Advanced Welding of Dissimilar Materials for Aerospace and Automotive Applications

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Introduction
The aviation and automotive sectors are characterised by dynamic requirements, which have spurred an ongoing quest for inventive approaches to attain portable, high-performance, as well as effective components [1].The emphasis on integrating dissimilar materials in the design and manufacture of aerospace and automotive components has increased in order to tackle these issues.The use of diverse materials has a variety of advantages, such as decreased weight, heightened fuel economy, and better mechanical characteristics.Nonetheless, the complex task of smoothly combining these materials is complicated by their inherent disparities in physical attributes, metallurgical properties, and thermal expansion coefficients [2].The objective of this study is to investigate the sophisticated welding methods that have become essential instruments in addressing the challenges related to the fusion of incompatible materials in aerospace and automotive sectors.
The analysis starts by examining the underlying reasons for the use of diverse materials, emphasising the competitive benefits they offer in terms of performance and efficiency.Notwithstanding these benefits, the difficulties associated with welding dissimilar materials are considerable, comprising the creation of fragile intermetallic compounds and the possibility of galvanic corrosion.The next sections of this article will explore the advanced welding techniques that have been devised in order to tackle these issues [3].The techniques encompassed in this category consist of laser welding, electron beam welding, and friction stir welding.Each of these technologies has distinct benefits in relation to accuracy, limited heat-affected zones, and diminished development of intermetallic compounds.This study also investigates the use of filler materials and interlayers in addressing the challenges associated with dissimilar material welding.Specifically, it examines their impact in enhancing mechanical characteristics, managing thermal stress, and minimising the formation of brittle phases [4].The feasibility and efficacy of advanced welding techniques for dissimilar materials are underscored via the examination of case studies and real-world applications [5].This study presents actual evidence demonstrating the enhanced performance, structural integrity, and weight reduction achieved by the joining of materials such as aluminium with steel or titanium with composites.The incorporation of disparate materials in aerospace and automotive sectors is driven by the imperative to achieve a harmonious equilibrium amidst competing considerations, including but not limited to performance optimisation, weight mitigation, and cost-efficiency.Conventional methodologies frequently depend on singular material solutions that may not provide the most advantageous amalgamation of characteristics necessary for contemporary, high-performance constituents [6].
The rationale for the decision to combine different materials arises from a variety of significant factors: Weight reduction may be achieved by the use of dissimilar materials, which involves the combination of materials with varying densities and strengths.This approach allows for the creation of lightweight structures.The aforementioned factors are of utmost importance in attaining optimal fuel efficiency, mitigating pollutants, and augmenting overall performance [7].
Various materials exhibit unique mechanical, thermal, and electrical characteristics [8].Through the deliberate integration of disparate materials, it is possible to build components that demonstrate distinct properties in various places, so enhancing their overall usefulness and endurance.Certain components necessitate varied functionality across distinct regions.The integration of different materials enables designers to include many functionalities, including structural integrity, thermal resilience, and electrical conductance, into a singular component.The use of a singular material for a complete component may lead to excessive costs if such material is excessively designed for certain locations.The process of combining dissimilar materials enables the efficient distribution of materials in a cost-effective manner, ensuring that they are utilised in the areas where they are most required.There are certain applications that require certain qualities that cannot be met by a single material alone.The process of combining dissimilar materials allows for the utilisation of the advantageous properties of each material, while simultaneously minimising their inherent constraints [9]- [11].
The use of diverse materials with complimentary qualities has been shown to result in enhanced performance, surpassing that of components manufactured from a single material [12].Consequently, this results in enhanced dependability, effectiveness, and overall operational capability.The dissimilar material components present a promising opportunity for achieving substantial weight reduction, a crucial consideration in the domains of aerospace and automotive engineering.The aforementioned reduction results in decreased fuel consumption, an expanded range, and enhanced cargo capacity.Designers possess the capability to customise components in order to fulfil specific criteria through the deliberate selection of materials possessing desirable attributes for distinct sections of the component.The ability to be flexible allows for the construction of complex and versatile structures [13].
Dissimilar material joining offers a cost-effective approach by strategically including high-performance materials in certain areas of a component, instead of utilising expensive materials across the whole structure.This approach enables significant cost reductions without sacrificing the overall quality of the component.The integration of disparate materials fosters innovation within the domains of material science, industrial processes, and engineering design.This phenomenon has the potential to facilitate significant advancements in both sectors, hence propelling advancements in technology and sustainability.The utilisation of lightweight different material components has been found to have a positive environmental impact, since it leads to a reduction in carbon emissions through enhanced fuel economy and improved energy usage.This is consistent with the increasing focus on sustainability and the need of environmental stewardship [12].

