Welded Magnesium Alloy Research Articles

Recent Advances in Dissimilar Friction Stir Welding of Aluminum to Magnesium Alloys

Abstract Welding of dissimilar magnesium alloys and aluminum alloys is a critical issue because of their worldwide increasing applications. Dissimilar welding technology has touched new frontiers to take up the benefits of both metals simultaneously through their local demands. Friction Stir Welding (TWI, 1991) is rapidly blooming in the contemporary fields of aerospace, defence, marine, automotive, and railway industries as proven approach of solid state joining. Owing to its versatility, affability to environment and energy efficiency, it is widely getting acceptance as “green technology” in modern industries. FSW has facilitated joining of high-strength, lightweight aluminum and magnesium alloys which were earlier treated as unweldable by conventional fusion welding. Present article significantly appraises the review of growth of research towards joining of dissimilar aluminium–magnesium alloys by friction stir Processing (FSP). The investigative approach is addressed through the description of joining mechanism and hurdle faced in unification of Al-Mg. Formation of intermetallic compounds (IMCs) are inevitable during joining of such heterogeneous alloys (Al-Mg) irrespective of joining methods. So it becomes challenging to impede formation and growth of IMCs, hence research community always looks for novel techniques, a few of which are covered in this piece of writing. Present review also addresses responsible theories for IMCs and its correlation with process parameters through (categorized A, B, C) evolution of microstructures. Unlike fusion welding different sorts of defects have also been reported in literature originating through FSP. Moreover, influence and correlation of process variants have been covered through study of mechanical and metallurgical characterization mentioned in literature. Mainly literature advocates research involving optimization of process parameters and their compounding effects that eventually govern quality of weld and joint efficiency during FSP of Al-Mg. Finally, article throws light on summary of FSW developments by novel techniques and untouched future endeavours being potential area of research for Al-Mg

Microstructural analysis of friction stir welded Mg AZ31 alloy

Magnesium alloys are the lightest of all structural metals and are in great demand in various automotive and aerospace industry. The current research work focusses on evaluating the effects of input process parameters on the metallurgical properties of friction stir welded magnesium alloys. The variable input parameters chosen are tool rpm, travel speed and the plunge depth. Microstructural studies revealed three distinct zones in the welded specimen, viz: stir zone also known as the weld nugget, thermo mechanical affected zone and the unaffected base material. Large sized grains were observed at the top surface of the welded specimens due to more heat input at the top. The microhardness of the workpiece was measured in the traverse direction and maximum hardness observed in the stir zone is about 16% higher than the parent material.

Model-based parameter optimization for arc welding process simulation

This paper presents a model-based parameter optimization for simulating a metal-inert gas welding process. The computational model used in this study is based on computational fluid dynamics methods and implemented using the finite volume approach on a 3D computational domain. The wire electrode, the arc plasma and the workpiece are treated as a self-consistent system. Important welding parameters, including arc current, wire feed rate, workpiece thickness, welding speed and geometry, as well as the metal alloy types used for the wire and workpiece, were implemented as adjustable parameters. By tuning these parameters, the performance of the arc welding can be predicted, and different settings can be compared to optimize welding performance.A benchmarking study of the arc model against experimental measurements is presented to demonstrate the model's capabilities in the prediction of the weld pool changes and thermal dynamics involved in the welding process. Two numerical case studies are presented to demonstrate the use of the model-based optimization to quantify welding pool variations with the change in welding parameters. The first case study is the determination of the optimal arc current and welding speed settings for different workpiece thicknesses. The optimization process shows that the predictions are not only in agreement with established experimental welding experience on the direct relationship between workpiece thickness and arc current, but more importantly quantify this relationship for a given workpiece thickness. The second case study focuses on the welding parameters optimization for different metal alloys. The comparison suggests that the welding parameters suitable for some aluminium alloys are less likely to be successful in welding magnesium alloys. A further model validation of Mg alloy AZ31 welding shows an agreement with experimental measurements. The work presented shows the potential of model-based parameter optimization to assist process engineers in the practical improvement of the welding process.

