Multi-directional Forging Process Research Articles

Microstructure Evolution and Mechanical Properties of Mg-Gd-Y-Zn-Zr Alloy Deformed by Multi-Directional Forging with Decreasing Temperature

The multi-directional forging process can achieve large plastic deformation, and has great application prospects in industrial production. The Mg-9.55Gd-3.28Y-1.77Zn-0.34Zr (wt%) alloy containing LPSO phase was deformed in different passes and then quenched immediately by the multi-directional forging process with decreasing temperature, and the microstructure and mechanical properties of the alloy were analyzed. It is found that as the number of deformation passes increases, the coarse grains decrease, and the dynamic recrystallization fraction increases. The dynamic recrystallization grains swallow the original grains, promote the continuous refinement of the grains, and greatly improve the uniformity of the microstructure. At the same time, the maximum texture intensity of the (0001) basal plane is significantly reduced, and the pole figure distribution is more dispersed, which is attributed to the random orientation of dynamic recrystallization. Due to the refinement of the microstructure and the weakening of the texture, the tensile strength and yield strength at room temperature increase significantly. After 3 passes of deformation, the alloy has the highest mechanical properties, with tensile strength, yield strength, and elongation reaching 317 MPa, 233 MPa, and 15%, respectively.

The Network Structure Formation of Cu-CNTs Composites During Multi-Directional Forging Process and its Mechanical Properties

Cu–[Formula: see text] CNTs composites ([Formula: see text], 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[Formula: see text]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.

Microstructure, texture, and mechanical properties of the extruded and multi-directionally forged Mg–xGd alloys

The microstructural and textural evolutions as well as room-temperature mechanical properties of three binary Mg–Gd alloys with 1, 2, and 3 wt% of Gd were studied in the as-extruded condition and after two, four, and six passes of multi-directional forging (MDF). Microstructural observations of the extruded samples were indicative of partial dynamic recrystallization resulting in bimodal grain structures comprised of elongated un-recrystallized patches and fine recrystallized grains. After six passes of the MDF process, the fraction of the un-recrystallized regions decreased because of dynamic recrystallization, and thus, relatively uniform microstructures were achieved in all alloys. The greater fraction of the un-recrystallized patches and the finer grains in the recrystallized regions of the Mg–3Gd alloy confirmed the more pronounced retardation of recrystallization via solute drag mechanism at the higher Gd concentrations. Evaluation of crystallographic texture revealed that by applying the MDF process, the conventional fiber texture of the extruded condition was replaced with a new randomized texture, in which the basal planes had a tendency to rotate at angles of lower than 90° to the transverse direction. Mechanical properties were evaluated using shear punch testing (SPT) and the results showed that with increasing the number of MDF passes in each alloy, the achieved finer grain structure was responsible for improving the shear strength. In addition, increasing the Gd content of the alloys resulted in finer grain size, more solute atoms, and higher fraction of Mg 5 Gd second phase particles, all of which led to the enhancement in shear strength.

Comparison of the microstructure evolution and mechanical properties via MDF and ITMT methods

Based on the multi-directional forging (MDF) method under decreasing temperature conditions, intermediate thermo-mechanical treatment (ITMT) method was proposed to control the microstructure of the deformed Mg-13Gd-4Y–2Zn-0.5Zr (wt%) alloy and improve its mechanical properties, especially the yield strength (YS). The results showed that compared with the MDF method, ITMT can significantly improve the mechanical properties of the deformed alloy and shorten the process flow. As the number of deformation passes increased, the microstructure became uniform, the average grain size gradually decreased, and the mechanical properties gradually improved during the MDF process. The average grain size of the alloy after 4 passes exhibited a minimum value of 2.4 µm, and the mechanical properties achieved a maximum value with an ultimate tensile strength (UTS) of 357 MPa and a YS of 304 MPa. The average grain size of the deformed alloy first decreased significantly and then slowly increased with an increase in the number of deformation passes via the ITMT method. After 2 passes, the alloy exhibited the minimum grain size and the best mechanical properties after T4-ITMT and T6-ITMT. The minimum grain size was 3.7 µm, and the UTS and YS were 341 MPa and 320 MPa via T4-ITMT method, respectively. The average grain size was 3.1 µm, and the UTS and YS were 356 MPa and 332 MPa via T6-ITMT method, respectively.

