Dissimilar Material Combinations Research Articles

3D interfacial geometries for co-optimized capacitance and mechanical properties in multi-material printing

Geometrical freedom in design brought upon by additive manufacturing (AM) has allowed for the fabrication of net shape object with complex geometry and more recently, functional multi-material parts. Multi-material printing of functional net shape objects has been demonstrated using combination of dissimilar materials. A common challenge in multi-material construct is the interfacial failure especially between dissimilar materials, and most reported work on multi-material printing have been limited to 2-D planar interface. In this work, we report the fused filament deposition (FDM) process of electrically conductive composite with an insulating polymer for a 3D capacitor, in which the interface geometry was designed to achieve maximum interfacial area between the two materials. Modelling of the 3-D interface geometry which is a periodic wave form with varying frequency, amplitude and curvature was conducted using Finite Element Analysis. FDM printed capacitors with the optimized 3D interfacial features showed an ∼8x increase in capacitance over similarly printed capacitor with planar interface design. Furthermore, the optimized 3D interface also resulted in an improved interfacial strength as demonstrated by a 3-point bending test. These 3D interfaces can be readily applied to 3D printed wearable/embedded electronics to improve upon their functionality and resistance to mechanical damage.

Effectiveness of an additively manufactured porous layer in dissimilar solid-state bulk joining of additively manufactured maraging steel and conventional AISI410 steel

Solid-state bulk joining of additively manufactured maraging steel and commercially available martensitic stainless steel (AISI410) specimens in a cylindrical shape is accomplished through electrically assisted pressure joining (EAPJ). The cylindrical maraging steel specimen is fabricated to have a porous layer on the joining side by selective laser melting additive manufacturing. During EAPJ, the porous layer, which serves as an interlayer with locally increased electrical resistance due to geometrically induced defects (pores), significantly and locally increases the maximum temperature while the joining load is dramatically decreased. The microstructure evolution suggests that grain refinement occurs on both the maraging steel and AISI410 sides due to recrystallization. The high residual stress induced during additive manufacturing of maraging steel specimens is significantly released during EAPJ. Martensite formation in the AISI410 steel and the reverted austenite in the maraging steel are characterized by the grain average image quality. Tensile tests show that the fracture always occurs in the transition region between the heat-affected region and the unaffected base metal region. The present study demonstrates that bulk joining of additively manufactured components and conventional components can be more easily and effectively achieved with the use of an additively manufactured porous layer, even for dissimilar material combinations. • AMed maraging steel and conventional AISI410 steel were solid-state joined. • The temperature was locally controlled by the AMed porous layer. • The high residual stress of AMed maraging steel was released during joining. • Microstructure evolution during joining was characterized by EBSD. • Base metal fracture in AISI410 side occurred during tension test.

Organic superstructure microwires with hierarchical spatial organisation

Rationally designing and precisely constructing the dimensions, configurations and compositions of organic nanomaterials are key issues in material chemistry. Nevertheless, the precise synthesis of organic heterostructure nanomaterials remains challenging owing to the difficulty of manipulating the homogeneous/heterogeneous-nucleation process and the complex epitaxial relationships of combinations of dissimilar materials. Herein, we propose a hierarchical epitaxial-growth approach with the combination of longitudinal and horizontal epitaxial-growth modes for the design and synthesis of a variety of organic superstructure microwires with accurate spatial organisation by regulating the heterogeneous-nucleation crystallisation process. The lattice-matched longitudinal and horizontal epitaxial-growth modes are separately employed to construct the primary organic core/shell and segmented heterostructure microwires. Significantly, these primary organic core/shell and segmented microwires are further applied to construct the core/shell-segmented and segmented-core/shell type’s organic superstructure microwires through the implementation of multiple spatial epitaxial-growth modes. This strategy can be generalised to all organic microwires with tailored multiple substructures, which affords an avenue to manipulate their physical/chemical features for various applications.

Joining of ultra-high-strength steels using resistance element welding on conventional resistance spot welding guns

Single-step joining of dissimilar material combinations between ultra-high-strength steels and high-strength aluminium alloys with sufficient mechanical joint properties by using conventional resistance spot welding equipment has not been reported yet. In this research paper, a novel single-step joining technology, so-called self-penetrating resistance element welding, is introduced. First, the motivation for this novel joining technology, the state of the art in joining, and the process characteristics are presented. In the results section, the welding rivet geometry is first determined using forming simulations and validated by head tensile tests. Followed by the description of the welding process and its characteristics, the mechanical joint properties are reported. The results show that a numerically optimised welding rivet geometry can guarantee sufficient joint strength. By this welding rivet geometry, a thermally assisted penetration of aluminium and therefore welding to steel is possible with and without adhesive. Furthermore, it is shown that the welding process can be designed by means of simulations. Finally, the shear tensile tests prove that an overall sufficient joint strength is ensured.

