Hot Forming Research Articles

Phenomenological model of hardening and flow for Ti-6Al-4 V titanium alloy sheets under hot forming conditions

Hardening is the core factor to determine deformation uniformity in sheet metal forming. Hot deformation of titanium alloy sheets encounters the coupled effects of strain hardening, strain rate hardening and softening, which makes the determination of forming parameters aiming for an enhanced hardening very difficult in practical processes. This paper presents a new model to quantify the hardening of Ti-6Al-4 V titanium alloy sheets under hot forming conditions based on the underlying correlation between uniform strain and hardening. Firstly, to precisely determine hot deformation characteristics of titanium alloy sheets, hot tensile uniaxial tests using Gleeble systems at various strain rates of 0.01–1 s−1 and temperatures of 973–1123 K were performed systematically. A newly developed volume-based correction method for stress–strain curves of Gleeble thermo-mechanical testing was proposed to eliminate the damaging effect of temperature gradients on strain calculations, which enables the strain hardening, strain rate hardening and softening to be determined precisely. Then, a simple unified formula of hardening components (n, m and s) was proposed to predict the achievable uniform strain at certain conditions efficiently. Using which, occupation of each hardening can be quantified and compared to facilitate the determination of process parameters. Finally, a phenomenological model based on the hardening and softening components was developed to predict the hot flow behaviour. The proposed quantitative model can provide an efficient and useful approach for process designers to design process parameters driven by the objective of enhancing hardening to maximize uniform deformation during hot forming of titanium alloy sheets.

Lightweight Materials in Electric Vehicles

Review Lightweight Materials in Electric Vehicles Xianyan Zhou 1,*, Jun Jiang 2, Zhili Hu 3, and Lin Hua 3 1 Department of Mechanical and Industrial Engineering, Norwegian University of Science and Technology (NTNU), 7491 Trondheim, Norway 2 Department of Mechanical Engineering, Imperial College London, Exhibition Road, London, SW7 2AZ, UK 3 School of Automotive Engineering, Wuhan University of Technology, Luoshi Road, Wuhan, 430070, China * Correspondence: xianyan.zhou@ntnu.no Received: 23 September 2022 Accepted: 21 November 2022 Published: 18 December 2022 Abstract: Lightweight materials are highly demanded in electric vehicles (EVs) to reduce environmental impacts and energy consumption. Aluminium alloys are promising materials in EVs due to their advantages such as high specific strength, corrosion resistance and recyclability. However, forming complex-shaped thin-wall aluminium products is challenging due to their poor formability and limited dimensional accuracy. Meanwhile, recycling some of the high-strength aluminium alloys from EVs is still challenging. This review highlights some of the future potential aluminium forming techniques for EV production, including incremental sheet forming (ISF), hot forming and quenching (HFQ ® ) technique, and transverse stretching and local bending (TSLB). Also, the issues associated with aluminium recycling are listed and discussed. This review provides scientific guidance to the industry and the scientific community for advancing the applications of aluminium alloys in EVs.

Design, Simulation and Experimental Evaluation of Hot-Stamped 22MnB5 Steel Autobody Part

The combination of complex geometry and martensitic microstructure, characterized by ultrahigh strength and hardness, can be obtained in a single hot stamping process. However, this technology requires a multifaceted approach, allowing for an effective and efficient design process that will ensure the elements with the desired properties and shape are produced because of the high tool cost. This paper presents a comprehensive case study of the design process, simulation and experimental evaluation of the hot forming of an automotive door beam. The U-shaped beam designed with CAD was analyzed using the finite element method in the Autoform v.10 software. The modeling process included: a shape definition of the flat blank; a FEM analysis and design of the die, punches, and clamps; and a forming and quenching simulation. The results covered visualization of the forming and quenching stages for different variables including a forming limit diagram; a distribution of the drawpiece thinning; and a diagram showing the hardness of the drawpiece and its microstructure. Based on the results, a full-size tool for hot stamping was first modeled in the CAD and next manufactured. The tool was used to produce an initial sample series that was used to investigate the conditions for continuous use of the tool. One of the produced hot-stamped products was investigated for its hardness and microstructure, which exhibited a beneficial and fully martensitic microstructure with high hardness of above 400 HV1.