Microstructure and mechanical properties of cold metal transfer welded galvanized steel/magnesium alloy dissimilar joints

The joining of magnesium alloy to galvanized steel was realized by cold metal transfer method with AZ31 magnesium alloy welding wire. Weld appearance, microstructure and tensile properties of Mg–steel joints under various welding parameters were investigated with different welding heat inputs. The results showed that magnesium alloy-steel brazed joints had good weld appearance. When the welding heat input was 141 J/mm, Zn elements were enriched in the Zn-rich zone (ZRZ), and the interface layer was composed of a large portion of Mg–Zn phases and minor Mg–Al phases. With the increase of welding heat input, Zn elements in the ZRZ gradually decreased, Fe/Al phase appeared in the interface layer, and the strength of welding joint increased. When the welding heat input was 159 J/mm, the tensile strength of welding joint reached the maximum value of 198 MPa. However, when the welding input was increased to 181 J/mm, Zn element in the ZRZ was burnt and volatilized seriously, resulting in poor wetting and spreading properties of liquid phase at the interface zone of the steel.

Investigation of Heat-Assisted Dissimilar Friction Stir Welding of AA7075-T6 Aluminum and AZ31B Magnesium Alloys

This study investigates the successful joining methods of dissimilar metals of AZ31B Mg and AA7075-T6 Al alloys. The specimens were joined by using open-flame heating system and investigated the effect of the friction stir welding (FSW) process parameters on the welding quality, transverse rupture strength (TRS), tensile strength, microhardness, and microstructure of the resulting specimens. The welding experiments were conducted based on the Taguchi mixed-orthogonal-array for tests, L16 (42 × 22), at a constant spindle speed of 500 rpm using a K10 grade carbide mixing tool with two different tilt angles (0° and 3°), and two tool tip geometries (square and triangle). The specimens were successfully welded, and the test results revealed that the welding temperatures and forces had the strongest effect on the welding quality. The achieved maximum tensile strength and TRS were approximately 122.1 MPa and 712.1 MPa, respectively, at a tool travel speed of 20 mm/min, tool offset value of 0.75 mm, tool tilt angle of 3°, and using a triangle tool tip. The microstructural analysis indicated that a dynamically recrystallized and grain refinement structure formed in the welded zone depending on the temperature and on the excessive deformation. The increase in the microhardness values depends on the intermetallic compounds ratio and fine-grained structure in the welded zone.

Micro-friction stir welding (μFSW) – A review

Micro-friction stir welding (μFSW) is a revolutionary joining process which is usually used for the welding of metallic alloys, like aluminium, magnesium, copper, lead, zinc, titanium and other softer structural alloys. Micro-friction stir welding is employed to join thin electrical components and micro-mechanical components which is primarily used in industries like; aerospace, automotive and other industrial applications. Tool rotational speed along with speed of welding and angle of tool tilting are most vital parameters for the μFSW process which affects the joint property. It gives better joint properties than the base material properties.

Friction Stir Weld of AZ91 Magnesium Alloy With and Without Nano-SiC Particle

In this article, the influence of SiC nanoparticles on the friction stir welding of AZ91 magnesium alloy has been studied. For this purpose, a groove was designed to incorporate the nanoparticles into the weldment without requiring any additional tool to cover the weld surface. The welding process was carried out with and without nanoparticles in different process conditions. The mechanical properties and microstructure of the prepared joints were also studied. The results indicated that without using the nanoparticles, the minimum grain size of 2.79 µm along with the strength of 99% of the base metal can be achieved by applying the highest examined welding traverse speed and the lowest rotational speed. By using the SiC nanoparticles, in addition to annealing and dynamic recrystallization (DRX) mechanisms, the weld microstructure is also affected by pinning and aggregation mechanisms. Furthermore, it was realized that an increase in the rotational and traverse speeds adversely affects the mean grain size of the welded joints in the presence of nanoparticles. For the welded samples with nanoparticles, the grain size can be refined to 1.06 µm at the lowest traverse speed and the highest rotational speed.

