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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]

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]

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]

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 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 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]

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]

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]

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]

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]

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]

In this paper, Ti-22Al-25Nb alloy bars were successfully prepared by elemental powder metallurgy and subsequent hot extrusion (1200 °C, extrusion ratio of 10.56:1). The microstructure characterization, texture and mechanical property have been systematically investigated. Results showed that DRX occurred prior near grain boundary and further refined the B2 grains during the hot extrusion process. Besides, the as-extruded microstructure consists of both DRX grains and elongated grains, in addition, the as-extruded Ti-22Al-25Nb alloy exhibited strong (110) B2 //ED. Meanwhile, {001}<111> and {111}<13-1> fiber textures were also introduced due to dynamic recrystallization. The good combination of tensile strength (1122.7 MPa) and elongation (7.9%) have been obtained in the as-extruded Ti-22Al-25Nb alloys at room temperature. Besides, the as-extruded alloy also exhibited super-high tensile strength at elevated temperatures (close to 916.5 MPa at 650 °C and 613.1 MPa at 800 °C). The enhanced properties can be attributed to the comprehensive effects including deformation textures, grain refinement and dissolution of bulks α 2 phase. [ABSTRACT FROM AUTHOR]

In this study, Aluminum matrix composite reinforced with 5, 10 and 15 vol% Al 2 O 3 particles were fabricated using microwave assisted rapid sintering technique followed by hot extrusion. The effect of concentration of Al 2 O 3 reinforcement particles on physical, structural, mechanical and thermal behavior of the extruded Al–Al 2 O 3 composites was investigated. Results showed that, as the content of hard ceramic particles increases, it improves overall mechanical properties including microhardness, 0.2% yield strength, ultimate compression/tensile strength, and Young's modulus while the ductility and co-efficient of thermal expansion decreases. XRD patterns and SEM/EDS mapping images show a uniform distribution of Al 2 O 3 particles in the Al matrix. Owing to the existence of the reinforcement particles, the Al-15vol%Al 2 O 3 composite attains an ultimate tensile strength and yield strength of 154±6 MPa and 139±8 MPa, respectively, representing an enhancement of 33% and 32.4% compared to the pure aluminum. In particular, the extruded Al-15vol%Al 2 O 3 composite exhibited superior tensile strength at higher temperatures (~128±3 MPa at 100 °C and 110±4 MPa at 200 °C) when compared to Al matrix. The reduction of coefficient of thermal expansion (CTE) was ascribed to the strong interface bonding in the Al/Al 2 O 3 composites. Findings presented are expected to pave the way to design, develop and synthesize aluminum based composites for weight critical applications at ambient and reasonable elevated temperatures. [ABSTRACT FROM AUTHOR]

This study was undertaken to evaluate the effect of extrusion ratio on the microstructure and mechanical properties of Mg–8Li–3Al–2Zn–0.5Y (wt%) alloy, which was prepared by casting and then deformed by hot extrusion at 200 ℃ with four different ratios of 4:1, 9:1, 16:1 and 25:1, respectively. It was identified that the as-cast Mg–8Li–3Al–2Zn–0.5Y alloy is composed of α -Mg, β -Li, AlLi, MgLi 2 Al and Al 2 Y phases. After hot extrusion with all four ratios, the microstructure was significantly refined. The mechanical properties of Mg–8Li–3Al–2Zn–0.5Y alloy at room temperature were improved, mainly caused by grain refinement and precipitation strengthening. As the extrusion ratio increases from 4 to 25, the grains of the alloy become elongated and refined, and the tensile properties first increase and then decline. Among all the tested alloys, the alloy with the extrusion ratio of 16 exhibits the highest yield strength, ultimate tensile strength and elongation of 214 MPa, 243 MPa and 41%. In addition, the fracture behavior and strengthening mechanism of the studied alloys were also investigated systematically. [ABSTRACT FROM AUTHOR]

An Al-5 wt% Ti composite was fabricated via powder metallurgy and hot extrusion from initial pure Al and Ti powders. The effect of subsequent heat treatment at 600 °C for different time intervals on microstructure and mechanical properties was investigated. XRD and EDS analyses showed the in-situ formation of Al 3 Ti intermetallic. SEM micrographs demonstrated the formation of core-shell structured particles in Al matrix for composites heat treated up to moderate heating times (4 h). Generation of voids and pores in the heat treated composites was considered as a result of the Kirkendall effect. Mechanical properties of composites were studied by hardness and tensile testing methods at room temperature. By increasing heating times up to 6 h, hardness and tensile strength of the composites increased due to the rise in Al 3 Ti volume fraction. Heat treating more than 6 h resulted in reduction of both hardness and strength of the composite. Ductility of Al-5 wt% Ti composites declined with increasing thermal exposure duration. SEM imaging was used to study fracture surface of tensile test specimens. It was revealed that failure mechanism of composites changed from particle fracture in moderate heating times, to particle debonding and particle pull-out in long heat treatment time intervals. [ABSTRACT FROM AUTHOR]