Challenges in Welding Dissimilar Materials
The process of welding materials that are different from one other presents a complex set of issues because to the inherent differences in their physical characteristics, metallurgical behaviours, and thermal reactions [14].The aforementioned issues require the implementation of creative methodologies and sophisticated procedures in order to effectively establish a cohesive unit and preserve the integrity of its constituent parts.Several notable obstacles may be identified, including: Metallurgical disparities frequently manifest in the form of disparate crystal structures, melting temperatures, and phase transitions across dissimilar materials.The act of welding some materials can give rise to notable heat gradients and residual stresses, which in turn can contribute to the possibility of fracture formation and diminished mechanical qualities [15].The production of intermetallic compounds can occur when incompatible materials are joined by welding, since the atomic diffusion at the interface facilitates their synthesis.The aforementioned compounds possess a propensity for brittleness and exhibit distinct mechanical characteristics in contrast to the underlying materials, hence diminishing the strength of the joint and jeopardising its structural soundness [16].
Thermal expansion mismatches can arise due to differences in the coefficients of thermal expansion between dissimilar materials.Thermal stresses occur during the process of welding and subsequent cooling as a result of the varying expansions and contractions of the materials being connected.The aforementioned stresses have the potential to induce deformation, warping, and alterations in the microstructure [17].
, 011 (2023) E3S Web of Conferences ICMPC 2023 https://doi.org/10.1051/e3sconf/20234300110808 430 Fig. 1 Working of galvanic corrosion joining in dissimilar materials [18] Galvanic corrosion is a phenomenon that occurs when two different metals come into contact, resulting in the generation of an electrochemical potential difference, which subsequently leads to corrosion, as shown in fig. 1.The effect can be further intensified by the welding process, as it modifies the microstructure and electrochemical characteristics of the joint, resulting in an increased rate of corrosion at the interface.The assessment of material compatibility is of utmost importance when considering the reactivity and diffusivity of different materials at increased temperatures [19].Certain materials have the potential to undergo unfavourable reactions, resulting in the production of undesired phases or compounds that can compromise the integrity of the joint.
The successful welding of dissimilar materials necessitates meticulous management of several parameters, including heat input, cooling rates, and interposes temperatures.Insufficient control has the potential to result in several problems, including but not limited to severe distortion, incomplete fusion, and overheating.The occurrence of brittle phases, such as martensite, in steel can manifest at extreme temperatures during the welding process and subsequent cooling.These conditions have the potential to make the joint vulnerable to fracture and diminished resilience [20].Fig. 2 Schematic illustration of welding direction in dissimilar materials [21] The process of choosing appropriate dissimilar materials for welding is of utmost importance [22].In order to achieve a joint that is both compatible and lasting, it is imperative to meticulously evaluate factors such as thermal expansion mismatch, disparities in melting temperatures, and the possibility of intermetallic compound formation.From fig. 2, schematic illustration of welding to effectively tackle these issues, it is important to possess a thorough comprehension of the characteristics of materials, the intricacies of welding techniques, and the impacts that welding has on the microstructural aspects [23].The use of sophisticated welding methodologies and meticulous material selection, in conjunction with the thoughtful evaluation of joint configuration and post-weld heat treatment, are important in overcoming these challenges.It is crucial to address these problems in order to fully exploit the potential of integrating dissimilar materials in aerospace and automotive sectors.This will facilitate the development of durable and highperforming components.Metallurgical distinctions among various materials pertain to disparities in their crystal structures, grain sizes, and phase compositions.The dissimilarities in melting points and thermal behaviours of the materials might give rise to problems in the welding process [24].When welding aluminium to steel, it is important to note that there are substantial differences in the crystal structures of these two materials.Aluminium has a face-centered cubic (FCC) crystal structure, whereas steel commonly possesses a body-centered cubic (BCC) crystal structure.Uneven heat distribution during the welding process can lead to several undesirable consequences, such as deformation, cracking, and non-uniform microstructural alterations.
The process of welding can lead to the creation of intermetallic compounds at the boundary between materials that are not alike.The mechanical characteristics of these compounds differ from those of the basic materials and are frequently characterised by brittleness, rendering them susceptible to breaking and diminishing the joint strength in its entirety.One illustrative instance pertains to the fusion of copper and aluminium through the process of welding.The formation of intermetallic compounds, such as Cu-Al phases, can result in the deterioration of joint strength.The regulation of the synthesis of these chemicals is of utmost importance in preserving the structural integrity of the joint [25].
The issue of galvanic corrosion emerges when there is contact between dissimilar metals that are submerged in an electrolyte, often occurring in settings that are humid or corrosive in nature [26].The corrosion phenomenon arises as a consequence of the electrochemical potential disparity existing between the materials involved, leading to an escalated degradation process at the interface of the joint.An example of a situation where galvanic corrosion may occur is when stainless steel is welded to carbon steel.In this case, the presence of a potential difference between the two metals can lead to the deterioration of the joint's durability and structural integrity [27].In instances where materials with disparate crystal structures, such as aluminium and steel, are being joined, the impact of heat input during the welding process varies for each respective material.The somewhat lower melting point of aluminium in comparison to steel can result in the expeditious liquefaction of aluminium, leading to its amalgamation with the molten steel.The cooling process might lead to the formation of a fragile intermetallic layer at the interface of the joint, so compromising the strength of the weld [28].
One instance in which intermetallic compounds are formed is by the process of welding copper to aluminium, which can lead to the creation of Cu-Al intermetallic compounds.The ductility and strength of these compounds are diminished in comparison to the basic materials, resulting in the brittleness of the joints.The process of soldering copper wires to aluminium contacts in electronic applications can result in the formation of intermetallic compounds, which can have an impact on both the electrical conductivity and the overall dependability of the system [29].This paper aims to discuss many instances of galvanic corrosion concerns.The welding of titanium to stainless steel can lead to the occurrence of galvanic corrosion as a result of the potential difference existing between the two metals.In the context of marine settings, the combination of aluminium components and steel structures can give rise to galvanic corrosion, which has the potential to cause accelerated degradation and impaired structural soundness.The resolution of these issues necessitates careful consideration of material choice, strict control over the manufacturing process, and the utilisation of modern welding methods that are specifically adapted to the unique mix of incompatible materials.In addition, it is necessary to take into account post-weld heat treatment and surface coatings as measures to alleviate the negative consequences arising from metallurgical disparities, the creation of intermetallic compounds, and galvanic corrosion.

