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Due to its high mechanical properties and low quench sensitivity, 7085 aluminum alloy is suitable for the aircraft industry. However, large cross-section forgings of 7085 alloy usually have over 40% anisotropy in mechanical behaviors, especially in the vertical direction. In this study, two-stage multi-directional forgings (MDFs) with different temperature combinations, isothermal medium-temperature composite MDF (MC-MDF) and isothermal hot MDF (H-MDF), were applied to 7085 aluminum alloy ingots. The results indicate that MC-MDF achieved anisotropy below 10% without losing ultimate tensile strength (UTS). Three-dimensional (3D) microstructure analysis suggested that the MC-MDF samples accumulated higher dislocation density and exhibited an enhanced recrystallization structure. The elongation of the vertical direction increased significantly, which lowered the directionality of MC-MDF and increased the effective utilization rate of forgings. Also, MC-MDF obtained a lower yield strength (YS) due to the forging temperature in exchange for higher work hardening and a ductility increase. The average 3D UTS, YS, and EL values of MC-MDF are 554 MPa, 472 MPa, and 13.4%, and the index value reflecting the anisotropy of EL decreased from 14.0% to 8.6% for H-MDF. [ABSTRACT FROM AUTHOR] more...

In this study, a commercial hot-extruded AZ80Mg alloy was multi-directionally forged (MDFed) at room temperature by employing pass strains of Δε = 0.1. The effects of the combined processes of MDFing and ageing on the microstructural evolution and strengthening were precisely examined in advance. The coarse initial grains were gradually subdivided into ultrafine grains by multiple mechanical twinning and kinking. As observed, the multiple twinning effectively suppressed the evolution of the sharp basal texture and enabled MDFing at room temperature to high cumulative strains. Although the combined processes of MDFing and ageing tended to increase the hardness and yield stress compared to those fabricated using simple MDFing at lower cumulative strain regions, the mechanical properties were almost comparable and independent of the processes at regions of higher cumulative strain beyond ΣΔε = 2.0. Yield strength over 505 MPa, ultimate tensile strength of over 612 MPa and ductility of over 7% were constantly achieved in all the processes. Although certain selected processes were applied to bulk samples for fabricating the mechanical components, frequent cracking hindered the MDFing to high cumulative strain regions. This finding signified that adequate MDFing process is dependent on sample size. However, MDFing with smaller pass strains than Δε = 0.1 enabled MDFing to regions of high cumulative strain. Thus, bulk AZ80Mg alloy with well-balanced mechanical properties--yield strength of 420 MPa, ultimate tensile strength of 540 MPa, and ductility of 10%--could be successfully fabricated. [ABSTRACT FROM AUTHOR] more...

Magnesium (Mg) and its alloys are currently the lightest structural metals in engineering applications, widely used in aerospace, defense technology, transportation and electronic 3C fields. Plastic deformation is a commonly used method to improve the comprehensive mechanical properties of Mg alloys. Multi-directional forging (MDF), as a severe plastic deformation (SPD) method, is considered as an effective technology for manufacturing large-sized Mg alloys with high strength and toughness. This paper outlines the process principle of MDF and analyzes the microstructure evolution, texture and mechanical properties of Mg alloys processed by MDF. The effect of deformation parameters, such as deformation temperature, accumulative strain and strain rate, and alloying elements on grain refinement, second phase evolution and texture are discussed systematically. Additionally, recent research highlights the Mg alloys with high strength and toughness processed by MDF. Furthermore, the contribution of grain refinement, precipitation, solid solution and texture-strengthening mechanisms on the mechanical properties are revealed. Finally, we conclude the research progress, analyze the shortcomings in development, and recommend further prospects. We hope this review will inspire new ideas on the development of Mg alloys with a high strength and MDF process. [ABSTRACT FROM AUTHOR] more...

Multi-pass multi-directional forging (MDF) was applied to enhance tribological properties of Zn–4Si alloy. According to the results, MDF effectively refined coarse irregular-shaped primary Si particles (PSPs) and encouraged their uniform distribution within the matrix. MDF also modified the microstructure by forging porosities and eliminating entrained bifilm oxides. The average size of PSPs and volume percentage of porosities decreased from 38.7 ± 11.5 μm and 0.82 ± 0.17% in the as-cast sample to 6.8 ± 3.1 μm and 0.19 ± 0.05% in the 8-pass MDFed sample, respectively. The maximum hardness was obtained in a 4-pass MDFed sample where its hardness was increased from 37.8 ± 3.2 in as-cast state to 52.7 ± 1.1 HB. The 4-pass MDFed sample also showed the maximum wear resistance where at applied pressures of 0.25, 0.5, and 0.75 MPa, its wear rate was lower than that of the as-cast sample by 83, 76, and 72%, respectively. MDFed samples also exhibited improved friction properties. At the applied pressures of 0.25, 0.5, and 0.75 MPa, the friction coefficient of the 4-pass MDFed alloy was lower than that of the as-cast alloy by 38%, 29% and 20%, respectively. [ABSTRACT FROM AUTHOR] more...