Ultrasonic welding of AZ31B magnesium alloy

Abstract

Effect of Rotational Speed on Microstructure and Mechanical Properties in Submerged Friction Stir Welding of ME20M Magnesium Alloy

Submerged friction stir welding of magnesium alloys has not been well investigated to date. ME20M is an important lightweight magnesium (Mg) alloy with enhanced yield strength and heat resistance that merits further research. In this paper, submerged friction stir welding of the ME20M Mg alloy was carried out using different parameters for the underwater cooling. Defect-free weld joints were produced, and the macrostructure, microstructure, tensile properties, and hardness were investigated. The results show that by increasing the rotational speed, the grain size of the weld nugget increased, the tensile strength of the joint decreased, and the microhardness of the different weld zones decreased. The finest obtained grain size was about 3.5 µm in the weld nugget at a rotational speed of 1100 rpm. The highest tensile strength achieved was 183.2 MPa, which was ~ 76.32% of the base metal. The highest and lowest hardness values of the weld joint were obtained at rotational speeds of 1100 and 1600 rpm, respectively, in the weld nugget and heat-affected zones.

Resistance element welding of magnesium alloy and austenitic stainless steel in three-sheet configurations

The Mg alloy and two austenitic stainless steel sheets were joined together by a metallurgical bond across the rivet and two austenitic stainless steel sheets. More heat was generated at the austenitic stainless/austenitic stainless interface than at the rivet/ austenitic stainless steel interface, leading to larger nugget size at the austenitic stainless steel /austenitic stainless steel interface at all welding currents. Thus, the nugget size at the austenitic stainless steel /austenitic stainless steel interface mainly influenced the transition from interfacial to pullout failure modes. The fusion zone microstructure consisted of ferrite and austenite. The microstructure in the edges of the nugget (both in the rivet and ASS) consisted of fine columnar dendritic grains. Owing to variation of temperature gradient and solidification growth rate, the grains morphology changed from columnar dendritic to equiaxed dendritic in the nugget center. The fine grains resulted in high fusion zone hardness. Digital image correlation analysis revealed that the joints could experience joining zone rotation/out-of-plane displacement during lap-shear tests, which reduced the magnitude of strain sustained by the joints in the loading direction. The joint configuration that did not undergo joining zone rotation and failed via pullout failure in the austenitic stainless steel sheet exhibited superior lap-shear performance.

The study of magnetic field assisted system for tungsten inert gas welding of magnesium alloy and steel

An external magnetic field was applied during the TIG welding-brazing of Mg/steel plates, which both has the thickness of 1.5 mm. The effects of magnetic field on the weld microstructure, micro hardness and tensile strength were studied by scanning electron microscope, Vickers hardness tester and tensile testing machine. The following conclusions can be drawn. The applying of magnetic field could lower the thickness of Mg–Zn reaction layer of brazed joint. With the continuous increase of coil current, the thickness value of IMC layer decreased gradually. Besides, electromagnetic force induced by magnetic field can promote the flow of molten pool and tend to break initial dendrite to pieces, which could turn into the new nucleation point. Hence noteworthy grain refinement was achieved by the applying of external magnetic field. For the magnetic field treated joint, the microhardness of welding seam enlarged from 49.9 HV to 56.8 HV and the maximum welding strength of 246 N mm−1 was obtained with coil current of 1.5 A.