From the viewpoints of particle refinement and homogeneous distributions of reinforcing phase, this work proposed a novel method to prepare Al/Mg 2 Si composites. Mg 2 Si particles were synthesized by solid-state reactions of Mg and Si powder mixtures at a high temperature, and then refined by mechanical milling (MM) for 12–36 h. Subsequently, the MMed Mg 2 Si particles were incorporated into Al powder followed by hot extrusion for consolidation. The effect of milling time on microstructure and mechanical properties of the Al/Mg 2 Si composites was investigated. As the milling time increased, the average size of the Mg 2 Si particles in the composites became smaller, but the grain sizes of Al matrix remained almost unchanged. The hot-extrusion process was found to eliminate some particle agglomerations and promote size reduction and uniform dispersion of Mg 2 Si particles in the Al matrix. The elastic modulus, yield strength, ultimate tensile strength (UTS), and wear resistance of the composites increased by 8%, 14%, 8.5%, and 38.2%, respectively, with increasing the milling time from 12 h to 36 h, but the elongation decreased by 41%. Furthermore, the hot-extruded Al/Mg 2 Si composites exhibited high strength and ductility, for example, the UTS and elongation of the composites with 15 wt% Mg 2 Si particles MMed for 36 h increased by 43% and 91%, respectively, compared to conventionally cast Al/Mg 2 Si composites. The predicated elastic modulus by the Halpin-Tsai model is close to the experimental results. Moreover, the thermal mismatch strengthening is the dominate strengthening mechanism to improve the yield strength of the Al/Mg 2 Si composites. [ABSTRACT FROM AUTHOR]

In order to achieve reliable connection between magnesium and aluminum alloys and to prepare composite structures and devices with excellent overall performance, it is critical to avoid the formation of brittle intermetallic compounds. In this regard, we describe hot stacked extrusion forming of 7075/Zr 44 Ti 11 Cu 10 Ni 10 Be 25 (Vit1b)/AZ31B in terms of extrusion process parameters and their influence on structure, interfaces, and mechanical properties. The study demonstrated that the composite had almost no defects such as extruded flying edges or bending. The nature of the samples varied considerably and the 450°C-4 mm/min sample showed a more desirable bonding appearance. The samples obtained under different extrusion conditions experienced different degrees of elemental diffusion at the interfaces. It is underscored that using amorphous alloy as the joining medium can effectively improve the strength of 7075/Vit1b/AZ31B composites, with the tensile strength increased by 12.5%. The 7075/Vit1b and AZ31B/Vit1b interfaces were studied systematically and the Al concentration layer was found at the AZ31B/Vit1b interface. [ABSTRACT FROM AUTHOR]

Magnesium matrix composites reinforced with 5 wt% AlN particles were fabricated using the hot-pressing sintering followed by hot extrusion. The effects of hot extrusion on the microstructure and mechanical properties were investigated and the strengthening mechanisms of the hot-extruded Mg-Al/AlN composites were presented. The results showed the matrix grain was significantly refined and the uniformity of AlN particles distribution was effectively improved. However, the reinforcement particles were still mainly distributed along the grain boundary after hot extrusion. The remarkable improvement of mechanical properties was primarily attributed to the decreased grain size, improved dispersion of AlN particles and increased dislocation density. The fracture mode changed from layer cracking to mixed fracture with cleaved facets, dimples and fractured particles for the composites under hot extrusion. [ABSTRACT FROM AUTHOR]

High energy vibratiory mill was used to produce Nanocrystalline Al-20 wt% Ti powders by mechanical alloying. The milled powders were then consolidated by hot extrusion at 530 ° C . Produced bulk nanocomposite samples were studied by XRD analysis, optical microscopy (OM), Field Emission Scanning Electron Microscopy (FESEM), EDS spectroscopy, densitometry and hardness tests. Three point bending on SENB specimens was applied under quasi static condition to determine the fracture toughness and also investigate the fracture surface using SEM. The results indicated that after extrusion a fully dense Al-Al 3 Ti nanocomposite with the crystallite size of 200−400 nm is produced in which the Al 3 Ti particles with the size of 50−500 nm were homogeneously distributed. The mechanical properties of samples such as modulus, flexural strength and hardness were significantly increased to 130 GPa, 910 MPa and 136 HV, respectively. These results are the consequence of refinement of Al matrix grain size, distribution of Al 3 Ti nano-particles and the absence of voids. The high density of grain boundries and particle-matrix interfaces provide a lot of sites for nucleation of dimples which leads to the delay in crack initiation stage. Accordingly, the fracture toughness of the nanocomposite sample obtained K Q = 27.4 MPa m which is a high value in comparison with the conventional Al composites. On a macroscopic scale, the fracture surface was brittle and flat, while SEM images showed dimpled fracture surfaces confirming microvoid coalescence as the main fracture mechanism. [ABSTRACT FROM AUTHOR]

