Multi-directional Forging Process Research Articles

Strengthening mechanism and interaction between nano precipitates and defects in wrought Mg-5Li-1Zn-0.5Ag-0.5Zr-xGd alloys

Mg-5Li-1Zn-0.5Ag-0.5Zr-xGd (x = 2.4, 6) alloys were subjected to multi-directional forging (MDF). The β1 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 β1 phase and the matrix is 022β1∥0002α and 111β1∥12¯10α.When the dislocations cut through the β1 phase, the {111} 〈110〉 slip system of the β1 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 β1 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 MgLi alloys.

Comparing the microstructural and mechanical improvements of AZ80/SiC nanocomposite using DECLE and MDF processes

The present study investigates the effects of two different severe plastic deformation (SPD) processes on an annealed AZ80/SiC nanocomposite. Specifically, the microstructure, texture, shear behavior, and hardness of the material were analyzed after being subjected to dual equal channel lateral extrusion (DECLE) for up to 5 passes, and multidirectional forging (MDF) for up to 8 passes, both carried out at a constant temperature of 300 °C. The effective strain was 1.44 and 0.5 in each DECLE and MDF pass. The annealed AZ80/SiC nanocomposite showed a reduction in average grain size from 68.4 μm to 2.7, 4.2, and 4.4 μm during 1, 3, and 5 passes of DECLE process, and to 8, 4.3, 2.3, and 5.4 μm during 2, 4, 6, and 8 passes of MDF process. Examination of the shear properties revealed that the ultimate shear strength (USS) of the nanocomposite increased after conducting both the DECLE and MDF processes. Specifically, the USS of the annealed nanocomposite increased by 23.1 MPa after 5 passes of the DECLE process and by 8.1 MPa after 8 passes of the MDF process. These results indicate that the DECLE process had a greater effect on the shear strength increase compared to the MDF process. The results of the hardness testing on the AZ80/SiC nanocomposite showed that the fifth pass of the DECLE process increased the hardness from 86.6 to 96.2 Hv, while the eighth pass of the MDF process increased this value to 90.1 Hv. The DECLE process was found to be more effective than the MDF process due to the simultaneous application of three types of shear deformation, pressing, and extrusion in each pass, as well as the higher effective strain.

Using different strategies to improve properties of the biodegradable Mg–4Li–4Zn alloy

Recently, novel super light Mg–Li based alloys have attracted wide attention for potential use as biodegradable implants. However, like most of the biodegradable Mg alloys, Mg–Li alloys suffer from high degradation rate and poor mechanical properties, but the degradation is much faster and thus critical in these alloys. Different strategies have been introduced and used to address these weaknesses, including alloying, heat treatment and severe plastic deformation. However, efficiency of these methods have not been yet evaluated and compared with each other. In this investigation, the effects of alloying (0.5 and 1.0 wt% Ca addition), homogenization heat treatment and multidirectional forging process on the microstructure, biodegradation behavior, and mechanical properties of the as-cast Mg–4Li–4Zn base alloy are evaluated and compared. The obtained results indicate that Ca addition is beneficial to improving both mechanical strength and corrosion resistance of the as-cast base alloy. In addition to microstructural refinement, the addition of Ca resulted in formation of Ca- and Zn-rich precipitates, with a network-like structure, which was found to be beneficial to inhibiting the corrosion progress. Although homogenization treatment led to a slight decrease in mechanical strength, it considerably improved the corrosion resistance, through partial dissolution of precipitates and more uniformity of the as-cast microstructure. Finally, it was found that the multi-directionally forged alloy demonstrated improved mechanical and corrosion properties in comparison with the as-cast alloy, which stemmed mainly from the more uniform distribution of fine secondary phases, as well as the reduced average grain size.

