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- Herausgeber: Bentham Science Publishers
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- Sprache: Englisch
Advanced Materials for Emerging Applications is a monograph on emerging materials – materials that have observable differences in physical properties and manufacturing requirements when compared to existing materials and industrial processes. The volume aims to showcase novel materials that can be used in advanced technology and innovative products.
The editors have compiled 17 chapters grouped into 3 sections: 1) Metals and Alloys, 2) Composite materials, and 3) Other materials. Chapters 1-5 discuss recent advances in friction stir welding, suitability of nickel-base shape memory alloys, thermal cycling studies of nickel-based shape memory alloys, nitrogen additions to stainless steel, and the evolution of zirconium alloy. Chapters 6-11 cover topics such as additive manufacturing of metal matrix composites, composite materials for biomedical applications, aluminum and magnesium metal matrix composites, aluminum nanocomposites for automobile applications, enhancing the strength of aluminum-boron carbide composites, and sisal fibers reinforced composites. Lastly, chapters 13-17 explore smart hydrogels, engineered iron-oxide nanomaterials for magnetic hyperthermia, emerging sustainable material technology for fire safety, recent advances in unconventional machining of smart alloys, and critical parameters influencing high-strain rate deformation of materials.
This monograph provides information for a broad readership including material and manufacturing engineers, researchers, students (at undergraduate levels or above) and entrepreneurs interested in manufacturing new products.
Readership
Engineers, researchers, students (at undergraduate levels or above) in materials science, engineering and technology sectors; entrepreneurs interested in manufacturing new products.
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Veröffentlichungsjahr: 2024
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PREFACE
“Advanced Materials” can safely be ascribed to those materials that have the potential of offering a useful combination of properties including physical properties, mechanical properties, electrical properties and chemical properties, which make them a potentially viable candidate for selection and use in a spectrum of applications spanning both performance-critical and non-performance-critical. This can be made possible through a healthy synergism of changes in composition, and changes in constituents coupled with the development and implementation of specialized and innovative techniques specific to both processing and synthesis. These materials have gradually grown both in stature and strength and include the following: (i) high value-added metals and their alloy counterparts, (ii) biomaterials, (iii) ceramics, (iv) ceramic-matrix composites, (v) electronic materials, (vi) high entropy alloys, (vii) multi-principal element alloys, (viii) metal-matrix composite materials, (ix) nanomaterials, (x) polymers, (xi) polymer-matrix composites, and (xii) semiconductors. The “emerging” materials and their traditional counterparts tend to differ significantly in terms of mechanical properties, physical properties and chemical properties. The properties offered by the newly developed and/or “emerging” materials can be customized, or tailored, specific to the primary purpose for use and application. Further, production and eventual commercialization of the family of “emerging” materials often tend to differ from the traditional counterparts in terms of the following input(s):
Overall importance of the engineered product(s).The importance given to the different steps and related intricacies in the processing sequence (including fabrication), andThe economics specific to cost, based entirely on the scale of production.The potential for an observable change in characteristics of the “emerging” materials and the markets to which they can serve are rapidly gaining in strength, which is made possible through a healthy combination of radically different materials and processes. Both cost benefits and structural advantage over the life of a newly developed material, or “emerging” material, can differ significantly from that of the traditional counterpart, thereby providing a clear indication that the traditional approaches to economic assessment may not be suitable and applicable to the family of “emerging” materials.
