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Aiming to achieve silicon nitride (Si 3 N 4) ceramics with high hardness and high toughness, one-dimensional textured Si 3 N 4 -based ceramics, with and without 0.5 vol% ZrB 2 additive, were prepared using spark plasma sintering combined with hot extrusion at temperatures of 1600 °C and 1800 °C. One-dimensional texture (f I = 0.89) was achieved at a hot extrusion temperature of 1600 °C for the Si 3 N 4 ceramic with the introduction of 0.5 vol% ZrB 2. The fracture toughness (7.49 ± 0.47 MPa m1/2) closely approached that of the Si 3 N 4 sample processed at the hot extrusion temperature of 1800 °C (7.95 ± 0.27 MPa m1/2), while the hardness (18.55 ± 0.18 GPa) was significantly higher than that of the Si 3 N 4 sample processed at a hot extrusion temperature of 1800 °C (16.48 ± 0.20 GPa). It was demonstrated that one-dimensional textured Si 3 N 4 -based ceramics with high hardness and toughness can be prepared by the introduction of ZrB 2 combined with low temperature hot extrusion. [ABSTRACT FROM AUTHOR]

• The effect of Yb on the microstructure and mechanical properties of Mg-Li-Zn alloy is proved. • A Mg-Li alloy with a fatigue strength of 130 MPa is developed. • The small-sized MgLiZn phase in the Mg-Li-Zn alloy has been observed. The transformation law of small-sized MgLiZn phase with the Yb content and hot extrusion treatment and its influence mechanism on the microstructure and mechanical properties have been clarified. In this paper, (0.2–1 wt%) Yb was added to improve the tensile properties and high-cycle fatigue behavior of the as-cast and as-extruded Mg-10Li-5Zn-0.5Er alloys. It is found that Yb mainly affects the mechanical properties of the alloy by changing the grain size, type and morphology of the second phases. Yb mainly exists in the formation of Mg 2 Yb and Mg-Zn-Yb phases in the metallographic structure. With the addition of Yb, the grains are refined and these Yb-containing phases replace the large-sized MgLiZn phase to be enriched at the grain boundaries. While the addition of excess Yb reduces the number of small-sized MgLiZn phases in the grain, thus reducing the alloys' mechanical performance. After extrusion, the small-sized MgLiZn phase is refined and the number increases, which effectively improves the tensile and fatigue strength of the alloy. The fatigue strength is mainly affected by the number and morphology of the second phase, positively correlated with the strength. Balanced in grain size and number and size of second phases, the extruded alloy with 0.2Yb added exhibits excellent mechanical properties with the yield strength, ultimate tensile strength and elongation of 292 MPa, 303 MPa and 11.7%, and an fatigue strength of 130 MPa. [ABSTRACT FROM AUTHOR]

To enhance the mechanical properties of Al–(La, Ce) alloys, melt spinning and hot extrusion were employed to fabricate Al-La-Mg-Mn alloy with an ultrafine-grained structure (∼0.56 μm). The as-extruded alloy exhibits the highest tensile strength of 621 ± 4 MPa among Al–(La, Ce) alloys fabricated by various methods while retaining an appreciable elongation of 6.8 ± 1.1 %. The high strength is mainly ascribed to the ultrafine grains and high-volume intermetallics, conferring robust grain boundary strengthening and Orowan strengthening effects. Additionally, this study delved into the high-temperature (400°C) coarsening behavior of the intermetallic and grain size. The findings unveil an exceptionally low coarsening rate of the intermetallic at 400°C (3.19×10−33 m4 s−1), accompanied by only slight grain coarsening, underscoring the remarkable thermal stability of the ultrafine-grained structure. • An ultrafine-grained Al-La-Mg-Mn alloy was fabricated by melt spinning and hot extrusion. • The alloy exhibits the highest strength among all Al-(La, Ce) alloys reported to date. • The microstructural evolution at different stages of hot extrusion was systematically studied. • The as-fabricated ultrafine-grained structure exhibits excellent thermal stability up to 400 °C. [ABSTRACT FROM AUTHOR]

A hundred kilograms of GH4975 extrusion bar, featuring fine equiaxed grains, were successfully fabricated using electron beam smelting layer solidification(EBSL) and hot extrusion techniques. Subsequent analysis focused on the microstructure and tensile properties of the extruded bar. The study also delved into the influence of temperature on tensile deformation behavior and mechanisms of the alloy after standard heat treatment(SHT). The results revealed uniformity in precipitated phase size and morphology across the extruded bar, with grain size being the largest at the center and smallest at the edge. Tensile tests conducted at 20 °C and 650 °C show an obvious work hardening phenomenon, and the deformation mechanism is dominated by APB coupled dislocation pairs shearing. With the increase of deformation temperature, the work-hardening phenomenon gradually weakens, and SFs emerge as the primary deformation mechanism at 750 °C. As the deformation temperature further rises, cross slip, Orowan bypass and dislocation climbing gradually dominate. The fracture mode changes from brittle fracture to ductile and brittle mixed fracture, and ultimately to brittle fracture. Compared with the traditional preparation method, the hundred kilograms of GH4975 extrusion bar prepared by this technology still show better mechanical properties. • A hundred kilogram level of superalloy with γ′ phase content of 64 % was prepared and forged. • The grain size distribution and strength distribution of extruded bar was analyzed. • The yield strength of the alloy at 20 °C, 650 °C and 750 °C is 7 %, 3 % and 12 % higher than that prepared by the traditional method. • The tensile deformation behavior and deformation mechanism at different temperatures are analyzed and discussed. [ABSTRACT FROM AUTHOR]

With rapid development of aerospace and automobile, the service condition of structural components becomes increasingly harsh, diverse and high mechanical properties are urgently needed. In this work, an advanced in-situ ZrB 2np /AA6111 composite with excellent room and high-temperature properties was prepared via Al-Zr-B reaction system. The microstructure revealed that ZrB 2 nanoparticles with regular polygonal shapes ranged from 10 to 150 nm approximately, and a good α-Al/ZrB 2 interface bonding was confirmed. The agglomeration of ZrB 2 particles was significantly weakened during hot extrusion. Due to the inhibiting effect on dislocation motion and pinning effect on grain boundaries induced by ZrB 2 particles, fine recrystallized grains were obtained in ZrB 2 /AA6111 composites after extrusion. Compared with AA6111 matrix alloy, the yield strength, ultimate tensile strength and elongation of AA6111-3ZrB 2 composites at room temperature and 300 °C were increased by 18.9 %, 12.7 %, 50.0 % and 34.1 %, 22.4 %, 42.4 %, respectively. An excellent room and high-temperature strengthening effect was simultaneously achieved assisted by ZrB 2 particles. The improvement of room-temperature properties was mainly owed to the Grain refinement and Orowan bypassing strengthening mechanisms. The good high-temperature properties mainly relied on the superior coarsening resistance of ZrB 2 particles which could fully played the Orowan strengthening effect and well protected the grain boundaries at high temperature. This work provides a feasible approach to design high-performance aluminum alloys and is beneficial for the further development of modern industries. • Room and high temperature properties of AA6111 were improved by ZrB 2 particles. • In-situ ZrB 2 particles showed excellent thermal stability at high temperature. • The DRX was significantly promoted by ZrB 2 particles during hot extrusion. [ABSTRACT FROM AUTHOR]

