Multi-directional Forging Research Articles

Effect of inter-pass annealing on the deformation microstructure of Ti-48Al-2Cr-2Nb alloy

TiAl alloy is a potential candidate structural material for lightweight and high temperature in aerospace, and multi-pass thermo-mechanical treatment, where dynamic recrystallization (DRX), static recrystallization (SRX), and post-dynamic recrystallization (PDRX) have significant effects on microstructure evolution, is commonly applied for microstructure control due to its poor plasticity. Accordingly, the complex recrystallization behaviors of Ti-48Al-2Cr-2Nb alloy were investigated by hot simulation compression experiments. The results of metallographic statistics showed that microstructure inhomogeneity of uniaxial compression could not be improved by changing the temperature and strain rate to adjust the DRX degree. Additionally, discontinuous dynamic recrystallization (DDRX) characterized by the formation of twining boundaries was a dominant DRX mechanism and generated at grain boundaries. Meanwhile, continuous dynamic recrystallization (CDRX) was formed within the grains and at grain boundaries, accompanied by the relatively high distortion at the initial stage. Residual deformed microstructure owing to the incomplete DRX could be eliminated by SRX and PDRX during the inter-pass annealing. A method based on the grain size difference induced by various recrystallization mechanisms was proposed to reveal that grain growth resulting from PDRX played a primary role and SRX was impaired with the increasing strain. The interaction effect of DRX, SRX, and PDRX during the multi-pass deformation could achieve the uniform microstructure, which is consistent with a near-isothermal multi-pass multidirectional canned forging process designed in the paper. Eventually, room-temperature tensile tests demonstrated that the mechanical properties of wrought billet were distinctly enhanced.

Dynamic recrystallization behavior and strengthening mechanism of Mg–Gd–Y–Zn–Zr alloy during isothermal MDF process

As one of severe plastic deformation (SPD) methods, multi-directional forging (MDF) technology is an effective way to refine grains. The microstructure, texture evolution and mechanical properties of homogenized Mg–13Gd–4Y–2Zn–0.5Zr (wt. %) alloy during isothermal MDF process were synthetically investigated in the paper. The results showed that the mean grain size of the alloy decreased gradually with the MDF passes increased. After 4 passes, the average grain size of the alloy was refined to 2.7 μm, and the microstructure distribution was uniform. On the one hand, with the increasing of the MDF passes, the massive intergranular LPSO phases are gradually broken up and formed a deformation zone. The plate-like Mg5(Gd,Y) precipitates were located interior the grains. On the other hand, the spherical Mg5(Gd,Y) phases were randomly distributed with the increasing of MDF passes. In addition, the maximum texture intensity of the MDFed alloy on (0001) basal plane gradually was weaken from 15.993 of the 1MDFed alloy to 4.245 of the 4MDFed alloy, which was attributed to the increasing of volume fraction of dynamic recrystallized (DRXed) grains via MDF method. And the dynamic recrystallization (DRX) mechanisms were continuous DRX (CDRX), discontinuous DRX (DDRX), particle stimulated nucleation (PSN) and kink induced DRX. The maximum ultimate tensile strength (UTS) and tensile yield strength (TYS) after 4 passes were 385 MPa and 360 MPa respectively. The excellent mechanical properties of the alloy were owing to the grain boundary strengthening, dislocation strengthening, texture strengthening and precipitation strengthening. In addition, the second phase particles such as lamellar LPSO phases, broken block-shaped LPSO phases, spherical Mg5(Gd,Y) phases and plate-like Mg5(Gd,Y) phases were demonstrated to be the strengthening phases.