Based on the thermal compression stress-strain curves and three-dimensional processing maps of the homogenized Mg-8.5Gd-2.5Y-1.5Zn-0.5Zr (wt%) alloy in our previous published work, we performed a comprehensive investigation to assess the influence of multi-directional forging parameter (i.e. per-pass reduction, pass number and temperature) on the strain uniformity of large-scale forged part by finite element simulation. The results indicate that compared to forging temperature and pass reduction, the pass number of deformation significantly influences the strain uniformity. The optimal forging parameters for a large-scale ingot with 430 mm in diameter and 440 mm in height were obtained, i.e., the forging temperature of 450 °C, pass reduction of 40%, pass number of 5 and forging speed of 10 mm/s. Finally, a large-scale forged part with the diameter of 900 mm and the height of 100 mm was successfully produced under the optimal forming condition. The average grain sizes of edge and center regions of the forged part are (4.08 ± 3.25) µm and (5.58 ± 2.19) µm, respectively, exhibiting a small microstructure difference. The properties are relatively uniform, with the tensile strength differences at each position being less than 20 MPa. [ABSTRACT FROM AUTHOR] more...

SiCp/2024Al composite was prepared by semi-solid stirring casting, and the distribution of SiCp was regulated by multi-step deformation of hot extrusion and multi-direction forging (MDF). The effects of SiCp distribution on the microstructure and properties of SiCp/2024Al composite ware studied. The results show that hot extrusion deformation cause SiCp to distribute along the extrusion direction (ED). After multi-directional forging, SiCp distribution is improved significantly, and it changes from directional distribution to uniform distribution. After 1MDF, the SiCp distribution along the ED changes to disordered distribution, and the mechanical properties of the material are sharply decreased. After 3MDF, the distribution uniformity of SiCp is improved, and the mechanical properties of the material are greatly improved. When the forging passes increase to 6, the distribution uniformity of SiCp is further improved, the mechanical properties of the material decrease with the partial SiCp breaking. When the forging number is 3, the mechanical properties of the composite are optimal, with yield strength, ultimate tensile strength and elongation are 264 MPa, 387 MPa and 7%, respectively. Compared with the directionally distributed composite, the uniform distribution of SiCp effectively relieves the local stress concentration, and the matrix alloy stores more dislocation. In addition, when the distribution uniformity of SiCp is improved, the Al2Cu phase is also refined. The diffuse distribution of Al2Cu phase hinders the slip of dislocation, resulting in a uniformly distributed composite with a higher work hardening rate and internal stress. In order to study the effect of SiCp distribution on softening behavior of composites, cyclic stress relaxation experiments are carried out. In the process of stress cycling, the uniformly distributed SiCp/2024Al composites with uniform distribution of SiCp and Al2Cu phases exhibit a better stress relaxation resistance. more...

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In this paper, the hot deformation behavior of Ti65 alloy was investigated over the temperature range of 930–1110 °C with the strain rate of 0.001–1 s−1. According to the stress-strain curves, the constitutive equation was developed to describe the flow behavior of Ti65 alloy. The processing maps were constructed based on the dynastic materials model (DMM) and the perfect formability zone of Ti65 alloy is found under the temperature of 970–1020 °C and the strain rate of 0.001–0.1 s−1. In addition, a three-dimensional nonlinear transient thermo-mechanically coupled finite element model of the multi-dimensional forging (MDF) process of Ti65 alloy was developed. The effects of the forging temperature and forging speed, on the temperature rise, residual stress, and grain refinement were predicted. By analyzing the temperature and stress distribution, the optimum forging temperature and speed for Ti65 alloys were determined to be 1000 °C and 10 mm/s, respectively. Increasing the forging temperature or reducing the forging speed reduces the temperature rise and the maximum tensile stress, thus reducing the risk of cracking. Additionally, the equivalent strain increases as forging speed decreases. Simultaneously, the accumulated strain is more significant for the inside of the forgings. The results of this research are instructive for the optimization of the MDF process. more...

Magnesium (Mg) and its alloys are currently the lightest structural metals in engineering applications, widely used in aerospace, defense technology, transportation and electronic 3C fields. Plastic deformation is a commonly used method to improve the comprehensive mechanical properties of Mg alloys. Multi-directional forging (MDF), as a severe plastic deformation (SPD) method, is considered as an effective technology for manufacturing large-sized Mg alloys with high strength and toughness. This paper outlines the process principle of MDF and analyzes the microstructure evolution, texture and mechanical properties of Mg alloys processed by MDF. The effect of deformation parameters, such as deformation temperature, accumulative strain and strain rate, and alloying elements on grain refinement, second phase evolution and texture are discussed systematically. Additionally, recent research highlights the Mg alloys with high strength and toughness processed by MDF. Furthermore, the contribution of grain refinement, precipitation, solid solution and texture-strengthening mechanisms on the mechanical properties are revealed. Finally, we conclude the research progress, analyze the shortcomings in development, and recommend further prospects. We hope this review will inspire new ideas on the development of Mg alloys with a high strength and MDF process. more...