With growing efforts of electrification, aluminum's role as a light-weight conductor material has become increasingly prominent. There is a critical need to improve the electrical performance of aluminum at room temperature and high operating temperatures. In this study, the effect of graphene nanoparticle additives on the electrical performance of a non-heat treatable alloy were (AA3003) explored. Graphene's unusual structure and electronic properties were used to improve AA3003 properties. Here, the effects of graphene on the evolution of electrical properties and microstructural features have been explored on lab scale hot extruded AA3003-graphene composites. Hot pressing schedules and extrusion temperatures were varied to investigate changes in intermetallic dispersion characteristics in the presence of dispersed graphene. We measured a reduction of 10.3 % in the temperature coefficient of resistance in the AA3003 sample with 0.05 wt% graphene extruded at 400 °C, along with a maximum increase of 1.1 % in electrical conductivity at 20 °C. Increasing the hot-pressing times up to 8 hours was also found to consistently increase the electrical conductivity, due to increased precipitation of intermetallic phases. Despite being a non-heat treatable alloy, AA3003 displays interesting precipitation dynamics and grain recrystallization trends that can be modulated with varying levels of heat treatment, graphene concentrations, and hot extrusion process parameters. [Display omitted] • AA3003 temperature coefficient of resistance decreased by >10 % by graphene addition. • Improved performance by optimized hot-pressing parameters, extrusion temperatures. • AA3003 precipitation dynamics modulated by processing conditions, graphene presence. [ABSTRACT FROM AUTHOR]

In order to prepare the Cu–18Sn-0.3Ti alloy with excellent mechanical properties to realize the favorable collaborative deformation of Cu–18Sn-0.3Ti alloy and Nb in the preparation process of Nb 3 Sn superconducting wires by bronze method, the hot extrusion process of the Cu–18Sn-0.3Ti alloy prepared by Direct Current assisted Hot Pressed sintering based on micron atomized spherical alloy powders was systematically investigated by the combination of experiments and finite element simulation in this work. The ultimate tensile strength, yield strength and elongation can reach 683.5 MPa, 414.3 MPa and 33.3 %, respectively, through the optimization of hot extrusion parameters and subsequent solution treatment. The results show that hot extrusion with high strain rate induced the formation of fine α grains and dispersed δ phases. Especially, strong dislocations-annealing twins (ATs) interaction occurred, which was manifested as the pile-up of dislocations at twin boundaries of ATs, slippage of dislocations in multiple directions inside ATs and storage of dislocations inside ATs. Meanwhile, the high strain rate induced the formation of deformation twins inside partial grains. The grain refinement of α matrix, formation of dispersed δ phases and strong interactions of crystal defects were the main reasons for the strength-ductility enhancement of hot extruded samples, and laid an excellent microstructure foundation for further improving the mechanical properties of alloy by subsequent solution treatment. The results not only describe a feasible method for simultaneously enhancing the strength and ductility of Cu–18Sn-0.3Ti alloy, but also provide a theoretical guidance for the strength-ductility enhancement of multicomponent alloys. • The Cu–18Sn-0.3Ti alloy with excellent strength and ductility was prepared. • Fine grains, dispersed phases were formed by hot extrusion with high strain rate. • The strong interaction between the annealing twins and dislocations was revealed. • Finite element simulation was established to reveal the extrusion process of alloy. [ABSTRACT FROM AUTHOR]

Digestibility and retrogradation properties of starch are important for the nutrition and quality of starch-based foods. In this study, a new idea on the synchronous delay the starch digestion and retrogradation was proposed, and the regulation mechanism was explored from perspectives of structural evolution using 13C NMR, XRD and SAXS techniques as well as the molecular dynamics simulations. Results showed that the chestnut starch treated with hot extrusion and 8% catechins (HE-8% CA)## could reach highest anti-retrogradation rate (AR 76.63%) and lowest rapidly digestible starch content (RDS 64.55%) at day 24. The starch digestion was slowed down by increasing single/double helix, V-type crystallinity and compactness of aggregates, while retrogradation process was suppressed by inhibiting the packing of short-range ordered structure into long-range ordered structure. The hydrogen bonding and van der Waals forces were the main driving force for the interactions between flavonoid polyphenols and starch molecules. Overall, this study is instructive for further investigations on the synchronous modulation of functional properties of starch. • The digestion and retrogradation of CS were synchronously slowed down. • The formation of crystalline structure was inhibited during retrogradation process. • The non-covalent interaction with flavonoid polyphenols promoted the formation of short-range ordered structure of CS. • The catechins had a better slowing effect due to the smaller molecular structure. • The correlation and regulation mechanism were further revealed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Effective dispersion and good structural integrity for high-content GNS resulted from the hybridization of SiCnp. • The (SiCnp + GNS)/Al composites exhibited refined nanograins and intra-crystalline nanoparticle distribution. • Significantly improved work-hardening capacity was attributed to SiCnp-induced lattice distortion. • Simultaneous enhanced strength and toughness of GNS/Al composite was achieved by hybrid effect with SiCnp and GNS. Good strength-ductility balance in graphene nanosheet (GNS)-reinforced aluminum nanocomposites can be achieved through tailorable and facile agglomeration control. Our previous study showed that pre-modulating the Al powder morphology by adding hard silicon carbide nanoparticles (SiCnp) during the two-step ball milling process effectively promotes the uniform dispersion of GNSs. However, excess SiCnp content causes SiCnp aggregate and premature cracking of composites. Here, GNS-reinforced aluminum nanocomposites with different SiCnp content (0.3–1.5 vol%) were prepared, and the optimal SiCnp-to-GNS ratio was determined after optimizing the SiCnp content in a pre-studied composite preparation process. The effect of SiCnp on the microstructure and mechanical properties of the composites was systematically investigated. The cold welding deformation of Al flakes increased with the SiCnp content. Nonetheless, inadequate or excessive SiC content caused insufficient lamination or excessive cold-weld stacking of Al flakes, respectively. Al-0.9vol.%SiCnp powders possessed the highest specific surface area which resulted in high homogeneous dispersion of 3.0 vol% GNS during the second ball-milling stage. Consequently, the resulting hybrid reinforced (GNS + SiCnp)/Al composites showed simultaneous improvement in strength and plasticity, unlike Al-3.0vol.%GNS composites. This showed that introducing hard nanoparticles (i.e., the hybridization strategy) is a promising method to simultaneously enhance strength and plasticity of aluminum nanocomposites. [ABSTRACT FROM AUTHOR]

Magnesium (Mg) alloys are promising materials for cardiovascular stent applications due to their good biocompatibility and biodegradability. However, in vitro and in vivo corrosion tests reveal that Mg alloy stents suffer from a rapid corrosion rate and severe localized corrosion, which is limiting their widespread application. To solve the problem of uneven degradation of stents, a HTHE (long-time and high-temperature heat treatment, large-reduction-ratio hot extrusion) process is used to manufacture Mg-Zn-Y-Nd alloy microtubes in this study. The heat treatment is to dissolve alloying elements and reduce the size of SPPs, and the hot extrusion is to acquire fine-grained and strongly textured microtubes. The microstructural characterization shows that coarse second phases in as-cast alloy are refined and uniformly distributed in matrix of microtubes. After hot extrusion, microtubes show strong texture with basal plain oriented parallel to the longitudinal section (LS). The corrosion testing indicates that severe localized corrosion occurs on the cross section (CS) while localized corrosion is alleviated on the LS. Based on the different corrosion properties of the LS and CS, HTHEed microtubes are promising for solving the problems of rapid corrosion rate and severe localized corrosion of Mg alloy stents. [ABSTRACT FROM AUTHOR]

In the present study, a new biodegradable Mg-Zn-Cu magnesium alloy was introduced for biological applications. The microstructural analysis showed the formation of MgZnCu intermetallics for the Mg-2Zn-0.1Cu alloy and also the Mg(Zn,Cu) 2 compounds for the Mg-2 Zn alloys with higher Cu contents. Moreover, the hot extrusion was applied for the grain refinement and changing the distribution of intermetallics. In vitro immersion tests, electrochemical and corroded surface analyses represented the enhancement of corrosion resistance with 0.1 wt.% Cu addition. Furthermore, the extruded alloys demonstrated more corrosion resistance behavior than that of the cast alloys. By considering the improved tensile properties of Mg-2Zn-0.1Cu alloy, this alloy was regarded as the potential candidate for use as the biodegradable magnesium implant. [ABSTRACT FROM AUTHOR]