A multi-response optimization of the multi-directional forging process for aluminium 7075 alloy using grey-based taguchi method

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.

Inhomogeneous microstructure and mechanical anisotropy of multi-directional forged Mg-Gd-Y-Zn-Ag-Zr alloy

Abstract In this paper, through multi-directional forging with strain controlled multi-passes under the conditions of initial forging temperature of 480 °C and an accumulative strain of 4.4 after 27 forging passes, a bulky Mg-Gd-Y-Zn-Ag-Zr alloy with a size of 460 mm × 260 mm × 160 mm is prepared. The microstructure, texture and mechanical properties of different regions (the center, 1/2R and edge regions) in the alloy bulk are discussed. The results show that the material has undergone significant grain refinement during the multi-directional forging process. Due to the uneven strain and temperature distributions in different regions, inhomogeneous microstructures with different levels of dynamic recrystallization are formed. The average grain size of the center, 1/2R and edge regions is 2.91 ± 1.77, 3.83 ± 2.22, and 17.78 ± 12.24 μm, respectively. The center region exhibits a double-peak basal texture, while the 1/2R and edge regions additionally show a “rare earth texture component”. The tilt of the basal poles in some specific direction causes obvious mechanical anisotropy of the bulk. However, the non-basal rare earth texture component weakens the mechanical anisotropy. The optimum comprehensive mechanical properties are obtained in the center region, with the ultimate tensile strength of 364 MPa, the yield strength of 295 MPa, and the elongation to failure of 4.8%.

Achieving an ultra-high strength and moderate ductility in Mg–Gd–Y–Zn–Zr alloy via a decreased-temperature multi-directional forging

In this study, an ultra-high yield strength (~417 MPa) and moderate ductility (~12.9%) was obtained in Mg–8.2Gd–3.8Y–1.0Zn–0.4Zr (wt%) alloy through a method of decreased-temperature multi-directional forging (MDF) processing followed by aging treatment. The ultra-fine grained structure with average grain size of ~0.9 μm was prepared after 6 passes of forging progress, which was ascribed to the occurrence of dynamic recrystallization (DRX). Both the decreased MDF temperature and precipitation of fine Mg5(Gd, Y) phase particles effectively hinder the DRX grain growth, so that the grain refinement can realize their full potential in strengthening effect. The formation of some DRX grains is also accompanied with the consumption of LPSO structures. Additionally, a weak fiber texture with c-axis perpendicular to normal direction was gradually formed during the reduplicative MDF process. As compared to the hot-extruded counterpart, the significant improvement in the yield strength of MDF-processed Mg-Gd-Y-Zn-Zr alloy can be attributed to the combined strengthening effects of the grain refinement, dynamic precipitation and broken secondary phase particles. Meanwhile, the homogenous microstructure induced by decreased-temperature MDF is also responsible for a resulting moderate ductility.

Microstructural evolution and mechanical properties in a Zn–Al–Cu–Mg hypoeutectic alloy processed by multi-directional forging at room temperature

Experiments were performed to examine the flow behavior and microstructural evolution in a Zn–Al–Cu–Mg alloy processed by up to 23 cycles of multi-directional forging (MDF). After a total strain (ε) of ~20.7 the grain sizes in the primary η-Zn, eutectic and eutectoid components were reduced to ~0.25, 0.4 and 0.3 μm, respectively. The metal exhibits profuse shear banding and twinning and undergoes work hardening in the 1st MDF cycle. Further straining up to ε ≈ 7 promotes significant grain refinement together with strain softening due to occurrence of grain boundary sliding. Afterwards, the plastic flow occurs under a constant stress and flow softening is again prevalent for ε > 12. The individual components in the Zn–Al hypoeutectic alloy display different kinetics of hardening and grain refinement such that the microstructural changes are first observed in the primary η-Zn areas and subsequently in the eutectoid and eutectic domains. Based on the average hardness in each component, the rule of mixtures was used to estimate the overall material strength after MDF. Although the results show similar trends, it is revealed that the rule of mixtures overestimates the flow stresses compared with the in-situ stress-strain curve. This undermines the hypothesis of iso-strain and suggests that deformation concentrates in the weaker areas in the flow softening stages of MDF processing.