Study on weldability and effect of post heat treatment on mechanical and metallurgical properties of dissimilar AA 2025, AA 5083 and AA7075 GTAW weld joints

Gas Tungsten Arc Welding (GTAW) has been extensively in use over a period in mechanical industry. Most of the problems associated with the structural development involving Aluminium is still a challenging and requires a methodological study to understand weldability of dissimilar Aluminium base materials. In this present study, mechanical and metallurgical properties of AA 2025, AA 5083 and AA 7075 weld joints made with GTAW have been presented. Mean pulse current of 80 A to 100 A was selected to join the similar and dissimilar base material combinations to make comparative studies. Difficult to weld base material combinations, AA 2027 with other selected base materials, and with non-heat treatable base materials were subjected to post weld heat treatment. Tensile and hardness tests were performed to evaluate the properties of as weld and post heated dissimilar weld joints.

Probing Magnetic Pulse Welding of Thin-Walled Tubes

Magnetic pulse welding is a solid-state joining technology, based on the use of electromagnetic forces to deform and to weld workpieces. Since no external heat sources are used during the magnetic pulse welding process, it offers important advantages for the joining of dissimilar material combinations. Although magnetic pulse welding has emerged as a novel technique to join metallic tubes, the dimensional consistency of the joint assembly due to the strong impact of the flyer tube onto the target tube and the resulting plastic deformation is a major concern. Often, an internal support inside the target tube is considered as a solution to improve the stiffness of the joint assembly. A detailed investigation of magnetic pulse welding of Cu-DHP flyer tubes and 11SMnPb30 steel target tubes is performed, with and without an internal support inside the target tubes, and using a range of experimental conditions. The influence of the key process conditions on the evolution of the joint between the tubes with progress in time has been determined using experimental investigations and numerical modelling. As the process is extremely fast, real-time monitoring of the process conditions and evolution of important responses such as impact velocity and angle, and collision velocity, which determine the formation of a metallic bond, is impossible. Therefore, an integrated approach using a computational model using a finite-element method is developed to predict the progress of the impact of the flyer onto the target, the resulting flyer impact velocity and angle, the collision velocity between the flyer and the target, and the evolution of the welded joint, which are usually impossible to measure using experimental observations.

Joining similar and dissimilar material combinations by laser shock forming

Abstract This paper verified the feasibility of joining similar and dissimilar material combinations by laser shock forming. Typical joining defects and failure modes during the deformation process were also discussed. Neck fracture often takes place in the lower foil, which was subjected to serious joint shearing effect from laser-induced shock wave and hole edge of perforated sheet. Meanwhile, bottom fracture was more likely to occur in the upper foil, in which the direct laser shock pressure was quite large. Process windows of Cu/Cu/Ss combination and Cu/Al/Ss combination were acquired after conducting an array of experiments. The influences of laser energy and material properties on interlocking structure were investigated by analyzing cross-sectional material flow and measuring key structural dimensions. With the increase of laser energy, interlocks gradually increased while neck thicknesses gradually decreased. Under the same processing conditions, interlocks of Cu/Al/Ss combination were larger than that in Cu/Cu/Ss combination, while both neck thicknesses showed an opposite trend. Single lap shearing tests showed that mechanical strength and failure modes of joints were notably influenced by interlocking structure, a high joining strength can only be obtained under larger interlocks and larger neck thicknesses.

Fatigue life performance of multi-material connections hybrid joined by self-piercing rivets and adhesive

Abstract The multi-material design presented contains EN AW-6016 aluminum and high strength CR330Y590T-DP steel. This dissimilar combination is an example of an affordable lightweight design solution, but it requires an adapted joining technology. Hybrid joining technologies such as selfpiercing riveting (SPR) in combination with a structural adhesive enables an assembly of such dissimilar material combinations. In addition to higher manufacturing costs for mechanical joining the design process still requires a great amount of effort. This study provides a simple approach for assessing hybrid joined multi-material connections. Therefore, tests for several combinations of the most relevant parameters on fatigue life (material properties, sheet thickness, load cases) were performed under quasi-static and cyclic loads. Based on the data acquired, it is shown that the fatigue life of hybrid joined connections can be estimated by superposing the contributing fatigue life of purely SPR and purely adhesive joints.