Microstructure evolution and grain refinement mechanism of fine-grained Mg-Gd-Y-Zn-Zr alloy during multi-directional forging

Fine-grained Mg-8.59Gd-3.85Y-1.14Zn-0.49Zr alloy was subjected to multi-directional forging (MDF). The corresponding grain refinement mechanism was analyzed by observing the microstructure before and after MDF, and the evolution mechanism of various phases and texture states was discussed. The results showed that the 9 passes MDF with deformation temperature of 350 ℃ and strain rates of 0.01 s−1 and 0.1 s−1 can further refine the grain structure. The average grain size decreases to 2.95 µm at the strain rate of 0.1 s−1. The refinement of the grain structure is dominated by dynamic recrystallization (DRX), while the β phase maintains the refinement results through the pinning effect. The main refinement mechanism of the original equiaxed grains is discontinuous dynamic recrystallization (DDRX), and the growth of the original equiaxed grains and new grains is hindered by the β phases. The dissolution of lamellar structures and continuous dynamic recrystallization (CDRX) at the deflected lamellar long-period stacking ordered (LPSO) lead to the fracture and refinement of large-sized deformed grains, while the β phases precipitated precede CDRX can hinder the growth of new grains. The effect of the deformation temperature on the grain refinement is more notable than that of the strain rate owing to the significant difference in the number of β phases at different temperatures. Because of the low nucleation rate and high dissolution rate associated with the high temperature sensitivity, the number of β phases is low at 400 ℃ and can not effectively maintain the refinement results. The random orientation of DRX grains and change in the load direction of each pass promote the weakening of the basal texture, making the MDFed microstructure exhibits multitextured components.

Effects of Multi-Directional Forging on the Microstructure and Mechanical Properties of an AZ80/SiC Nanocomposite

Effects of Multi-Directional Forging on the Microstructure and Mechanical Properties of an AZ80/SiC Nanocomposite

Effects of deformation twins on microstructure evolution, mechanical properties and corrosion behaviors in magnesium alloys - A review

Due to lattice reorientation, grain segmentation, induced recrystallization, twins play a very important role in regulating texture, refining grains, improving mechanical properties and corrosion resistance, and has received more extensive attention. Numerous studies have shown that {10-12}<10-11> tensile twins (TTWs) are easily activated in large quantities due to the lower critical resolve shear stresses (CRSS). Introduction of TTWs under uniaxial compression improved the strength, ductility, and formability of magnesium (Mg) alloys. Moreover, TTWs produced by multi-directional impact forging (MDIF) can optimize the microstructure by dividing grains and promoting recrystallization, resulting in significant improvement of mechanical properties. Although {10-11}<10-12> compressive twins (CTWs) and {10-11}-{10-12} double twins (DTWs) can promote dynamic recrystallization (DRX), they are also favorable nucleation sites for cracks. In addition, the type and volume fraction of twins can affect the corrosion resistance, and they also play different roles in the corrosion process of different Mg alloys. Twins have shown great potential for improving structure and properties, but a comprehensive and critical discussion of twins in Mg alloys is still lacking. Therefore, based on previous studies, this article reviews the common types and variants of twins in Mg alloys, influencing factors, and their effects on the microstructure, mechanical properties and corrosion resistance. In addition, some interesting ideas are being proposed for further research.

Research on multi-cylinder synchronous control system of multi-directional forging hydraulic press

A master-slave synchronization control strategy based on RBF network adaptive sliding mode control is proposed to solve the problem of lack of effective control strategy and control accuracy in the process of synchronous motion of three horizontal cylinders of multi-directional die forging hydraulic press in VL ball cage forming process. According to the high-order nonlinear mathematical model of the single-cylinder electro-hydraulic servo system, the RBF network adaptive sliding mode controller is designed. The joint simulation model is established by using AMEsim and MATLAB to solve the tracking accuracy and synchronous control accuracy of the system, and the control effect is verified by comparing with the conventional PID control. The simulation results show that the RBF network adaptive sliding mode controller has strong robustness, and the three horizontal cylinder displacement synchronization controllers of the multi-directional die forging press designed in this paper have good synchronization performance.

