Parameter investigation and optimization of friction stir welded AA6061/TiO2 composites through TLBO

This paper explicates the joining of AA 6061/TiO2 composites by the friction stir welding (FSW) process. FSW experiments were conducted as per the three factors, three-level, central composite ivy– face-centered design method. Mathematical relationships between the FSW process parameters, namely tool geometry, welding speed, and tool rotational speed, and the output responses such as hardness, yield strength, and ultimate tensile strength were established using response surface methodology. Adequacies of established models were assessed through the analysis of variance method. Further, the paper elucidates the application of the teaching–learning-based optimization (TLBO) algorithm to identify the optimal values of input variables and to obtain an FSW joint with superior mechanical properties. The optimized experimental condition obtained from the TLBO yields an FSW joint with a UTS of 174 MPa, yield strength of 120 MPa, and hardness of 126HV. The study revealed that the result of the TLBO algorithm matched the findings of the FSW experiments.

Bobbin Tool Friction Stir Welding of Aluminum Using Different Tool Pin Geometries: Mathematical Models for the Heat Generation

In this work, three mathematical models for the heat generation during bobbin tool friction stir welding (BT-FSW) of aluminum using three tool pin geometries have been proposed. The models have utilized and updated the available models for the heat generation during the conventional tool friction stir welding (CT-FSW). For the validation of the models, BT-FSW experiments have been carried out for aluminum alloy AA1050 using three different pin geometries (cylindrical, square, and triangular), at different welding speeds of 200, 400, 600, 800, and 1000 mm/min and a constant tool rotation speed of 600 rpm. The welding temperatures during BT-FSW have been measured to be compared with that calculated from the models at the same parameters. It has been found that the calculated welding temperatures from the models and that measured during BT-FSW are in good agreement at all the investigated welding speeds especially in case of the square and cylindrical pins, proving the validity of the developed models for the predication of the heat generation as well as the welding temperatures. This will allow proper designing of the BT-FSW parameters and avoiding the conditions that can deteriorate the joint quality and properties.

Analysis of Torque in Friction Stir Welding of Aluminum Alloy 5052 by Inverse Problem Method

Torque influences the main phenomena that occur during friction stir welding (FSW) process. However, models for torque have received little attention. In this paper, inverse problem method is used to estimate the parameters for a model for torque, measured during FSW experiments for different combinations of rotational and welding speeds. The experimental results are used as input data to estimate the model parameters. The results showed a good agreement between the experimental data and the model obtained using the inverse problem method. The influence of the tool geometry on torque was observed by comparing previously published experimental results and the experimental data presented.

Effect of Flat Heat Pipe on the Properties of the FSW Joint

Friction stir welding (FSW) joint is characterized with asymmetric gradient in three dimensions. The purpose of this thesis is trying to find the effective methods to improve the microstructure and strength of AZ31 magnesium alloy joint of FSW. In order to achieve this aim, one heat pipes was designed and applied to the FSW process. Using different cooling methods, FSW experiments were carried out in air and under the conditions of heat pipes controlling. The welding temperature fields, macrostructure, microstructure and mechanical property of the joint were investigated. The result shows that with the heat pipes controlling, the maximum peak temperature decreased by 100 °C. The average duration of high temperature was 36s which shortens 11s compared to that in air. After applying the heat pipes the microstructure in the weld nugget zone were slightly finer than that in air. The average tensile strength of the welding joints was higher than that in air. The highest tensile strength reached 220.4 MPa, more than 90% of the base material strength; The fracture position located between thermal mechanical affected zone and heat affected zone. Under the condition of applying heat pipes, the number of dimple gradually increased and the tensile rupture pattern was ductile-brittle fracture.

Optimization of Tensile Properties Based on Spin Tool Shoulder Geometry for Friction Stir Welded 6061 Aluminum Alloy

This study reported the statistical optimization based on Taguchi designed experiments to improve the tensile properties of 6061 Aluminum alloy by the friction stir welding (FSW) experiments. The morphology and the structure of the friction stir welded experiments were characterized by scanning electron microscopy. Based on analysis of variance, the impacts of control factors have been identified for the tensile strength of 6061 aluminum alloy by friction stir welding. Experimental results revealed that the defect free butt joints could be obtained by cylindrical-screw type of tool shoulder and the joints made with a cylindrical-screw type resulted in better tensile properties compared to the other two shoulder geometries. Furthermore, it was clear that the tensile properties are greatly improved by friction stir welded experiments in the Taguchi design, and these findings have achieved the desired values in regard to the friction stir welded Experiments. The proposed procedure was applied at friction stir welded experiments, and the implementation results demonstrated its feasibility and effectiveness to enhance the tensile properties by FSW .