Simultaneously Enhanced Mechanical Properties and Damping Capacities of ZK60 Mg Alloys Processed by Multi-Directional Forging

In this study, the mechanical properties and damping capacities of cast Mg-5.5Zn-0.6Zr (weight percent, ZK60) alloys have been simultaneously improved by a facile multi-directional forging (MDF) processing, and the mechanisms of microstructure evolution and texture modification are systematically investigated. The activation of tension twinning occurs during the initial MDF stage, due to the coarse-grained structure of the as-cast alloy. With increasing MDF passes, the continuous dynamic recrystallization (CDRX) results in a fine equiaxed-grain structure. The typical non-basal texture is formed in the as-MDFed alloy for 6 passes, with the (0001) planes inclined 60°–70° to forged direction and 10°–20° to transverse direction, respectively. A good balance between the strength (~ 194.9 MPa) and ductility (~ 24.9%) has been achieved, which can be ascribed to the grain refinement, non-basal texture and fine precipitate particles. The damping capacity is remarkably improved after MDF processing, because the severe deformation increases the dislocation density, which effectively enlarges the sweep areas of mobile dislocations.

Microstructure and mechanical properties of TiC nanoparticle-reinforced Mg−Zn−Ca matrix nanocomposites processed by combining multidirectional forging and extrusion

TiC nanoparticle-reinforced Mg−4Zn−0.5Ca matrix nanocomposites were processed by combining multidirectional forging (MDF) and extrusion (EX). The grain size of the nanocomposite after MDF+EX multi-step deformation was significantly decreased compared with that processed only by MDF. The average size of the recrystallized grains gradually increased after EX with increasing the number of MDF passes at 270 °C. However, the grain size significantly decreased by MDF processing at 310 °C. Both fine and coarse MgZn2 phases appeared in the (MDF+EX)-processed nanocomposites, and their volume fractions gradually increased with increasing the number of MDF passes before EX. Ultrahigh tensile properties (yield strength of ~404 MPa, ultimate tensile strength of ~450.3 MPa and elongation of ~5.2 %) were obtained in the nanocomposite after three MDF passes at 310 °C followed by EX. This was attributed to the refinement of the recrystallized grains, together with the improved Orowan strengthening provided by the precipitated MgZn2 particles that were generated by MDF+EX multi-step deformation.

The Role of Long Period Stacking Ordered Phase in Dynamic Recrystallization of a Mg-Gd-Y-Zn-Zr Alloy during Multi-Directional Forging Process.

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.

Flow stress of 2024 aluminum alloy during multi-directional forging process and natural aging after plastic deformation

The hardening behavior of heat treatable alloys during deformation is attributed to three mechanisms of forest dislocations, solid solution and precipitation hardening which hinder the motion of dislocations and increase the density of statistically stored dislocation. In this paper, a model for the flow stress of a 2024 heat treatable aluminum alloy during plastic deformation is developed combining the superposition of these three hardening mechanisms. This model was then implemented into the finite element model in order to evaluate the evolution of the flow stress of 2024 aluminum alloy during multi-directional forging (MDF). Subsequently, an equation is developed for evaluating the material strength changes during natural aging after MDF. The experimental results from compression and hardness tests show a good agreement between modeling and experimental data. The results show that the flow stress is increased about 90% after the first pass of MDF and then increased just about 2% after the second pass. Through natural aging process, the hardening rate is higher in non-deformed samples and is decreased with increasing the aging time.

Investigation of A413 alloy with reinforcement of SiC and flyash hybrid composites by stir cast cum forged process on electric vehicle In-wheel motor casing

The Cardinal goal of this research work is to fabricate a new combination of hybrid composite material and it was suited for a casing cover of an In-wheel motor drive system that works in an electric vehicle. The main objective of the proposed work is to prepare the hybrid metal matrix composite through stir cast cum forging process to attain enhanced property. The preparation of stir casted A413 alloy with 5% SiC and 5% flyash hybrid composites are further processed through uni/bi/multi-directional forging process to enrich the properties. Each cast cum forged samples are tested under various aspects such as density, hardness, ultimate tensile strength, thermal conductivity and coefficient of thermal expansion. By carrying out the above test, it was found that hybrid composite under multi-directional forging process shows an 73% increase in thermal property, 3% lesser in physical property and 20–45% increase in mechanical property when it compared with hybrid composite under un-forged process. The newly fabricated hybrid composite under multi-directional forging has higher properties under all testing aspects due to reduction of grain size. In addition comparing with uni and bi-directional forging process. Multi-directional forging attains higher strength and will reduce the weight of the hybrid composites. Due to reduction of unsprung mass of the vehicle, we recommend hybrid composite obtained by stir cast cum multi-directional forged process for incorporation in In-wheel motor drive system.