Combination of severe plastic deformation and heat treatment for enhancing the corrosion resistance of a new Magnesium alloy

In the present study, various processes have been carried out on the extruded Mg-4Zn-4Al-0.6Ca-0.5Mn (wt%) alloy to achieve a low corrosion rate Magnesium (Mg) alloy. Microstructure studies revealed that the extruded alloy contained the needle-like Al-Mn second phases and the globular and elongated (Mg,Al)2Ca + ϕ(AlMgZn) phases. After solution treatment, the area fraction of the second phase decreased drastically from 5.1 % to 2.4 %. The later multi-directional forging (MDF) formed a modified ultrafine grain structure with an average grain size of 0.9 µm. The post-annealing process reduced the dislocation density of the heavily-deformed grains of the MDFed alloy, resulting in a grain size of 5.89 µm and an area fraction of 2.8 %. The annihilation of dislocations and homogeneous distribution of broken second phase particles after MDF and post-annealing processes improved the ultimate compressive strength and compressive strain from 352 MPa and 4.2 % for the extruded to 376 MPa and 5.1 % for the post-annealed alloy. Moreover, by applying solution treatment, MDF, and post-annealing, the corrosion rate of the extruded alloy drastically decreased from 2.13 mm/y to 0.76 mm/y due to grain refinement and reduced area fraction of phases and their random distribution. According to the corrosion results, the area fraction of second phase particles and the grain size obtained after different processes significantly influenced the corrosion properties, which was discussed in detail in the present study. On the one hand, the post-annealed alloy contained a significantly lower area fraction of particles than the extruded alloy, reducing micro-galvanic corrosion. On the other hand, significant grain refinement after the MDF process lowered the corrosion rate compared to the extruded alloy. However, the short-time annealing process annihilated the dislocations and high-energy sites while not significantly increasing the grain size and deteriorating the mechanical properties. Therefore, the combination of MDF and short-time annealing could be a remarkable route to obtaining the low corrosion rate and high strength Mg alloy.

Improved corrosion resistance and mechanical properties of biodegradable Mg–4Zn–xSr alloys: effects of heat treatment, Sr additions, and multi-directional forging

The effects of Sr additions, heat treatment (T4 and T6), and multi-directional forging on the microstructural evolution, mechanical properties and biodegradability of Mg–4Zn–xSr alloys were investigated. Corrosion behavior of the alloys was evaluated by the polarization and hydrogen evolution tests. Shear punch and hardness tests were employed to determine the mechanical properties. It was found that mechanical properties and corrosion resistance of the as-cast Mg–4Zn alloy increased by 0.3 wt% Sr addition. However, further increasing the Sr content not only did not improve the mechanical strength, but also had detrimental effects on the corrosion resistance, due to the increased size and volume fraction of the intermetallic particles. While T4 heat treatment decreased the corrosion current density of Mg–4Zn–0.3Sr alloy from 2.58 to 2.1 μA/cm2, it resulted in some mechanical softening. On the other hand, T6 heat treatment significantly improved mechanical strength of the Mg–4Zn–0.3Sr alloy by about 10 MPa, while its effect on corrosion resistance was minor. Multi-directionally forged Mg–4Zn–0.3Sr alloy also demonstrated improved mechanical and corrosion properties compared to the as-cast condition, which was mainly attributed to the smaller grain size as well as better distribution of the secondary phases.

On the microstructure evolution and controlling of a 2 vol% TiCp/β-Ti composite during hot deformation

In this study, microstructure and texture evolution of TiC p /β-Ti composites during hot deformation were investigated. The results indicated that high deformation temperature and low strain rate are beneficial to promote dynamic recrystallization (DRX). Besides, the DRX mechanism is dominated by continuous dynamic recrystallization and discontinuous dynamic recrystallization during hot compression. During hot compression, the 〈101〉-oriented grains will rotate to the 〈111〉 orientation with the highest Taylor factor, the <111>-oriented grains will change to the 〈001〉 orientation with the lowest Taylor factor, and the <001>-oriented grains tend to rotate to the <101> orientation with higher Taylor factor under relatively long deformation time. Moreover, the lower strain rate is conducive to the formation of θ-fiber and γ-fiber and reduces the texture strength. In addition, compared with hot compression, multi-directional forging (MDF) can significantly refine the grains without producing texture. And TiC p plays a role in particle-stimulated nucleation during hot deformation • The microstructure evolution and the dynamic recrystallization mechanism during hot compression were investigated. • The transformation of grain orientation and effect of strain rate on texture evolution during deformation were revealed. • Compared with hot compression, multi-directional forging can significantly refine the grains without producing texture. • TiC p play a role in particle-stimulated nucleation during hot deformation.