Similar and Dissimilar FSWed Joints in Lightweight Alloys: Heating Distribution Assessment and IR Thermography Monitoring for On-Line Quality Control

The heating distribution assessment on similar and dissimilar friction stir welded joints in AA6082 and AA5754 aluminium alloy sheets was investigated. The FSW experiments were carried out using constant rotational and welding speeds of 1500 rpm and 60 mm/min, respectively. Temperature was locally measured by means of K-type thermocouples inserted into thin grooves located on the bottom side of the sheets, in fixed positions, very close to the welding line. It was observed that the mechanical properties of joints are related to the heat distribution. In order to obtain a completely non intrusive temperature monitoring, that was able to follow the process dynamic, a non-contact measurement system based on infrared thermography was also developed. Such system, used for the experimental evaluation of temperature on the upper surface of the joints, is also able to detect the presence of flow defects with a non-destructive method, demonstrating its effectiveness as a diagnostic instrument for the on-line quality control of welded joints.

Microstructures and Mechanical Properties of Mg Alloy FSW Joint Characterized with Asymmetric Gradient in Three Dimension

Friction stir welding (FSW) experiments were carried out on AZ31 magnesium alloy under the optimized welding parameters. The temperature distribution, macrostructure and microstructure, mechanical properties of the joint were studied along three dimensions (transverse direction, longitudinal direction, thickness direction). Temperature distribution, joint appearance and microstructure demonstrate asymmetric gradient in three dimensions. The peak temperature of featured points at the welding beginning stage was lower, and the one in the ending stage was higher. The temperature of advancing side was higher than that of the retreating side. More in detail, the dynamically recrystallized microstructure in weld nugget zone (WNZ) was uniform and small. The thermomechanically affected zones (TMAZ) closed to the WNZ, which were characterized with bended and elongated grains. At advancing side, the interface between TMAZ and WNZ was very distinct. The microhardness distribution showed a typical W shape. The profile showed a slightly lower hardness in the WNZ than in the base metal,HAZ, and TMAZ correspond to the lowest one. The FSW joints were observed to fail mostly at the boundary between WNZ and TMAZ at the advancing side.

Improving Friction Stir Welding between Copper and 304L Stainless Steel

As a solid-state welding technology, friction stir welding (FSW) can join dissimilar materials with good mechanical properties. In this paper, friction stir welding between 304L stainless steel and commercially pure copper plates with thicknesses of 3 mm was performed. A number of FSW experiments were carried out to obtain the optimum mechanical properties by adjusting the rotational speed to 1000 rpm and welding speed in the range of 14-112 mm/min and with an adjustable offset of the pin location with respect to the butt line. Microstructural analyses have been done to check the weld quality. Cross-sectioning of the welds for metallographic analysis in planes perpendicular to the welding direction and parallel to the weld crown was also performed. The mechanical properties of the welds were determined using a combination of conventional microhardness and tensile testing. From this investigation it is found that the offset of the pin is an essential factor in producing defect free welds in friction stir welding of copper and steel.

Research of Material Flow for Friction Stir Welding Using Smooth Pins Based on Plasticine Analog

Material flow during friction stir welding is very complex and not fully understood. Most of studies in literature used threaded pins. However, analyzing material flow using smooth pins is of great interest for the validation of a numerical model in which threads are difficult to represent. In this study, FSW experiments were performed using smooth pin based on plasticine analog. Longitudinal, horizontal and transverse sections of welds were observed with the use of plasticine of identical type but different color as material marker to investigate the material flow. A horizontal ‘vortex-like’ action has been occurred. In the agitating-extruding region (inside the pin diameter), a clockwise (identical to the rotating tool) layer appears around the tool, as a result the material both the advancing side and retreating side is mixed. In the deformation region (outside the pin diameter), the material is driven by the clockwise viscous force of the rotating pin, and the effect is reduced with the increase of the distance to the weld center.

Metallurgical Nature at the Interface between Tool Shoulder and Workpiece during Friction Stir Welding

Knowledge on the contact condition at the tool/workpiece interface is essential for understanding many aspects of FSW. In the present study, FSW experiments were conducted using aluminium alloys followed by metallographic examination focusing on the tool shoulder-workpiece interface region. It was observed that an interfacial intermetallic layer and hence metallurgical sticking/soldering readily formed. Temperature measurements have suggested the presence of interface liquid, hence suggesting a mechanical sliding contact condition dominant. This has been supported by the observation on material flow within the shear layer.