Microstructure, texture evolution and mechanical properties of a large-scale multidirectionally forged Mg-Gd-Y-Zn-Zr-Ag alloy

A large-scale Mg-6.2Gd-3.7Y-0.9Zn-0.3Zr-0.3Ag (wt.%) magnesium component with the dimension of 480 × 250 × 160 mm3 was fabricated via direct-chill (DC) casting, homogenization and multidirectional forging (MDF). The evolution of the microstructure, texture and uniaxial tensile properties during MDF process were comprehensively investigated. 2.5%, 5.6% and 10.9% anisotropy were obtained in the MDF alloy subjected to 9, 18 and 27 passes, respectively. The MDF alloy subjected to 27 passes tensile along FD exhibits superior comprehensive mechanical properties, with a yield strength (TYS) of 292 MPa, ultimate tensile strength (UTS) of 384 MPa and elongation of 9.0%. Interdendritic Mg5(Gd, Y, Zn) phases dissolved after homogenization, with the precipitation of intragranular lamellar 14H long period stacking ordered (LPSO) phases from α-Mg matrix. During the MDF process, intragranular lamellar LPSO phases were initially kinked, suppressing dynamic recrystallization (DRX) behavior in the first 9 passes, and subsequently partially dissolved. Dynamic precipitation of Mg5(Gd, Y) and ultrafine LPSO phase were also induced by MDF. With the cumulative deformation of MDF, increased volume fraction of Mg5(Gd, Y) phases, enhanced texture and refined α-Mg grains are likely responsible for the improved mechanical properties via MDF. We also found that prismatic <a> slip is activated in the deformed grains with the c-axis around FD and multiple slip is activated in the other deformed grains during the MDF process. This paper provides a superior MDF processing route to manufacture high-performance large-scale Mg-Gd-Y-Zn-Zr-Ag components for industrial production.

Achievement of high strength and good ductility in the large-size AZ80 Mg alloy using a designed multi-directional forging process and aging treatment

Most high-performance Mg alloy samples obtained by severe plastic deformation processes are difficult to implement in industrial utilization due to their small size. The strength of large samples developed using the multi-directional forging (MDF) process is significantly lower than that of small samples. This work developed a large commercial AZ80 alloy sample with dimensions of 100 × 100 × 140 mm3 using a two-step MDF process and artificial aging. The designed process is different from the reported MDF and aging processes. The T5 treated sample exhibits uniform mechanical properties with the ultimate tensile strength of 430 MPa (Engineering stress) and elongation to failure of 11.4%, reaching the level of wrought Mg-RE alloys. MDF at elevated temperatures improves the plasticity of the sample resulting in a good forgeability at 180 °C. The high density defects introduced by the MDF process include grain boundaries, dislocations and stacking faults (SFs) that accelerate the subsequent aging response. The good strength-ductility synergy is attributed to the simultaneous effect of an overall bimodal microstructure composed of fine grains and coarse grains, nanoscale β-Mg17Al12 precipitates, and a high density of dislocations and SFs. The designed process can benefit the general community of Mg alloys since the excellent mechanical properties do not rely on the strengthening mechanism due to the addition of specific elements. This work provides an effective way to develop large-size Mg alloy billets applied to load-bearing components.

The Wear and Electrical Performance of Cu-CNTs Composites with Network Structure CNTs Fabricated by Multi-Directional Forging

Cu-[Formula: see text] CNTs composites ([Formula: see text], 1, 2[Formula: see text]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[Formula: see text]vol.% CNTs were added, with an average value of 5.87[Formula: see text]m[Formula: see text]. The contact resistance volatility of the Cu-2[Formula: see text]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.

Decreasing the mechanical anisotropy of the forged Mg-8.5Gd-2.5Y-1.5Zn-0.5Zr alloy by modulating blocky LPSO particles using multi-directional forging

The blocky LPSO particles were modulated by single-directional and multi-directional forging, and the effect of blocky LPSO particles on the anisotropy of mechanical properties of Mg-8.5Gd-2.5Y-1.5Zn-0.5Zr alloy forged parts was investigated. In the present work, 3D processing maps are established, and the forming domain that is both stable and power efficient is in the temperature range from 430 to 500 °C and strain rate range from 0.001 to 0.06 s − 1, which is used to guide the single-directional forging (SDF) and multi-directional forging (MDF) experiments. The tensile mechanical properties reveal that the blocky LPSO particles have an influence on the mechanical anisotropy, especially in terms of the elongation anisotropy. The blocky LPSO particles after the MDF process have a more regular shape and smaller size and are homogeneously distributed, which is responsible for the low anisotropy of the elongation. In addition, the age-hardening capability of the MDF part is higher than that of the SDF part.

