Search Results (20)

Joining high-strength, cold-drawn Cu-Mg alloy conductors is a critical challenge for ensuring the reliability of high-speed railway catenary systems. This study investigates the evolution of mechanical properties and microstructure in Cu-0.43 wt% Mg alloy wires joined by multi-pass butt-upset cold welding without special surface preparation. High-integrity joints were achieved, exhibiting a peak tensile strength of 624 MPa (~96% of the base material’s strength). After four upsetting processes, the tensile strength of the weld can reach 90% of the original strength, and the gains from subsequent upsetting processes are negligible. Microstructural analysis revealed the joining process is governed by localized severe shear deformation, which forges a distinct gradient microstructure. This includes a transition zone of fine, equiaxed-like grains formed by dynamic recrystallization/recovery, and a central zone featuring a nano-laminar structure, high dislocation density, and deformation twins. A multi-stage dynamic bonding mechanism is proposed. It progresses from initial contact via thin film theory to bond consolidation through a “mechanical self-cleaning” process, where extensive radial plastic flow effectively expels surface contaminants. This work clarifies the fundamental bonding principles for pre-strained, high-strength alloys under multi-pass cold welding, providing a scientific basis to optimize this heat-free joining technology for industrial applications. Full article

In this study, a biodegradable Mg-Zn-Nd-Gd alloy was processed via multi-directional forging (MDF) to evaluate its microstructural evolution, mechanical performance, and corrosion behavior. Electron backscattered diffraction (EBSD) analysis was conducted to evaluate the influence of grain size and texture on mechanical strength and corrosion resistance. The average grain size decreased significantly from 118 ± 5 μm in the homogenized state to 30 ± 10 μm after six MDF passes, primarily driven by discontinuous dynamic recrystallization (DDRX). Remarkably, this magnesium (Mg) alloy exhibited a rare synergistic enhancement in both strength and ductility, with ultimate tensile strength (UTS) increasing by ~59%, yield strength (YS) by ~90%, while elongation improved by ~44% unlike conventional severe plastic deformation (SPD) techniques that often sacrifice ductility for strength. This improvement is attributed to grain refinement, dispersion strengthening from finely distributed Mg₁₂Nd and Mg₇Zn₃ precipitates, and texture weakening, which facilitated the activation of non-basal slip systems. Despite the mechanical improvements, electrochemical corrosion testing in Hank’s balanced salt solution (HBSS) at 37 °C revealed an increased corrosion rate from 0.1165 mm/yr in homogenized condition to 0.2499 mm/yr (after six passes of MDF. This was due to the higher fraction of low-angle grain boundaries (LAGBs), weak basal texture, and the presence of electrochemically active fine Mg₇Zn₃ particles. However, the corrosion rate remained within the acceptable range for bioresorbable implant applications, indicating a favorable trade-off between mechanical performance and degradation behavior. These findings demonstrate that MDF processing effectively enhances the strength–ductility synergy of Mg-rare earth alloys while maintaining a clinically acceptable degradation rate, thereby presenting a promising route for next-generation biomedical implants. Full article

The Mg-8Li-3Al-0.3Si dual-phase alloy (LA83-0.3Si) was subjected to six multi-directional forging (MDF) passes in the present work, then its microstructure, mechanical properties, and work hardening and work softening effects were examined and analyzed. The results indicate that the continuous dynamic recrystallization (CDRX) mechanism of the LA83-0.3Si dual-phase alloy gradually transitioned to a discontinuous dynamic recrystallization (DDRX) mechanism as the temperature increased after MDF. This temperature change induced a transition in the basal texture from bimodal to multimodal, significantly reducing the texture intensity and weakening the alloy’s anisotropy. At 310 °C, the AlLi phase nucleated into coated particles to stabilize the structure. Additionally, the increase in the forging temperature weakened the synergistic deformation capability of the α/β phases, while the hardening behavior of the β-Li phase provided a nucleation pathway for dynamic recrystallization (DRX). MDF significantly enhanced the strength and ductility of the LA83-0.3Si alloy. The alloy’s strength continued to rise, while elongation decreased as the forging temperature increased. The ultimate tensile strength (UTS) and elongation (EL) reached 267.8 MPa and 11.9%, respectively. The work hardening effect increased with the forging temperature, whereas the work softening effect continuously diminished, attributed to the enhanced hardening behavior of the β phase and the reduced ability to transfer dislocations. Full article