There does exist a need to establish meaningful boundaries for an “emerging” material in terms of both the input material and the end-product of interest, i.e.,
When in the processing chain or processing sequence can a material be classified as new, novel and “emerging” ?, andWhen can an “emerging” material be chosen for use for a specific product?In several cases, the categories of information that is both needed and essential with specific reference to an “emerging” material is the same as for the traditional counterpart. However, the primary focus of the general categories often tends to show observable differences. An example of which is suitability of a specific material for the purpose of selection and use in a specific application. Identifying the need for an adequate amount of information coupled with a thorough analysis of the “emerging” materials does necessitate the need for a fundamental rethinking of why information of various kinds is essential and to whom and for what purpose is the specific information needed, essential and required. The information that is found, established and subsequently collected, categorized and documented should not only be concise but also capable of being updated periodically. It should essentially represent areas of “valued” interest and much desired concern to representatives from both industry and policy makers. Over the years, the gradual development and emergence of new, improved and novel materials did get the much-needed interest, attention, participation and contribution from several researchers. This is evident from the fact that during the last four decades [i.e., 1990 to present], several hundreds of papers have been published in the open literature on aspects specific to the development and emergence of new and improved materials made possible through a healthy synergism of novel changes in material chemistry coupled with an appropriate combination of innovative processing sequences to get the desired material.
The chapters contained in this bound volume attempt to provide an insight into the advances while concurrently addressing the potential areas of observable growth and resultant application of the new and improved materials resulting from a healthy combination of novel compositions and innovative processing techniques that were successfully developed and used for the synthesis of new and improved materials, referred to henceforth through this bound volume as “emerging materials”. The manuscripts, or chapters, chosen for inclusion in this bound volume have been written by authors having varying backgrounds and experience in the domains specific to the synthesis, processing, manufacturing, experimentation, analysis, quantification and even modeling of materials and structures. This has essentially formed the basis of their writing style and technical content of their manuscript chosen for inclusion in this bound volume.
Overall, this bound book contains three sections. Each section, i.e., Section ‘A’, Section ‘B’ and Section ‘C’ contains a few well laid-out technical chapters. In an attempt to make every effort to meet with the needs and requirements of the different readers, each chapter has been written and presented by one or more authors to ensure that it offers a clean, clear, cohesively complete and convincingly compelling presentation and discussion of the intricacies specific to their analysis, observations and resultant interpretations of their research and findings in a convincing manner.
In the first section of the book (Section ‘A’), the focus is on “METALS AND ALLOYS” specific to the family of emerging materials. This section has five chapters. The first chapter [Chapter 1] introduces the interested reader to aspects pertinent to recent advances in friction stir welding of magnesium alloys for the purpose of selection and use in performance specific applications. The second chapter, [i.e., Chapter 2], provides an in-depth analysis, in a cohesively complete and convincing manner, of the suitability of nickel-base shape memory alloys for selection and use in sensing applications. The follow-on chapter, [i.e., Chapter 3] is devoted to presentation and healthy discussion of the intricacies specific to thermal and thermo-mechanical cycling studies on nickel-base shape memory alloys for selection and use in applications in both engineering and medical field. The authors present and adequately discuss all of the relevant and required aspects that are key for the purpose of selection and use of the nickel-base shape memory alloys in the two applications. The fourth chapter [Chapter 4] presents in a well laid out, neatly explained and convincing manner all of the related and relevant intricacies specific to the addition of nitrogen to Type 316L stainless steel with the prime objective of enhancing the performance of the chosen stainless steel at high temperatures when chosen for use in structural applications specific to fast reactors. All of the details and specifics are neatly presented and adequately discussed at all of the relevant and appropriate locations through the entire length of this chapter. The follow-on chapter on pressurized heavy water reactors [i.e., Chapter 5] is thorough, exhaustive and illuminating in detail in a cohesively complete and convincing manner all of the intricacies specific to the evolution of zirconium alloy for use as pressure tubes in pressurized heavy water reactors. All of the findings, observations and interpretations are neatly explained with the aid of appropriate micrographs to include both scanning electron micrographs and transmission electron micrographs. This is certainly a complete, well written and laid-out chapter that offers a wealth of information that is neatly explained using principles of Materials Science and Materials Engineering thereby significantly strengthening technical content of the chapter.