Microstructure and mechanical properties of in situ TiB2•TiAl3/2024Al composite subjected to multidirectional forging

The TiB2•TiAl3/2024Al composite fabricated by in situ reaction method was subjected to multidirectional forging (MDF) and the effects of temperature and pass number of MDF on the microstructure and mechanical properties of the composite were investigated. By increasing the MDF temperature (from 350 to 500 °C) or increasing the number of MDF passes (from 1 to 4 passes), the fraction of high-angle grain boundaries (HAGBs) increased, and the average grain size of the Al matrix decreased. The tensile strength and elongation of the composite improved with increasing MDF temperature and pass number. After 4 MDF passes at 450 °C, the average grain size of the composite decreased from 45.00 to 3.08 μm, and the tensile strength and elongation increased by 12.78% and 282.46%, respectively. During the MDF process, a great number of TiAl3 particles fractured, and the size of TiAl3 decreased. Meanwhile, the agglomeration of TiB2 particles reduced, and the clustering of TiB2 particles tended to elongate and directional alignment. Both discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX) occurred during the MDF process, which had a close relationship with the size and distribution of TiB2 and TiAl3 particles. The improvement of strength caused by MDF processing for the studied composite was quantitatively analyzed by models of the strengthening mechanism. The calculated results indicate that the load transfer effect and thermal expansion mismatch effect may partially counteract the effects of grain refinement on the enhancement of strength.

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.

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.

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.

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.

Effect of heat treatment on the microstructure and mechanical properties of a multidirectionally forged Mg-Gd-Y-Zn-Zr-Ag alloy

Multidirectional forging (MDF) was successfully applied to fabricate large-size Mg-Gd-Y-Zn-Zr-Ag alloy in this work and effects of T4, T5 and T6 treatments on the microstructure and mechanical properties of the as-forged alloy were analyzed. Results show that dynamic recrystallization (DRX) occurs and second phase particles precipitate along the grain boundary during the MDF process. After annealing treatment (T4), the volume fraction and size of dynamic precipitates slightly increase at a lower temperature (430 °C) compared with those of MDFed sample, while they are dissolved into the α-Mg matrix at a higher temperature (450 °C). At the meantime, short plate-shaped long-period stacking ordered (LPSO) phases are observed in the DRX grains of the MDFed sample and then dissolved into the α-Mg matrix during annealing at both temperatures. Typical basal texture is identified in the MDFed sample, but the basal pole tilts away from final forging direction and rare-earth texture component with <112¯1> orientation parallel to penultimate forging direction becomes visible after annealing. The T6 sample annealing at 430 °C for 4 h and ageing at 200 °C for 34 h exhibits the superior strength and ductility in this study. The ultimate tensile strength, tensile yield strength and elongation to failure, which is 455 MPa, 308 MPa and 7.7%, respectively, are overall improved compared with the directly-aged (T5) sample. This paper provides a superior heat treatment schedule to manufacture high-performance large-scale Mg-Gd-Y-Zn-Zr-Ag components for industrial production.