Titanium clad plate forming: critical consideration and how different it is from solid titanium forming

Titanium offers exceptional corrosion resistance both in organic & inorganic acid media. Thus, it is a preferred material by various industries such as Oil and Gas refining, Petrochemical (PTA Plant) including Nickel refining by Hydrometallurgy. These equipment are operated at high temperature and pressure, necessitating the use of higher thickness for safety and efficient functioning. Therefore, use of solid titanium is not economical, and often substituted with explosion bonded Ti-Clad steel. Fabrication of certain components of this equipment like Dished heads are required to be made by forming with options of cold, warm or hot forming. Selection of forming method for Ti-clad steel component is often governed by its effect on Clad-Base metal bond integrity and reduction shear strength unlike other commonly used Stainless steel or Ni-based alloy clad material, wherein thickness of the base metal is major deciding factor. In case of Ti-Clad steels both cladding and base metal are not metallurgically compatible as well as differs significantly in their physical properties, forming temperature plays a crucial role. This paper describes the effect of various Dished heads forming methodology on integrity of clad plate. Also, it brings out how the Ti-clad steel forming is critical than the forming of solid Titanium.

MUELLER BRASS C48500

Abstract Mueller Brass C48500, also known as leaded naval brass, is a wrought copper-zinc-lead-tin alloy. It is a high-zinc brass to which a small amount of tin is added to improve its corrosion resistance and also to impart higher strength. Tin, like arsenic, antimony, and phosphorus, reduces susceptibility to dezincification. Mueller Brass C48500 possesses good hot formability and is fairly well adapted to any hot working process including forging. Due to its lead content, the alloy has poor cold forming characteristics. Due to this limitation, this alloy is best suited for machining applications rather than typical cold working operations. This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties. It also includes information on corrosion resistance as well as forming, heat treating, machining, and joining. Filing Code: Cu-936. Producer or source: Mueller Brass Company.

Simulation of Continuous Dynamic Recrystallization Using a Level-Set Method

Dynamic recrystallization is one of the main phenomena responsible for microstructure evolution during hot forming. Consequently, obtaining a better understanding of dynamic recrystallization mechanisms and being able to predict them is crucial. This paper proposes a full-field numerical framework to predict the evolution of subgrain structures upon grain growth, continuous dynamic recrystallization, and post-dynamic recrystallization. To be able to consider a subgrain structure, two strategies are proposed. One relies on a two-step tessellation algorithm to generate a fully substructured microstructure. The second strategy enables for the simulation of the formation of new subgrains during hot deformation. Using these tools, the grain growth of a fully substructured microstructure is modeled. The influence of microstructure topology, subgrain parameters, and some remaining stored energy due to plastic deformation is discussed. The results highlight that the selective growth of a limited number of subgrains is observed only when mobility is a sigmoidal function of disorientation. The recrystallization kinetics predicted with different criteria for discrimination of recrystallized grains are quantitatively compared. Finally, the ability of the framework to model continuous dynamic and post-dynamic recrystallization is assessed upon a case study representative of the hot extrusion of a zircaloy-4 billet (T=650 °C;ε˙=1.0s-1;εf=1.35). The influence of grain boundary properties and nucleation rules are quantified to evaluate the model sensitivity and suitability. Application of these numerical tools to other thermomechanical conditions and microstructures will be presented in an upcoming article.

Property profile development during wire extrusion and wire drawing of magnesium alloys AZ31 and ZX10

This paper deals with the impact of the wire manufacturing process on the mechanical property development of two magnesium alloys, AZ31 and ZX10. For this study, wires were produced with different diameters of up to 0.2 mm via direct one-step extrusion as a hot forming route and were directly compared to conventional cold drawing manufacturing routes with diameters up to 0.3 mm and associated heat-treatment. The alloy dependent microstructure development is resolved with respect to the underlying recrystallization mechanisms, which determines the texture development and concurrently the strength and ductility properties of the wires. The experimental results clearly show that the manufacturing process, the degree of deformation (wire diameter) as well as the alloy itself have a major impact on the texture development and mechanical properties of the wires. While AZ31, does not enable a strong impact on the microstructure development, ductility in ZX10 is enhanced with a concurrent weak texture development due to adjusted dynamic recrystallization during hot forming. In contrast, such microstructures cannot be adjusted in the cold forming routes due to static recrystallization. However, it is possible to improve of the properties significantly by drawing, which is limited by the first two drawing passes.