A novel (10 wt%B 4 C p +3.6 wt%Gd)/Al6061 neutron absorber material having great potential commercial applications was designed by calculating equivalent B content (B Eq) and its neutron absorber ability was evaluated based on an equivalent B areal density (EBAD) calculation as well as a Monte Carlo simulation. The designed material was successfully fabricated by ultrasound assisted casting method. The added B 4 C particles were distributed uniformly in the matrix and the newly formed large-sized Al 3 Gd particles existed along the grain boundaries (GBs) in the as-cast composite. It was found that a small amount of Si was solubilized in Al 3 Gd lattice and the solution behavior of Si was revealed using first-principles calculation. After hot extrusion (HE) and heat treatment (HT), the large-sized Al 3 Gd particles were broken into small ones and nano-sized βʺ phase was precipitated in the matrix. The mechanical properties of the modified composite were enhanced remarkably and the reason of which was mainly attributed to the following two aspects. On the one hand, HE induced the grain refinement and the fragmentation of large-sized Al 3 Gd particles as well as their more homogeneous distribution within grains from GBs were beneficial for the improvements in both strength and ductility of composite. On the other hand, HT induced the precipitation of βʺ phase could work as strengthening phase in the modified composite. The size and distribution of Al 3 Gd particles played an important role in improving the mechanical properties since cracking easily occurred on the large-sized Al 3 Gd particles which existed along GBs, leading to the severe degradation of mechanical properties of the as-cast composite. Furthermore, the related mechanism of cracking behavior of large-sized Al 3 Gd particles was discussed. This research provides a low-cost method to prepare easy-deform Al based neutron absorber material with desirable mechanical properties. [ABSTRACT FROM AUTHOR]

In this paper, Al-8.3Zn-2.3Mg-2.5Cu alloys with different oxygen contents were prepared through complex techniques including blending or ball milling, cold isostatic pressing, vacuum sintering, hot extrusion, and heat treatment, and their microstructure and mechanical properties were investigated. For the samples containing 0.15 wt% and 0.33 wt% oxygen, the sintered density values are 99.1% and 98.7% of the theoretical density, and the corresponding average grain sizes are 5.60 μm and 4.83 μm. After heat treatment, the average grain sizes of the samples with 0.15 wt% oxygen subjected to the extrusion ratios of 4:1, 9:1, and 17:1 are 5.17 μm, 4.28 μm and 3.83 μm, respectively, and the corresponding yield strengths are 607 MPa, 615 MPa, and 621 MPa. Moreover, the {111}<112> deformation texture changes to {001}<001> and {001}<111> recrystallization textures. In contrast, for the extruded sample (9:1 extrusion ratio) with 0.33 wt% oxygen, the grains are finer, and static recrystallization barely occurs with little variation in texture after heat treatment. This is due to the increase in content of thermostable γ-Al 2 O 3 particles. Accordingly, the sample with high oxygen content exhibits excellent comprehensive mechanical properties with the ultimate tensile strength of 719 MPa, yield strength of 690 MPa, and elongation of 11.5%. Regarding the strengthening mechanism, apart from the common precipitation strengthening, the contributions of dislocation strengthening and grain boundary strengthening are greater in the 0.33 wt% oxygen alloy than in the 0.15 wt% oxygen alloy. This is due to the pinning effect of γ-Al 2 O 3 particles on dislocations and grain boundaries. • The oxygen content of powder was increased by ball milling. • The effects of extrusion ratios on mechanical properties of Al–Zn–Mg–Cu alloys. • Static recrystallization was suppressed by thermostable γ–Al 2 O 3 particles. • Ultrahigh strength and toughness of Al–Zn–Mg–Cu alloy were obtained by fine grains, γ–Al 2 O 3 particles and precipitates. [ABSTRACT FROM AUTHOR]

The effects of Ga content on the microstructure and mechanical properties of the hot-extruded Mg–2Zn-xGa alloys (x = 1, 3, 5 and 7 wt%) were investigated. The microstructure was characterized using X-ray diffraction spectroscopy (XRD), optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM) and electron back-scattered diffractometer (EBSD). The results showed that the Mg–2Zn-xGa alloys were mainly composed of α-Mg matrix phase and Mg 5 Ga 2 precipitates. The grains were continuously refined from 28.6 μm to 16.4 μm with increasing Ga content from 1 wt% to 7 wt%. The amount of micron-scale and nano-scale Mg 5 Ga 2 precipitates increased with increasing Ga content and they were distributed both at the grain boundaries and inside the grain interiors. The tensile tests revealed that the addition of Ga element significantly enhanced the yield strength (YS) and ultimate tensile strength (UTS) due to the synergistic effects of refinement strengthening and precipitation strengthening. This strengthening effect was positively correlated with Ga content. The elongation (EL) firstly increased as Ga content increased from 1 wt% to 5 wt% and then decreased as Ga content further increased to 7 wt% because of the formation of excessive Mg 5 Ga 2 precipitates. [ABSTRACT FROM AUTHOR]