In this study, a commercial hot-extruded AZ80Mg alloy was multi-directionally forged (MDFed) at room temperature by employing pass strains of Δε = 0.1. The effects of the combined processes of MDFing and ageing on the microstructural evolution and strengthening were precisely examined in advance. The coarse initial grains were gradually subdivided into ultrafine grains by multiple mechanical twinning and kinking. As observed, the multiple twinning effectively suppressed the evolution of the sharp basal texture and enabled MDFing at room temperature to high cumulative strains. Although the combined processes of MDFing and ageing tended to increase the hardness and yield stress compared to those fabricated using simple MDFing at lower cumulative strain regions, the mechanical properties were almost comparable and independent of the processes at regions of higher cumulative strain beyond ∑ Δε = 2.0. Yield strength over 505 MPa, ultimate tensile strength of over 612 MPa and ductility of over 7% were constantly achieved in all the processes. Although certain selected processes were applied to bulk samples for fabricating the mechanical components, frequent cracking hindered the MDFing to high cumulative strain regions. This finding signified that adequate MDFing process is dependent on sample size. However, MDFing with smaller pass strains than Δε = 0.1 enabled MDFing to regions of high cumulative strain. Thus, bulk AZ80Mg alloy with well-balanced mechanical properties--yield strength of 420 MPa, ultimate tensile strength of 540 MPa, and ductility of 10%--could be successfully fabricated. [ABSTRACT FROM AUTHOR] more...

Noteworthy ductility Mg-8Gd-4Y-1Nd-0.5Si (wt.%) alloy with a strong non-basal texture was developed by 12 passes of multi-directional forging (MDF) combine with extrusion. The slip trace analysis indicated that deformation mechanism after 3 passes of MDF and extrusion were basal < a > , pyramidal < a > and pyramidal < c + a > slips. The intensity of non-basal texture increased from 5.37 to 8.03 with the MDF passes increased from 3 to 12, which means grain orientation tends to be more consistent and makes the basal < a > slips easy to pass through grain boundaries to accommodate ductility. With more basal < a > slips crossing the grain boundaries, dislocation interaction in grain interior caused stress accumulation, exceeding the critical shear stress (CRSS) of slips with low schmidt factor (SF), and multiple slips appeared. The activation of slip cross grain boundary and multiple slip improved the elongation from 14.7% to 25.6% of MDFs-extruded Mg-8Gd-4Y-1Nd-0.5Si alloy. [ABSTRACT FROM AUTHOR] more...

In this study, the microstructure and mechanical properties of severely deformed Al–12Si–3Cu–0.5Mn alloy were systematically investigated. The alloy produced by permanent mold casting was homogenized and processed with multi-direction forging (MDF) up to four cycles at 200 °C. MDF gave rise to fragmentation of hard particles, formation of dispersoids, and fine grains with high angle grain boundaries. The grain size of the alloy after one-cycle MDF decreased from 27.30 μm to sub-micron levels of about 0.5 μm. After one-cycle MDF, the formed microstructure consisted of ultrafine grains (UFG) with and without intense dislocations. Lattice microstrains and dislocation densities of the alloy decreased with increasing forging cycles. In general, hardness, yield and tensile strength, elongation and impact toughness of the alloy increased after MDF. The highest hardness, yield and tensile strength of the alloy were obtained after the two-cycle MDF, while the four-cycle MDF produced the highest elongation and impact toughness values. Fracture surface of the tensile tested alloy before MDF consisted of large cleavage planes and hills. However, narrow cleavage planes and plenty of dimples occurred on the tensile fracture surface of the alloy after MDF. These findings were elucidated according to microstructural alterations as a result of fragmentation of hard particles, formation of dispersoids and fine grains, annihilation of dislocations and grain growth. [ABSTRACT FROM AUTHOR] more...

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. more...

AZ80-1.5 Vol.% SiC nanocomposite was produced by the stir-casting method. The cast specimens were annealed and subjected to multi-directional forging (MDF) for up to 8 passes at 250 °C. Shear punch test (SPT), Vickers microhardness test, and uniaxial tension test were employed to evaluate the mechanical properties of nanocomposite before and after MDF process. Microstructural studies showed that the average grain structure was refined and the grain size distribution became more uniform after all MDF passes. The most pronounced grain refinement was obtained after eighth passes of MDF, where the average grain size of the unprocessed material was reduced from 31.4 to 4.9 µm. Based on the results of shear punch test (SPT), both shear yield stress (SYS) and ultimate shear strength (USS) of the nanocomposite were significantly improved after eight passes of the MDF process. The values of SYS and USS in the unprocessed specimen were 123.7 and 158.9 MPa, respectively, which increased to 164.6 and 194.1 MPa after eight MDF passes. Processing by MDF resulted in the enhancement of microhardness, strength, and ductility of the nanocomposite. After 8 MDF passes, improvements of 22.4, 48.1, 45.2, and 8.5% were obtained for the microhardness, TYS, USS, and elongation, respectively. The mechanisms of these improvements were discussed based on the microstructural features of the material. [ABSTRACT FROM AUTHOR] more...