Laser welding of AZ31B magnesium alloy with beam oscillation

Circular beam oscillation was introduced to laser welding of 2mm-thick AZ31 magnesium alloy. The appearance, microstructure and tensile properties of the welds were investigated. It was found that the low frequency about 50Hz and the small radius about 0.5mm are more beneficial to improve the weld appearance, under the given parameters of laser power 2kW, welding speed 2m/min and beam oscillating diameter 0.35mm. The undercut defect and even the totally collapse of the weld appear when employing the frequency higher than 75Hz or the radius larger than 1.5mm. The microstructure evolution mainly reflects in the variation of the proportions of the equiaxed zone (PEZ) and the average grain size (SG). The PEZ decreases from 85% to 42% with the beam oscillating frequency increasing from 25Hz to 100Hz, while the SG reaches the maximum of 37.5μm at 75Hz. The PEZ decreases and the SG increases with the increase of beam oscillating radius. The results showed that the tensile strength and elongation are closely related to the PEZ, the SG and the twins. According to the experimental results, the relationship of oscillating parameters, microstructure, and tensile properties was established.

Influence of Welding Temperature on Material Flow During Friction Stir Welding of AZ31 Magnesium Alloy

In this work, the effect of welding temperature on material flow during friction stir welding (FSW) of AZ31 magnesium alloy was examined. To this end, FSW was conducted in the temperature range of 0.65-0.85 Tm (Tm is the melting point) and sample-scale EBSD mapping was employed to characterize texture distribution. Despite that the low-temperature welds contained macro-scale defects (which presumably affected material flow), several important observations were made. In the entire temperature range, the global material motion was shown to consist of two principal components, viz. shoulder-induced flow and probe-induced flow. In some cases, however, a synergetic effect of these two constituents resulted in transitional orientation of macro-scale shear plane thus giving rise to a transitional material flow. During low-temperature FSW, the global material transportation was dominated by the probe. However, the contribution of the shoulder and transitional components was found to increase with welding temperature. This effect was attributed to the dominant role of the shoulder in generation of FSW heat. Above ~ 0.8 Tm, however, the transitional material flow was found to abruptly disappear. This result was associated with reduction of temperature sensitivity of flow stresses and the resulting equilibration of their distribution within the stir zone.

A COMPARATIVE STUDY TO EVALUATE THE CORROSION PERFORMANCE OF FRICTION STIR WELDED AZ31B MAGNESIUM ALLOY UNDER IMMERSION, SALT FOG, PITTING AND GALVANIC CORROSION TESTS UNDER NACL ENVIRONMENT

An investigation was carried out to quantify and characterize the corrosion behaviour of AZ31B magnesium alloy joints. Extruded Mg alloy plates of 6 mm thick of AZ31B grade were butt welded using a solid state, environmentally cleaner welding process, friction stir welding process. The weld specimens were underwent immersion, salt spray, pitting and galvanic corrosion tests in order to quantify and characterize the corrosion rates of the welds with the influence of different pH values, chloride ion concentration and the corrosion time. The corrosion rates, microstructure, scanning electron microscopy and X-ray diffraction analysis concludes the optimum parameter for the usage of the magnesium alloy welds for the best service applications. Keywords: Keywords: EDM, Alumina and Genetic Algorithm

Optimization of current parameters during variable polarity GMAW of magnesium alloy

Magnesium alloy welding suffers from problems such as burn through and loss of alloying elements during conventional welding process due to high heat input. Variable polarity gas metal arc welding (VP-GMAW) features low heat input. Therefore, it is an attractive method for welding of magnesium alloy. However, the principles governing the correlations among welding current parameters, metal transfer modes, and bead formation are not well understood. Identifying optimal welding current parameters by trial and error is unrealistic. Therefore, peak current, base current, and negative current were selected as independent variables. Their impact mechanism on metal transfer and bead formation were investigated by experiments with high-speed photographs. Then, weld quality evaluation was conducted by a fuzzy comprehensive evaluation. A mathematical method was proposed to calculate optimal current parameters for VP-GMAW of magnesium alloy. In addition, a significant sequence of current parameters is obtained. The results indicate that almost defect-free weld joint is produced by the optimal welding current parameters. The significance sequence of current parameters on weld quality is negative current, peak current, and base current.