• Highly c -axis textured β-silicon nitride (β-Si 3 N 4) ceramics without seeding was prepared by a new method of hot extrusion using spark plasma heating at 1800 °C in 10 min. • The (002) pole figure showed a characteristic of center rotational symmetry and an average cline angle between hot extruding direction and [ 00l ] direction of β-Si 3 N 4 grains as low as 8.7°. • Higher hardness was achieved mainly due to the finer grain size compared to that of c -axis textured Si 3 N 4 ceramics with seeding. Highly c -axis textured β-silicon nitride (β-Si 3 N 4) ceramic with fine grains was prepared by a new method of hot extrusion for the first time. The (002) pole figure on the section plane vertical to extruding direction showed a characteristic of center rotational symmetry. The average cline angle between elongated β-Si 3 N 4 grains and hot extruding direction was about 14.4°. The degree of c -axis texturing by hot extrusion was comparable to that achieved by rotating magnetic field. The hardness and toughness anisotropy in different direction was apparent and relatively higher hardness was achieved in the present work mainly due to the finer grain size. Therefore, many different compositions of c -axis aligned Si 3 N 4 -based ceramics with tailored mechanical properties could be achieved by the strategy of hot extrusion. [ABSTRACT FROM AUTHOR]

• Effect of extrusion temperature on properties of Mg–Zn–Ca–(Mn) alloys was studied. • Addition of Mn and decrease in extrusion temperature caused grain refinement. • Addition of Mn significantly reduced the corrosion rate of the alloys. • Mg–2 wt% Zn–0.7 wt% Ca–1 wt% Mn showed excellent mechanical and corrosion properties. Biodegradable Mg-based implants are widely used in clinical applications because they exhibit mechanical properties comparable to those of human bone and require no revision surgery for their removal. Among Mg-based alloys, Mg–Zn–Ca–(Mn) alloys have been extensively investigated for medical applications because the constituent elements of these alloys, Mg, Zn, Ca, and Mn, are present in human tissues as nutrient elements. In this study, we investigated the effect of the hot extrusion temperature on the microstructure, mechanical properties, and biodegradation rate of Mg–Zn–Ca–(Mn) alloys. The results showed that the addition of Mn and a decrease in the extrusion temperature resulted in grain refinement followed by an increase in the strength and a decrease in the elongation at fracture of the alloys. The alloys showed different mechanical properties along the directions parallel and perpendicular to the extrusion direction. The corrosion test of the alloys in the Hanks' solution revealed that the addition of Mn significantly reduced the corrosion rate of the alloys. The Mg–2 wt% Zn–0.7 wt% Ca–1 wt% Mn alloy hot-extruded at 300 °C with an ultimate tensile strength of 278 MPa, an yield strength of 229 MPa, an elongation at fracture of 10%, and a corrosion rate of 0.3 mm/year was found to be suitable for orthopedic implants. [ABSTRACT FROM AUTHOR]

During hot extrusion of copper, the material tends to stick to the extrusion die due to strong adhesive forces between hot working steel and copper at high temperatures. In this context, surface modifications like nanocomposite coatings deposited by plasma enhanced chemical vapor deposition or boriding of nickel-based alloy 718 (DIN 2.4668) create hard and wear resistant thin solid films that offer high temperature stability. Ti–Si–B– C –N nanocomposite coatings consist of nanocrystalline grains embedded in a thin amorphous matrix. Due to this particular nanostructure, hardness values of up to 39.3 GPa were reached. Boriding of alloy 718 leads to formation of phases consisting of alloying elements like nickel, iron, and chromium and the diffusing element boron. The borides form a boriding zone that offers high hardness. Extrusion of Ø122 mm × 300 mm copper billets preheated to 850 °C was carried out and adhesive wear on tool's surfaces was analyzed. The comparison between hot working steel DIN 1.2367 without surface modification and with Ti–Si–B– C –N coating or borided alloy 718 showed remarkable differences between conventional tools made of hot working steels/alloy 718 and tools with surface modification. A strong decrease particle adhesion was observed. [Display omitted] • Extrusion dies' surfaces were modified to increase thermal stability and hardness. • Extrusion experiments with Cu showed decrease in adhesive wear on extrusion dies. • Boriding of alloy 718 was carried out during precepitation hardening. [ABSTRACT FROM AUTHOR]

In the present work, 0.6 wt% graphene nanoplatelets reinforced 6061Al (GNPs/6061Al) composite was prepared by pressure infiltration process and hot extruded (HE) at 420 °C∼500 °C in order to investigate the evolution of GNPs in different extrusion temperature, which has not been reported yet. The GNPs agglomeration were eliminated by extrusion and were arranged in an orientation. In the sample extruded at 420 °C, the dispersion effect was not significant and agglomeration of large-sized GNPs was still found. However, the agglomeration of the GNPs was eliminated when extruded at 450 °C, and waved structure, exfoliation and bend of GNPs were observed. While in the sample at 500 °C, interlayer sliding of GNPs and interfacial reaction product Al 4 C 3 , due to excessively high extrusion temperature, were detected. The composites extruded at 450 °C showed the highest yield strength and ultimate tensile strength of 389 MPa and 500 MPa, respectively, which increased 16.8% and 40.1% comparing with the unreinforced matrix. The present results indicate that the uniform dispersion of graphene is still one of the main challenges in Graphene/Al composites, while the deformation treatment provides the possibility of further dispersion of graphene. Image 10409751 [ABSTRACT FROM AUTHOR]

Mg matrix composites were often reinforced by non-deformable ceramic particles. In this paper, a novel Mg matrix composite reinforced with deformable TC4 (Ti–6Al–4 V) particles was fabricated and then extruded. The evolutions of microstructure and mechanical properties of the composite during hot extrusion were investigated. Hot extrusion refined grains and eliminated the segregation of TC4 particles. TC4 particles, as deformable particles, stimulated the nucleation of dynamic recrystallization during extrusion. However, since the deformation of TC4 particles partly released the stress concentrations around them, the recrystallized grains are just slightly smaller around TC4 particles than that away from them, which is evidently different from the case in Mg matrix composites reinforced by non-deformable ceramic particles. Compared with AZ91 matrix composites reinforced by SiC particles, the present composite possesses the superior comprehensive mechanical properties, which are attributed to not only the strong interfacial bonds between TC4p and matrix but also the deformability of TC4 particles. [ABSTRACT FROM AUTHOR]

Hot extrusion, a process to eliminate casting defects and regulate microstructure, is an industrial commonly used approach for preparing synchronizer rings. In this present study, the titanium-silicon brass tube reinforced by Ti 5 Si 3 short fibers with different orientations were prepared through the hot extrusion. Correspondingly, the effect of Ti 5 Si 3 orientation on the mechanical properties and wear resistance of titanium-silicon brass were investigated and revealed. Results demonstrated that, through hot extrusion, the original randomly distributed Ti 5 Si 3 short fibers are arranged parallel to the extrusion direction with the aspect ratio reducing from 20 to 5. It is also suggested that significant anisotropy is exhibited in tensile strength and wear resistance of the titanium-silicon brasses with different Ti 5 Si 3 short fibers orientations. The yield strength of the sample obtained from the extrusion direction improves by ∼12 % compared with that of obtained from the transverse direction. In addition, Ti 5 Si 3 short fiber, parallel to the friction surface and parallel to the sliding direction, exhibits the best wear resistance by resisting the plastic deformation of the subsurface layer. However, for Ti 5 Si 3 perpendicular to the friction surface, the matrix of brass would undergo the coordinated deformation deteriorating the wear resistance. Such underlying mechanism for the effect of Ti 5 Si 3 orientation on the strengthening mechanism and wear mechanism was discussed and clarified with incorporation of finite element simulation. It is anticipated that this present study would provide an effective strategy and significant guidance for designing the brass with excellent mechanical properties and wear resistance. • Hot extrusion result in the formation of aligned Ti 5 Si 3 short fibers and elongated grain. • Strength anisotropy originating from elongated grain and aligned Ti 5 Si 3 short fibers is revealed with corporation of FEA. • Ti 5 Si 3 short fibers parallel to the friction surface and sliding direction significantly improve the wear resistance. • Hot extrusion is an effective process to obtain excellent wear resistance for titanium-silicon brass. [ABSTRACT FROM AUTHOR]