Biomimetic laminated basalt fiber-reinforced composite with sinusoidally architected helicoidal structure integrating superior mechanical properties and microwave-transmissibility

High-efficient microwave-transmissibility, mechanical durability, and lightweight are in significant demand for wireless communication components. Unfortunately, conventional materials can hardly meet the requirements for emerging radio-frequency (RF) devices so far. Herein, inspired by the sinusoidally architected helicoidal structure of mantis shrimp's dactyl club, a biomimetic laminated basalt fiber-reinforced composite (BL-BFRC) is designed and manufactured through a method combining linear helicoidal layup and hot press forming. Remarkably, the flexural strength and flexural modulus of BL-BFRC are 259.71 MPa and 22.61 GPa, which increase by 28.4% and 36.9% over those of conventional BFRC (202.27 MPa and 16.52 GPa). In addition, BL-BFRC exhibits a dielectric constant of 2.2858 and a loss tangent of 1.55 × 10−3, which are much lower than those of conventional BFRC (3.6459 and 9.73 × 10−3). Accordingly, the microwave-transmissibility increases from 93.53% (conventional BFRC) to 98.34% (BL-BFRC). In fact, the superior mechanical durability of BL-BFRC is mainly attributed to the crack deflection of helicoidal structure and stress dissipation of sinusoidal morphology. And the efficient microwave-transmissibility benefits from dielectric transition effect on non-smooth sinusoidal surface. This work uniquely combines the features of high-efficient microwave-transmissibility and mechanical durability into RF devices and would enable a broad range of wireless communication applications.

Effect of the interspacing of intragranular lamellar LPSO phase on dynamic recrystallization behaviors of Mg-Gd-Y-Zn-Zr alloys

The microstructures with different interspacings of intragranular lamellar long period stacking ordered (LPSO) phase were designed by altering the cooling rate after solid solution heat treatment, and the effect of the interspacing on the dynamic recrystallization (DRX) of Mg-Gd-Y-Zn-Zr alloy was investigated. During hot compression in the temperature range of 350–500 °C and strain rate from 0.001 s−1 to 1 s−1, the water-quenched (WQ) alloy containing closely spaced LPSO lamellae exhibits higher peak stress, larger critical strain, and smaller area fraction of DRX grains than the furnace-cooled (FC) alloy containing widely spaced LPSO lamellae. It is concluded that closely spaced intragranular LPSO lamellae suppress DRX. We further revealed the underlying mechanism using EBSD analyses and TEM characterizations. The larger lamellar LPSO interspacing imposes a much weaker constraint on the activation of the non-basal [c]-containing dislocations, which act as obstacles for the gliding <a > dislocations and hence offer favorable conditions for continuous DRX (CDRX). These findings provide a microstructural guidance for tuning the hot formability of LPSO-containing Mg alloys.

The Deformation Behavior and Microstructure of Aluminum Alloy Al–6Mg–0.3Sc under Conditions of Hot Forming

The Deformation Behavior and Microstructure of Aluminum Alloy Al–6Mg–0.3Sc under Conditions of Hot Forming

The Effect of Extrusion and Heat Treatment on the Microstructure and Tensile Properties of 2024 Aluminum Alloy.

Hot extrusion forming is one of the best cost-effective processing methods to obtain high-strength aluminum alloys. In order to obtain high performance 2024 aluminum alloy for the aero and automobile industries, this research comprehensively uses heat treatment and reverse isothermal extrusion technology to prepare 2024 alloy. The effects of homogenization, extrusion and post-extrusion annealing treatment on the microstructure and mechanical properties of 2024 aluminum alloy were discussed in detail. The results indicate that the grain refinement of the extruded alloy material is significant. The coarse eutectic microstructure at the grain boundaries was refined, and these grains tended to be uniformly distributed after the annealing treatment. Extruded 2024 aluminum alloy material mainly has S (Al2CuMg) and Al7Cu2Fe second phases. The appearance of a large number of S phases led to a significant improvement in the properties of the alloy with an increase in tensile strength and elongation of 176% and 547%, respectively. In addition, EBSD analysis showed a significant meritocratic growth in the extrusion direction with the appearance of Copper {112} &lt;111&gt; rolling weaving, which led to process hardening and the strength improvement of the alloy.

