Friction Stir Welded AZ31B Magnesium Research Articles

Mechanical and microstructural characterisation on the effect of increasing tool rotational speed of friction stir welded AZ31-B magnesium alloy

ABSTRACT This article intends to deliver the mechanical and microstructural characterisation of the impact of increasing the tool rotational speed on friction stir-welded similar AZ31-B magnesium alloy. The variable tool rotational speeds of 1000, 1200, 1400, and 1600 rpm with a fixed tool traverse speed of 30 mm/min were chosen based on the trail welding method. The macrostructural examination reveals that the lower tool rotational speed of 1000 rpm produced micro tunnel defects due to insufficient heat input, which causes less material intermixing. The microstructural examination shows finer grain size values when increasing the tool's rotational speed for 1000 rpm (12.5μm), 1200 rpm (9μm), 1400 rpm (7μm), and 1600 rpm (7.6μm). The tool rotational speed of 1400 rpm produced a defect-free welded joint with a higher tensile strength value of 215 MPa and a higher hardness value of 74 HV. Fractography analysis reveals all four welded samples were ductile fractured at an angle of 450. The higher welded joint efficiency of 78% was attained at the 1400 rpm welded parameters and the lower efficiency of 48% was achieved at the tool rotational speed of 1000 rpm.

Tensile Test on Friction Stir Welded AZ31B and AZ91B Magnesium Alloys

Rare earth materials containing magnesium alloy AZ91B and AZ31B is finding widespread use in the automotive, aerospace and military industries due to its greater strength-to-weight ratio and formability. Magnesium is typically regarded as difficult to fuse together through material fusion procedures due to flaws found in welding inclusions, porosity and welded junction distortions. Friction stir welding solid state joining procedure is used for Mg joining alloys successfully. The process variables influencing the combined characteristics of weldments include tool pin geometry, downward axial force, tool welding speed (rpm). In the current research, five distinct tool types were used to create friction stir weldment geometries. There were 18 trials overall with 3 components and 8 stages run in accordance with the primary composite design matrix. The information produced by a mathematical model through response surface approach was sufficient for the developed ANOVA was used to verify the model. Large interaction between welding parameters and tensile strength graphs are utilised to depict its behaviour. It was discovered that the cylindrical straight pin has the greatest tensile qualities. The mathematical model is beneficial for adjusting the tensile strength forecast to enhance the weld quality by choosing suitable process parameters for AZ31B and AZ91B welded magnesium alloys.

Experimental investigation and optimization of quality characteristics during friction stir welding of Al- and Zn-based magnesium alloy using artificial intelligence

Friction stir welding is successfully used to weld different wrought magnesium alloys. This work investigated the mechanical and microstructural behavior of the friction stir-welded AZ31B magnesium alloy. The experiments were conducted as per experimental runs designed by response surface methodology. An artificial neural network model was developed to produce a relationship between process variables (tool rotational speed, welding speed, and tool shoulder diameter) and characteristics of the friction stir-welded joints (tensile strength, percentage elongation, impact strength, microhardness, and grain size). The acceptable range of statistical parameters validated the adequacy of the model. The multi-objective optimization technique, genetic algorithm was used to obtain a set of Pareto optimal solutions. The best-compromised optimum solution for maximum tensile strength (164.2 MPa), percentage elongation (8%) impact strength (3.5 J), microhardness (85 Hv), and minimum grain size (13.1 μm) was validated by confirmation test with <3 percent absolute error percentage. The fractographical analysis has been performed and dimples and torn edges observed in fracture zones.

Galvanic corrosion behavior of friction stir welded AZ31B magnesium alloy and 6N01 aluminum alloy dissimilar joints

The corrosion behavior and corrosion rate of friction stir welded AZ31B magnesium alloy and 6N01 aluminum alloy dissimilar joints were studied using real-time imaging, potentiodynamic polarization, EIS, and hydrogen evolution tests. The corrosion rate was found to increase, in order, Al base metal (BM-6N01) < Mg base metal (BM-AZ31B) < stirred zone. The galvanic coupling of the Mg phase to the other phases enhanced the corrosion of both BM-AZ31B and BM-6N01. Accompanying the intense corrosion at BM-AZ31B, water reduction on the cathodic particles of BM-6N01 elevated the interfacial pH to a level where the Al matrix corroded to AlO2−.