The second section of this book [i.e., Section ‘B’] is focused on “COMPOSITE MATERIALS” and includes six desirable and well laid out chapters. The first chapter in this section (i.e., Chapter 6) attempts to provide the ‘interested’ reader with an overview of the desirable highlights specific to the selection and use of biomaterials and implants in orthopedics. Also provided and adequately discussed are key issues, or specifics, relevant to an evaluation of their future. This chapter can safely be categorized to be a healthy refresher to both the knowledgeable reader and ‘learned’ engineer while concurrently providing the novice and inquisitive learner useful information specific to the potential use of biomaterials and implants. In the following Chapter [i.e., Chapter 7], key aspects specific to additive manufacturing of composite materials for use in biomedical applications are well presented and adequately discussed from both a scientific perspective and engineering viewpoint. In the next chapter [i.e., Chapter 8], the theme for presentation and discussion is the key aspects specific to aluminum metal-matrix composites and magnesium metal-matrix composites. The contributing authors devote their attention and focus to providing adequate insight into developing an understanding of the role, importance and contribution of processing influences on corrosion properties of the chosen metal-matrix composites for the purpose of selection and use in environment-sensitive applications. In the following chapter [i.e., Chapter 9], the contributing authors present their views, following a comprehensive study of aluminum nanocomposites that were developed by additive manufacturing for the purpose of selection and eventual use in both emerging and demanding automotive applications. In this chapter, the contributing authors also provide an adequate discussion of all intricacies specific to understanding processing influences on microstructural development, and microstructural influences in governing mechanical properties and resultant mechanical performance. In the following chapter [i.e., Chapter 10], the contributing authors clearly present and thoroughly discuss lucidly all the key aspects and intricacies specific to enhancing the strength of aluminum-boron carbide composites to an adequately high level by the addition of magnesium. This enabled making the resultant composite material to be suitable for selection and use in a spectrum of applications in the automobile industry. In the following chapter [i.e., Chapter 11], an adequate review of processing and fabrication of the sisal fibers-reinforced composite materials is neatly presented and adequately discussed with specific reference to understanding all of the intricacies specific to processing influences on microstructural development and the resultant influence of microstructure in governing mechanical properties and overall mechanical performance. This chapter based on both content and description can be considered to be educative, enlightening, and informative from the standpoint of an analysis and rationalization of the findings. In the same chapter [i.e., Chapter 11] all of the key aspects specific to mechanical performance that result from the development of the engineered composites are well presented and adequately discussed.
The third section of this book [Section ‘C’] is devoted to aspects both related to and relevant to “OTHER MATERIALS AND TECHNIQUES”. In the opening chapter of this section [i.e., Chapter 12], the contributing authors elegantly present and discuss the numerous benefits that arise from the selection and use of biomaterials and implants in orthopedics. The authors present and adequately discuss the basic principles behind biomaterials and implants and the overall benefits of selecting them for use in orthopedics. In the following chapter [i.e., Chapter 13], the contributing authors make a comprehensive and complete review of “Smart Hydrogels” with adequate emphasis given to both theory and applications in the domain specific to biomedical sciences. The contributing authors attempt to focus their review on studying and rationalizing the influence of basic theory in governing the selection and use of “Smart Hydrogels” in bioscience-dominated applications. In the following chapter [i.e., Chapter 14], the contributing authors provide a neat and convincing review with appropriate discussion on the development of engineered iron-oxide-based nanomaterials for magnetic hyper-thermia. In the following chapter [i.e., Chapter 15], the contributing authors provide a lucid and well-written overview of all of the intricacies specific to emerging and sustainable materials technology with an emphasis on fire safety. They present and adequately discuss the many attributes of the available alloys and materials for the purpose of their selection and use both in existing and emerging fire-safety critical applications. They also list and discuss the key considerations for both the existing materials and the newly developed materials while concurrently providing an overview of the future of the existing materials from the standpoint of eventual commercialization. In the following chapter [i.e., Chapter 16], the authors provide an adequate review specific to recent advances in the unconventional machining of smart alloys in order to ensure their selection and use in critical manufacturing sectors. The following chapter [i.e., Chapter 17] is well presented and appropriately discusses all the relevant aspects specific to critical parameters that exert an influence on the high strain rate deformation of engineering materials. The contributing authors provide a review of the published results from tests conducted on different materials using the pressure bar apparatus.