The Zn-rich Al-11.3Zn-2.65Mg-1Cu alloy was prepared by spray forming rapid solidification technology and then processed by hot extrusion and heat treatment to T6-temper condition. The characteristics of spray-formed and extruded materials are systematically investigated, and accordingly, solution treatment parameters are derived at an intermediate temperature. The tensile results indicate that the alloy can reach yield strength as high as 807 MPa due to massive precipitation of ή phase which is attributed to the high supersaturation of the solutionized alloy because of the cumulative effect of spray forming and optimal solution treatment. • The spray-formed microstructure exhibited equiaxed grains with some porosity. • The hot extrusion densified the material to 99.4% relative density. • The solutionized alloy showed less residual phases and fewer recrystallized grains. • The peak-aged alloy displayed yield strength of 807 MPa. • The technique demonstrated superior characteristics than conventional casting. [ABSTRACT FROM AUTHOR]

Cyclic stability is vital for the application of the elastocaloric effect. We demonstrated here the enhanced cyclic stability in a Ni 50.4 Mn 27.3 Ga 22.3 alloy via hot extrusion. The fine equiaxed grains with 〈111〉 A texture were obtained after hot extrusion at 1323 K. The extruded alloy showed >250 stable elastocaloric cycles without degradation. The mechanism for the enhanced cyclic stability was the presence of fine grains and low energy dissipation related to the 〈111〉 A texture. So, hot extrusion may provide a feasible strategy for improving the eCE stability in polycrystalline ferromagnetic shape memory alloys. Unlabelled Image [ABSTRACT FROM AUTHOR]

Abstracts The electrochemical behaviors and discharge performance of an as-extruded Mg-1.5 wt%Ca alloy anode were investigated as well as the corrosion behaviors. The as-extruded Mg-1.5 wt%Ca anode exhibits a superior discharge performance than the as-extruded CP Mg anode. It can exhibit high energy density of 1413 mWh·g−1 with a satisfactory specific capacity (1296 mAh·g−1) at 20 mA·cm−2. The fine DRXed grains (15 ± 2 μm) and the active Mg 2 Ca particles around grain boundaries are responsible for the promoted discharge performance. Furthermore, the fine and dispersive Mg 2 Ca particles are favor of the uniform consumption of Mg anode during discharge. The detachment of discharge products of Mg-1.5 wt%Ca anode is more difficult than that of CP Mg, resulting an early failure of discharge at 80 mA·cm−2. The corrosion behaviors are also discussed in detail. Highlights • The as-extruded Mg-1.5 wt%Ca anode exhibits superior discharge performance. • It exhibits both high energy density and specific capacity at 20 mA·cm−2. • The high discharge performance is due to the dispersed Mg 2 Ca phase by extrusion. [ABSTRACT FROM AUTHOR]

In this work, nanostructured aluminum titanate (Al 2 TiO 5 or AT) was synthesized by the citrate sol gel method. Then, different volume fractions of this ceramic were blended with Al powder through different durations of the high-energy vibratory milling. The effect of mechanical milling on the thermal degradation of AT in exposure to Al and formation mechanism of in-situ Al 2 O 3 and Al 3 Ti particles were explored in three conditions: (i) in the powder form; (ii) after annealing of green compact; and (iii) after hot extrusion. In the powder form, it was shown that the mechanical milling is able to significantly diminish the thermal stability of AT, so that the required temperature for the Al 3 Ti formation decreases from 600 to about 450 °C. Also, by extending the mechanical milling duration, the contact surface for interfacial reactions between Al and AT increases and the formation of Al 3 Ti and Al 2 O 3 is facilitated. By selecting the optimum duration of mechanical milling, this study successfully fixed the microstructure problems of not-milled as-annealed composites i.e. unreacted AT particles and oxygen evolution-arisen cracks, and produced in-situ composite inside each Al particle. However, the induced work hardening of these milled particles hinders the perfect consolidation. To deal with this challenge, the hot extrusion at 535 °C was conducted. The obtained microstructure was composed of very fine (≤200 nm) semi-spherical Al 3 Ti and Al 2 O 3 particles uniformly distributed within the Al matrix. To evaluate the mechanical response of the fabricated nanocomposites, the micro-hardness and nanoindentation testing were carried out. The results proved that the hardness and elastic modulus of the nanocomposites reach 143 HV and 90 GPa, respectively, indicating a significant improvement in the mechanical properties of these systems compared to not-milled extruded composites. Finally, the role of reinforcing particles in strengthening of composite was evaluated. • Nanostructured Al 2 TiO 5 particles were synthesized by the citrate sol gel method. • The high-energy ball milling was used to destabilize the ceramic particles. • Hybrid in-situ Al-(Al 3 Ti + Al 2 O 3) composite was produced by conventional sintering. • Hot extrusion was used after the sintering to obtain a fully dense nanocomposite. • Nanoindentation studies were conducted to measure elastic modulus and hardness. [ABSTRACT FROM AUTHOR]

Abstract In this study, the effect of hot extrusion on the microstructure and anti-corrosion performance of LDHs (layered double hydroxides) conversion coating on AZ91D magnesium alloy was investigated by means of microscopic observation and electrochemical measurement. After hot extrusion, the refinement and rearrangement of the β-Mg 17 Al 12 phase promotes the microgalvanic effect in the formation process, and the increase of dislocation density, twin, grain boundary and texture accelerates the dissolution rate of the Mg matrix. Due to microstructural differences, the electrochemical activity of various specimens in the formation process can be ranked as the increasing series: as-cast < transverse < longitude. Therefore, a thicker and more compact LDH conversion coating is formed on the longitudinal section of the extruded alloy, indicating the highest anti-corrosion performance. Highlights • The CO 2 pressurization method is the most environmentally friendly method. • The microstructure of the alloy was combined with the formation mechanism. • The formation mechanism of effect for β-Mg 17 Al 12 phases was found. • The role of microgalvanic and electrochemical activity was confirmed. [ABSTRACT FROM AUTHOR]

The microstructure, texture, and mechanical properties of as-extruded Mg- x Li-3Al-2Zn-0.2Zr alloys (x = 5, 7, 8, 9, 11 wt%) were investigated. After hot extrusion, the filamentous AlLi phase in α-Mg is crushed into tiny particles, while the morphology of round-like AlLi phase in β-Li remains unchanged. The threadlike MgLi 2 Al phase precipitated during hot extrusion only distributes along the grain boundaries of β-Li phase. The grains of as-extruded alloys are refined markedly due to dynamic recrystallization (DRX), and α-Mg phase undergoes discontinuous DRX while β-Li phase undergoes continuous DRX. The { 0001 } basal, { 10 1 ¯ 0 } and { 11 2 ¯ 0 } prismatic fiber textures formed in α-Mg phase suggest the activation of both basal and prismatic slip, and the intensity of prismatic texture is higher than that of basal texture. In β-Li phase, as the extrusion temperature increases and the Li content decreases, the intensities of α fiber and { 110 } 110 textures decrease while those of γ fiber and { 110 } //ED textures increase. Compared with as-homogenized alloys, the mechanical properties of as-extruded alloys are significantly improved owing to grain refinement strengthening, texture hardening, strain hardening, and second phase strengthening. [ABSTRACT FROM AUTHOR]