Resistance spot welding and self-pierce rivet of non-combustible magnesium alloys

Resistance spot welding and self-pierce rivet of non-combustible magnesium alloys

Effect of beam wobbling on laser welding of aluminum and magnesium alloy with nickel interlayer

The influence of conventional laser keyhole welding and beam wobbling was evaluated at two weld travel speeds and power settings. Fracture in linear lap welds would occur during specimen preparation due to the presence of Al-rich brittle fusion zone, unless one utilizes a circular laser wobbling path (at 1000 Hz). Wobbling provided better integrity due to the presence of a Mg-rich ductile fusion zone and a larger bonded width. It can be concluded that laser beam wobbling enhances joint quality by widening the joint area and mitigating formation of brittle secondary phases at the joint fusion zone.

Improving microstructural and tensile properties of AZ31B magnesium alloy joints by stationary shoulder friction stir welding

Sound AZ31B magnesium alloy welds with glossy surface appearance and little flash were achieved for the first time by lower heat input stationary shoulder friction stir welding (SSFSW) at different rotational speeds (700–1500 rpm) and a constant welding speed (50 mm/min). Results show that a bowl-shaped stir zone (SZ) with fine equiaxed grains is present, and its grain size increases as increasing the tool rotational speed. The lowest Vickers hardness appears in the thermo-mechanically affected zone (TMAZ) on the advancing side. As the rotational speed increases, the ultimate tensile strength of joints also increases, while the yield stress and elongation at fracture decrease. An exceptionally high joint efficiency of 97% has been achieved at the rotational speed of 1500 rpm. In addition, the SSFSWed joints show higher strain hardening capacity due to dynamic recrystallization in the SZs. The fracture locations of joints shift from TMAZ to SZ with the increase of rotational speed. Fracture morphologies of the SSFSWed joints are characterized as the mixture of shear and ductile fracture modes.

Analysis of Weak Zones in Friction Stir Welded Magnesium Alloys from the Viewpoint of Local Texture: A Short Review

Friction stir welding (FSW) is a promising approach for the joining of magnesium alloys. Although many Mg alloys have been successfully joined by FSW, it is far from industrial applications due to the texture variation and low mechanical properties. This short review deals with the fundamental understanding of weak zones from the viewpoint of texture analysis in FSW Mg alloys, especially for butt welding. Firstly, a brief review of the microstructure and mechanical properties of FSW Mg alloys is presented. Secondly, microstructure and texture evolutions in weak zones are analyzed and discussed based on electron backscatter diffraction data and Schmid factors. Then, how to change the texture and strengthen the weak zones is also presented. Finally, the review concludes with some future challenges and research directions related to the texture in FSW Mg alloys. The purpose of the paper is to provide a basic understanding on the location of weak zones as well as the weak factors related to texture to improve the mechanical properties and promote the industrial applications of FSW Mg alloys.

Effect of ultrasonic vibration field on tungsten inert gas welding of magnesium alloy and galvanized steel

In this paper, the authors introduced ultrasonic vibration into the molten bath via ultrasonically vibrating welding wire and investigated the effect of ultrasonic vibration on the mechanical properties, microstructures and macrostructures of tungsten inert gas (TIG) welded AZ40 Mg alloy and DP780 galvanized steel joints. The main results are summarized as follows. During the ultrasonic vibration aided TIG welding, ultrasonic vibration can improve the wettability of welding pool on the steel plate and eventually increase the width of welding seam than that without ultrasonic vibration. The average grain size of fusion welding area is obviously reduced with the assistance of ultrasonic vibration and gives rise to the increase of micro hardness. A 4 μm thickness intermetallic compound layer occurs at the brazing area of joint and the ultrasonic vibration aided process has no obviously effect on the microstructure of brazing area of Mg/steel joint. The maximum tensile strength of Mg/steel workpiece increases 8.2% to 252 MPa over the workpiece welded without ultrasonic vibration, owing to the effective refinement strengthening. Besides, the fracture surface of Mg/steel workpiece obtained with the aid of ultrasonic vibration is characterized with more plastic fracture features.