High strength-ductility synergy Mg–5Al–1Mn-0.5Zn-xCa (x = 0.5, 1 and 2, in wt.%) alloys without rare earth elements were prepared by conventional extrusion at 360 °C with an extrusion ratio of 25:1. The microstructure evolution and mechanical properties of Mg–5Al–1Mn-0.5Zn-xCa alloys were investigated by OM, XRD, SEM, EBSD, TEM and tensile tests. The as-extruded alloys are almost fine equiaxed grains with dispersed particles (Al 2 Ca, Al 8 Mn 5, Mg 2 Ca and nanoscale (Al, Mn)-rich precipitates). With the increase of Ca addition, the average grain size decreases, the fine particles increase and basal textures become stronger, which result that the strength of the extruded alloy increases gradually while the elongation decrease. As-extruded Mg–5Al–1Mn-0.5Zn–2Ca exhibits excellent comprehensive mechanical properties of the ultimate tensile stress (UTS) of 340 MPa and fracture elongation (FE) of 12.8% with fine grains (2.42 μm), strong basal texture, high density of precipitates and dislocations. The TEM results show that Ca and Zn are segregated at the grain boundaries and a large amount of dispersed second-phase particles existed in the Mg–5Al–1Mn-0.5Zn–2Ca alloy, which is beneficial to grain refinement. Besides, the activated nonbasal slips are beneficial to the ductility which result from the restriction of twinning in fine grains and high Schmid factor (SF) of nonbasal slips. • RE free Mg–5Al–1Mn-0.5Zn–2Ca prepared by conventional extrusion exhibits high strength-ductility synergy of the tensile yield stress, ultimate tensile stress of and fracture elongation of 269 MPa, 340 MPa and 12.8%, respectively. • The average grain size decreases from 2.88 μm to 2.42 μm with the increase of Ca addition, which is related to the co-segregation of Zn and Ca to grain boundaries and dispersed distribution of fine (Mg, Al) 2 Ca phase particles.. • High density dislocations bypassing the nanoscale Al–Mn precipitates are generated in fine grains during deformation, which contribute to the strength of alloys, and the activation of non-basal dislocations is beneficial to the ductility of alloys. [ABSTRACT FROM AUTHOR]

An ultrafine-grained (UFG) Mg-RE alloy with superior yield symmetry and strength-ductility synergy was successfully fabricated by simple hot extrusion. The as-extruded specimen was composed of nearly fully recrystallized UFG microstructure with a mean grain size of 0.93 μm and exhibited a nearly random texture (maximum intensity is 1.38). The abundant nano-precipitates and the segregation of alloying elements at grain boundaries played key roles in inhibiting the growth of freshly recrystallized sub-micrometer grains formed during hot extrusion. The mechanical tests revealed that the extruded alloy exhibited an excellent tension/compression yield ratio of 1.03, which was attributed to the suppression of the extension twinning and the extremely weak texture. The suppression of extension twinning mainly resulted from the grain refinement, high concentration of rare earth solute in Mg matrix, precipitates in parts of grains and randomly oriented grains. The main deformation mode of UFG specimen was basal slip in both tension and compression, leading to the similar strain hardening behavior. This work suggests that the high tension-compression symmetry of Mg alloys can be achieved by grain refinement and texture randomization. [ABSTRACT FROM AUTHOR]

The microstructure–property relation of an extruded Mg–11Gd–4.5Y–1Nd–1.5Zn–0.5Zr (wt%) alloy was investigated by conducting hot compression and high temperature creep at temperatures upto 250 °C. The alloy exhibits an average compressive yield strength ( σ CYS ) of 363±1 MPa and an average elongation to failure ( ε CF ) of 10.5±0.2% at room temperature, 301±13 MPa and 12.8±1.1% at 200 °C. In creep the minimum creep strain rate ( ε ̇ min ) is 1.94×10 −9 s −1 at 175 °C/160 MPa and 6.67×10 −9 s −1 at 200 °C/100 MPa. The obtained stress exponent n is in the range of 3.7–4.7, suggesting that the creep is controlled by the dislocation climb mechanism. The improvement in compressive strength and creep resistance is attributed to the fine recrystallized grains, SFs in the grain interior, Mg 5 RE and LPSO phases at grain boundaries. The alloy exhibits a bimodal texture with 〈0001〉 and 〈 10 1 ¯ 0 〉 components. Its strengthening effect is determined by the competition between these two texture components. In compressive deformation, the textural evolution from 〈 10 1 ¯ 0 〉 to 〈0001〉 is mainly attributed to the operation of basal 〈a〉 slip and { 10 1 ¯ 2 }〈 10 1 ¯ 1 〉 tensile twinning. This texture evolution is not seen in creep. [ABSTRACT FROM AUTHOR]