Advanced Welding Techniques
To overcome the challenges of welding dissimilar materials in aerospace and automotive applications, advanced welding techniques have emerged as crucial solutions.These techniques offer greater control over the welding process, reduced heat-affected zones, and improved joint integrity, making them well-suited for joining materials with disparate properties.Fig. 3 Layout of laser welding process [30] Laser welding, one of the advanced techniques, utilizes a focused laser beam to generate intense heat at the joint interface, as shown in fig. 3. The localized heat input minimizes thermal distortion and limits the formation of brittle intermetallic compounds [31].Electron beam welding, on the other hand, employs a focused beam of high-energy electrons to melt the materials.This technique operates in a vacuum, reducing the risk of contamination and enabling precise control over the welding process.Friction stir welding involves a rotating tool that generates frictional heat, plasticizing the materials and forging them together without melting.This method results in refined microstructures, reduced distortion, and the absence of solidification-related defects.
These advanced welding techniques offer several benefits specifically tailored for dissimilar material joining.Laser welding's localized energy input minimizes the chances of intermetallic compound formation, making it suitable for materials prone to such reactions [32].Electron beam welding's vacuum environment reduces oxidation and minimizes the heat-affected zone, making it effective for welding materials with high thermal sensitivity.Friction stir welding's solid-state nature avoids issues related to melting, allowing for the joining of materials with significant melting point disparities [33].
Laser welding is a joining process that utilises a high-energy laser beam to fuse materials together.Laser welding is a sophisticated methodology that utilises a high-energy laser beam to achieve the fusion of materials.The laser beam induces a high level of thermal energy at the interface of the joint, resulting in the localised fusion and subsequent solidification of the material.This approach presents several benefits in the context of connecting different materials.Laser welding has the advantage of achieving accurate heat management, so minimising the extent of the heat-affected zone and mitigating the potential for deformation and the production of intermetallic compounds [34].The laser beam's concentrated characteristics contribute to reduced thermal distortion in comparison to conventional welding techniques, rendering it well-suited for complicated components and dissimilar material junctions.The phenomenon of quick solidification observed in laser welding has the potential to mitigate the production of intermetallic compounds, which are known to induce brittleness in dissimilar material junctions.The high energy density of laser welding allows for rapid heating and cooling cycles, which in turn facilitates the efficient creation of welds and contributes to a reduction in overall production time [35].Electron beam welding (EBW) is a high-energy welding process that utilises a focused beam of electrons to join metal components together.The process of electron beam welding (EBW) involves the use of a rapid stream of electrons with high velocity to induce thermal energy and cause the fusion of materials at the interface of a joint.The aforementioned procedure occurs under a vacuum environment, hence effectively mitigating the occurrence of oxidation and contamination.Electron beam welding (EBW) presents distinct advantages in the realm of dissimilar material welding.The phenomenon of high-energy electrons exhibiting significant penetration into the material enables the creation of thick material seams while reducing the need on filler materials [36].It offers a high degree of precision in regulating heat input, hence leading to little deformation and a limited heat-affected zone.The presence of a vacuum environment effectively inhibits atmospheric reactions, leading to a limited heat-affected zone and a decreased likelihood of intermetallic compound production.The electron beam welding (EBW) [37] process possesses the capability to produce welds of exceptional quality due to its capacity to create highly focused heat.This attribute results in the creation of homogenous welds with minimum imperfections, so guaranteeing a high level of joint quality.
Friction stir welding (FSW) [38] is a solid-state joining process that involves the use of frictional heat and mechanical deformation to create a weld between two workpieces.Friction stir welding (FSW) is a solid-state welding method that employs a revolving tool to induce heat by friction, causing the materials to undergo plasticization without reaching their respective melting temperatures.Friction stir welding (FSW) presents notable benefits when used for joining different materials [39].Friction Stir Welding (FSW) is conducted at temperatures below the melting point of the materials involved, hence mitigating concerns connected with solidification.This approach effectively prevents the occurrence of intermetallic formation and flaws caused by cooling.The plasticized materials experience substantial plastic deformation, leading to the development of finer microstructures and enhanced mechanical characteristics [40].
The mitigation of distortion resulting from the absence of melting in friction stir welding (FSW) is advantageous as it decreases the necessity for subsequent corrective measures, such as post-weld straightening.Consequently, FSW is deemed appropriate for precision applications.The process of friction stir welding (FSW) demonstrates a high degree of versatility in its ability to efficiently combine materials that possess different melting temperatures and characteristics.This characteristic renders FSW a versatile option for the purpose of combining incompatible materials [41].Overall, these advanced techniques represent a significant leap forward in addressing the challenges posed by dissimilar material welding, as shown in table.1.They provide the necessary precision, control, and adaptability required to create durable joints between materials with varying metallurgical behaviours, contributing to the advancement of aerospace and automotive technologies [42].