Experimental study and numerical simulation of α lamellar globularization for TC21 titanium alloy during multidirectional forging

Evolution of microstructure and the globularization mechanism of α lamellar for TC21 titanium alloy during multi-directional forging (MDF) were analyzed with the help of OM, SEM, EDS and TEM techniques, FE simulation was also used to observe the above process. The main conclusions are as follows: With the increase of temperature, forging cycle and single pass strain, the fraction of globularization of α lamellar gradually improved. The volume fraction of globularization of α lamellar achieves a high value about 85%, the average grain size of TC21 titanium alloy can be refined to 2 μm through MDFed at 910 °C with strain of 0.69 in 3 cycles. Forging cycle is the most key factor to obtain the ideal microstructure. Increasing temperature and MDFed pass can not only promote the fraction of DRX (dynamic recrystallization), but also achieve uniformity of deformation. The error between simulation and experiment is below 14%. DRX is the major globularization mechanism of the α lamellar during MDF. In the early stage of MDF process, the globularization mechanism is boundary splitting accompanied by CDRX (continuous dynamic recrystallization) and DDRX (discontinuous dynamic recrystallization), which is formed by the β phase into α lamella along the sub-grain boundaries. In the later stage of the process, the globularization mechanism is termination migration, which is caused by elements diffusion due to variant curvature of different position of α lamellar, while a slow process for globularization.

Prediction of microstructure evolution during multidirectional forging of the railway wagon bogie adpter

The railway wagon bogie adapter is a critical component in train operation, with stringent quality requirements. Microstructure uniformity is an effective method for improving adapter quality. A three-dimensional thermodynamic coupling model of the railway wagon bogie adapter hot forging was established by Deform-3D, and the evolution of the grain size of the forging during the hot forging was predicted. In conjunction with orthogonal tests, the effect of process parameter interaction on adapter uniformity was investigated. The adapter had uniform microstructure distribution when the forging temperature was 1100 °C, the die forging speed was 27.5 mm/s, and the friction coefficient was 0.21. The hot forging test of the adapter was performed using the optimized parameters, and the forging was sampled at different positions for metallographic experiments, which measured the grain size of the forging at different positions in agreement with the simulation results and verified the simulation's accuracy.

On the solution treatment of severely deformed AA2024-O and subsequent natural aging

In this research, the effect of applying severe strain before solid solution treatment (SST) for AA2024-O was studied. Providing concurrent insights into solutionizing behavior and microstructural evolution corresponding to hardness is important. Multi-directional forging (MDF) was used as a severe plastic deformation (SPD) method. After applying SST on MDFed (4 passes) and as-annealed samples, natural aging (NA) was used as the following treatment to examine the role of severe strain on the solutionizing behavior. In most previous attempts, SPD has been used after SST, but one of the innovations of the present work is the study of SPD before SST. Experimental results show that adding a severe strain using the MDF method before SST results in a significant refinement in the grain size of the solutionized recrystallized microstructure (47 μm). In contrast, coarse-grained microstructures with grain sizes of 150 μm–300 μm are used in prior tries. The results indicate that continuous static recrystallization (CSRX) with a grain size of 47 μm occurs during the solution treatment of the MDFed sample, which is 220% less than that during solution treatment of the as-annealed sample (150 μm); also, rich presence of the second phase particles after its aging by FE-SEM was analyzed. By measuring the difference in hardness before and after NA in solution-treated MDFed and as-annealed samples, 500 °C and 5 min were found to be the most desirable temperature and times in terms of mechanical properties and microstructure. While, in previous efforts, no suitable time has been found for solution treatment of this alloy, and times of 2 h–24 h have been used. The present work found a suitable time of 5 min for solution treatment, which has significant energy savings. In the solution-treated MDFed sample, the maximum hardness of NA (100 HV) was reported; additionally, the percentage of increase in hardness before and after NA (ΔH %) for solution-treated MDFed and as-annealed samples were obtained at 43% and 23%, respectively. Using the DSC test, it was found that in the solution-treated MDFed sample, the peak of S′/S (Al2CuMg) phase formation spreads and shifts from 262 °C to a lower temperature of 235 °C. Using Johnson-Mehl-Avrami (JMA) equations, the values of 103 kJ/mol and 108 kJ/mol were obtained for the activation energy of solution-treated MDFed and as-annealed samples, respectively. Lower activation energy means utilizing Severe Plastic Deformation (SPD) before SST generates a high density of dislocations and vacancies that accelerate solute atoms dissolution and provide S′/S -phase nucleation sites.