This study refers to the application of an advanced tool in the form of numerical modelling in order to develop a low-waste hot die forging technology to produce a connecting rod forging. The technology aims at ensuring a limited amount of the charge material is necessary to produce one forging, as well as minimizing forging forces, and thus the electric energy consumption. The study includes a verification of the current production technology, which constituted the basis for the construction and development of a numerical model. A new construction of the forging tools was developed, with an additional pre-roughing pass (0X). The new process consists of die forging in the pre-roughing pass (0X), the roughing pass (1X) and the finishing impression (2X). Numerical modelling was subsequently conducted with the use of the Forge 3.0 NxT software. A detailed analysis was conducted on the accuracy of the tool impression filling (including the pre-roughing pass) by the deformed material, the distribution of temperatures for the forgings and the plastic deformations, as well as the courses of forging forces and energy. The results were verified under industrial conditions and compared with the forgings obtained in the previous technology (a roughing pass and a finishing impression). As a result of introducing the pre-roughing pass 0X, the forces were distributed between three impressions, including the especially developed pre-roughing pass. It was confirmed that the abovementioned changes in terms of forging tool construction had a positive effect on relieving the roughing pass and the finishing impression as well as limiting the charge material, and they also lowered the process energy consumption by 10%. This study also validated the relevance of using FE modelling to verify processes under virtual conditions before being implemented under industrial conditions. Therefore, the proposed approach based on multi-variant numerical simulations can be successfully used to improve other manufacturing processes in terms of reducing energy and material consumption and increasing tool service life. Full article

This study investigates the preparation of ultrahigh-strength AZ80 magnesium alloy bulks using room temperature multidirectional forging (MDF) at different strain rates. The focus is on elucidating the effects of multidirectional loading and strain rates on grain refinement and the subsequent impact on the mechanical properties of the AZ80 alloy. Unlike hot deformation, the alloy subjected to room temperature MDF exhibits a lamellar twinned structure with multi-scale interactions. The key to achieving effective room temperature MDF of the alloy lies in combining multidirectional loading with small forging strains per pass (6%). This approach not only maximizes the activation of twinning to accommodate deformation but ensures sufficient grain refinement. Microstructural analysis reveals that the evolution of the grain structure in the alloy during deformation results from the competition between {10$\overline{1}$2} twinning or twinning variant interactions and detwinning. Increasing the forging rate effectively activates more twin variants, and additional deformation passes significantly enhance twin interaction levels and dislocation density. Furthermore, at a higher strain rate, more pronounced dislocation accumulation facilitates the transformation of twin structures into high-angle grain boundaries, promoting texture dispersion and suppressing detwinning. The primary strengthening mechanisms in room temperature MDF samples are grain refinement and dislocation strengthening. While increased dislocation density raises yield strength, it reduces post-yield work hardening capacity. After two passes of MDF at a higher strain rate, the alloy achieves an optimal balance of strength and ductility, with a tensile strength of 462 MPa and an elongation of 5.1%, significantly outperforming hot-deformed magnesium alloys. Full article