Superplastic properties in a Ti5Al3Mo1.5 V titan alloy processed by multidirectional forging process

In this study, ultrafine grains in microstructures of Ti5Al3Mo1.5 V titan alloy was achieved by the multidirectional forging (MDF) process. The essence of the MDF is pressing steps combined with rotations of the workpiece in all directions within a forging cycle. The MDF process was performed for one to three cycles at temperatures from 850 °C to 950 °C. The achieved average grain size in the microstructure is about 1 µm at 900 °C after the third cycle. Subsequently, the superplastic properties after the MDF process were studied. Tensile tests that evaluate the superplastic deformation ability of alloy are performed at high temperatures from 800 °C to 900 °C and the strain rates in the range 10-3 s−1 –9.10-3 s−1. The result obtained the maximum relative elongation of 1120%, showing an exceptional enhancement of superplasticity of the studied alloy.

Strengthening of low-cost rare earth magnesium alloy Mg-7Gd-2Y–1Zn-0.5Zr through multi-directional forging

Conventional rare-earth magnesium alloys have high strength but are not accepted by some fields because of their relatively high price. Magnesium alloys with the addition of small amounts of rare earth elements can improve the mechanical properties by severe plastic deformation while saving cost. In this paper, the effects of multidirectional forging (MDF) process on the microstructure and mechanical properties of low-cost rare earth magnesium alloy Mg-7Gd-2Y–1Zn-0.5Zr were investigated, and the plastic deformation mechanism, dynamic recrystallization mechanism and property strengthening mechanism during the MDF process were analyzed. The results showed that the yield strength, ultimate tensile strength and elongation of Mg-7Gd-2Y–1Zn-0.5Zr alloy were 395.2 MPa, 435.3 MPa and 17.6% after extrusion, MDF at reduced temperature conditions and T5 treatment. The increase in alloy strength is related to solid solution strengthening and is more attributed to the combined effect of grain refinement and aging precipitation. The dynamic recrystallization mechanism leading to grain refinement converts from discontinuous dynamic recrystallization to continuous dynamic recrystallization during MDF at reduced temperatures. And the decrease in deformation temperature leads to difficulties in prismatic and pyramidal slipping, where grain boundary sliding from fine grains and twinning in a few relatively coarse grains play a role in coordinating deformation.

Development of Al 6061 MWCNT MMC processed by Multi-Directional Forging

Al 6061 alloys are benchmarked in aircraft industries due to its remarkable weight to strength ratio, the advancement in this alloys trends exponentially increases. In the present work, Al 6061 metal matrix composite (MMC) is prepared with 2 wt% multi walled carbon nano tubes (MWCNT) reinforcement by stir casting process. After stir casting, the cast material is heat-treated at 555 °C for 8 h, followed by air cooling. The heat-treated material is processed in multi-directional forging (MDF) technique at 200 °C. To study the effect of adding MWCNT reinforcement material to Al 6061 alloy, microstructure study is carried out in scanning electron microscope (SEM) and hardness test is conducted. Also, to study the effect of MDF technique on Al 6061 reinforced with MWCNT microstructural characterization and hardness test is conducted. Increased hardness is noticed after MWCNT reinforcement compared to Al 6061 alloy without reinforcement. Also, MDF processing improved the hardness of the reinforced Al 6061 with MWCNT

Effects of forming parameters on metal flow behaviour during the MDF process: taguchi and response surface methodology optimisation

ABSTRACT In this study, multidirectional forging (MDF) process parameters were optimised using Taguchi analysis and response surface methodology (RSM) for damage and effective strain. The parameters considered in the study were: temperature, friction coefficient, strain per pass, and die speed. Aluminium alloy 7075 (AA 7075) was used as a specimen for analysis during MDF processing. The output responses selected were maximum damage and effective strain. The MDF was undertaken at four levels for each input parameter. The Taguchi L16 orthogonal array was used to determine the interaction of the inputs and the contribution of the parameters. Simulations of the process were carried out on Deform 3D software. The analysis of variance demonstrated that the contribution of strain per pass was the most significant in causing damage and an increment in effective strain. Temperature and die speed were shown to have minimal effects on the outputs. The confirmation simulations demonstrated that the optimal solutions obtained by the Taguchi method had damage of 1.29, and the effective strain was 2.88. The RSM results were 0.19984 and 4.02193 for damage and effective strain, respectively.

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.