Microstructural Evolution in Large-Section Plastic Mould Steel during Multi-Directional Forging

To obtain excellent mechanical properties from large cross-sections of plastic mould steel (SDP1), we conducted multi-directional forging (MDF) to control the microstructure of ingots. To investigate the microstructural evolution of SDP1 steel during MDF, we performed hot forging at 1150 °C using a THP01–500A hydraulic press. The dimensions of the specimens were Φ38 mm × 80 mm. The microstructure of the specimens after forging was observed under a metallographic microscope. Furthermore, the results of the finite element method (FEM) simulations were employed to improve the quality of the forgings. The predicted results agreed well with the experimental ones, indicating that FEM is effective for analysing microstructural evolution during MDF. Thus, MDF for large cross-sections of SDP1 steel (Φ1000 mm × 2200 mm) was simulated. The results showed that the average grain size of SDP1 steel at the core of an ingot after MDF ranged from 40.6 to 43.3 μm. Although this was slightly higher than the grain size of the sample after traditional upsetting and stretching forging (TUSF) (35.7–46.0 μm), the microstructure of the SDP1 steel sample after MDF was more uniform than that after TUSF. Compared with TUSF, MDF not only refines the grain size but also improves the microstructure uniformity of the sample.

Development of Ultrafine–Grained and Nanostructured Bioinert Alloys Based on Titanium, Zirconium and Niobium and Their Microstructure, Mechanical and Biological Properties

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.

Microstructure, texture and mechanical properties of extruded AZ31 Mg alloy during small strain multi-directional forging with gradient cooling

A new small strain multi-directional forging (MDF) with gradient cooling was proposed to tailor the microstructure and improve the mechanical properties of Mg alloys. Using MDF with a cumulative strain of 2.7, a uniform fine-grained microstructure with an uncommon bimodal basal texture was achieved. Influenced by the Schmid factor, the twins in the< 10–10 > type grains rotated the basal poles toward the last forging direction (LFD), whereas the twins in the< 11–20 > type grains refined the microstructure. The dominant refinement mechanisms at high temperatures were twinning segmentation (TS) and discontinuous dynamic recrystallization (DDRX). It gradually became continuous dynamic recrystallization (CDRX) as the temperature was lowered. Twinning-induced recrystallization (TDRX) also occurred at 200 ℃. The plastic deformation and DRX mechanism affected the texture evolution of the grains. With a cumulative strain of less than 0.3, {10–12} twinning was dominant and responsible for the formation of the< 0001 > //LFD texture. As the cumulative strain increased to 0.9, multiple slips began to dominate the deformation, and a relatively stable< 10–12 > –< 11–24 > //LFD bimodal basal texture was formed. In contrast, the DRXs had little effect on texture types. The yield strengths were affected by the grain sizes and textures during MDF. The fluctuations of strength in the initial stage were mainly attributed to the texture change. When the texture was stabilized, the increases in strength were owing to grain refinement. The yield strengths can be accurately estimated by an improved Hall-Petch relation that includes the texture effect. • A newly small strain multi-directional forging with gradual cooling was proposed. • Fine-grained microstructure achieved undergoing sequential TS, DDRX, CDRX and TDRX. • Uncommon bimodal basal texture attributed to multiple slips activated by the MDF path. • Yield strengths and the anisotropy well estimated by an improved Hall-Petch relation.