Abstract High-temperature shape memory alloys are promising candidates for actuation/damping applications at elevated temperatures. To account for pronounced instabilities at elevated temperatures of conventional alloys, novel alloy systems have been developed to address this issue. Yet, most systems suffer from high costs/limited formability. Bamboo-like microstructures have proven to provide for a suitable microstructural condition for superior performance in numerous alloys, however, robust processing of promising high-temperature shape memory alloys is challenging. The current study reports on a novel thermo-mechanical processing route allowing robust processing of hard to form Co-Ni-Ga shape memory alloys. This will assist to overcome a major roadblock towards widespread use of these materials. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

Abstract In this paper, Ti600 alloy was successfully prepared by elemental powder metallurgy method followed by subsequent hot extrusion (950 °C, extrusion ratio of 9:1) and vacuum annealing. The microstructure and mechanical properties were systematically investigated. The as-sintered alloy presented Widmanstatten microstructure and large amount of pores. After extrusion, the pores had been closed, and the as-extruded microstructure consisted of both DRX grains and elongated grains. In addition, the as-extruded Ti600 alloy exhibited (0002) αTi //ED fiber texture and two types of ultrafine precipitates Y 2 O 3 and (TiZr) 6 Si 3 were observed within the grains. In comparison with the as-sintered sample, the mechanical properties of the specimen after extrusion were significantly improved, and the maximum yield strength of 1450 MPa was achieved. After annealing below the β transition temperature, the microstructure mainly contained equiaxed grains. The corresponding yield strength and hardness gradually reduced but the failure strain increased, and the maximum compressive failure strain of 38% was obtained after annealing at 950 °C. After annealing at 1050 °C in the β single-phase region, the bi-model structure was obtained. As the annealing temperature increased to 1100 °C, the alloy completely changed to Widmanstatten structure. The corresponding yield strength and hardness increased but the failure strain reduced. [ABSTRACT FROM AUTHOR]

Abstract Simultaneous enhancement of the strength and ductility in metal-matrix nanocomposites with high content nano-reinforcements is crucial for the development of novel composite materials. Here SiC/Al nanocomposites with ultrafine Al grains and intragranular 10 vol% SiC nanoparticle were prepared by mechanical alloying and hot pressure sintering followed by hot extrusion. The results show that nanocrystalline Al grains and uniformly distributed SiC nanoparticles (SiC np) in the composite powders are obtained after ball-milling. The prior particle boundary (PPB) in the composite powders cannot be fully removed by sintering at 580 °C under 20 MPa, but can be eliminated by subsequent hot extrusion at 450 °C with a ratio 25:1. The extruded nanocomposites possess ultrafine Al grains with diameter 320 nm and intragranular SiC np created by the dynamic recrystallizations (DRX). Such optimal microstructure favors a significant improvement of 284% in yield strength (YS) and 259% in ultimate tensile strength (UTS) compared with monolithic Al, and more interestingly, maintains an elongation up to 12% due to the homogeneous nanoparticles in fine Al grains. Theoretical analysis shows that the dominant strengthening factor is Orowan strengthening related to the high content intragranular SiC np , with second factor grain boundary strengthening due to ultrafine Al grains. [ABSTRACT FROM AUTHOR]

Abstract In general, graphene nanoplatelets (GNPs) did not entirely imparted their extraordinary properties to the particulate magnesium matrix composites (PMgMCs) due to the poor wettability between GNPs and Mg matrix alloys as well as presence of agglomerated GNPs. Therefore, in this study, microstructure and mechanical characterizations were used to investigate effect of GNPs content on the microstructural and mechanical properties of AZ80 magnesium alloy. Current study explored the potential and mechanism of GNPs in improvement of mechanical properties of PMgMCs with insight of microstructure. Therefore, AZ80 reinforced by low contents of GNPs (0.1 and 0.6 wt%) were fabricated by rheo casting followed by hot extrusion. Simultaneously enhancement of tensile properties, the strengthening and the fracture strain efficiencies were achieved in AZ80/0.1GNPs composite by cost effectiveness and simple adaptability of manufacture method which results fairly uniform distribution of GNPs. The addition of 0.1 wt% GNPs led to grain refinement (~10%), dynamic recrystallization, stronger basal texture (~750%), more dissolution of β-eutectic phase (~66%) which results more dynamic precipitates (~70%) and reduction of yield asymmetry (~23%). Compared to the AZ80 alloy, the tensile and compressive yield strengths of AZ80/0.1GNPs composite were enhanced by 40% and 15%, respectively. In both tensile and compressive testes, the effective load transfer was the most important strengthening mechanism. Also, the tensile and compressive failure strains of AZ80/0.1GNPs nanocomposite were enhanced by 50% and 37%, respectively. The uniform dispersion of GNPs, increase of non-basal slip, grain refinement, lower eutectic content and smaller discontinuous intergranular precipitates increased failure strain. [ABSTRACT FROM AUTHOR]

Abstract Mechanical properties of Mg‑Al‑Ca in-situ composite in the as-cast state and after hot deformation (by extrusion process) were evaluated and discussed based on the detailed microstructural analysis. The as-cast microstructure, containing α‑Mg, primary Al 2 Ca particles, and eutectic cells (α‑Mg + Mg 2 Ca and α‑Mg + Al 2 Ca), showed poor room temperature mechanical properties due to the presence of a large fraction of intermetallic phases with unfavorable morphology. The extrusion process resulted in a grain-refined microstructure introduced by dynamic recrystallization (DRX) accompanied with homogeneously distributed fragmented intermetallic particles. It was shown that the grain size of extruded specimens decreases with decreasing deformation temperature (decreasing the Zener-Hollomon parameter) and increasing extrusion ratio. Based on the electron backscattered diffraction (EBSD) analysis, the particle-stimulated nucleation (PSN) was characterized to be a major recrystallization mechanism during hot extrusion of Mg‑Al 2 Ca‑Mg 2 Ca composite. The room temperature, tensile properties of the as-cast composite were comparable to those obtained for the as-cast AZ91 (Mg‑9Al‑1Zn) alloy. The mechanical properties of the composite were significantly enhanced by the hot extrusion process. Moreover, the results of the tensile tests at 300 °C revealed that the tensile strength of the extruded Mg‑Al 2 Ca‑Mg 2 Ca composite is much higher than that of the extruded AZ91 alloy. Such improvement was related to the presence of thermally stable intermetallic phases in the composite microstructure. As a result, the designed Mg‑Al 2 Ca‑Mg 2 Ca composite might be suitable for use in high-temperature structures, where many commercial alloys are not applicable. Graphical Abstract Unlabelled Image Highlights • The effect of hot extrusion on the microstructural and tensile properties of Mg‑Al2Ca‑Mg2Ca in-situ composite. • The highest UTS of 411 MPa was observed. • Composite is suitable for use at elevated temperatures. • The preparation of this composite is easy and not expensive compared to usual high-temperature strength Mg composites. [ABSTRACT FROM AUTHOR]

The pursuit of strong and ductile titanium alloys for critical structural applications remains a constant focus in metallurgical engineering research. To evaluate the microstructure evolution and strengthening effect of Rhenium (Re) addition, binary alloys of Ti– x Re (x = 0, 2, 4, 6 wt%) were fabricated via spark plasma sintering and hot extrusion techniques. Microstructure characterization by electron backscatter diffraction (EBSD) and transmission electron microscope (TEM) revealed the presence of equiaxed α and β phases in the extruded materials, with an increased fraction of β phase corresponding to higher Re concentrations. X-ray diffraction (XRD) analysis indicated lattice expansion in the β phase due to Re diffusion, suggesting solid solution formation and preferential diffusion of Re into the β phase. Moreover, Re increments of 4 and 6 wt% resulted in significant grain refinement towards the formation of ultrafine grains (0.8 and 0.6 µm, respectively). The extruded Ti–Re alloys exhibited a linear strengthening trend, with an increase of 250–300 MPa per 2 wt% Re added. The yield strength of Ti–6Re exceeded three times higher than that of commercially pure (CP) Ti produced via a similar process, while maintaining over 13 % elongation. Re increment was also found to influence the deformation behavior of the extruded Ti–Re alloys during tensile test. This comprehensive investigation provides valuable insights into the microstructural changes and strengthening mechanisms associated with the addition of Re in titanium alloys, contributing to the ongoing efforts in developing high-performance materials for critical structural applications. • High strength and ductile Ti–Re alloys were fabricated by SPS and hot extrusion. • Multi-factor strengthening mechanisms were studied quantitatively. • Re addition triggered the formation of ultrafine grain microstructures. • Re strongly affected the work hardening behavior of Ti–Re alloys. [ABSTRACT FROM AUTHOR]