Fatigue life performance of multi-material connections hybrid joined by self-piercing rivets and adhesive

Abstract The multi-material design presented contains EN AW-6016 aluminum and high strength CR330Y590T-DP steel. This dissimilar combination is an example of an affordable lightweight design solution, but it requires an adapted joining technology. Hybrid joining technologies such as selfpiercing riveting (SPR) in combination with a structural adhesive enables an assembly of such dissimilar material combinations. In addition to higher manufacturing costs for mechanical joining the design process still requires a great amount of effort. This study provides a simple approach for assessing hybrid joined multi-material connections. Therefore, tests for several combinations of the most relevant parameters on fatigue life (material properties, sheet thickness, load cases) were performed under quasi-static and cyclic loads. Based on the data acquired, it is shown that the fatigue life of hybrid joined connections can be estimated by superposing the contributing fatigue life of purely SPR and purely adhesive joints.

Dilution Ratio and the Resulting Composition Profile in Dissimilar Laser Powder Bed Fusion of AlSi10Mg and Al99.8

A variant of a hybrid manufacturing process combines the benefits of laser powder bed fusion (LPBF) and conventional manufacturing. Hybrid manufacturing can result in dissimilar material combinations which are prone to process errors. This study is motivated by the future application of a hybrid manufacturing variant and focusses on dissimilar aluminium alloys were hot cracks are the dominant process errors. A theoretical model was derived for the composition profile based on the dilution ratio known from fusion welding. The theory was validated with penetration depth measurements and energy-dispersive X-ray spectroscopy line scans on samples manufactured by LPBF (powder AlSi10Mg, building platform Al99.8 and line energies Pv−1 = 0.26–0.42 J·mm−1). A material combination with a low hot crack susceptibility was chosen to establish the theory. The results suggest that the dilution ratio is dependent on the penetration depth and the layer thickness. The used line energies result in a dilution ratio of 67–86% which results in 2–6 re-melted and mixed layers per added layer. A specific process design metric, the mixture height, is proposed to estimate the spatial effect of the dilution. The results can be used to adjust process parameters to lessen the effect of process errors in dissimilar hybrid manufacturing and increase mechanical performance.

Detection Method for Liquid Metal Embrittlement Cracks Inside the Intermediate Sheet Zone of Dissimilar Resistance Spot Welds

Liquid metal embrittlement (LME) is a phenomenon where a liquid metal damages a solid bulk metal. Notwithstanding previous investigations, LME remains an actual as well as a still not fully understood topic. A so far not yet investigated area can be defined with ultra‐high strength austenitic stainless steels for passenger cars. The most commonly used joining procedure in car body engineering is still resistance spot welding. During this vehicle assembly step, the uncoated surface of an austenitic stainless steel is because of the process‐related lap joint configuration in direct contact with zinc‐coated surface‐finished steels as a dissimilar material combination. During welding, liquid zinc could penetrate inside the intermediate sheet zone in the grain boundaries of the austenitic steel and is therefore able to initiate cracks in the heat‐affected welding zone. Herein, the radiographic inspection is introduced, which is a process‐reliable, nondestructive detection method for the inaccessible intermediate sheet zone area, which is usable in automotive big‐industrial scale. With the implemented detection method, liquid metal‐induced cracks can be detected in the intermediate sheet zone down to a crack length of 50 μm. Subsequently, the radiographic inspection helps to analyze the crack characteristic depending on surrounding conditions and welding parameters.

An Overview of Laser Welding of High Strength Steels for Automotive Application

High strength steel and their variations are found in abundance and are an excellent material selected for automotive applications. However, their usage in automotive applications requires the joining of components via conventional joining and welding techniques. Recently, there has been advancement in photons-based manufacturing technology where laser as a localized and robust heat source is employed to join similar or dissimilar material combinations. A brief overview of lasers employed in welding technology is outlined. Secondly, various types of steel important for automotive applications are introduced. Thereafter, laser welding of steel and the corresponding effect of parameters and their effect on weld geometry are discussed. It can be concluded that the variation of laser welding parameters can cause high thermal distortion and greatly affects the mechanical performance of the joint. Hence, an optimum parameter value should be investigated to obtain a strong joint. It is iterated that additional literature review should be carried out investigating various ways of improving weld quality, techniques, jigs development to avoid welding defects formation. Additionally, better observation and characterization through the state of art available materials testing could be employed to further gain insights and to have a better understanding of microstructural behaviour

Singularity of Electromechanical Coupling Field in Piezoelectric Composite Junctions

The double singularities including singular stress field and singular electric displacement field, in the tips of piezoelectric composite junctions, are analyzed by the interpolation matrix method (IMM). The double singularity analysis problem of piezoelectric composite junctions is converted into eigenvalue solution problem of ordinary differential equations with variable coefficients under corresponding boundary conditions. In numerical examples, the first couple of singularity orders and the corresponding characteristic angular functions of displacement and electric potential for the electromechanical coupling field are obtained and comparisons are presented to validate the accuracy of the proposed method. The singularity of the electromechanical coupling field at the tip of piezoelectric composite material junctions is closely related to the bonding angle and fiber direction. According to the numerical results, the best scheme can be configured for the combination of dissimilar materials.