The evolution of microstructure, phase composition and physico-mechanical properties of the biocompatible Ti-39Nb-7Zr alloy (wt.%) after severe plastic deformation by rotary forging (RF) was studied using various methods including light optical microscopy, scanning and transmission electron microscopies, X-ray diffraction, microindentation, tensile testing and investigation of thermophysical properties during continuous heating. The hot-rolled Ti-39Nb-7Zr with initial single β-phase structure is subjected to multi-pass RF at 450 °C with an accumulated degree of true deformation of 1.2, resulting in the formation of a fibrous β-grain structure with imperfect 500 nm subgrains characterized by an increased dislocation density. Additionally, nano-sized α-precipitates formed in the body and along the β-grain boundaries. These structural changes resulted in an increase in microhardness from 215 HV to 280 HV and contact modulus of elasticity from 70 GPa to 76 GPa. The combination of strength and ductility of Ti-39Nb-7Zr after RF approaches that of the widely used Ti-6Al-4V ELI alloy in medicine, however, Ti-39Nb-7Zr does not contain elements with limited biocompatibility and has a modulus of elasticity 1.5 times lower than Ti-6Al-4V ELI. The temperature dependences of physical properties (elastic modulus, heat capacity, thermal diffusivity) of the Ti-39Nb-7Zr alloy after RF are considered and sufficient thermal stability of the alloy up to 450 °C is demonstrated. Full article

The study refers to the application of numerical modeling for the improvement of the currently realized precision forging technology performed on a hammer to produce connecting rod forgings in a triple system through the development of an additional rolling pass to be used before the roughing operation as well as preparation of the charge to be held by the robot’s grippers in order to implement future process robotization. The studies included an analysis of the present forging technology together with the dimension–shape requirements for the forgings, which constituted the basis for the construction and development of a thermo-mechanical numerical model as well as the design of the tool construction with the consideration of the additional rolling pass with the use of the calculation package Forge 3.0 NxT. The following stage of research was the realization of multi-variant numerical simulations of the newly developed forging process with the consideration of robotization, as a result of which the following were obtained: proper filling of the tool impressions (including the roller’s impression) by the deformed material, the temperature distributions for the forging and the tools as well as plastic deformations (considering the thermally activated phenomena), changes in the grain size as well as the forging force and energy courses. The obtained results were verified under industrial conditions and correlated with respect to the forgings obtained in the technology applied so far. The achieved results of technological tests confirmed that the changes introduced into the tool construction and the preform geometry reduced the diameter, and thus also the volume, of the charge as well as provided a possibility of implementing robotization and automatization of the forging process in the future. The obtained results showed that the introduction of an additional rolling blank resulted in a reduction in forging forces and energy by 30% while reducing the hammer blow by one. Attempts to implement robotization into the process were successful and did not adversely affect the geometry or quality of forgings, increasing production efficiency. Full article

Magnesium-based alloys hold potential for medical applications, but face challenges like rapid bioresorption and limited mechanical strength during early bone healing. In our study, we present a novel Mg–Zn–Zr–Ce alloy with low cerium content (up to 0.1 wt.% Ce) processed using two severe plastic deformation (SPD) techniques. Through an innovative combination of multiaxial forging and multipass rolling, we have achieved a fine-grained structure with an average grain size of the primary α-Mg phase of 1.0 μm. This refined microstructure exhibits improved mechanical properties, including a substantial increase in yield strength (σ_YS) from 130 to 240 MPa, while preserving ductility. The alloy’s composition includes α-Mg grains, cerium and zinc hydrides, and intermetallic phases with cerium and zinc elements. Tensile testing of the fine-grained alloy demonstrates an enhancement in yield strength (σ_YS) to 250 MPa, marking a 2.8-fold improvement over the conventional state (σ_YS = 90 MPa), with a modest 2-fold reduction in ductility. Crucially, electrochemical tests conducted in physiological solutions highlight substantial advancements in corrosion resistance. The corrosion current was reduced from 14 to 2 μA/cm², while polarization resistance decreased from 3.1 to 8.1 kΩ∙cm², underlining the alloy’s enhanced resistance to biodegradation. Our results show that the novel Mg–Zn–Zr–Ce alloy, after combined SPD, demonstrates mitigated bioresorption and enhanced mechanical properties. Our findings highlight the fact that the introduction of this innovative alloy and the application of SPD represent significant steps towards addressing the limitations of magnesium-based alloys for medical implants, offering potential improvements in safety and effectiveness. Full article