Laser Welding Electron Beam Welding Friction Stir Welding
Heat Input Control Precise control over heat input, minimizing HAZ and distortion.
Exceptional heat input control due to focused electron beam, leading to minimal HAZ.
No melting involved, avoiding HAZ and related issues.

Intermetallic Compound Formation
Rapid solidification can prevent or minimize intermetallic compound formation.
Vacuum environment reduces atmospheric reactions, lowering the risk of intermetallic formation.Solid-state process avoids intermetallic formation.

Distortion
Focused energy reduces thermal distortion compared to traditional methods.
Minimal distortion due to small HAZ and vacuum environment.
Low distortion due to the absence of melting.

Microstructure Improvement
Depending on cooling rates, refined microstructures can be achieved.
Results in uniform microstructures due to controlled heating and cooling.
Plastic deformation leads to improved microstructure and properties.

Joining Dissimilar Melting Points
Can effectively join materials with varying melting points.
Can join materials with differing melting points due to its vacuum nature.

Can handle materials with varying melting points effectively. Filler Material Requirement
May require filler materials depending on the materials being joined.
Often doesn't require filler materials due to deep penetration.
Generally, no filler materials needed due to solid-state nature.

Case Studies and Real-world Applications
The use of sophisticated welding methods for the purpose of combining dissimilar materials has gained considerable momentum in the aerospace and automotive sectors, leading to noteworthy enhancements in the performance and design of components [44].Laser welding has been utilised within the aerospace industry to effectively combine different materials, such as aluminium and titanium.In the field of aviation engine components, the utilisation of laser welding has facilitated the joining of aluminium and titanium alloys, therefore capitalising on their individual attributes of low weight and high temperature resistance.This methodology has resulted in improved engine efficiency, decreased fuel consumption, and prolonged lifespan of components [45].The electron beam welding has shown to be highly effective in several aircraft applications.Aerospace manufacturers have effectively employed the technique of welding dissimilar materials, such as nickel-based superalloys and stainless steel, in order to fabricate crucial engine and structural components.The utilisation of a vacuum environment in electron beam welding effectively reduces the potential for oxidation and contamination, hence safeguarding the structural soundness of joints even in challenging operational environments [46].
Friction stir welding has significantly transformed the process of connecting different materials within the automobile sector.An exemplary instance may be observed in the integration of aluminium and steel inside lightweight vehicle constructions.This strategy successfully strikes a delicate equilibrium between the ability to withstand crashes and the use of fuel resources.The solid-state characteristic of friction stir welding prevents the occurrence of fragile intermetallic compounds, leading to the development of joints that possess enhanced mechanical qualities and resistance to corrosion.Furthermore, the use of sophisticated welding methodologies transcends the confines of the production process.Electric vehicles (EVs) get advantages from the utilisation of these techniques in the production process of battery packs.The utilisation of laser welding facilitates the amalgamation of disparate materials within battery enclosures, therefore guaranteeing sturdy seals and effective temperature regulation.These technological improvements play a significant role in enhancing the durability and security of electric vehicles [47].
Electron beam welding has played a significant role in the domain of offshore constructions by facilitating the fusion of incompatible metals, such as high-strength steel and corrosion-resistant alloys.These applications highlight the technique's capacity to produce joints that possess structural integrity and can endure challenging maritime conditions.The presented case studies and practical implementations serve to highlight the adaptability and efficacy of modern welding methods in joining incompatible materials.The use of these approaches serves as a catalyst for innovation in several sectors, such as aviation component enhancement, automotive design optimisation, EV technology enablement, and offshore structure reinforcement.These techniques empower companies to surpass existing limits and attain heightened levels of efficiency and dependability.The utilisation of sophisticated welding techniques for dissimilar materials presents a multitude of advantages that surpass mere enhancements in immediate performance, therefore exerting a significant impact on the future course of the aerospace and automotive sectors.