Efficient reconstruction of prior austenite grains in steel from etched light optical micrographs using deep learning and annotations from correlative microscopy

The high-temperature austenite phase is the initial state of practically all technologically relevant hot forming and heat treatment operations in steel processing. The phenomena occurring in austenite, such as recrystallization or grain growth, can have a decisive influence on the subsequent properties of the material. After the hot forming or heat treatment process, however, the austenite transforms into other microstructural constituents and information on the prior austenite morphology are no longer directly accessible. There are established methods available for reconstructing former austenite grain boundaries via metallographic etching or electron backscatter diffraction (EBSD) which both exhibit shortcomings. While etching is often difficult to reproduce and strongly depend on the investigated steel’s alloying concept, EBSD acquisition and reconstruction is rather time-consuming. But in fact, though, light optical micrographs of steels contrasted with conventional Nital etchant also contain information about the former austenite grains. However, relevant features are not directly apparent or accessible with conventional segmentation approaches. This work presents a deep learning (DL) segmentation of prior austenite grains (PAG) from Nital etched light optical micrographs. The basis for successful segmentation is a correlative characterization from EBSD, light and scanning electron microscopy to specify the ground truth required for supervised learning. The DL model shows good and robust segmentation results. While the intersection over union of 70% does not fully reflect the model performance due to the inherent uncertainty in PAG estimation, a mean error of 6.1% in mean grain size derived from the segmentation clearly shows the high quality of the result.

Optimization design of process parameters for cold and hot composite roll forming of the AHSS square tube using response surface methodology

Advanced high-strength steel (AHSS) is a highly competitive material for the automobile industry to resolve the challenge of weight reduction and passenger safety. Cold and hot composite roll forming is a newly developed manufacturing technology, which aims to overcome the defects such as microcrack, severe work hardening, thickness reduction, and large corner radius in the traditional cold roll forming process of AHSS. In this paper, the mathematical models that represent the effect of line velocity, heating power, and deformation amount on the yield strength, outer corner radius, and microcrack length in the corner section of cold and hot composite roll-formed AHSS square tube are investigated by the response surface methodology with Box-Behnken design. The analysis of variance shows that the linear velocity has the greatest influence on the three responses, followed by the heating power and deformation amount. Furthermore, the experimental verification is carried out under the optimal combination of process parameters to manufacture the AHSS square tube with the desired performance. Compared to the cold roll-formed AHSS square tube, the product of strength and elongation in the corner section is increased by 53%, the corner thickness is increased by 60%, the outer corner radius is decreased by 94%, and the microcrack defect is not generated. The average magnitude of errors between the predicted and actual values is about 5%, which implies that the optimization design is accurate and reliable.

PARALLEL SOLUTION OF THERMOMECHANICAL INVERSE PROBLEMS FOR LASER DIELESS DRAWING OF ULTRA-THIN WIRE

The paper discusses the solving of inverse thermomechanical problems requiring a large number of FEM tasks with various boundary conditions. The study examined the case when all tasks have the same number of nodes, finite elements, and nodal connections. In this study, the speedup of the solution of the inverse problem is achieved in two ways: 1. The solution of all FEM tasks in parallel mode. 2. The use by all FEM tasks a common matrix with addresses of nonzero elements in the stiffness matrices. These algorithms are implemented in the own FEM code, designed to solve inverse problems of the hot metal forming. The calculations showed that developed code in parallel mode is effective for the number of tasks late than 0,7-0,9 of the number of available processors. Thus, at some point, it becomes effective to use a sequential solution to all tasks and to use a common matrix of addresses of nonzero elements in the stiffness matrix. The achieved acceleration at the optimal choice of the algorithm is 2–10 times compared with the classical multivariate calculations in the FEM. The paper provides an example of the practical application of the developed code for calculating the allowable processing maps for laser dieless drawing of ultra-thin wire from copper alloy by solving the thermomechanical inverse problem. The achieved acceleration made it possible to use the developed parallel code in the control software of the laboratory setup for laser dieless drawing.