In situ synthesized TiB whisker reinforced 3.5 vol% TiBw/Ti6Al4V composites have been synthesized by pre-sintering and hot extrusion with steel cup processes. The effects of pre-sintering temperature and time on densification behavior and mechanical properties of the as-extruded composites were investigated. The results indicated that as-extruded TiBw/Ti64 composite sintered at 1100 °C had the highest relative density of 99.4% along with ultimate tensile strength of 1352 MPa and elongation of 4.72%. With increasing pre-sintering temperature from 900 to 1100 °C, the in situ synthesized TiB whiskers which construct a quasi-continuous network microstructure produced by pre-sintering and hot extrusion techniques grow rapidly, while the relative density of the composites increases obviously. At the same time, the fracture type changes from brittle fracture to the hybrid-fracture characteristic of plastic fracture and brittle fracture. The strengthening effects can attribute to the matrix refine and the in-situ reaction TiB whiskers reinforcement due to pre-sintering and hot extrusion plastic deformation. The results also suggest that the optimal pre-sintering and hot extrusion with steel cup techniques are sintered at 1100 °C for 1 h in consideration of the comprehensive properties and the cost. [ABSTRACT FROM AUTHOR]

FeCrAl oxide dispersion strengthened (ODS) steel is regarded as one of the most promising candidate materials for nuclear fission reactors such as supercritical pressurized water reactor (SCPWR), sodium-cooled fast reactor (SFR), and lead bismuth-cooled fast reactor (LFR) and so on, since it has excellent irradiation resistance and good corrosion resistance of super-critical water and Pb–Bi coolants. In the present work, irradiation response of a Zr-added FeCrAl ODS steel (15Cr–4Al-0.1Ti-0.6Zr) together with an Al-free ODS (16Cr-0.1Ti) steel and a non-ODS steel T91 was studied. Electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM) were used to characterize the microstructures including grains, dislocations, and oxides in the pristine specimens and irradiation defects in the irradiated specimens. Nano-indentation tests were used to evaluate the change in hardness after irradiation. The oxides in the 15Cr–4Al-0.1Ti-0.6Zr specimen are slightly larger than those in the 16Cr-0.1Ti specimen, but with a similar number density. After irradiated with 9.45 MeV 83Bi35+ to 26 dpa at ambient temperature, hardening was observed in all the specimens. Irradiation hardening of the 15Cr–4Al-0.1Ti-0.6Zr specimen is slightly higher than the 16Cr-0.1Ti specimen but significantly lower than the non-ODS steel T91. The irradiation defects in the ODS steel specimens are apparently smaller than those in T91 with a similar number density. By calculating sink strength of the initial microstructures such as grains, dislocations and oxides, the evolution of irradiation defects was discussed. A linear relationship between the irradiation hardening and the sink strength was established. A similar linear relationship between the calculated irradiation hardening using the TEM data (based on dispersion barrier hardening model (DBH) and Friedel-Kroupa-Hirsch (FKH) model, respectively) and sink strength was also found. The calculated irradiation hardening is relatively lower than the experimental value, indicating the possible contribution of Cr segregation to hardening which needs further study. • Hardening of a Zr-added FeCrAl ODS ferritic steel was investigated in comparison with 16Cr-0.1Ti ODS and T91 steel. • The irradiation defects and their contribution to hardening of the three steels was investigated. • A linear relationship between the irradiation hardening and the total sink strength was established. [ABSTRACT FROM AUTHOR]

Abstract: The W-30wt%Cu composite bars and strips were obtained by hot extrusion with steel cup from spray-drying powders. The relative density of cold-compressed billets is about 71.4%, and after they are extruded by an extrusion rate of 8.35 at 1200°C, it reaches 91%. XRD and metallographic microscope were used to study the properties and microstructures of the materials. After extruded at 1100°C, the bars have good properties of which the conductivity is about 41%IACS and the hardness is about 287HV. [Copyright &y& Elsevier]

Abstract: Hot extrusion was performed on a Ti–42Al–9V–0.3Y alloy at 1200–1325°C to explore effects on mechanical properties and hot workability. The microstructure after hot extrusion was analyzed, tensile tests were conducted, and hot workability was assessed. Three types of microstructures resulted from extrusion at increasing temperature, including a dual-phase microstructure (DPM), a bi-lamellar microstructure with retained gamma phase (BLMG), and a bi-lamellar microstructure (BLM). Hot extrusion of the TiAl alloy in the range of 1275–1325°C produced the BLM microstructure, yielding superior comprehensive properties. The predominant fracture mode was transgranular cleavage fracture in the DPM, translamellar cleavage and delamination in BLM, and mixed fracture in BLMG. Aggregation of the YAl2 phase accelerated the fracture of the as-extruded alloy. As-extruded Ti–42Al–9V–0.3Y alloy exhibited excellent high-temperature mechanical properties and hot workability, demonstrating the feasibility of precision forming TiAl alloy components by conventional hot forging with nickel-based alloy dies. [Copyright &y& Elsevier]