Cu- X CNTs composites (X = 0 , 1, 2 vol.%) were successfully prepared through a combination of pre-treatment, powder metallurgy and multi-directional forging (MDF) processes. It provided a solution for the industrial production of structural composites with reticulated CNTs. The effect of CNTs contents on wear and electrical performance of the composites was investigated. The addition of CNTs results in a significant increase in the wear resistance of the composites. During the wear process, reticulated CNTs will carry the load barrier to high temperature softening and plastic deformation of the Cu-matrix, which protects the matrix eventually. In general, the addition of CNTs will reduce the conductivity of the composites. Under MDF process, the CNTs were organically linked together and formed a network structure as the volume fraction increased from 1% to 2%, resulting in a significant promotion of conductivity by providing paths for electron transfer. The contact resistance increased slightly when 2 vol.% CNTs were added, with an average value of 5.87 m Ω. The contact resistance volatility of the Cu-2 vol.% CNTs was the most stable (variance of 1.485). Reticulated CNTs can effectively attenuate the erosive effect of molten pools and welding bridges on the anode material, and are ideal reinforcers for Cu-based electrical contact materials. After the multi-directional forging process commonly used in factories, the CNTs exhibit a network structure distribution in composites. During the wear process, reticulated CNTs will carry the load barrier to high temperature softening and plastic deformation of the matrix, which protects the substrate eventually. With network structure CNTs, the electrical contact property of the composites improved obviously. Reticulated CNTs can effectively attenuate the erosive effect of molten pools and welding bridges on the anode material, and are ideal reinforcers for Cu-based electrical contact materials. [ABSTRACT FROM AUTHOR] more...

A dual-phase high-entropy alloy Fe 50 Mn 30 Co 10 Cr 10 is treated via multi-directional forging (MDF) and subsequent annealing at 600°C–1000°C. Different microstructures with totally different grain sizes and phase ratios are obtained. The MDF increases yield strength and ultimate tensile strength at the expense of ductility. Via annealing the MDF-processed alloy at 1000°C, the full recrystallized sample yields a excellent combination of high strength and good ductility due to the grain boundary strengthening, transformation-induced plasticity and twinning-induced plasticity. The yield strength, ultimate tensile strength and elongation at failure are 16.2%, 14.2% and 35.3% than those of the as-cast sample. The postmortem characterizations of this annealed sample show strong 〈 111 〉 texture in the austenite phase along the loading direction and intense martensite transformation with the gradually disappearance of the annealing twins. [ABSTRACT FROM AUTHOR] more...

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. [ABSTRACT FROM AUTHOR] more...

The multi-directional forging process of pure molybdenum was numerically simulated by using DEFORM-3D finite element simulation software. Based on the forging experiment, the effects of deformation temperature, forging reduction, and forging steps on the equivalent strain and uniform distribution of the forgings were studied, and the forging process of repeatedly drawing and upsetting was optimized. It is found that, with the forging process, the equivalent strain distribution tends to be uniform. After the third drawing, the equivalent strain value at the core of the forging can reach more than 3.75, and the overall relative density of the forging is close to 100%. After the multi-direction forging, the sintered pores of the pure sintered molybdenum billets with the initial average grain size of about 55 μm are reduced obviously, the relative density is increased, and the grain size is reduced to 2~3 μm. more...

Abstract The multi-directional forging process of aluminium alloy 7075 (AA 7075) is studied using Deform 3D Version 11.0 simulation software. This process results in grain refinement in the bulk material. The 7075 aluminium alloy is used widely in the aerospace and automobile industries. Thermomechanical processing affects the mechanical properties of this alloy. This study focuses on optimising process parameters that affect the multi-directional forging using simulation. In the Taguchi design of experiment, four-factors and five levels are selected. The process input parameters considered are temperature, the strain per pass, the plunger speed, and the friction coefficient (μ). From Taguchi’s orthogonal array, forging simulations are undertaken and analysed. The significance of the process output parameters: material damage, stress and strain are analysed by analysis of variance. The results show that the friction coefficient and strain per pass highly affect the stress/strain distribution. Grey relational analysis is adopted to determine the optimum process parameters. The results show that the optimal combination of parameters is: temperature (200 °C), plunger speed (5 mm/s), friction coefficient (0.6), and strain per pass (0.6). Confirmation of simulation is carried out using the optimum input parameters. From the simulation results, the grey relational grade's optimal parameters have the highest maximum effective strain of 5.57, maximum effective stress of 665 MPa, and maximum damage of 0.416 compared to other simulated results. more...