Potential of high-feed milling structured dies for material flow control in hot forming

Hot forming processes of complex parts with small cavities demand high-performance tools made of hardened steels. Their surface can be tribologically modified in order to control the material flow for improving the mold filling of functional elements. Surface structuring here offers great potential for adjusting the frictional properties and thus controlling the material flow in forming processes. In this study, high-feed milling (HFM) of surface structures in hot work tool steel (HWS) components is investigated. The process performance was determined by cutting force measurements and tool life tests. The achievable surface topography was measured and evaluated in terms of structure quality and roughness parameters, and friction properties were derived based on the results. In a hot ring compression test, the influence of certain structure variants on the material flow was analyzed. The results conclude that HFM is a suitable process for structuring HWS components with constant structure quality and low tool wear. In addition, a variety of structures showed significant influence on the hot ring compression test. This indicates a relevant potential of HFM for the modification of hardened tool surfaces to improve the performance of hot forming processes and increase the manufactural quality and productivity.

Rice husk ash: Economical and high-quality natural-based reinforcing filler for linear low-density and high-density polyethylene

Rice husk ash (RiHA) was employed as the bio-originated and inexpensive filler prepared from agricultural wastes for reinforcing high-density polyethylene (HDPE) and linear low-density polyethylene (LLDPE). X-ray fluorescence (XRF) spectroscopy showed ∼80.82% for the silica content of RiHA as well as the values of other components present in this bio-based filler. The composites were obtained via melt mixing followed by the compression molding by the hot press forming. Characterization of the composites by FT-IR spectroscopy revealed that the filler has the sheer effects on the vibrational bands of the polymers. The usage of X-ray diffraction (XRD) analysis to investigate the d-spacing values and the crystallinity of the samples, exhibited the increase of d-spacing upon reinforcing the polymers with RiHA. The scanning electron microscopy (SEM) images showed an average size of 32 µm for the irregular RiHA particles which uniformly dispersed in the polymeric matrices. The energy dispersive X-ray (EDX) analysis displayed C, O, and Si as the main constituting elements of the composites and alternatively confirmed the well dispersion of the filler particles into the polymer matrices. The mechanical measurements showed the significant improvements in Young’s modulus, yield stress, and hardness results of the polymers after reinforcing with the rice husk ash. For example, Young’s modulus of HDPE was increased ∼15% after incorporating 7 wt.% of RiHA into this polymer. These mechanical properties of the polymers were increased upon increasing the RiHA content, while the parameter of elongation at break was decreased.

Prediction of the peak and steady-state ply–ply friction response for UD C/PAEK tapes

Excessive ply–ply friction can lead to process-induced defects during the hot press forming of thermoplastic composite laminates. Process simulations can be used to enable first-time-right defect-free manufacturing. However, a good understanding of the ply–ply friction is required to improve the constitutive models to allow simulation of more complex parts. We performed friction experiments on UD C/PAEK tapes, showing a typical response with a peak followed by a steady-state friction. Micrographs of tested specimens were analyzed to evaluate the matrix interlayer thickness distribution in the ply–ply interface, which we combined with the matrix viscosity to predict the peak friction. Generated fiber distributions, mimicking the ply–ply interface, were successfully used to obtain the matrix interlayer as well. The steady-state friction was accurately described by including a critical shear stress to represent wall slip, substantiating the concept of wall slip as the dominant underlying mechanism for the start-up friction response.

Characterization of Hot Deformation of near Alpha Titanium Alloy Prepared by TiH2-Based Powder Metallurgy.