Investigating the combination effect of warm extrusion and multi-directional forging on microstructure and mechanical properties of Al–Mg2Si composites

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.

Influence of Strain Amplitude on the Microstructural Evolution and Flow Properties of Copper Processed by Multidirectional Forging

Commercial‐purity copper (99.8%) is processed by multidirectional forging (MDF) using strain amplitudes per compression (Δε) of 0.15 and 0.30, leading to accumulated strains (ε) of up to ≈10.8. It is shown that increasing the accumulated strain causes continuous reactions at the substructural level, involving the progressive evolution of dislocation arrangements toward structures having high misorientation angles. This evolution depends upon the strain amplitude in MDF processing and is characterized by the fragmentation of the original grains due to formation and intersection of micro shear bands (MSBs) assisted by dynamic recovery processes. Higher Δε enhances the “monotonic” character of processing, resulting in a higher fraction of MSBs and band intersections, increased work hardening, flow stresses, and dislocation density, lower cell/subgrain and grain sizes, and faster grain refinement kinetics, compared with MDF under lower Δε. The yield strength of copper, measured along a direction orthogonal to that of the previous compression step, is lower than the flow stress at the end of this compression step, and this behavior becomes more prominent with increasing ε and Δε.

Comparison of the effects of isothermal equal channel angular pressing and multi-directional forging on mechanical properties of AM60 magnesium alloy

This study investigates the correlation between the microstructure and the mechanical strength of AM60 magnesium alloy processed by equal channel angular pressing (ECAP) and multi-directional forging (MDF) at a constant temperature of 220 °C. The maximum number of passes was six for both severe plastic deformation (SPD) techniques. The minimum achievable grain size was ~1.9 μm for ECAP while it was only ~2.7 μm for MDF. Despite the monotonous reduction of the grain size, the yield and the ultimate tensile strength values decreased for high equivalent strains which was attributed to the decrease of the dislocation density. The maximum achievable strength was higher for ECAP than that for MDF mainly due to the higher dislocation density. Both ECAP and MDF processing led to an improvement of ductility. Based on the strength results, it is evident that the ECAP process is more effective in improving the mechanical properties of AM60 alloy at 220 °C, compared to the MDF process.

Microstructure, texture evolution and mechanical properties of multi-directional forged Mg-13Gd-4Y–2Zn-0.5Zr alloy under decreasing temperature

In this study, homogenized Mg-13Gd-4Y–2Zn-0.5Zr alloys were applied to multi-directional forging (MDF) process at decreasing temperatures from 480 °C to 420 °C by 4 passes. The microstructure, texture evolution and mechanical properties of the alloys during the MDF process were investigated. The result showed that the average grain size was refined remarkably to 4.0 μm and the microstructure distribution became homogeneous after 3 passes with cumulative strain of 9. After 4 passes with cumulative strain of 12, the average grain size increases to 5.4 μm. It is observed that large number of dynamic recrystallized (DRXed) grains and spherical precipitated phases of Mg5(Gd,Y,Zn) occurred during the MDF processing. The area fraction of DRXed grains was increased to 97.3% that can be regarded as achieving complete dynamic recrystallization (DRX) after 3 passes. The grain refinement was mainly caused by DRX, and the DRX was induced via particle stimulation nucleation (PSN) mechanism. Moreover, part of lamellar long-period stacking ordered (LPSO) phases were kinked and brought about numerous kink bands during multi-directional forging (MDF) process, which had an important impact on the grain refinement. As the MDF passes and cumulative strain increase, the basal texture transformed from strong basal texture to a random distribution gradually. The maximum ultimate tensile strength (UTS) and tensile yield strength (TYS) were 399 MPa and 308 MPa after 3 passes. The maximum failure elongation (FE) was 18.1% after 4 passes.