The three-dimensional (3D) processing maps of cast Mg-9.0Gd-3.0Y-2.0Zn-0.5Zr alloy were established based on isothermal compression tests and dynamic material model (DMM). The stable and power-efficient forming domains were determined by considering both the instability and power dissipation efficiency maps. Multi-directional forging (MDF) was then simulated by employing finite element (FE) analysis in the Deform-3D software, using the 3D power dissipation efficiency maps as input. The optimal forging parameters were thus obtained for a large-scale ingot with 430 mm in diameter and 440 mm in height, i.e., a forging temperature of 450 °C and forging speed of 10 mm/s. Finally, a Mg-9.0Gd-3.0Y-2.0Zn-0.5Zr cake-shaped forged part with 900 mm in diameter and 100 mm in height was produced. After T6-heat treatment, the edge and center of the forged part exhibit homogeneous microstructure and relatively consistent properties, with the tensile strength, yield strength, and elongation being about 400 MPa, 320 MPa, and 14.0%, respectively. Using transmission electron microscopy, the main strengthening phases were revealed to be the dense nano-scale β′ phases that are uniformly distributed inside the material. [ABSTRACT FROM AUTHOR] more...

Multi‐directional forging technology, as a representative severe plastic deformation technology, is urgent to be developed because it has strong microstructure refinement and performance improvement effects. In this paper, multi‐directional forging experiments of TA15 titanium alloy with different passes were carried out at 700 °C using unrestricted multi‐directional forging die structure. Then the samples of TA15 titanium alloy after multi‐directional forging deformation were subjected to a high‐temperature vacuum annealing treatment. The test results reveal TA15 alloy was effectively refined through multi‐directional forging without any cracking with the increasing of deformation passes. The mechanism of grain refinement during multi‐directional forging included dynamic recrystallization, grain crushing and adiabatic shear deformation bands refinement. The amount and grain size of recrystallization grains increased when the annealing time increased from 1 hour to 4 hours. Supplemented by annealing, the adiabatic shear deformation bands microstructure with the mixed microstructure of coarse αp and fine αs were obtained and the hardness after multi‐directional forging and annealing was investigated. The yield strength and ultimate tensile strength increased by 26.1 % and 25.5 % respectively when the deformation pass increased to 3 passes compared with the initial specimen. The present work revealed that multi‐directional forging deformation combined with appropriate annealing could represent an efficient route to improve the microstructure and mechanical property of TA15 alloy. [ABSTRACT FROM AUTHOR] more...

Evolution of grain structure during isothermal multi-direction forging (MDF) of an Al-Zn-Mg-Cu alloy at 400 °C and 450 °C with strain rates from 10−3 s−1 to 10−5 s−1 was investigated with electron backscattering diffraction (EBSD) and transmission electron microscopy (TEM). The results demonstrated that the evolution of grain structure was dominated by discontinuous dynamic recrystallization (DDRX), during which the continuous forming of new recrystallized grains at grain boundaries was found. Characteristics of DDRX was enhanced with the decrease of MDF strain rate or temperature, which promoted the formation of recrystallized grains at grain boundaries. Besides, the increase of total strain enhanced such grain refinement effect until the grain structure reached the stable state, in which fine recrystallized grains replaced most of the initial coarse grains. more...

Severe Plastic Deformation (SPD) leads to grain refinement and strengthening of metals. Among the many SPD processing methods, Multi-Directional Forging (MDF) is the only one where in-situ material stress–strain curves can be obtained. These are adequate only for specimens re-machined after each compression step, thus avoiding problems connected to specimen shape distortions; re-machining involves complex, expensive and time consuming procedures. This difficulty has been circumvented using confined plane strain compressions, where the strain path, however, differs from that in simple, unconfined free compression. A new processing method involving, for each processing step, an initial free simple compression followed by a confined compression (Multi-Directional Confined Forging – MDCF) is proposed, eliminating the specimen re-machining. Strengthening by MDF depends on strain amplitude; low strain amplitude MDF (LSA-MDF) leads to lower work hardening of the material than high strain amplitude MDF, as well as to limited softening and to an increase in the residual work hardening capacity of material previously deformed monotonically or in successive deformation steps with high strain amplitudes. This supplies a highly desired enhanced uniform elongation of the material after SPD. It is shown that Low Strain Amplitude Multi-Directional Confined Forging (LSA-MDCF) of aluminum leads to adequate stress–strain curves up to the contact of the specimen with the confining die walls, as well as to microstructures very similar to those obtained using free compressions with re-machined specimens. This processing route is simpler, faster and cheaper than LSA-MDF with re-machined samples, and thus emerges as a more practical MDF route. more...