TiH2-basd powder metallurgy (PM) is one of the effective ways to prepared high temperature titanium alloy. To study the thermomechanical behavior of near-α titanium alloy and proper design of hot forming, isothermal compression test of TiH2-based PM near-α type Ti-5.05Al-3.69Zr-1.96Sn-0.32Mo-0.29Si (Ti-1100) alloy was performed at temperatures of 1123–1323 K, strain rates of 0.01-1 s−1, and maximum deformation degree of 60%. The hot deformation characteristics of alloy were analyzed by strain hardening exponent (n), strain rate sensitivity (m), and processing map, along with microstructure observation. The flow stress revealed that the difference in softening/hardening behavior at temperature of 1273–1323 K and the strain rate of 1 s−1 compared to the lower deformation temperature and strain rate. The strain hardening exponents at temperatures of 1123 K are all negative under all strain rates, and the most severe flow softening with minimum value of n was observed at 1123 K and 1 s−1. The strain rate sensitives showed that the peak region with m value greater than 0.5 generally appeared in the high temperature range of 1273–1323 K, while strain rate sensitivity at low temperature behaved differently with strain rates. The processing map developed for strain of 0.6 exhibited high power dissipation efficiency at high temperatures of 1273–1323 K and a low strain rate of 0.01 s−1, due to microstructure evolution of β phase. The decrease of strain rate at 1323 K resulted in the formation of globularization of α lamellae. The instability domain of flow behavior was identified in the temperature range of 1123–1173 K and at the strain rate higher than 0.01 s−1 reflecting the localized plastic flow and adiabatic shear banding, and inhomogenous microstructure. The variation of power dissipation energy (η) slope with strain demonstrated that the power dissipation mechanism during hot deformation has been changed from temperature-dependent to microstructure-dependent with the increase of temperature for the alloy deformed at 0.1 s−1. Eventually, the optimum processing range to deform the material is at 1273–1323 K and a strain rate range of 0.01–0.165 s−1 (ln = −4.6–−1.8).

Analysis of texture evolution and slip activity of a near-α titanium alloy sheet under different biaxial-tension strain paths

Understanding of the texture evolution and slip activity of titanium alloys during hot forming is crucial for designing reasonable strain path and improving formability of materials. To this goal, a hot gas bulging test was developed to investigate the texture evolution and slip activity of a near-α TA32 titanium alloy sheet under different biaxial-tension strain paths at elevated temperature. Four elliptical through-hole dies with different minor–major axis ratios and two dies with different suddenly-changed cavities were designed to realize various strain paths. The deformation texture was characterized by electron backscatter diffraction (EBSD) technique. The global Schmid factor (GSF) was adopted to analyze the dominant slip systems under different strain paths and their effects on texture evolution. Results showed that when the strain path changed from equi-biaxial tension to plane strain, the formability of the material decreased due to the decrease of the prismatic slip activity of the initial transverse texture. Meanwhile, the deformation texture changed from a band with (0001) orientation perpendicular to RD to TD-split basal bimodal texture. Furthermore, nonlinear strain paths at elevated temperature can be effectively realized by bulging with cavities suddenly-changed dies. When the first principal stress direction was converted from TD to RD during continuous deformation, the activity of pyramidal-2 slip obviously increased, and the preference of (0001) orientation transformed from perpendicular to RD into rotation towards RD. The formability of titanium alloy sheets during hot deformation can be improved by controlling texture based on the relationship between strain paths, texture evolution and slip activity.

Physically-based constitutive models for hot gas pressure forming of laser-welded titanium alloy blank

Weld seam (WS) has a different microstructure with base metal (BM), which could result in nonuniform deformation of the welded titanium alloy blank during hot forming process. In this paper, physically-based constitutive models considering microstructure evolution during the hot deformation were developed for both WS and BM to improve prediction accuracy of simulation. Uniaxial tensile tests of WS and BM were carried out to get stress-strain curves at temperatures ranging from 850 to 950 °C and strain rates ranging from 0.001 to 0.1 s−1. Microstructure evolutions of both WS and BM were characterized to reveal the deformation mechanisms. The developed models were validated by both strain rate jumping tensile tests and hot gas pressure forming of the welded blank. Results show that the physically-based constitutive models have good predictions of flow stress, globularization of WS and dynamic recrystallization of BM. The effect of WS on nonuniform deformation during the hot gas pressure forming of a laser-welded TA15 titanium alloy blank was accurately simulated. Physically-based constitutive models could reflect the effects of loading history on the microstructure evolution and flow stress. Therefore, compared with the simulation using the phenomenological constitutive models, the prediction accuracy of thickness distribution could be improved from 73.7 % to 90.8 % by the application of physically-based constitutive models.