Superplasticity of fine-grained Mg–xGd alloys processed by multi-directional forging

Microstructural development and superplastic behavior of Mg–xGd (x = 1, 2, 3 wt%) alloys were investigated after the multi-directional forging (MDF) process. Microstructural observations of the extruded materials revealed non-homogeneous structures with bimodal grain sizes, consisting of coarse elongated grains resulting from deformation, surrounded by fine grains formed by partial dynamic recrystallization. The grain sizes of the recrystallized regions in the Mg–1Gd, Mg–2Gd and Mg–3Gd alloys were 5.6, 3.9 and 3.1 μm, respectively. After six passes of the MDF process, the bimodal grain structure disappeared as a result of complete dynamic recrystallization and almost homogeneous microstructures with the grain sizes of 2.5, 2.2 and 1.9 μm were obtained in the Mg–1Gd, Mg–2Gd and Mg–3Gd alloys, respectively. The smaller fraction of the recrystallized region in the extruded Mg–3Gd alloy and the smaller grain size in the MDF processed condition imply that more pronounced recrystallization retardation occurs through solute drag mechanism at the highest Gd content. Superplasticity was assessed by measuring the strain rate sensitivity index (m-value), through shear punch testing (SPT) in a temperature range of 623–698 K at various strain rates. After six passes of MDF, peak m-values of 0.45 and 0.46 were obtained at 648 K for Mg–1Gd and Mg–2Gd alloys, respectively, while for the Mg–3Gd alloy the peak m-value of 0.48 was achieved at a lower temperature of 623 K. According to the m-value of about 0.5 and the corresponding activation energies of 101–114 kJ/mol, the governing superplastic deformation mechanism was determined as grain boundary sliding (GBS) controlled by grain boundary diffusion.

Investigation of dry sliding wear properties of multi-directional forged Mg–Zn alloys

Abstract Effect of multi-directional forging (MDF) on wear properties of Mg–Zn alloys (with 2, 4, and 6 wt% Zn) is investigated. Dry sliding wear test was performed using pin on disk machine on MDF processed and homogenized samples. Wear behavior of samples was analyzed at loads of 10 N and 20 N, with sliding distances of 2000 m and 4000 m, at a sliding velocity of 3 m/s. Microstructures of worn samples were observed under scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and x-ray diffraction (XRD) and the results were analyzed. Mechanical properties were evaluated using microhardness test. After 5 passes of MDF, the average grain size was found to be 30 ± 4 µm, 22 ± 3 µm, and 18 ± 3 µm, in Mg–2%Zn, Mg–4%Zn, and Mg–6%Zn alloys, respectively, with significant improvement in hardness in all cases. Wear resistance was improved after MDF processing, as well as, with increment in Zn content in Mg alloy. However, it decreased when the load and the sliding distance increased. Worn surface exhibited ploughing, delamination, plastic deformation, and wear debris along sliding direction, and abrasive wear was found to be the main mechanism.

Microstructural evolution of Al2Cu phase and mechanical properties of the large-scale Al alloy components under different consecutive manufacturing processes

The large-scale Al alloy components are usually manufactured based on the ultra-large Al ingots through different manufacturing processes, i.e. direct-chill (DC) ultrasonic casting, multidirectional forging (MF), and solution-aging treatment (SAT). The Al2Cu particles with different microstructural features significantly affect the mechanical properties of such large-scale Al alloy components. In the present work, an ultra-large cylindrical 2219 Al alloy ingot (with a diameter of 1380 mm and a length of 3700 mm) was cast using ultrasonic casting technology. Then, the ingot experienced a MF process, followed by a slight SAT. The continuous microstructural variation across DC casting, MF process and SAT was examined regarding this ultra-large ingot, particularly for different types of (θ, θ′ and θ″) Al2Cu particles. Al2Cu particles mainly developed from solidification, precipitation and the MF-stimulated fragmentation. Most of the Al2Cu particles fragmented from θ-Al2Cu/α-Al eutectic networks still retained after SAT, but with partial dissolution. Other types of θ′- and/or θ″-Al2Cu particles were nearly dissolved into the α-Al matrix. SAT improved the ultimate tensile strength and the yield strength while MF evidently increased elongation. However, casting generated very low tensile strength. Further, the correlation between Al2Cu particles and mechanical properties was accordingly discussed.