of high rotational speed FSW joint increased significantly due to moderate heat input and strain rate. The weld zone was seriously softened at low rotational speed, whereas it was alleviated at high rotational speed and was affected slightly by rotational speed and transverse speed. The excellent mechanical properties of the friction stir welded 6061-T6 joints were obtained at a combination of high rotational speed and fast transverse speed. The maximum tensile strength reached 301.8 MPa, 85.8% of the base material.

Submerged friction stir welding (FSW) is used to improve the weld zones mechanical properties in the present study. This research aims to obtain the optimized process parameters used to fabricate the AA6063 Submerged FSW joint. In the Submerged FSW process, the most important influential factors are tool rotational speed, traverse speed, and pin profile in a seawater environment. The different workpieces are friction stir welded while submerged in seawater at different tool rotational speeds, traverse speeds, and tool pin profiles such as square pin, cylindrical taper pin, and threaded pin. The produced weldments were tested for the mechanical properties of higher tensile strength, microhardness, corrosion rate, and the microstructure of weldments was characterized by using a scanning electron microscope, transmission electron microscope, and X-ray diffractometer. The corrosion rate is investigated by using an electrochemical analyzer by potential dynamic polarization open-circuit technique. For this investigation, The Taguchi method with the L9 orthogonal array design of experimentation is adopted. The maximum UTS was acquired in the weld joint fabricated with 1250 r/min of tool rotational speed, 45 mm/min traverse speed, and a square tool pin. The stirred zone is tested for microhardness. High hardness is achieved with high tool rotational speed and low traverse speed with a square tool pin profile. The corrosion rate is also decreased with high tool rotational speed, low traverse speed, and a square tool pin profile.

A novel rotation extrusion processing system was self‐designed to prepare high‐performance polyethylene (PE) pipes. In this study, during the extrusion of the PE pipes at a high mandrel rotation speed, compressed air, as a cooling medium, was introduced through their interior to achieve the quick cooling of the inner wall and the effects of the inner wall cooling rate on the microstructure and mechanical properties of the obtained PE pipes were investigated. The experimental results showed that in contrast to conventional extrusion, the molecular orientation deviated from the axial direction under a high mandrel rotation speed and was fixed by the inner wall cooling; with increasing cooling rate, the orientation degree also increased. On the other hand, cooling promoted the augmentation of spherulites. So when the cooling rate reached a certain high point, the effect of cooling on the formation of spherulites was stronger than that on the fixation of the orientation. A much higher cooling rate decreased the orientation degree, which was closely related to the performance of the PE pipe. As a result, there was an optimal cooling rate of the inner wall during the rotation extrusion for better performance of the PE pipe. When the cooling rate was 1.5°C/s, the hoop strength of the PE pipe produced by the novel extrusion method increased from the original 24.1 MPa up to 37.1 MPa without a decrease in the axial strength, and the pipe's crack initiation time increased from 27 to 70 h. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Single-pass friction stir welding of AA2219-O aluminum alloy was carried out at high rotation speed (1180 rpm), and transverse travel rate of 33.5 mm/min was selected. The microstructural, mechanical and electrochemical characteristics of the weldment are investigated in this study. The high rotational tool speed resulted in a less uniform distribution of the intermetallic θ-phase (CuAl2) in the thermo-mechanically affected zone (TMAZ) than in the weld nugget zone (WNZ). The higher transfer coefficient and lower charge transfer resistance (Rct + Rθ) were observed in case of TMAZ as evaluated from potentiodynamic polarization and impedance spectroscopy, respectively. These results confirmed that microstructural variations could deteriorate the electrochemical performance of the weldment. TMAZ provided the least corrosion resistance than the base metal (BM) and WNZ due to the high concentration of cathodic intermetallic particles and possibly due to the large mechanical distortion of the grain structure.

Macrostructure, microstructure and mechanical properties of bobbin tool friction stir welded ZK60 Mg alloy joints

Microstructure and mechanical properties of dissimilar friction stir welded joints of laser powder bed fusion processed AlSi10Mg and conventional hot rolled 6061-T6 thin sheets

In this work, sheets of an Al-Mg-Si alloy were joined by double-side friction stir welding and tempered by standard post-weld artificial aging. The combination of relatively high FSW tool rotation and welding speed with subsequent post-weld artificial aging allowed obtaining welds with high joint efficiency. However, a high sensibility of joint efficiency from FSW tool rotation speed at constant welding speed was found. In turns, the joint efficiency of the friction-stir welds for ultimate tensile strength was found to be 72% at 800 rpm and 92% at 1100 rpm, respectively. The reasons of difference in the mechanical properties of the welds are studied.