Abstract: The hot deformation behavior of nickel-based superalloy 740H has been investigated by hot compression experiments. The tests were carried out in the temperature range of 1050–1200°C with strain rates of 0.1–20s−1 to a total strain of 0.6. True stress–true strain curves and deformation microstructures were studied. The results show that dynamic recrystallization, which is the principal softening mechanism in the hot working of 740H, determines the shape of flow curves. The fraction of DRX grains at the strain of 0.6 is increased by deformation temperature while at a particular temperature, it is lower at strain rate of 1s−1 than at other strain rates. A hyperbolic-sine type equation has been established between peak stress and deformation conditions through Z parameter, giving activation energy value of 357.3kJ/mol. The hot working windows of alloy 740H was briefly discussed using the processing map. Temperature range of 1160–1200°C with strain rate larger than 10s−1 is the probable domain for hot extrusion of 740H. [Copyright &y& Elsevier]

Abstract: In the present study, the effect of the ram speed was investigated on the final microstructure and mechanical properties of the Al–SiCp composites through the hot extrusion process. The extrusion process was conducted at 550°C by applying different ram speeds in the range of 0.2–4mms−1. Optical image microscopy (OIM) results showed that by applying the higher value of ram speed, a microstructure can be obtained including oriented SiC particles in the Al matrix. Finite element analysis (FEA) was also utilized to examine the velocity components values at different ram speeds during the extrusion process. The differences in spacing between particle chains at the edge and center of the extruded samples were minimum at ram speed 2mms−1. The mechanical properties of the final products were examined by the means of uni-axial tensile and Vickers micro-hardness tests. The tensile test results showed that the highest values of ultimate tensile and yield stresses were obtained at the ram speed 2mms−1. There is a good agreement between the change in the microstructure and the hardness values gradient through the longitudinal cross-section. [Copyright &y& Elsevier]

Abstract: Tensile and compression experiments were carried on Mg–3Al–1Zn alloys containing different levels of Sr (0.05, 0.4 and 0.8wt%) extruded at elevated temperatures of 250, 300, 350 and 400°C and the results were compared to AZ31 alloy. The addition of 0.05wt%Sr to the alloy produces the highest strength and the alloy containing 0.4wt%Sr has the highest elongation during tensile tests. High levels of Sr (0.8wt%) reduce the yield strength by decreasing the solid solubility of Al in α-Mg and thereby decreasing the solute pining effect of dislocations under both compression and tension loading. The ultimate tensile strength (UTS) is also reduced due to the cracking of Al–Sr precipitates perpendicular to the tension direction. Cracking is also seen in compressed samples; however, the cracks which initiate are parallel to the compression axis, which impedes crack opening and the formation of large voids. As a result, fracture in compression becomes less sensitive to high concentrations of Sr. It is found that increasing the extrusion temperature increases the yield asymmetry and the improvement in yield symmetry is less significant in alloys containing the high levels of Sr. [Copyright &y& Elsevier]

Abstract: In this study, firstly, dynamic microstructural changes of an as-cast Mg–5.0 Zn–0.9 Y–0.16 Zr (wt.%) alloy (designated ZWK510) during hot extrusion at 350°C and a ram speed of 3.33mms−1 was systematically investigated by electron backscattering diffraction (EBSD) analysis. The dynamic recrystallization (DRX) mechanism during hot extrusion was discussed. Then, the effect of microstructure and texture on the mechanical properties of the as-extruded alloy specimens at room temperature was discussed. The as-cast ZWK510 alloy consists of a-Mg and quasicrystalline I-phase. During hot extrusion at 350°C, the main DRX mechanism is the continuous DRX near the original grain boundaries. The I-phase can accelerate the DRX behavior near these areas by obstructing the slip of dislocations. The deformation twins and massive blocky substructures formed in original grains can coordinate the DRX process near the original grain boundaries, however the DRX seldom occurs inside of these area. After further deformation, these deformation twins and massive blocky substructures are elongated along the material flow and become so-called unDRXed area, then a bimodal “necklace structure” composed of fine DRXed grains of about 2.1μm and unrecrystallized coarse area is formed. The extruded ZWK510 alloy shows a DRX ratio of about 58% and a typical basal fiber texture of extrusion direction (ED). In the DRXed area around the crushed eutectic I-phase a large number of fine I-phase precipitates are observed pinning at the newly formed DRXed grain boundaries. The 0.2% proof strength and the ultimate tensile strength of the extruded ZWK510 alloy specimen are 317 and 363MPa, respectively, with an elongation to failure of 12%, which have been attributed to strong basal fiber texture, refined grain size as well as the existence of fine precipitates formed during the hot extrusion. [Copyright &y& Elsevier]