Blue high-power laser sources for processing solutions in e-mobility and beyond

The laser based processing of copper components with blue lasers with 450nm wavelength gained significance in the last years due to the increasing demand in eMobility applications. The high absorption level allows new process approaches, which were formerly however restricted by the limited power level of blue laser systems. With the availability of multi-kilowatt blue laser systems with 450 nm wavelength, a further step has been achieved to extend the application range for copper components. Process stages from heat conduction welding to keyhole welding can be precisely adjusted. The properties of these process stages however vary from the conventional behavior known from IR laser sources. In this contribution, the properties and differences compared to IR sources are investigated. This is achieved by an evaluation of the process stages by high speed videography and an investigation of the process robustness e.g. gap bridgeability in the example of battery applications. Furthermore, we will review the latest application results regarding blue laser welding for the battery cell manufacturing and the battery module interconnection. This consists of welding results of copper to copper connections and also dissimilar material combinations.

Process design for the forming of semi-tubular self-piercing rivets made of high nitrogen steel

The aim to reduce pollutant emission has led to a trend towards lightweight construction in car body development during the last years. As a consequence of the resulting need for multi-material design, mechanical joining technologies become increasingly important. Mechanical joining allows for the combination of dissimilar materials, while thermic joining techniques reach their limits. Self-piercing riveting enables the joining of dissimilar materials by using semi-tubular rivets as mechanical fasteners. The rivet production, however, is costly and time-consuming, as the rivets generally have to be hardened, tempered and coated after forming, in order to achieve an adequate strength and corrosion resistance. A promising approach to improve the efficiency of the rivet manufacturing is the use of high-strength high nitrogen steel as rivet material because these additional process steps would not be necessary anymore. As a result of the comparatively high nitrogen content, such steels have various beneficial properties like higher strength, good ductility and improved corrosion resistance. By cold bulk forming of high nitrogen steels high-strength parts can be manufactured due to the strengthening which is caused by the high strain hardening. However, high tool loads thereby have to be expected and are a major challenge during the production process. Consequently, there is a need for appropriate forming strategies. This paper presents key aspects concerning the process design for the manufacturing of semi-tubular self-piercing rivets made of high-strength steel. The aim is to produce the rivets in several forming stages without intermediate heat treatment between the single stages. Due to the high strain hardening of the material, a two stage forming concept will be investigated. Cup-backward extrusion is chosen as the first process step in order to form the rivet shank without forming the rivet foot. Thus, the strain hardening effects in the area of the rivet foot are minimized and the tool loads during the following process step can be reduced. During the second and final forming stage the detailed geometry of the rivet foot and the rivet head is formed. In this context, the effect of different variations, for example concerning the final geometry of the rivet foot, on the tool load is investigated using multistage numerical analysis. Furthermore, the influence of the process temperature on occurring stresses is analysed. Based on the results of the investigations, an adequate forming strategy and a tool concept for the manufacturing of semi-tubular self-piercing rivets made of high-strength steel are presented.

Bending Property of Multi-Material Hat Shaped Member of CFRTP and Aluminum Alloy

CFRTP (Carbon Fiber Reinforced Thermoplastics) are expected to be used in the automobile parts due to their properties such as high specific strength and high specific stiffness in order to reduce the weight of car body. However, due to the expensive carbon fiber, the cost of CFRTP is high and its application to automobiles is limited. For mass-produced automobiles, a multi-material concept using a combination of dissimilar materials has been attracting attention. While the multi-material concept is often used to joint dissimilar materials, such as composite materials, high tensile strength steel, Al alloy and so on, the method of combining dissimilar material into one part is also expected. For the development of automotive parts, CAE technology is required and in order to apply multi-material concept to mass-produced automobiles, optimization method of materials and shape is necessary to be developed in the future. In this study, multi-material hat shaped members of CFRTP and aluminum alloy were molded by using hybrid molding method and their bending properties were evaluated. Their FEM analysis was also carried out and the relationship between material cost and mechanical properties were evaluated. When the surface of Al alloy is treated by electrolytic polishing, delaminating between Al alloy and CFRTP was suppressed and high stiffness multi-material hat shaped member can be obtained. The multi-material hat shaped member of CFRTP and Al alloy has superior specific stiffness as compared with molded products using only CFRTP for surface material, although the specific maximum bending load was lower.