In most metallic materials, the strength-ductility trade-off serves as an inevitable scenario. Therefore, improving the room/high-temperature strength/ductility of high Nb-TiAl alloys based on a lamellar microstructure is important for practical applications. In this work, a novel microstructure with fine lamellar colonies and a certain number of residual γ grains was developed through hot extrusion in the near α phase region. The results indicated that the lamellar colony size and spacing of the as-cast alloy were significantly refined by hot extrusion. The as-extruded Ti-45Al-8Nb-(W, B, Y) alloy demonstrated a good combination of high strength and ductility. The tensile strength and ductility were 1129 MPa and 2.04% at room temperature (RT), respectively, and 744 MPa and 51.20%, respectively, at 850 °C. A simultaneous improvement in strength and ductility below ductile-brittle transition temperature (DBTT) could be attributed to the abundant deformation twins and their intersections, as well as prominent strain working caused by high-density dislocations in the γ phase. Due to dynamic recrystallization, the ductility was significantly enhanced when stretched over DBTT. This extrusion-assisted microstructure tailoring strategy could be extended to other TiAl systems and may serve as a useful solution for addressing the significant engineering constraints posed by the low RT ductility and poor hot-working capabilities of high Nb-TiAl alloys. • A newly developed high Nb-TiAl alloy with a fine and uniform microstructure was prepared by simple hot-extrusion. • The tensile behavior and flow stress of alloys are sensitive to temperature. • A good combination of high strength and ductility of as-extruded specimen are 1129 MPa and 2.04% at RT. • Grain refinement, dislocations, twins, twin intersections, and DRX improve strength and ductility of high Nb-TiAl alloy. [ABSTRACT FROM AUTHOR]

The microstructure and corrosion behavior of Mg-8Li-3Al-2Zn(−1.0Gd) alloys were investigated. In as-homogenized LAZ832(−1.0Gd) alloys, galvanic corrosion occurs at α-Mg/β-Li phase interface, and pitting corrosion occurs in α-Mg matrix and β-Li matrix. After hot extrusion, the corrosion form of α-Mg matrix changes to intergranular corrosion. The corrosion resistance of LAZ832 alloy is effectively improved by combining Gd alloying and hot extrusion, and as-extruded LAZ832–1.0Gd alloy exhibits the best corrosion resistance with a corrosion rate of 0.64 mm·y−1. Gd alloying improves corrosion resistance mainly due to the formation of Al 2 Gd phase, the reduction of AlLi phase, and the formation of oxide film containing Gd 2 O 3. Hot extrusion improves corrosion resistance mainly attributed to the increase in the share of basal orientation and the crushing of fibrous AlLi phase. • Hot extrusion turns the corrosion of α-Mg from pitting to intergranular corrosion. • Gd alloying and hot extrusion improve the corrosion resistance of LAZ832 alloy. • Gd alloying leads to the formation of protective oxide film containing Gd 2 O 3. • The increase in the share of basal orientation benefits to corrosion resistance. • As-extruded LAZ832-1.0Gd alloy has the best corrosion resistance (P W =0.64 mm·y−1). [ABSTRACT FROM AUTHOR]

In this paper, the microstructural evolution, precipitation behavior and mechanical properties of 2195 Al-Li alloys prepared by powder metallurgy (PM) combined with hot extrusion were investigated systematically. The results show that the deformation of PM 2195 Al-Li alloys during hot extrusion is dominated by the coupling of dynamic recovery with continuous dynamic recrystallization. The homogeneously distributed needle-like T 1 phase is precipitated in the matrix after T6 treatment. The T6-treated sample exhibits a perfect combination of strength and ductility, that is, ultimate tensile strength of 662 MPa, yield strength of 617 MPa and uniform elongation of 6.6 %. The strengthening of heat-treated alloys originates from densification, work hardening, grain refinement and precipitation strengthening. It is noted that the precipitation strengthening of T 1 phase is the dominant mechanism. Therefore, this work should suggest a strategy for developing novel Al-Li alloys with excellent mechanical properties. • The 2195 Al-Li alloys were successfully prepared by powder metallurgy and hot extrusion. • The tensile strength, yield strength and elongation of the 2195 Al-Li alloy were 662 MPa, 617 MPa and 6.6 %, respectively. • Mechanical properties of the alloy were enhanced by densification, work hardening, grain refinement and precipitation. • The precipitation strengthening of T 1 phase is the dominant mechanism. [ABSTRACT FROM AUTHOR]

Novel in-situ polycarbosilane (PCS)-derived TiC particles reinforced Ti6Al4V composites with ultrahigh strength and good ductility were fabricated by powder extrusion. The grain microstructure, dynamic recrystallization (DRX), texture orientation, mechanical properties and strengthening mechanisms were systematically investigated. The pyrolysis of PCS and in-situ reaction with Ti6Al4V matrix promote the formation of TiC particles and Si atoms solid-solution. TiC particles provide many heterogeneous nucleation sites for DRX and restrict grain growth by pinning effect, forming many fine equiaxed α grains. The average grain size of α-Ti is refined from 50.17 μm in as-sintered Ti6Al4V alloy to 3.17 μm in as-extruded Ti6Al4V-3PCS composite. The basal texture with {0001}<11 2 ‾ 0> orientation is dominant in the as-extruded microstructures, originating from the deformed α grains during β single-phase extrusion. The incorporation of PCS activates the occurrence of DRX and weakens the {0001}<11 2 ‾ 0> basal texture. Benefiting from the in situ formed TiC particles, solid solution Si atoms and low interstitial oxygen (O) contamination, the as-extruded Ti6Al4V-3PCS composite achieves the best combination of room-temperature strength and ductility, with 1307 ± 18 MPa in ultimate tensile strength (UTS), 1178 ± 25 MPa in yield strength (YS) and 10.0 ± 0.8% in elongation (EL), much higher than those of wrought Ti6Al4V alloy (ASTM B381). This work offers a feasible route for fabricating novel ultrastrong and ductile Ti6Al4V composites. [ABSTRACT FROM AUTHOR]

A preferentially-aligned lamellar structure in TNM alloy with enhanced strength-ductility synergy is successfully obtained by texturing the high-temperature α phase through hot extrusion. The lamellar orientations of the resultant lamellar colonies inherit the texture feature of the extruded high-temperature α phase ({0001} basal fiber texture), exhibiting a preferential distribution with 60% of the lamellar traces {0001}α/{111}γ nearly parallel to the extrusion direction (ED). The influence of the microstructural variables on the deformation mechanisms and fracture mechanisms are elucidated by microstructural characterization and crystallographic analysis. Results show that when the lamellar trace is parallel to the tensile direction (TD//ED), twinning and stacking faults in the γ laths are favorable to be activated. The origin of the enhanced strength-ductility synergy is attributed to the combined effects of twinning, stacking faults and its induced dislocation slip, as well as the extra interaction stresses introduced by the multiple deformation mechanisms and the α 2 /γ interfaces. This study can provide a novel strategy for microstructural regulation and design of high-performance β-solidifying TiAl alloys. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Glass lubricants have great potential in industrial metal forming processes such as hot extrusion of titanium and titanium alloys. In this work, based on the extrusion process of commercial-purity titanium (TA2) at 800 °C, glass lubricants with low melting points are designed. The thermal properties, high-temperature oxidation resistance and friction properties of uncoated and glass-coated TA2 samples are systemically studied, which reveals the good lubricating and anti-oxidation properties of the samples. The glass lubricant melts into a viscoelastic film at 800 °C to insulate TA2 from oxygen and reduce friction, and automatically peel off during cooling due to the significantly mismatched thermal expansion between the glass coating and TA2 substrate. This work provides a guidance for designing glass-based lubricants used in hot extrusion of metals. [ABSTRACT FROM AUTHOR]