Abstract: An experimental investigation into the microstructure, mechanical properties and aging behaviors of as-extruded Mg–5Li–3Al–2Zn–1.5Cu alloy is conducted. The results show that, during the hot extrusion process, the large bulk intermetallic compounds (AlLi, AlCuMg and Al2Cu phases) of as-cast alloy are crushed into small bulk compounds. The dynamic recrystallization (DRX) takes place, which results in the refinement of grains significantly. A fibrous type texture of (0002) basal plane is formed through the hot extrusion. Tensile tests reveal that the mechanical properties of the alloy are greatly improved after the hot extrusion. Due to the continuous and discontinuous precipitations of AlLi phases, the as-extruded alloy presents age hardening effect at the aging time of 14h and 48h, respectively. [Copyright &y& Elsevier]

Abstract: Effect of hot extrusion on microstructure and mechanical properties of near eutectic casting Al–12.0%Si–0.2%Mg alloy was investigated by mechanical properties testing and microstructure observation using OM (optical microscope), SEM, and TEM. Dynamical recrystallization of Al matrix, dynamical precipitation of deep sub-micron Si and Mg2Si particles and deformation-induced twinning of Si particle occur during extrusion. The mechanism of dynamical precipitation and recrystallization during hot extrusion for near eutectic Al–Si–Mg alloy is concluded according to microstructure observation. The dynamically precipitated particles are thought to play a Zener pinning role on the growth of recrystallized grains, resultantly leading to a much finer grain size of Al matrix. A good combination of tensile strength (256.3MPa) and elongation (15.0%) when aged for 12h after post-extrusion solution treatment is mainly due to fine aging precipitates and recrystallized fine grain structure. The negligible aging hardening effect of extruded samples is due to dynamical precipitation of sub-micron Si and Mg2Si particles. [Copyright &y& Elsevier]

Abstract: Low alloyed steel bars were co-extruded with pre-sintered tool steel powders with the addition of tungsten carbides (W2C/WC) as hard particles. During the hot extrusion process of these massive and powdery materials, an extrudate is formed consisting of a completely densified wear resistant coating layer and a bulk steel bar as the tough substrate core. This work combines experimental measurements (EPMA) and diffusion calculations (DICTRA™) to investigate the effect of hard particle addition and its dissolution, as well as the formation of M6C carbides on the properties of two different PM tool steel coatings hot extruded with a 1.2714 steel bar. A carburization effect resulting from the W2C hard particles is responsible for an increase of the 1.2344 steel matrix hardness. The mechanical properties of the interface region between coating matrix and substrate are influenced by chemical interdiffusion of carbon and other alloying elements occurring during heat treatment. [Copyright &y& Elsevier]

Pure titanium particles reinforced Mg–6Zn-0.2Ca magnesium matrix composites were fabricated by semi-solid stirring casting followed by hot extrusion in this work. The microstructures and mechanical properties of the Mg–6Zn-0.2Ca alloy and its composites were studied. The Ti particles in as-extruded composites are significantly elongated along the extrusion direction. The average aspect ratio of Ti particles increases while the average size decreases, with the extrusion temperature decreasing. Ti particles promote the dynamic recrystallization of the matrix alloy, break the long-strip Ca 2 Mg 6 Zn 3 phases and refine the size of MgZn 2 phases in the Mg–6Zn-0.2Ca matrix, especially for low extrusion temperatures. The Ti p /Mg–6Zn-0.2Ca composite extruded at 240 °C exhibited a high yield strength (YS) of 383.6 MPa with an ultimate tensile strength (UTS) of 404.8 MPa and a decent elongation to failure (EL) of 4.8%. The high strength is associated with fine grains, nano-precipitates as well as Ti particles. In addition, the work hardening rate of Ti p /Mg–6Zn-0.2Ca composite is higher than that of Mg–6Zn-0.2Ca alloy at the early stage of plastic deformation due to the combined effects of the elongated Ti particles, the grain refinement and nano-scale MgZn 2 precipitates. However, the work hardening rate of the composite decreases faster owing to dislocations cross-slip. And the composite is easier to soften, which results from grain boundary sliding of fine grains and work hardening of deformable Ti particles. [Display omitted] • The Ti particles are elongated significantly in Ti p /Mg–6Zn-0.2Ca composites along extrusion direction after hot extrusion. • The Ti p /Mg–6Zn-0.2Ca composite exhibited a high yield strength of 383.6 MPa with an ultimate tensile strength of 404.8 MPa and a decent elongation to failure of 4.8%. • The strain hardening rate of Mg–6Zn-0.2Ca matrix increased by the addition of Ti particles. • Dislocation slip inside Ti particles plays an important role in the softening of Mg–6Zn-0.2Ca matrix during the process of plasitic deformation. [ABSTRACT FROM AUTHOR]