Microstructure, forming limit diagram, and strain distribution of pre-strained DP-IF steel tailor–welded blank for auto body application

In the present study, tailor-welded blanks (TWBs) of dissimilar material combination were fabricated by laser welding of interstitial-free (IF) and dual-phase (DP) steels using 2.4-kW power and 4 m/min scan speed. Subsequently, TWBs of as-received sheet materials and IF steels were pre-strained up to 20% major strain in the deformed specimens through an equi-biaxial pre-straining setup. It was found that highly non-uniform strain distribution with nearly plane strain deformation mode was induced in the pre-strained TWBs, whereas an equi-biaxial strain was recorded for IF monolithic blank. Microhardness profiles and the effect of weld zone on the microstructural and mechanical properties of the as-received and pre-strained TWBs were studied. Further, the forming limit diagrams (e-FLDs) of as-received TWB and IF steel were experimentally evaluated. The e-FLD of pre-strained TWBs was experimentally determined, and e-FLD of the pre-strained IF material was estimated using the Yld89 anisotropy plasticity model with the Hollomon hardening law. Subsequently, all these respective e-FLDs were implemented as damage models in the FE simulations for predicting the limiting dome height (LDH) of as-received and pre-strained TWBs. It was observed that the error in LDH prediction of pre-strained TWB domes was within 9.1% when the estimated e-FLD of the pre-strained IF material was used as a damage model. The FE-predicted strain distributions and weld line movements of TWBs after the second stage of deformation were also successfully validated with the experimental data.

Solid-state dissimilar joining of stainless steel 316L and Inconel 718 alloys by electrically assisted pressure joining

Electrically assisted solid-state joining (or electrically assisted pressure joining, EAPJ) of dissimilar stainless steel 316L (SUS316L) and Inconel 718 (IN718) alloys is experimentally investigated. The specimen assembly for the experiment is comprised of two cylindrical solid specimens (SUS316L and IN718) with an identical geometry. In EAPJ, electric current and plastic compression are directly and simultaneously applied to the specimen assembly. The microstructural analysis confirms that crack/void-free joints are successfully fabricated by EAPJ in the selected dissimilar metal alloys without melting and solidification. An obvious atomic diffusion region at the joint interface is identified. The results of tensile tests show that all the joints fracture from the SUS316L side, which undergoes typical ductile fracture with large plastic deformation. The results of the present study confirm that the concept of EAPJ is applicable to solid state joining of dissimilar material combination.

Brazing filler metals

ABSTRACTBrazing is a 5000-year-old joining process which still meets advanced joining challenges today. In brazing, components are joined by heating above the melting point of a filler metal placed between them; on solidification a joint is formed. It provides unique advantages over other joining methods, including the ability to join dissimilar material combinations (including metal-ceramic joints), with limited microstructural evolution; producing joints of relatively high strength which are often electrically and thermally conductive. Current interest in brazing is widespread with filler metal development key to enabling a range of future technologies including; fusion energy, Solid Oxide Fuel Cells and nanoelectronics, whilst also assisting the advancement of established fields, such as automotive lightweighting, by tackling the challenges associated with joining aluminium to steels. This review discusses the theory and practice of brazing, with particular reference to filler metals, and covers progress in, and opportunities for, advanced filler metal development.

Galling resistance of nanostructured CVD tungsten/tungsten carbide coatings

Nanostructured tungsten/tungsten carbide (W/WC) coatings produced by chemical vapour deposition are promising WC based coatings for applications where galling wear is prevalent due to the high hardness, toughness and stacking fault energy which the coatings possess despite low hardness to elastic modulus ratio (H/E). In this work the galling resistance of W/WC coatings has been studied through tibometer tests using sliding speeds of 0.014 m s−1 and contact pressures of up to 810 MPa. The study investigates the effects of surface finish and the use of similar and dissimilar material combinations on galling wear. Results show that self-mated stainless steel AISI 316 behave poorly under dry sliding wear conditions whilst uncoated stainless steel tested versus W/WC coating combinations are affected by galling due to material transfer forming a stainless steel on stainless steel tribosystem. The best performance was recorded for self-mated W/WC which did not develop any signs of galling even at the highest contact pressures (810 MPa) contradicting the common practice that the use of dissimilar materials can help prevent galling.