The true stress–strain curve of the thermal deformation of 30Cr2Ni4MoV steel was obtained by conducting a hot compression experiment. On the basis of the results, the constitutive equation of the material's thermal deformation was constructed. Then, the microstructure of the hot compression specimen was observed and analyzed, and the microstructure evolution model of 30Cr2Ni4MoV steel during thermal deformation was established accordingly. The programming of the related mathematical model was realized using the secondary development interface provided by Deform. The experimental plan was subsequently developed using an orthogonal method, and the microstructure evolution of 30Cr2Ni4MoV steel during multi-directional forging deformation was simulated. Through an orthogonal experiment analysis, the influence weight difference of each influencing factor was obtained. A back propagation neural network prediction model for the microstructure of 30Cr2Ni4MoV steel under multi-directional forging deformation was then established. The neural network prediction of the microstructure evolution of 30Cr2Ni4MoV steel under multi-directional forging was finally realized. [ABSTRACT FROM AUTHOR] more...

This paper takes the ultra-fine grain AZ80 magnesium alloy multi-directionally forged as the research object. We observe its heating behavior at 673 K with an optical microscope, analyze the grain size distribution, and the change of average grain size and hardness with different heating time, study the effect of heating time on the grain size change of ultra-fine grain AZ80 magnesium alloy, deduce and verify the grain growth model of ultra-fine grain AZ80 magnesium alloy during its heating process. The research results show that the 24-pass multi-directional forging can make ultra-fine grain AZ80 magnesium alloy of an average grain size of 0.73 μm. When ultra-fine grain AZ80 magnesium alloy is isothermally heated at 673K, its average grain size grows continuously as time extends. Its average grain size and hardness fall into two stages as the heating time changes, namely rapid grain growth stage and stable grain growth stage. If the heat preservation time is less than 300 s, the average grain size grows rapidly as temperature rises; When the heat preservation time reaches 300 s, the grain growth speed will be stable. A grain growth model is established for AZ80 magnesium alloy, which is D2.8932 = D02.8932 + 4.09086 × 10-3t1.6284 under the conditions of isothermal heating, whose computed result well coincides with the measured value. more...

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. more...

Cu– X CNTs composites (X = 0 , 1, 2, 3 vol.%) were successfully prepared using a combination of pre-treatment, powder metallurgy and multi-directional forging processes, which provides a solution for the industrial manufacture of the composites with network CNTs structures. During the multi-directional forging process, the CNTs in the composites were distributed in a network under the synergy of metal flow and copper particle squeeze. Compared with other structure modes, the network CNTs can effectively carry and transfer loads resulting in the promotion of mechanical properties (such as, the tensile strength approximately 1.5 times higher than those of composites with the same volume fraction without network structure). The composite with 2 vol.% CNTs had the highest elongation in this experiment (41%), which is about 5 times higher than the composites with other CNTs distribution patterns. At a low CNTs content level (1 vol.%), a complete load transfer network cannot be formed, resulting in a relatively insufficient mechanical properties of the composites. As the content level is exceeded (3vol.%), it caused significant agglomeration of the CNTs, which lead to fracture in the agglomerated CNTs and elongation degradation of the composites. After the multi-directional forging process commonly used in factories, the CNTs exhibit a network structure distribution in composites. The formation mechanism of the network structure has been analyzed. It was found that the mechanical properties of the composites with network structure CNTs were superior to the other patterns of CNTs distribution. This paper provides a solution for the industrial manufacture of the composites with network structure CNTs. [ABSTRACT FROM AUTHOR] more...

A commercial hot-extruded AZ80Mg alloy was multi-directionally forged (MDFed) to a cumulative strain of ΣΔε = 5.6 at maximum under decreasing temperature conditions from 623K down to 433K at an initial strain rate of 3.0 © 10-3 s-1. In addition to the above MDFing method, a simplified MDFing method, i.e., MDFing under two-step decreasing temperature conditions, was proposed and applied. These MDFing led to homogeneous grain refinements to have average grain sizes down to 0.6 µm. The MDFed Mg alloys were further extruded to form plates and tubes at temperatures between 453K and 523K at various initial strain rates from 3.0 © 10-4 s-1 to 1.0 © 10-2 s-1. Extrusions of the MDFed AZ80Mg alloys were successfully carried out even at such relatively low temperatures. Under some conditions, the strain-rate sensitivity of the flow stress exceeded 0.3, which suggested occurrence of superplastic deformation. By the above warm extrusion employing superplasticity accompanied by work hardening, high-strength AZ80Mg alloy tubes with tensile strength over 400 MPa could be successfully fabricated. [ABSTRACT FROM AUTHOR] more...