Overall, this archival monograph devoted to addressing the family of emerging materials provides a background that should enable an interested reader to comprehend with ease the immediate past, the prevailing present and the possible future, or emerging trends, and approaches in the domain specific to the gradual development. Also, the emergence of these materials with an emphasis on innovation is highlighted in an attempt to ensure their applicability for use in a wide spectrum of applications to include both performance-critical and non-performance-critical. Thus, based entirely on the contents included in this bound volume it can very well serve as a single reference book or even as textbook for the following:
Students spanning seniors in the undergraduate program of study in the fields of: (i) Materials Science and Engineering, (ii) Mechanical Engineering, and (iii) Manufacturing Engineering/Manufacturing Technology.Fresh graduate students pursuing graduate degrees in: (i) Materials Science and Engineering, (ii) Mechanical Engineering, and (iii) Manufacturing Engineering/ Manufacturing Technology.Researchers working in research laboratories and industries striving to specialize and excel in aspects related to research on materials science and engineering and the resultant development to ensure the emergence of new and improved products.Engineers striving and seeking novel and technically viable materials for the purpose of selection and use in both performance-critical and non-performance-critical applications.We certainly anticipate this bound volume to be of much interest and value to scientists, engineers, technologists, and even entrepreneurs.
ACKNOWLEDGEMENTS
The editors graciously and generously acknowledge the “valued” understanding and timely support, both by way of cooperation and encouragement, they received from the contributing authors of the different chapters contained in this bound volume. Efforts made by the contributing authors to lucidly present and adequately discuss the different topics have certainly contributed to enhancing both the scientific merit and technological content of this bound volume and this is greatly appreciated. The useful comments, corrections, recommendations, and suggestions provided by the chosen peer reviewers on the different chapters have certainly helped in enhancing the technical content and scientific merit of each chapter included in this bound volume.
Our publisher, Bentham Science Publishers Pvt. Ltd., [Singapore, Sharjah (Emirates)], has been very supportive and patient through the entire process initiating from the moment of conception of this intellectual scholarly endeavor. We extend an abundance of thanks, “valued” appreciation, and boundless gratitude to the editorial staff at Bentham Science [Bentham Books]. Specifically, we mention Ms. Humaira Hashmi [Editorial Manager Publications; Bentham Books (Sharjah, Emirates)] for her sustained interest, involvement, meticulous emphasis on all of the desired and essential specifics and providing spontaneous assistance arising from an understanding of the situation coupled with her disposition towards extending help to the editors. This certainly helped in ensuring the timely execution and successful completion of the numerous intricacies related to the smooth completion of this bound volume from the moment of its approval and up until completion to essentially include both compilation and publication. Also, most deserving of appreciation and applause is the timely and valuable assistance provided by Ms. Rabia Maqsood and Ms. Fariya Zulfiqar [Managers: Publications at Bentham Books (Sharjah, Emirates)]. Their emphasis and insistence given to precision in the compilation of the intricacies so as to ensure perfection in the end-product, i.e., bound volume, did necessitate the need for a diligent execution of all related and relevant requirements specific to the compilation of the bound volume. This emphasized using a systematic, methodical and organized approach to putting together the desired ingredients, i.e., the chapters, thereby enabling and ensuring both an effective and efficient execution of the needful requirements specific to the compilation and completion of the bound volume. At moments of need, we the editors, did find the enthusiastic response of Ms. Humaira Hashmi, Ms. Rabia Maqsood and Ms. Fariya Zulfiqar along with their willingness to extend help to ensure the timely completion of this bound volume on “Advanced Materials for Emerging Applications: Innovations, Improvements, Inclusion and Impact” to be both useful and valuable.