Analysis of the Multi-Directional Forging of Aluminium Alloy 7075 Process Parameters: Numerical and Experimental Analysis

In this study, a multi-directional forging process was conducted on AA 7075. Analysis of the evolution of the mechanical properties (tensile and hardness) and the microstructure was done. The effects of the process parameters (temperatures, die speed, and strain per pass) on the process outputs were investigated. The hardness of the MDF processed samples was determined using Brinell hardness tester, the tensile tests were conducted on a universal tensile machine (GT-7001-LS50), while the grains were observed using the Zeiss Axio Zoom V16 microscope and Tescan VEGA3 scanning electron microscope. It was observed that the MDF process leads to grain refinement with increase temperature and strain per pass. However, large strains per pass caused damages to the samples. The hardness and the tensile strength were seen to generally improve with an increase in strain per pass.

Multi-scale analysis of void evolution in large-section plastic mold steel during multi-directional forging

Multi-scale analysis of void evolution in large-section plastic mold steel during multi-directional forging

Application of multi-directionally forged high-strength titanium to dental implants in beagle dogs.

Pure titanium is widely used as a material in dental implants. However, it possesses inferior mechanical strength. This study aimed to elucidate the efficacy of acid treated multi-directionally forged (MDF) pure titanium in vivo. We verified the temporal changes until osseointegration in beagle dogs. Using two types of experimental materials (conventional pure titanium or MDF pure titanium), new bone formation was assessed using morphological examinations, and the bone-to-implant contact (BIC) value was evaluated at each time point (14, 30, and 90 days after the operation). As such, new bone formation was observed around the acid-etched MDF group, in which the BIC value was highest, followed by that in the acid-etched pure titanium group. MDF pure titanium implants showed early promotion of new bone formation compared to conventional titanium implants. The new acid-treated MDF made of pure titanium could be applied to humans in the future to prove its practicality.

Thermal stability of Copper processed by Multidirectional forging: Effect of deformation amplitude and cumulative Strain

Experiments were performed in order to evaluate the effect of deformation amplitude (Δε) and cumulative strain (ε) on the thermal stability of Copper 99.8% pure, after processing with 8 and 48 Multidirectional forging (MDF) cycles at room temperature with Δε ≈ 0.075 (MDF0.075) or 2 and 12 MDF cycles with Δε ≈ 0.30 (MDF0.30), leading to cumulative deformations of ε ≈ 1.8 and 10.8. The microstructural stability at elevated temperatures was evaluated through Differential Scanning Calorimetry (DSC) and heat treatments, combined with Vickers microhardness measurements and Electron Backscattered Diffraction (EBSD). Further analyses were carried out through thermodynamic considerations about the stored energy and driving pressures for boundary migration. The results showed that the thermal stability associated with static recrystallization decreases as ε and Δε in MDF increase, due to the presence of finer grain structures and higher dislocation density in the as-deformed material. In addition, the MDF-processed specimens deformed with high ε and Δε exhibited finer recrystallized grains than those processed with low ε and Δε as a result of their increased number of nucleation sites. Thermal stability increases in the following order: 12C-MDF0.30, 2C-MDF0.30, 48C-MDF0.075 and 8C-MDF0.075.

Grain refinement during isothermal multidirectional forging due to β-phase heterogenization in Al-Mg-based alloys

Multidirectional forging (MDF) is an effective severe plastic deformation method that provides grain refinement and improves the mechanical strength of metallic materials. In this study, the microstructural homogeneity was improved in the MDF-treated Al-Mg alloy due to coarse particles of the β(Al3Mg2)-phase precipitated during intermediate heterogenization annealing. The β-phase stimulated recrystallization due to a particle stimulated nucleation mechanism, improved the grain refinement effect during MDF that increased the yield strength of the alloy.