For this paper, studies of the microstructure as well as the mechanical and biological properties of bioinert titanium, zirconium, and niobium alloys in their nanostructured (NS) and ultrafine-grained (UFG) states have been completed. The NS and UFG states were formed by a combined two-step method of severe plastic deformation (SPD), first with multidirectional forging (MDF) or pressing into a symmetrical channel (PSC) at a given temperature regime, and then subsequent multi-pass groove rolling (MPGR) at room temperature, with pre-recrystallization annealing. Annealing increased the plasticity of the alloys in the NS and UFG states without changing the grain size. The UFG structure, with an average size of structural elements of no more than 0.3 μm, was formed as a result of applying two-step SPD and annealing. This structure presented significant improvement in the mechanical characteristics of the alloys, in comparison with the alloys in the coarse-grained (CG) or small-grained (SG) states. At the same time, although the formation of the UFG structure leads to a significant increase in the yield strength and tensile strength of the alloys, their elastic modulus did not change. In terms of biocompatibility, the cultivation of MG-63 osteosarcoma cells on the polished and sandblasted substrates demonstrated high cell viability after 10 days and good cell adhesion to the surface. Full article

The paper presents the results of fatigue-testing ultrafine-grained and coarse-grained Ti-45 wt.% Nb alloy samples under very high cycle fatigue (gigacycle regime), with the stress ratio R = −1. The ultrafine-grained (UFG) structure in the investigated alloy was formed by the two-stage SPD method, which included multidirectional forging (abc–forging) and multipass rolling in grooved rollers, with further recrystallization annealing. The UFG structure of the Ti-45 wt.% Nb alloy samples increased the fatigue limit under the high-cycle fatigue conditions up to 1.5 times compared with that of the coarse-grained (CG) samples. The infrared thermography method was applied to investigate the evolution of temperature fields in the samples under cyclic loading. Based on numerical morphology analysis, the scale invariance (the Hurst exponent) and qualitative differences for UFG and CG structures were determined. The latter resulted from the initiation and propagation of fatigue cracks in both ultra-fine grained and coarse-grained alloy samples under very high-cycle fatigue loading. Full article

In this paper, in order to improve the microstructure uniformity of an ultra-high strength martensitic steel with a strength greater than 2500 Mpa developed by multi-directional forging in the laboratory, a single-pass hot compression experiment with the strain rate of 0.01 to 1 s⁻¹ and a temperature of 800 to 1150 °C was conducted. Based on the experimental data, the material parameters were determined, the constitutive model considering the influence of work hardening, the recrystallization softening on the dislocation density, and the recrystallized grain size model were established. After introducing the model into the finite element software DEFORM-3D, the thermal compression experiment was simulated, and the results were consistent with the experimental results. The rule for obtaining forging stock with a uniform and refinement microstructure was acquired by comparing the simulation and the experimental results, which are helpful to formulate an appropriate forging process. Full article

In order to not only produce an open-die forged part with the desired final geometry but to also maintain economic production, precise process planning is necessary. However, due to the incremental forming of the billet, often with several hundred strokes, the process design is arbitrarily complicated and, even today, often only based on experience or simple mathematical models describing the geometry development. Hence, in this paper, fast process models were merged with a double deep Q-learning algorithm to enable a pass schedule design including multi-objective optimization. The presented implementation of a double deep Q-learning algorithm was successfully trained on an industrial-scale forging process and converged stably against high reward values. The generated pass schedules reliably produced the desired final ingot geometry, utilized the available press force well without exceeding plant limits, and, at the same time, minimized the number of passes. Finally, a forging experiment was performed at the institute of metal forming to validate the generated results. Overall, a proof of concept for the pass schedule design in open-die forging via double deep Q-learning was achieved which opens various starting points for future work. Full article