Most important and worthy of recording is that the timely compilation and publication of this bound volume have been made possible because of:
The understanding, cooperation, and importantly the ‘patience’ and assistance extended by the contributing authors, andThe positive and timely contributions provided by the chosen peer-reviewer(s).One of the editors (Dr. T.S. Srivatsan) would like to record in print his ceaseless, endless and unbounded amount of gratitude to Dr. K. Manigandan [Associate Professor in the Department of Mechanical Engineering at The University of Akron (Akron, Ohio USA)] for his enthusiastic willingness and timely intervention in providing the “desired” assistance with reference to intricacies specific to the front cover of this archival bound volume.
Thanks and appreciation are also extended to a fellow junior professional colleague Dr. Jimmy Karloopia [Punjab Engineering College (Chandigarh, Punjab, India)] for his basic efforts in motivating, inspiring, encouraging, and ensuring the submission of “valued” contributions to this archival bound volume from two of his research scholars [Mr. K. Chauhan and Mr. Divyanshu] and two of his “peer” colleagues [Dr. Krishnakant Dhakar and Colonel A. Charak].
List of Contributors
Recent Advances in Friction Stir Welding of Magnesium Alloys for Use in Performance-Specific Applications
Divyanshu1,Kunal Chauhan1,Jimmy Karloopia1,*,N. M. Suri1,T. S. Srivatsan2Abstract
Magnesium is the sixth most abundant material in the earth’s crust that finds its applications in the fields of automobiles, aerospace, and biomedical. With noticeable advances in the domain enveloping engineering and technology, there does exist a growing need for new and improved materials to meet the demands put forth by the industries spanning the aerospace and automobile sectors. One of the important requirements for a material is light in weight. Magnesium is one such promising material, which is lighter than aluminum making it an ideal candidate for selection and use in both performance-critical and non-performance critical applications in the domains specific to automobile, aerospace and even biomedical. There are various processing routes for the manufacturing of magnesium alloys, and there exists a need for the joining of the magnesium alloys. The conventional joining processes possess defects, such as porosity, which are detrimental to achieving acceptable to good mechanical properties. Friction Stir welding is one method of solid-state joining, which offers good properties of the weld. The technique of friction stir welding (FSW) operates by rotating and plunging a non-consumable tool into the interface of two workpieces that require to be joined. Promising advantages that are offered by friction stir welding (FSW) are eco-friendly, versatile, and energy efficient. This manuscript highlights (i) the friction stir welding processing technique, as well as recent and observable advances, (ii) the classification of the magnesium alloys, (iii) the welding tool and its influence on welding, microstructural development and mechanical properties of the friction stir welded magnesium alloy, (iv) welding parameters and its influence on governing the relationships between the weld and the workpiece, and (v) typical practical applications and the variants of friction stir welding (FSW).
INTRODUCTION
With sustained and noticeable advances in technology, the world is gradually moving forward towards the selection and use of materials that are light in weight, have an excellent combination of mechanical properties and tribological qualities to offer coupled with other desirable characteristics. Magnesium is one such material, having acceptable mechanical properties and tribological qualities, coupled with chemical and biological capabilities and is low in weight [1]. Magnesium is often chosen for use in a variety of fields to include the following: (i) electrical industry, (ii) the aerospace industry, (iii) the vehicle industry, (iv) biomedical applications, and (v) industry that caters to the domain of sports, i.e., sporting goods [2-4].
Magnesium makes up around 2.7% of the earth's crust and stands as the sixth most abundant element in the earth's crust [5]. The density of magnesium is 1.74 g/cm3, which is two-thirds that of aluminum and one-fourth that of steel [6]. The properties of magnesium are summarized in Table 1. Magnesium-based materials are extensively sought by firms for use in weight-critical applications essentially because of their low density coupled with high specific mechanical properties.