Enhancing the corrosion resistance of stir zone of friction stir welded AZ31b magnesium alloy using micro arc oxidation coatings

Abstract To explore the feasibility of micro-arc oxidation (MAO) coating, a study has been made to analyze the effect of process parameters namely, oxidation time and current density on the coating hardness and coating porosity. The parameter, current density was varied from 0.04 to 0.20 A/cm2 and the oxidation time was varied from 10 to 50 min for the fabrication of coatings. The coating has been tested for potentiodynamic polarization of uncoated and MAO coated samples of FSW-Mg joints. The coating has been characterized using scanning electron microscope on the top and cross section. The study concludes that MAO coating is found to be beneficial to enhance the resistance to corrosion of stir zone of AZ31B magnesium alloy joints up to 17 to 28 ti.

Effect of Travel Speed on Quality and Welding Efficiency of Friction Stir Welded AZ31B Magnesium Alloy

Weight reduction is one of the most concerning issues of automotive and aircraft industries in reducing fuel consumption. Magnesium (Mg) alloys are the lightest alloys which can be used in the structure due to low density and high strength to weight ratio. Developing a reliable joining process of magnesium alloys is required due to limited ductility and low workability at room temperature. Friction stir welding (FSW) is a solid-state welding process that can be performed to produce sound joints in magnesium alloys. Researchers have performed investigations on the effect of rotation and travel speeds in FSW of AZ31B magnesium alloy. However, there is lack of study on the FSW parameters, i.e. travel speed below 50 mm/min and rotation speed lower than 1000 rpm. In this research, FSW of AZ31B magnesium alloy was performed at a constant rotation speed of 700 rpm and varied travel speeds below 50 mm/min. The results showed the development of finer grain size in stir zone with increasing of welding travel speed from 20 mm/min to 40 mm/min. It was found that the finer grain size improved the mechanical properties while maintaining the elongation at different welding parameters.

Detection and assessment of flaws in friction stir welded joints using ultrasonic guided waves: experimental and finite element analysis

Abstract Ultrasonic guided waves (GWs), e.g. Lamb waves, have been proven effective in the detection of defects such as corrosion, cracking, delamination, and debonding in both composite and metallic structures. They are a significant tool employed in structural health monitoring. In this study, the ability of ultrasonic GWs to assess the quality of friction stir welding (FSW) was investigated. Four friction stir welded AZ31B magnesium plates processed with different welding parameters and a non-welded plate were used. The fundamental symmetric (S 0 ) Lamb wave mode was excited using piezoelectric wafers (PZTs). Further, the S 0 mode was separated using the “Improved complete ensemble empirical mode decomposition with adaptive noise (Improved CEEMDAN)” technique. A damage index (DI) was defined based on the variation in the amplitude of the captured wave signals in order to detect the presence and asses the severity of damage resulting from the welding process. As well, computed tomography (CT) scanning was used as a non-destructive testing (NDT) technique to assess the actual weld quality and validate predictions based on the GW approach. The findings were further confirmed using finite element analysis (FEA). To model the actual damage profile in the welds, “Mimics” software was used for the 3D reconstruction of the CT scans. The built 3D models were later used for evaluation of damage volume and for FEA. The damage volumes were correlated to the damage indices computed from both experimental and numerical data. The proposed approach showed high sensitivity of the S 0 mode to internal flaws within the friction stir welded joints. This methodology has great potential as a future classification method of FSW quality.

Investigation of the Effects of Plunge Depth on the Resulting Temperature Distribution, Microstructure and Mechanical Properties of Friction Stir Welded AZ31B Magnesium Alloy

Investigation of the Effects of Plunge Depth on the Resulting Temperature Distribution, Microstructure and Mechanical Properties of Friction Stir Welded AZ31B Magnesium Alloy

Influence of tool material and rotational speed on mechanical properties of friction stir welded AZ31B magnesium alloy

Abstract In this investigation, the effect of friction stir welding (FSW) parameters such as tool material rotational speed, and welding speed on the mechanical properties of tensile strength, hardness and impact energy of magnesium alloy AZ31B was studied. The experiments were carried out as per Taguchi parametric design concepts and an L9 orthogonal array was used to study the influence of various combinations of process parameters. Statistical optimization technique, ANOVA, was used to determine the optimum levels and to find the significance of each process parameter. The results indicate that rotational speed (RS) and traverse speed (TS) are the most significant factors, followed by tool material (TM), in deciding the mechanical properties of friction stir processed magnesium alloy. In addition, mathematical models were developed to establish relationship between different process variables and mechanical properties.