Abstract The production of fully dense Mg-SiC nanocomposites with a homogeneous distribution of SiC nanoparticles through powder metallurgy techniques is still a challenging issue. We propose to combine sintering and hot extrusion of mechanically milled composite powders to encompass the known difficulties of conventional processing. Here, we report on the effect of SiC nanoparticle content on the compressibility, microstructure and hardness of SiC-Mg nanocomposites during the different consolidation steps. Cold-isostatic pressing, sintering and indirect hot extrusion were used for compaction and consolidation. Near dense Mg-SiC nanocomposites with 1 and 10 vol% SiC nanoparticles were successfully produced with a homogeneous distribution of the nanoparticles. Scanning electron microscopy, X-ray diffraction and transmission electron microscopy were used to characterise the microstructure of the powders and of the sintered and extruded Mg-SiC nanocomposites. Vickers microhardness tests were done to reveal the hardening effect after sintering and extrusion. The nanoparticles pin the grain boundaries and foster dynamic recrystallisation, so that a nanograined Mg matrix develops and is preserved even after the final consolidation step. The results further show a very good interface adherence between nanoparticles and matrix contributing to the high hardness of the nanocomposites. [ABSTRACT FROM AUTHOR]

Abstract In this study, Al/AlN in-situ nanocomposites were fabricated using Al/BN as the starting composite powders. The impact of adding hexagonal boron nitride (BN) to the Al matrix of commercial purity on the microstructure and mechanical behavior of the fabricated in-situ nanocomposites was investigated. Samples including 1, 2, and 4 wt.% boron nitride nanoparticles were produced by planetary ball milling of the composite powders and a post-process of hot extrusion. Scanning transmission electron microscopy revealed that boron nitride nanoparticles dissolved as a solid solution of B and N in the Al matrix at the as-milled state. Through the process of hot extrusion, AlN as the in-situ phase was formed by a reaction between Al and N. These led to improve the mechanical properties as well as grain refinement of Al/AlN nanocomposite. The average grain size of the fabricated composites with the use of 1, 2 and 4 wt.% BN was measured about 910, 823, and 760 nm respectively. It was found that combined strengthening mechanisms of grain refinement, a solid solution of mostly B and AlN in-situ phase formation improved the mechanical properties of Al/AlN nanocomposite. With the use of 1, 2, and 4 wt.% BN, the tensile strength of nanocomposite samples increased approximately 40, 56, and 57% in comparison with pure Al, respectively. The remarkable change in microstructure and mechanical properties of the nanocomposite was obtained when the content of BN is up to 2 wt.%. Highlights • Al/AlN nanocomposites were fabricated by planetary ball milling and hot extrusion. • BN particles were dissolved as solid solution in matrix at the as-milled state. • The in-situ AlN phase was created during hot extrusion process. • The high fraction of N and all the B were remained as solid solution in matrix. • The solid solution and AlN phase improve the mechanical property of nanocomposite. [ABSTRACT FROM AUTHOR]

Abstract To obtain the optimal mechanical properties, several processes including spray forming technology, two passes hot extrusion and substantial heating treatments were operated on an Al-Zn-Mg-Cu-Zr alloy. The characterization methods used in this study include tensile tests, X-ray diffraction, differential scanning calorimetry and microstructure observations by optical microscope, scanning and transmission electron microscopy. The typical characteristics were the refined grain, homogeneous precipitates and porosity in the as-deposited pre-forms. The ultimate tensile strength, yield strength, hardness and elongation improved significantly after two passes hot extrusion. A good combination of ultimate tensile strength at 704 MPa and elongation at 9.7% were achieved under peak-aged treatment. The best ultimate tensile strength was obtained at 732 MPa after re-aging and regression. It was main dimple fracture in the extruded and aging treated specimens while brittle fracture for the as-deposited. The secondary phases were main MgZn 2 and Al 3 Zr dispersoids throughout all the states. The contributions of grain boundaries, dislocations, solid-solution and precipitates on the yield strength were analyzed using a quantitative equation. Highlights • The spray forming technology was used to fabricate ultra-high strength aluminum alloy. • The alloy under RRA state obtained the highest ultimate tensile strength of 732 MPa. • The effects of dislocations, solutes and precipitates etc., on yield strength were calculated. • Precipitation was characterized as the main strengthening mechanism for aging states. [ABSTRACT FROM AUTHOR]

In the present study, aluminum based metal matrix composites containing various amounts of boron nitride (BN) nanoparticulates (0, 0.5, 1.0 and 1.5 vol.%) were fabricated by using the powder metallurgy (PM) technique involving microwave sintering and hot extrusion process. The microstructure, physical, thermal, mechanical and damping characteristics of the extruded nanocomposites were investigated. Field emission scanning electron microscopy (FE-SEM) study shows the evenly distributed BN particles in Al matrix. Mechanical analysis indicates that the compression, hardness and tensile strength of Al-BN nanocomposites increases with increasing amount of BN content. Particularly, a significant improvement in the tensile strength (∼36%) is achieved in Al-1.5 vol.% BN nanocomposite when compared to the pure aluminum (Al). This improvement strength can be attributed to the dispersion hardening of the Al matrix due to the presence of hard BN nanoparticles. Thermal analysis shows that the coefficient of thermal expansion (CTE) decreases with increasing amount of BN which may be ascribed to inherent low CTE of BN nanoparticles used as reinforcement. The addition of BN nanoparticulates enhanced the damping characteristics of pure Al with Al-1.5 vol.% BN nanocomposite exhibiting the maximum damping capacity and damping loss rate with a minimum change in elastic modulus. The improved combination of properties exhibited by Al-BN nanocomposites make them potential candidates for a wide spectrum of industries especially for weight critical applications. [ABSTRACT FROM AUTHOR]

A novel Al-based composite reinforced with Ti-based metallic glass (MG) nanoparticles was fabricated by powder metallurgy through mechanical alloying combined with hot extrusion. During the ball-milling process, MG microparticles were refined into nanosized particles through severe plastic deformation. Hot extrusion of the milled powders resulted in a dense and uniform dispersion of the metallic glass nanoparticles in the Al-7075 matrix. This unique homogeneous structure led to a significant enhancement of strength without adversely affecting the plasticity, thus developing super-high specific yield strength. The yield strength increased from 297 MPa for Al-7075 matrix to 530, 610, 880, and 1014 MPa for the composites milled for 10, 15, 30, and 50 h, respectively. A critical analysis of the different factors contributing to the strength of the composites was carried out. Grain refinement, Orowan strengthening, and dislocation–dislocation interactions were demonstrated to be the most important contributors to the enhanced strength of the nanocomposite. [ABSTRACT FROM AUTHOR]