There are a variety of solid-state processing and liquid-state processing techniques, such as Additive Manufacturing (AM), Stir Casting, Melt Infiltration method, Spray forming, Friction Stir Processing, and Powder Metallurgy for the purpose of manufacturing magnesium alloys and magnesium composites. For the joining of a magnesium alloy and a magnesium alloy-based composite material with both comparable materials and different materials, friction stir welding, resistance spot welding, laser welding, and diffusion bonding are all viable options [8-17].
Thomas and co-workers were the ones who initially created friction welding in 1991 [18]. When welding magnesium alloys and magnesium-based composites, Friction Stir Welding (FSW) offers a number of benefits that are not easily available with the other welding techniques. These benefits essentially include the following [19-22]:
(a) A fine microstructure,
(b) An absence of microscopic cracking,
(c) No loss of alloying elements during processing,
(d) Good dimensional stability and repeatability,
(d) Shielding gas is not required,
(e) High weld strength and toughness, and
(f) Capability of the weld to resist fatigue stress.
The basic idea behind friction stir welding is the same as that behind friction welding. During this process, heat is produced at the contact surface by the application of friction. The heat initiates the diffusion process at the surface where the two materials are to be joined. The application of a high-pressure force to these mating surfaces expedites the metal diffusion process and forms a metal- to- metal junction. This is the fundamental concept of friction welding [23-26].
Stages in Friction Stir Welding
The friction stir welding (FSW) process is broken up into three stages as shown in Fig. (1). The first stage is known as the Plunging phase. The second stage is known as the Dwelling phase, and the Third stage is known as the Welding phase [27].
The friction stir welding (FSW) technique essentially consists of only three stages, namely: (i) plunging phase, (ii) dwelling phase, and (iii) welding phase. Despite its seeming complexity, it is overall a very simple technique. A non-consumable revolving tool is used in the plunging process. The non-consumable revolving tool is composed of material that is stronger than the workpiece and has a shoulder that is bigger in diameter as well as a pin and will plunge into the workpiece to a depth that has been pre-programmed. This causes the generation of heat by penetrating the abutting edges of the workpieces that are clamped together. While the tool is being dwelled, it continues to spin in its place; as a consequence, the temperature directly underneath the rotating tool is gradually raised. An additional source of heat contribution comes from the adiabatic heat that is generated when material of the workpiece experiences plastic deformation around the revolving tool. The material surrounding the tool pin gradually softens as a result of plastic deformation, which occurs when the temperature is high. In the last step, i.e., welding phase, a travel velocity is assigned to the tool along the joining line so that it can agitate the material and create a junction. The wider diameter of the tool shoulder aids in confining the hot material, which would otherwise flow out readily to generate a flash and can result in a loss of material and a resultant poor weld if the loss of material is not contained [27].
Fig. (1)) The friction Stir Welding (FSW) process: (a) Plunging phase; (b) Dwelling phase, and (c) Welding phase.Classification of Magnesium alloys
When alloying elements are added to pure magnesium, it contributes to altering the characteristics of pure magnesium. Because magnesium is a chemically active element, it is capable of reacting with other elements used in the process of alloying to produce intermetallic compounds. For magnesium alloys, there is no designation system that is recognized universally. The trade names of the firms that were pioneers in the production of magnesium alloys have given way to chemical and numerical naming systems.
The industry relies heavily on the Standard Alloy Designation System developed by ASTM International. In accordance with ASTM B275, every alloy will have a label consisting of letters and numbers. The letters will designate the primary alloying elements, and the numbers are a reflection of the percentages of the alloying elements [28]. The usual abbreviations that are used to indicate magnesium alloys are summarized in Table 2. These abbreviations are letters that stand for alloying elements according to ASTM.
There are three components that make up the designation of a common magnesium alloy.
(i) Part 1 starting alphabet of the two principal alloying elements creates two abbreviation letters see Table 3, which indicate the components present in the order of decreasing proportion. The letters are arranged in alphabetical order if the percentages of the various alloying elements are the same.