Multi-directional forging (MDF) is one of the most promising severe plastic deformation (SPD) methods used in fabricating large-scale bulk metal materials with ultra-fine grains (UFG). A finite element model for MDF is developed to investigate the strain evolution of Ti-6Al-4V alloy subjected to MDF. Results show that the billet subjected to MDF can be divided into four individual strain zones in terms of the equivalence of effective strain evolution, and that the strain increment in each individual strain zone varies from pass to pass. The deviation between the maximum and the minimum strain increases with the increase of passes and friction coefficient. The effective strain linearly decreases from the core to the exterior of the billet in all three directions after the MDF process. With the increase of the passes and friction coefficient, the gradient of the effective strain in the billet increases in all three directions due to the difference of deformability in different individual strain zones. For the definite friction coefficient, the average and maximum effective strains are in proportion to the accumulative compression strain. more...

Ultrafine-grained AlMgSc alloys were fabricated by multi-directional forging (MDF) with different number of forging passes of 3, 9 and 15, i.e., to cumulative strains of ΣΔε = 1.2, 3.6 and 6.0, at room temperature. The achieved average grain sizes were 950, 680 and 360nm at 3, 9 and 15 passes, respectively. Peak-aging treatments at 473K for 172.8 ks were adopted for a portion of specimens after MDF in order to obtain finely dispersed Al3Sc precipitates. Grain coarsening did not take place in all the specimens during the aging. The activation volume for plastic deformation was estimated from the strain-rate jump tensile tests before and after the aging. Aging-free 3- and 9-pass specimens showed positive temperature dependence of the activation volume, while that of the aging-free 15-pass one bearing the smallest grain size exhibited a negative temperature dependence. Contrary to these results, values of the activation volume in the peak-aged specimens were approximately identical regardless of grain size or deformation temperature. These results strongly suggested that, due to the precipitation of Al3Sc, the rate-controlling process of deformation was changed from interaction between forest dislocations and mobile dislocations for the aging-free 3- and 9-pass specimens to interaction between mobile dislocations and Al3Sc precipitates, or from bowing-out of dislocations from grain boundaries for the aging-free 15-pass specimen to the interaction between the mobile dislocations and precipitates. [ABSTRACT FROM AUTHOR] more...

In this study, mechanical and tribological properties of multi-directional hot forged Al-7Si-4Zn-3Cu alloy at different cycles were investigated. Multi-directional hot forging resulted in both breaking up the silicon particles and the elimination of dendritic structure of the alloy. This process increased the yield and tensile strength with percentage elongation of the alloy but decreased its hardness. The highest yield and tensile strength were obtained from the alloy forged two cycles, while the alloy forged three cycles showed a lowest hardness but the highest percentage elongation. On the other hand, hot forged alloy exhibited higher friction coefficient and lower wear resistance than those of its homogenized state. After the wear test, smeared and delaminated layers were observed on the worn surface of the alloy in all test conditions. This observation showed that smearing and delamination were effective wear mechanisms of the alloy in all states. [ABSTRACT FROM AUTHOR] more...

Strength, ductility and fracture toughness are the most important mechanical properties of engineering materials. In this work, an Al–Zn–Mg–Cu alloy was subjected to multi-directional forging (MF) and ageing treatment. Microstructural evolution was studied by optical and electron microscopy and strength, ductility and fracture toughness were researched. After MF, the dislocation density was increased and the microstructure was refined. The strength and fracture toughness were increased, while the ductility was decreased sharply. Without compromising the strength, the ductility was improved significantly after ageing. The fracture toughness was increased further. The coarse and discontinuously distributed grain boundary precipitates were found to be responsible for higher fracture toughness of the fine-grained structure Al–Zn–Mg–Cu alloy. [ABSTRACT FROM AUTHOR] more...

The combined effect of extrusion and multi-directional forging (MDF) was investigated on microstructure and mechanical properties of aluminum-based composite with 10, 15, and 20 wt% Mg2Si. In the casted Al–Mg2Si composites, the primary and eutectic Mg2Si particles are generally coarse which lead to decreasing their mechanical properties and formability. Extrusion process was utilized to overcome this shortcoming by breakage of the eutectic structure, reduction of Mg2Si size, and the decrease of casting defects. Then, MDF process was applied up to failure on the extruded composites at room temperature. It led to the morphological modification of primary and eutectic Mg2Si phases and the reduction of their size. It was found that the MDF process resulted in a considerable improvement in hardness and shear strength of materials. This may be related to the reduction in the average size of Mg2Si particles with their uniform distribution. In addition, ultimate shear strength is, respectively, increased from 94, 99, and 81 MPa to 119, 116, and 117 MPa for the 10, 15, and 20 wt% Mg2Si aluminum composites after the final pass of MDF. Meanwhile, the normal displacement of composites is reduced at initial passes and increased by the addition of more pass numbers. [ABSTRACT FROM AUTHOR] more...