Effect of Tool Rotational Speed on Tensile and Microstructural Behaviour of Friction Stir Welded AZ31B Magnesium Alloy Joints

Effect of Tool Rotational Speed on Tensile and Microstructural Behaviour of Friction Stir Welded AZ31B Magnesium Alloy Joints

Microstructure Stability During Creep of Friction Stir Welded AZ31B Magnesium Alloy

Friction stir welding (FSW) was applied in the current study in order to butt weld AZ31B-H24 alloy plates. Creep tests were conducted both on the parent material and on the friction stir welded specimens. The microstructure of the AZ31B alloy was found to be unstable under creep conditions. In the case of friction stir welded AZ31B, the material undergoes during FSW both recrystallization and grain growth, then the exposure to temperature during creep yields an extensive additional grain growth. On the other hand, twinning and twin-induced recrystallization occur as well during creep so that ultrafine grains are being created concurrently.

Fatigue Behaviour of Friction Stir Welded AZ31B Magnesium Alloy Joints

Friction stir welding (FSW) is a relatively better joining technique particularly for magnesium and aluminum alloys that are difficult to weld by fusion welding techniques. Fusion welding of these alloys is not preferable due to hot cracking, formation of porosity, etc. However solid state welding techniques, such as, friction sitr welding are found to offer solution to the above problems. Many research papers available in open literature focusing tensile properties, microstructural characteristics, and corrosion behaviour of friction stir welded AZ31B magnesium alloys but fatigue behaviour of these welds are not yet investigated. Hence, in this investigation, an attempt has been made to evaluate fatigue behaviour of friction stir welded rolled plates of AZ31B magnesium alloys.Fatigue experiment was conducted using servo hydraulic controlled fatigue testing machine. Fatigue strength, fatigue notch factor and notch sensitivity factor were evaluated. It is found that the fatigue strength of AZ31B welded joints is 46 MPa at 2x106 cycles which is approximately 34 % lower than that of the base metal fatigue strength.

Improving the Mechanical Properties of Friction Stir Welded AZ31B Magnesium Alloy Flat Plates through Axial Force Investigation

In this paper, the effects of axial force on the mechanical properties of AZ31B magnesium alloy flat plates during the Friction Stir Welding (FSW) process were investigated by carrying out the tensile tests as per the American Society for Testing and Materials (ASTM) E8M-11 standards. The tensile test results indicated that the increase of the axial force greatly improved the tensile shear load (TSL) of the friction stir welded joints at a constant tool rotational speed of 800 rpm and welding speed of 50mm/min. Sound lap joints with low distortion, lack of cavity and high tensile strength were successfully obtained with an axial force of 5kN. However, the TSL of the friction stir welded joints decreased when the axial forces were 3kN and 4kN with the same constant tool rotational and welding speed.

Influence of Welding Processes on Tensile Properties, Microstructure, and Hardness of Friction Stir Welded AZ31B Magnesium Alloy

Friction Stir Welding (FSW) was performed on 5-mm thick plates, machined from rolled AZ31B Magnesium alloy.The microstructure and defects formation were investigated by optical microscope. The mechanical properties were determined by tensile and hardness tests. Frictional heat and plastic flow during friction stir welding create the fine recrystallized grain (Stir Zone, SZ) and the elongated and recovered grain (Thermo-Mechanical Affected Zone, TMAZ) in the weld zone. Heat affected zone (HAZ), which can be identified only by hardness test due to no difference in grain structure compared with the base metal, is formed beside the weld zone. In this study, the effect of rotational speed on microstructure , hardness and mechanical properties of Friction stir welded Mg AZ31B alloy have been investigated. Friction stir welding (FSW) is carried out at different rotational speeds of 900 rpm, 1120 rpm, 1400 rpm and 1800 rpm with High speed steel (HSS) at a constant welding speed of 40 mm/min, tilt angle of 2.5 0 and axial force of 5 KN. It is observed that the joint fabricated using HSS tool material at a rotational speed of 1400 rpm obtained higher mechanical properties as compared to those of 900 rpm, 1120 rpm and 1800 rpm.

Effect of tool pin profile on microstructure and mechanical properties of friction stir welded AZ31B magnesium alloy

In this investigation the effect of friction stir welding pin geometry on the microstructure and mechanical properties of AZ31B magnesium alloy joints is studied. The considered pin geometries are simple cylindrical, screw threaded cylindrical and taper. The joints are friction stir welded at different traverse and rotational speeds. Microstructures of the joints are examined using the optical and scanning electron microscopes. Also, the tensile properties and hardness of the joints are measured. The results show that taper and screw threaded cylindrical pins produce defect free joints. In addition, the taper pin results in finest microstructure and highest mechanical properties. Furthermore, it is found that rotational speed has a more significant role on the final microstructure and mechanical properties of the joints, compared to the traverse speed.