(ii) In Part 2, the percentage (weight) of the two primary alloying elements is provided, expressed as a percentage of the total weight. Two whole numbers represent the two alphabets.
(iii) In Part 3, it differentiates between the numerous alloys that include identical proportions of the two principal alloying constituents. It consists of a letter of the alphabet that is allotted in sequence as compositions become standard. This is shown in Fig. (2).
Fig. (2)) ASTM designation for a Magnesium alloy [Reference 29].The ASTM B296-03 standard was used to determine the temper designations. For the designation AZ91C-T4, a dash is used to distinguish between the alloy identification and the temper designation. The temper designations for the magnesium alloys are shown in Fig. (3).
The commonly used magnesium alloys in which aluminium is the primary or key alloying element are as follows: (i) AJ52A, (ii) AJ62A, (iii) AM50A, (iv) AM60B, (v) AS41B, (vi) AZ31B, (vii) AZ61A, (viii) AZ80A, (ix) AZ81A, (x) AZ91D, and (xi) AZ91E. The classification of magnesium alloys based on manufacturing route is shown in Fig. (4). It may be possible to manufacture an alloy having the same major alloying constituents by using more than one manufacturing technique. This is dependent on the precise composition of the specific alloy as well as the requirements imposed by alloy design. The WE43 magnesium alloy is often chosen for use in biomedical applications. The AZ91 A, B, and D alloys are chosen for use in both automobile applications and aerospace applications.
PROCESS PARAMETERS FOR FRICTION STIR WELDING (FSW)
The chosen material undergoes or experiences a significant amount of movement during friction stir welding (FSW), which could result in plastic deformation. Tool geometry, welding parameters, and joint design exert a substantial impact on both the material flow pattern and temperature distribution, which exerts an influence on the microstructure development of the material.
Fig. (3)) Temper designations for the magnesium alloys [Reference 29].Friction Stir Welding: Joint Design
When it comes to friction stir welding, a large majority of the joints can be categorized into three primary categories: (a) butt joint, (b) lap joint, and (c) fillet joint. Several other joints may be conceptualized as a mixture of these two types of joints and is shown in Fig. (5) (a-c) Butt Joint, (d-f) Lap Joint, g) Fillet Joint.
The Butt joints and lap joints are the easiest joint configurations to work with while working with friction stir welding (FSW). For the butt joint, a backing plate is often used, and then two plates or sheets having the same thickness, are put on top of it and securely held in order to prevent the abutting joint faces from being driven apart. Since the pressure that is exerted during the first plunge of the rotating tool is very significant, further caution is essential to ensure that the plates in a butt configuration do not get separated. In order to produce a weld along the abutting line, a rotating tool is first inserted into the joint line. The rotating tool is then traversed slowly along this line while maintaining close contact between the shoulder of the tool and surface of the plates. On the other hand, in order to create a basic lap junction, it is necessary to attach two lapped plates, or sheets, onto a backing plate. In order to link the two plates, a rotating tool is vertically inserted through the top plate and then into the lower plate. The tool is then traversed along the appropriate path. The combination of butt joints and lap joints enables the production of a wide variety of additional joints. Other kinds of joint designs, such as the fillet joints in addition to the butt joint and lap joint configurations, are also feasible depending on requirements of the particular engineering application at hand.
Fig. (4)) Classification of the Mg alloys based on manufacturing route.(Data ASTM Handbook).Friction Stir Welding (FSW) Tool
The introduction of new welding tools has been responsible for many of the advances that have been achieved in the technique of friction stir welding. Design of the welding tool, which must account for geometry of the tool as well as the material from which it is constructed, is essential to ensure an efficient execution of the operation [30]. The friction stir welding (FSW) tool often comprises a spinning round shoulder and a threaded cylindrical pin in most cases. The moving shoulder warms the workpiece mostly due to friction, while the threaded pin pushes the pliable alloy around the workpiece to essentially create the joint.