The Mg–Gd–Y–Zn–Zr alloy containing a long period stacking ordered (LPSO) phase was subjected to multi-pass deformation by means of a multi-directional forging process, and the microstructure evolution and the influence of the LPSO phase on its dynamic recrystallization (DRX) were studied. The results showed that multi-directional forging can effectively refine the grain with the DRX fraction increased, and DRXed grains lead to the decrease of the texture intensity, which can significantly improve the mechanical properties of the alloy. The different morphologies of the LPSO phase have different degrees of promotion relative to DRX behavior. The lamellar LPSO phase with kinks promoted dislocation plugging, where there could be a potential nucleation site for DRX grains. The fragmented lamellar LPSO phase promoted the DRX process through the particle-stimulated nucleation mechanism, and the block-shaped phase was more prone to stress concentration, which promoted DRX. These effects resulted in continuous grain refinement and a more uniform microstructure. Full article

The current work systematically investigated the microstructure, texture evolution, and mechanical properties of MDFed Mg-13Gd-4Y-2Zn-0.5Zr (wt%) alloy (GWZ) on the condition of high and low temperature cycle deformation. The high and low temperature cycle deformation was proposed on the basis of the conventional multi-directional forging (MDF) at decreasing temperature and annealing treatment. As a new method, it was aimed to timely uniform the microstructure and strengthen magnesium (Mg) matrix during the deformation process. A low accumulative strain of 3 after 1 pass resulted in a bimodal microstructure with undynamic recrystallized (unDRXed) regions and dynamic recrystallized (DRXed) grains, while a high accumulative strain of 12 after 4 passes lead to a homogeneous microstructure with fine DRXed grains. According to the experimental results, it indicated that the average grain size of 63 μm after homogenization treatment at 520 was refined remarkably to 5.20 μm after 4 passes at 420 °C through high and low temperature cycle deformation. The area fraction of DRXed grains was increased to 98.4%, which can be regarded as achieving complete DRX after 4 passes. The grain refinement was mainly caused by particle stimulation nucleation (PSN) and mechanism. As the MDF passes and accumulative strain increased, the basal texture was weakened and transformed from a strong basal texture to a random distribution gradually. Compared with conventional MDF at decreasing temperature, the mechanical properties were enhanced effectively. After 4 passes, the ultimate tensile strength (UTS), tensile yield strength (TYS), and failure elongation (FE) were 405 MPa, 305 MPa, and 13.1%, respectively. Full article

In the present study, a new complex methodology for the analysis the closure of voids and a new forging system were developed and tested. The efficiency of the forging parameters and the effective geometric shapes of anvils to improve void closure were determined. A new cogging process provided a complete closure of an ingot’s axial defects, as confirmed by experimental tests. The evolution behavior of these defects with different sizes was investigated during the hot cogging process by means of the professional plastic forming software Deform-3D. A comprehensive procedure was developed using the finite-element method (FEM) for the three-dimensional cogging process and laboratory experimentation to predict the degree of void closure. The hot multi-pass cogging process was used to eliminate void defects in the forgings so as to obtain sound products. In the compression process, the effects of the reduction ratio and forging ratio, the void size, and the types of anvil were discussed to obtain the effective elimination of a void. For the purpose of the assessment of the effectiveness of the void closure process, the following indices were introduced: the relative void volume evolution ratio, the relative void diameter ratio, and the internal void closure evaluation index. Moreover, the void closure process was assessed on the basis of stress triaxiality, hydrostatic stress, forging ratio, value of local effective strain around the void, and critical reduction ratio. The results of this research were complemented by experiments predicting the formation of fractures in the regions near the void and in the volume of the forging in the course of the cogging process. The comparison between the predicted and the experimental results showed a good agreement. Full article