The experimental study of hypoeutectic Al-7.3Si alloy on microstructure and mechanical properties processed by MDF at room temperature was reported in this paper. A commercial LM-25 aluminium alloy ingot was melted in an electric casting furnace and poured into a preheated rectangular casting die. The samples were then solutionized for 10 h at 535 °C and quenched in water for MDF processing. Microstructure analysis of the samples was done with the help of optical microscopy and scanning electron microscopy. Microstructural observation of MDF processed up to six passes sample showed that coarse eutectic silicon particles with an average length of 16 µm are effectively broken into fine particles with an average length of 4 µm and uniformly distributed in aluminium phase. After six passes, UTS of as-cast specimen is increased from 177 to 441 MPa and microhardness is increased from 75 to 127 Hv. XRD analysis of the samples confirmed the presence of Al phase and eutectic Si phase. Therefore, modification of eutectic Si particle with Al phase refinement has been demonstrated to be a very important factor for enhancing mechanical properties of aluminium–silicon alloy. [ABSTRACT FROM AUTHOR] more...

Mg-5Li-1Zn-0.5Ag-0.5Zr-xGd (x = 2.4, 6) alloys were subjected to multi-directional forging (MDF). The β 1 coherent phase and β incoherent phase precipitated during the MDF process significantly improve the properties of the alloy. The results show that the orientation relationship between the β 1 phase and the matrix is 022 β 1 ∥ 0002 α and 111 β 1 ∥ 1 2 ¯ 10 α.When the dislocations cut through the β 1 phase, the {111} 〈110〉 slip system of the β 1 phases is activated, forming anti-phase boundaries (APBs) by directional motion in the <110> direction, which provides strengthening effects. The APB structure leads to the increase of system energy, deformation resistance, and yield strength. Besides, the activation of the β 1 phases slip system makes the alloys exhibit satisfactory plasticity and toughness. After MDF at 350 °C, Mg-5Li-1Zn-0.5Ag-0.5Zr-2.4Gd alloy has a yield strength of 270 MPa, a tensile strength of 295 MPa, and an elongation of 12.7%, respectively. The results are beneficial for the design and manufacture of high-performance Mg Li alloys. • After multidirectional forging (MDF) at 350 °C, the mechanical properties of the alloys are improved. • When the coherent β1 interacts with defects leads to increasing strength and also promotes satisfactory plasticity. [ABSTRACT FROM AUTHOR] more...

The effect of forging pass on the deformation structure of high purity aluminum at room temperature during multi-direction forging process was investigated by experiment. The multi-direction forging process was analyzed by using software of DEFORM-3D. The results show that an X-shape fine grain zone (in the center of the sample) and four coarse grain zones (near the end surface of the sample) are initially formed on the cross section of the sample as forging passes increase to 3. With a further increasing the passes to 9, this X-shape zone tends to spread the whole sample. However, the grain difference between the coarse grain zone and fine grain zone still exists on the sample forged by 9 passes. Limitation in the structural refinement is observed in the center of the sample with the increment of equivalent strain. The grains size in the center is refined to a certain size (about 70μm) as equivalent strain reaches 2.5, and no further grain refinement in the center with increasing the equivalent strain to 6.0. However, the grains size in the area near the surface is continuously refined with the increasing the equivalent strain to 4.0. This indicates that the local deformation state and the equivalent strain are two important factors that affect the grain size. more...

The Al-Zn-Mg-Cu alloy with different sub-grains and recrystallized grains was isothermal forged at 400 °C with strain rate of 10−4 s−1, and the grain structures were examined by electron backscatter diffraction (EBSD). The results showed that the coarsening of sub-grains and the formation of recrystallized grains at grain boundaries were the primarily changes of grain structures during isothermal forging. Besides, it found that the coarsening of sub-grains occurred first, and then recrystallization started at grain boundaries when quite a few sub-grains were found within grain interiors. Coarsening of sub-grains was found during isothermal forging of the one containing many sub-grains, and the recrystallization was hindered as strain energy was consumed by such coarsening of sub-grains. But more recrystallized grains were found after isothermal forging of the one containing many fine grains. [ABSTRACT FROM AUTHOR] more...

Extruded Mg alloy (ZAXM4211) was subjected to multi-directional forging (MDF) at different temperatures from 180 to 300 °C. Microstructure was analyzed using optical microscope (OM), scanning electron microscope (SEM), electron backscattered diffraction (EBSD), and X-ray diffraction (XRD) studies. Tensile and compression properties were evaluated and corrosion behavior was examined using electrochemical and immersion corrosion tests. It was found that the increase in MDF temperature decreased the yield strength due to an increase in the grain size. Furthermore, the corrosion rate was decreased as the MDF temperature was increased could be due to the dissolution of the second phases, which was further substantiated by the image analysis and scanning Kelvin probe force microscope (SKPFM) studies. The relationship between yield strength and grain size and furthermore, corrosion rate and second phases were quantitatively analyzed. [ABSTRACT FROM AUTHOR] more...