The design of the tool does exert an influence on the following:
(a) The amount of heat that is generated,
(b) The flow of plastic,
(c) The amount of power that is needed, and
(d) Overall uniformity of the welded seam.
Fig. (5)) FSW Joint Configuration (a) Square Butt, (b) Edge Butt, (c) T Butt, (d) Lap Joint, (e) Multiple Lap Joint, (f) T Lap Joint, and (g) Fillet Joint [Reference 19].The shoulder is responsible for producing the majority of the heat and concurrently preventing the plasticized material from escaping from the workpiece. Both the shoulder and the tool-pin are responsible for influencing the flow of material.
In recent years, a number of novel aspects have been considered and included in the construction of tool design. The tools that have been developed at TWI are shown in Fig. (6). For butt welding, a tool that is designed to be cylindrical shape, Whorl shape, and MX triflute shape is chosen for use. For the lap joint, a tool designed of Flared triflute and A-skew is chosen for use. When minimum asymmetry in weld property is desired, the Re-stir shape tool is used according to TWI [31].
Fig. (6)) FSW tools designed at TWI (a) Cylindrical, (b) WhorlTM, (c) MX trifluteTM, (d) Flared trifluteTM, (e) A-skewTM, and (f) Re-stirTM [Reference 32].The tool shoulders are constructed in such a way that they provide the required downward forging action that facilitates in the following:
(a) Welding consolidation,
(b) Heating the surface regions of the workpiece by frictional heating, and
(c) Restricting the flow of hot metal under the bottom shoulder surface.
The usual outer surfaces of the shoulder, the bottom end surfaces and end characteristics, and the tool probes used during Friction Stir Welding (FSW) are shown in Fig. (7). In most cases, the outside surface of the shoulder is shaped like a cylindrical cylinder. However, on occasions, a conical surface is also employed or used [19]. Since the shoulder plunge depth is typically very small (i.e., 1–5% of the gauge thickness), it is generally anticipated that the shape of the shoulder outer surface (cylindrical or conical) will have a negligible impact on overall quality of the weld.
The tool materials that are often chosen for use for the welding of magnesium alloys and composites are the following: (i) tool steel, (ii) H13 steel, (iii) High speed steel (HSS), (iv) Stainless steel (SS), (v) Mild Steel, and (vi) High carbon high chromium steel [34-36]. In Table 3 is provided a summary of the tool material, workpiece, tool shape, tool size for the magnesium alloys and magnesium-based composites.
Welding Parameters of Friction Stir Welding (FSW)
The following are the key factors that are involved in Friction Stir Welding (FSW): (i) traverse speed, (ii) tool rotation speed, (iii) thickness of the workpiece, (iv) applied pressure, (v) profile of the pin, (vi) height of the pin, (vii) angle of deviation, (viii) pin direction, and (ix) the presence of both obstruction and inhibitor forces [48, 49]. With friction stir welding for a magnesium alloy, the tool rotation speed and tool traverse speed are the two welding parameters that are considered to be of utmost importance.
The main welding parameters and their effects are neatly summarized in Table 4. The tool rotational speed is a highly essential characteristic because it has a significant influence on both the flow of the material and the formation of heat, which in turn allows for a modification of both the mechanical properties and microstructure of the joint [50]. A sound weld now depends upon the regulation of rotating speed during welding. The chances of mixing the deformed materials in the weld zone will increase as the tool rotation speed increases. This is a positive variable since it enhances the likelihood of mixing the chosen materials. Since the shoulder is responsible for about 95% of the total heat that is created by the pin, an increase in the pin rotation speed will also result in an increase in shoulder speed. This results in an observable increase in the amount of heat that is generated in the joint region.
A summary of the friction stir welding (FSW) parameters used in the welding of magnesium alloy and composites is shown in Table 5. There was a minimum welding speed of 120 mm/min and a maximum welding speed of 2000 mm/min. The rotational speed ranged from 100 to 2000 revolutions per minute (rpm), with the average being about 800 to 1600 rpm.