The use of sophisticated welding techniques to integrate disparate materials results in components that exhibit improved performance characteristics.The incorporation of lightweight constructions, enhanced mechanical characteristics, and optimised thermal behaviour plays a significant role in enhancing efficiency, minimising fuel consumption, and augmenting load-bearing capabilities.These advantages not only adhere to existing industry norms but also establish novel criteria for performance.The use of advanced welding techniques facilitates the creation of strong connections that exhibit low deformation, decreased production of intermetallic compounds, and enhanced microstructural characteristics, hence enhancing the structural integrity and durability of the welded components.This results in improved structural integrity and increased durability, hence prolonging the lifespan of components in challenging operational environments.In the pursuit of enhanced dependability, businesses place significant emphasis on the use of sophisticated welding processes, which serve as a crucial factor in the attainment of durable and trustworthy structures.
The capacity to join incompatible materials by welding provides opportunities for creative design options.Engineers has the ability to use the distinct characteristics of several materials in order to fabricate multifunctional components that were previously unachievable using single-material approaches.The provision of design flexibility facilitates the creation of complicated and tailored structures that enhance performance in certain applications, ranging from aeroplane fuselages to car frames [48]- [49].The enhancement of fuel efficiency and the mitigation of carbon emissions are directly facilitated by the reduction in weight achieved via the utilisation of sophisticated welding techniques for different materials.Lightweight vehicles and aeroplanes have the potential to reduce energy consumption, hence contributing to the achievement of global sustainability objectives.Furthermore, the efficient utilisation of resources leads to a reduction in waste and resource consumption, hence augmenting the total environmental footprint of the aerospace and automotive sectors.When considering the future, the ramifications of employing improved welding processes on different materials have extensive repercussions.
The continuous progress in research and development will lead to the emergence of innovative material combinations, hence enhancing the potential of combining different materials.This phenomenon is anticipated to result in significant advancements in the field of material science, hence creating novel opportunities for engineering design.The integration of sensors, actuators, and electronics directly into components using advanced welding processes will facilitate the construction of intelligent and interconnected structures that possess the capability to autonomously monitor their own health and performance.The amalgamation of modern welding techniques with additive manufacturing technologies will facilitate the production of intricate, multifunctional components with unparalleled accuracy and effectiveness.The global industry transformation is expected to bring about a significant shift in production processes across several sectors through the broad use of these methodologies.Industries spanning from aerospace to automotive will adopt the notion of using lightweight, high-performance, and long-lasting components.

Conclusion
The integration of different materials through improved welding processes has brought forth a new age of possibilities in the dynamic landscapes of aerospace and automotive sectors.The pursuit of lightweight, high-performance components has spurred the investigation of novel methods to address the inherent difficulties associated in joining different materials.
• The aerospace and automotive industries are increasingly recognising the potential of combining modern welding processes with the integration of incompatible materials.• The integration of material science, welding technique, and engineering applications has resulted in a significant transformation, wherein the attainment of lightweight and high-performance characteristics is no longer considered contradictory.• The integration of disparate elements continues to be a fundamental aspect of advancing towards excellence.The ongoing advancements in aerospace and automotive technology have significant implications for the future design, manufacturing, and user experience of cars and aeroplanes.