The effects of combined addition of Sn and Y on the microstructure, texture, and mechanical properties of as-extruded Mg-5Li-3Al-2Zn alloy were investigated. The results show that the microstructure of as-extruded Mg-5Li-3Al-2Zn alloy mainly consists of α-Mg and AlLi phases. With the addition of Sn and Y, Mg 2 Sn and Al 2 Y compounds form, while AlLi phase gradually disappears with increasing Y content. These second phases are crushed into smaller particles during hot extrusion process, and Al 2 Zn particles are found in Mg 2 Sn-rich regions and distribute along the grain boundaries. Meanwhile, the microstructure is significantly refined, and the combined addition of 0.8 wt% Sn and 1.2 wt% Y produces the smallest grain size of 4.78 µm and the uniform microstructure is entirely composed of equiaxed grains. Additionally, the addition of Sn and Y weakens the basal texture of as-extruded alloy and introduces recrystallization texture due to solute drag effect and dynamic recrystallization. As-extruded Mg-5Li-3Al-2Zn-0.8Sn-1.2Y alloy exhibits a superior combination of tensile properties with ultimate tensile strength and elongation of 328.0 MPa and 25.1%, which are increased by approximately 32.2% and 41.0% compared with those of as-extruded Mg-5Li-3Al-2Zn alloy (248.2 MPa and 17.8%), respectively. The improvement of mechanical properties is mainly attributed to solution, dispersion, and grain refinement strengthening. [ABSTRACT FROM AUTHOR]

The properties of nickel-base superalloy pipes are determined by microstructure, and the microstructure can be tuned by hot extrusion process. There are two major questions in hot extrusion: one is how to successfully extrude pipes without apparent defects, the other is how to make the microstructure under control. However, up to now, there is no systematical report about hot extrusion process and microstructure control for nickel-base superalloys. In present study, a series of technical control principles for hot extrusion are proposed basing on practical manufacture facts, large amounts of experimental studies and finite element simulation of several typical nickel-base superalloys. The common used technical control principles can be applied for hot extrusion parameters determination to maintain safety hot extrusion and microstructure control. In the investigation of microstructure control based hot extrusion principles, the action rules of different working parameters on hot extrusion field quantities were established. The upper and lower limits of different principles were obtained in consideration of materials characteristics and extruder conditions. The limitations were overlapped on the action rules to determine the optimized hot extrusion parameters. The microstructure-based control principle proposed in present work can provide theoretical guidance for hot extrusion parameter determination and optimization. [ABSTRACT FROM AUTHOR]

In this study, composites of aluminum alloy 6063 reinforced with 10 wt% boron carbide microparticles were successfully fabricated by a combination of spark plasma sintering and stir casting methods, followed by hot extrusion. A systematic study on the relationship between extrusion process variables (i.e. extrusion ratio, temperature, and punch speed) and porosity, particle refinement, particle distribution and consequently tensile properties and fracture behavior of the composites was performed. Extensive electron microscopy analysis and tensile testing of the composites revealed a multifactoral interdependency of microstructural evolution and mechanical properties on the extrusion process variables. For example, while increasing the extrusion ratio at higher temperatures led to moderate particle refinement, better densification of the composites, and improvement in mechanical properties, concurrent particle fragmentation and microvoid formation around the particles at lower temperatures had opposing effects on the mechanical behavior. We show that the dependency of mechanical properties on all such microstructural factors makes it difficult to predict optimum extrusion conditions in aluminum matrix composites. That is, unlike the common approach, extruding the composites at higher temperatures and achieving more reduction in area may not necessarily lead to the most favorable mechanical properties. [ABSTRACT FROM AUTHOR]

Hot extrusion is used to improve the distribution of whiskers and refine the whisker sizes of 2024Al/Al 18 B 4 O 33 w composite. The grain size and the ultimate tensile strength of the extruded 2024Al/Al 18 B 4 O 33 w composite are analyzed. The results show that the average length of whiskers decreases due to the whisker breakage. The nonuniform distributions of stress and velocity along the whisker lead to whisker breakage. The microcrack between the broken whiskers can propagate into the interface or the matrix, related to the wedge angle of the broken whisker. The extrusion is beneficial to the whisker staggered and makes it easy for the microcracks filled with matrix. The whisker breakage and the whisker staggered result in the decreasing distance between the neighboring whiskers. Due to the dislocation motion constrained by matrix and the overlap of the deformation areas, the decreasing distance between the neighboring whiskers promoting the recrystallization results in the smaller grain size. During tensile tests, due to the smaller resistance with the smaller distance between the neighboring whiskers, the cracks between the progressive broken whiskers are easy to coalesce resulting in the lower ultimate tensile strength of the extruded composite. [ABSTRACT FROM AUTHOR]

Hydrothermal synthesis-coreduction techniques were used to convert a mixture of sodium tungstate, copper nitrate and lanthanum nitrate into La 2 O 3 doped nano-W-25Cu-La 2 O 3 composite powders. These high density fine-grain W–25Cu–La 2 O 3 composites were then fabricated using a series of preforming, sintering and canned hot extrusion techniques to afford alloys whose microstructures and properties were characterized using SEM, HRTEM, and XRD analysis. These results revealed that the composite powders were comprised of W, Cu and La 2 O 3 phases that had been formed through a two-stage hydrogen reduction process. Importantly, doped La 2 O 3 with a diameter of 15–30 nm were found to be present on the surfaces of both the W and Cu particles, as well as being distributed throughout the Cu phase. The presence of La 2 O 3 dopant was found to have an important influence on the physical and mechanical properties of their W-Cu alloys. When the content of La 2 O 3 was 2.0 wt%, the resultant alloy demonstrated the best overall performance, affording conductivity, hardness and tensile strength values of 52.5% IACS, 288 HB and 375.9 Mpa, respectively. [ABSTRACT FROM AUTHOR]

Bulk ultrafine grained Cu-0.8 wt%C alloy samples were fabricated by spark plasma sintering (SPS) of a nanocrystalline Cu-0.8 wt%C alloy powder prepared by high energy mechanical milling. The SPS temperature was 800 °C. The SPSed samples exhibited a bimodal microstructure consisting of ultrafine and coarse Cu grains (average grain sizes: ~95 nm and ~1 µm respectively) and a yield strength of 483 MPa, but underwent a premature fracture at a stress of 511 MPa with a low elongation to fracture of only 0.3%. It is established that the premature fracture and low tensile ductility are caused by the high flow stress associated with grain boundary strengthening and reaching the strength of IPBs before reaching its maximum. Hot extrusion of the SPSed sample at 800 °C caused substantial growth of the ultrafine Cu grains and enhancement of the strength of IPBs, leading to a clearly lower tensile yield strength of 353 MPa, but mature fracture with an ultimate tensile strength of 428 MPa and a significantly improved elongation to fracture of 6.5%. [ABSTRACT FROM AUTHOR]

Aluminum matrix composites reinforced by carbon nanotubes (CNTs) were fabricated by ball-milling (with aluminum powder; average diameter 30 µm), followed by hot extrusion of the powders encapsulated in aluminum containers (at 550° with an extrusion ratio of 9). The CNTs were intended to improve the mechanical properties and thermal conductivity of the aluminum composites formed by powder metallurgy. The CNTs were of two types—vapor-grown carbon fibers (VGCFs) with a diameter of 150 nm and multiwalled CNTs (MWCNTs) with a diameter of 65 nm. The composites were evaluated by their Vickers microhardness, tensile strength, and thermal conductivity. The microhardness exceeded 100 HV and increased with increasing volume fraction of reinforcement. The MWCNT-reinforced composites were harder than the VGCF-reinforced composites and exhibited higher ultimate tensile strength (over 450 MPa). The maximum fracture strain (37.2%, observed at a volume fraction of 0.5%) is the highest reported in the literature. Conversely, the VGCF-reinforced composites exhibited higher thermal conductivity than the MWCNT-reinforced composites. The thermal conductivity of the 0.5% VGCF-reinforced composites (203.7 W/m K) also exceeds any previously reported value. In summary, composites with unprecedentedly high ultimate tensile strength, fracture strain, and thermal conductivity were fabricated by a simple process that minimized damage to the CNTs during mixing, protected them from oxidation and excessive reaction with the aluminum matrix and effectively densified composites by hot extrusion. [ABSTRACT FROM AUTHOR]