Corrosion behavior of friction stir welded AZ31B magnesium alloy with plasma electrolytic oxidation coating formed in silicate electrolyte

A protective ceramic coating of about 50 μm thick on a friction stir welded (FSW) joint of AZ31B magnesium alloy was prepared by plasma electrolytic oxidation (PEO) in silicate electrolyte. Electrochemical corrosion behavior of uncoated and coated FSW joints was evaluated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The equivalent circuits of EIS plots for uncoated and coated FSW magnesium alloy were suggested. The corrosion resistance of FSW magnesium alloy depended on microstructure of the FSW joint. The heat-affected zone with severe grain growth was more susceptible to corrosion than the stir zone and base metal. The PEO coating consisted of a porous outer layer and a dense inner layer. The inner layer of PEO coating played a key role on corrosion protection of the FSW joint of magnesium alloy. Meanwhile, corrosion potential, corrosion current density and impedance at different zones of coated FSW joint were almost the same. The PEO surface treatment significantly improved the corrosion resistance of FSW joints of AZ31B magnesium alloy.

Prediction of Tensile Strength and Optimization of Process Parameters for Friction Stir Welded AZ31B Magnesium Alloy

An attempt has been made to develop an empirical relationship to predict the tensile strength of friction stir welded AZ31B magnesium alloy by incorporating process parameters such as tool rotational speed, welding speed, and axial force. The experiments were conducted based on three factors, three levels of central composite face centred design with a full replications technique. The developed relationship can be effectively used to predict the tensile strength of friction stir welded joints at the 95 per cent confidence level. The results indicate that tool rotational speed has the greatest influence on tensile strength, followed by welding speed and axial force.

Tensile properties and strain-hardening behavior of double-sided arc welded and friction stir welded AZ31B magnesium alloy

Microstructures, tensile properties and work hardening behavior of double-sided arc welded (DSAWed) and friction stir welded (FSWed) AZ31B-H24 magnesium alloy sheet were studied at different strain rates. While the yield strength was higher, both the ultimate tensile strength and ductility were lower in the FSWed samples than in the DSAWed samples due to welding defects present at the bottom surface in the FSWed samples. Strain-hardening exponents were evaluated using the Hollomon relationship, the Ludwik equation and a modified equation. After welding, the strain-hardening exponents were nearly twice that of the base metal. The DSAWed samples exhibited stronger strain-hardening capacity due to the larger grain size coupled with the divorced eutectic structure containing -Mg17Al12 particles in the fusion zone, compared to the FSWed samples and base metal. Kocks-Mecking type plots were used to show strain-hardening stages. Stage III hardening occurred after yielding in both the base metal and the welded samples. At lower strains a higher strain-hardening rate was observed in the base metal, but it decreased rapidly with increasing net flow stress. At higher strains the strain-hardening rate of the welded samples became higher, because the recrystallized grains in the FSWed and the larger re-solidified grains coupled with particles in the DSAWed provided more space to accommodate dislocation multiplication during plastic deformation. The strain-rate sensitivity evaluated via Lindholm's approach was observed to be higher in the base metal than in the welded samples. © 2010 Elsevier B.V. All rights reserved.

Effect of Tool Materials on Tensile Properties of Friction Stir Welded AZ31B Magnesium Alloy

Effect of Tool Materials on Tensile Properties of Friction Stir Welded AZ31B Magnesium Alloy

Effect of post weld heat treatment on mechanical properties and microstructures of friction stir welded AZ31B magnesium alloy

The effects of post weld heat treatment (PWHT) on microstructures and mechanical properties of friction stir welded AZ31B magnesium alloy were investigated. Average grain sizes at the upper region and at the bottom region in the stir zone (SZ) of as welded joint were 9.5 μm and 14.4 μm, respectively. When heat treatment temperature at 673 K, a few relatively large grains were formed at the retreating side in upper region, subsequently the region extended in the stir zone as heat treatment time increased. It is believed that the abnormal grain growth is caused by inhomogeneous distribution of dislocation. The elongation to failure of joint was improved by the heat treatment at 573 K for 7.2 ks. However, the formation of abnormal large grains caused degrading elongation. The yield stress at upper side in SZ of as welded joint was larger than that at bottom side and was decreased gradually as the joint was annealed. Because the additional strength at the upper side was due to the work hardning that was added by the shoulder of tool.