TiB/Ti–6Al–4V composites with controllable orientation were synthesized by powder consolidation and hot extrusion. The in situ reaction of TiB 2 and Ti–6Al–4V occurs during hot extrusion. The produced composites show an excellent tensile strength of 1350 ± 20 MPa and an elongation 4.5 ± 0.5% due to distribution of the TiB whiskers along extrusion direction. [ABSTRACT FROM AUTHOR]

Abstract: The fabrication conditions of Cu–Al–Ni–Mn alloy powder by mechanical alloying and powder metallurgy have been systematically studied. The mechanically alloyed powder (MAed powder) was fabricated at a speed between 100rpm and 300rpm for various milling times with and without process control agent (PCA). With an increasing of milling time, the size of crystallite grain decreases. Only the Cu diffraction pattern appear as the rotation speed is up to 300rpm for 25h. The elemental powders with PCA agglomerate slightly, but the degree of alloying is lower than that without PCA. The shape memory recovery of the quenched sample hot-extruded at extrusion rate of 50:1 is measured to be 100% recovered in 250°C oil bath for 40s after deformed to 4.0%. After aging at 120°C for 10 days, the shape memory recovery of the alloy remains 98%. [Copyright &y& Elsevier]

The present study is concerned with nucleation and growth of α phase during heat treatment in Ti–Al–Mo–Mn intermetallic alloys processed by hot extrusion of elemental powders. TEM and X-ray diffraction analysis show that the microstructure of the as-hot extruded alloy consists of γ, α2 and B2 phases. The volume fractions of α2 and B2 phases are 16 and 20%, respectively, which shows that B2 phases that contain significant amounts of Mo have an orientation relationship with γ plates inside them. Microstructural evolution during heat treatment reveals that the α2 phase nucleates and grows in lamellar form by edgewise and sidewise mechanism. Edgewise growth of the α2 phase is more rapid than sidewise growth due to the coherent interface between α2 and γ phases along the sidewise direction. Sidewise growth of the α2 phase occurs by a ledge mechanism. It has been shown that α phase nucleates in γ plates located at the lamellar boundaries and grows along a direction that can produce an incoherent interface. γ phase present in the B2 phase affects the growth of the α phase by providing a preferential site for α growth. [Copyright &y& Elsevier]

Structural changes in thermally treated microcrystalline Al–11 wt.%Si ribbon were studied by x-ray diffraction, differential scanning calorimetry, transmission electron microscopy and optical microscopy. Two successive types of microstructure development were found to appear in different temperature intervals: decomposition of supersaturated Al solid solution in range from 423 to 473 K, and structural coarsening of silicon particles between 723 and 800 K. The final microstructure of ribbon exhibits a nearly random distribution of silicon particles between 0.8 and 1.8 μm in diameter depending on time and temperature of annealing. [Copyright &y& Elsevier]

In this study, pure Ti rods were fabricated by hot extrusion of vacuum sintered-powder compacts first, and then the extruded rods were further processed by rotary swaging. The effects of annealing temperature on the microstructure, texture, and mechanical properties of the as-rotary swaged Ti were studied using tensile test, electron backscattered diffraction (EBSD), and transmission electron microscopy (TEM). The results show that the as-swaged Ti rods have high yield strength (930 MPa) but its ductility is relatively low (4%). The annealing significantly helps increase the uniform elongation of as-swaged Ti, with only slightly decrease in its yield strength. A desirable combination of high yield strength (596 MPa) and remarkable uniform elongation (20.4%) is obtained for the samples annealed at 500 °C, and this is mainly attributed to fully recrystallized microstructure and high-density texture along the ⟨ 01 1 ‾ 0 ⟩ and ⟨ 1 ‾ 2 1 ‾ 0 ⟩ directions. [ABSTRACT FROM AUTHOR]

Aluminum-Al 3 Ti reinforced MMCs were produced with a large amount (up to ~30 vol%) of Al 3 Ti phase via mechanical alloying, hot extrusion and heat treatment (as a supplementary process) of the Al–Ti elemental powder mixture, respectively. Samples in each stage were studied precise and comprehensive by field emission electron microscope, energy dispersive spectroscopy, X-ray diffraction, differential scanning calorimetry, densitometry, macro and micssro hardness, nanoindentation and tensile tests. The results indicated that after 4-h vibratory milling, the aluminum crystallite size reached 63 nm and Al 3 Ti phase formed in powder mixture. After hot extrusion, the volume percentage of Al 3 Ti increased by the formation of new Al 3 Ti nanoparticles, and a densed structure was achieved. As the milling time increased and crystallite and particle sizes of aluminum and titanium become smaller, the mechanical behavior of the hot extruded nanocomposites was improved. After heat treatments, the amount of Al 3 Ti phase significantly increased, and by thickening the Al 3 Ti layers around the titanium microparticles at high temperatures and long time periods, the voids in the structure proliferated. Increase in Al 3 Ti content can improve the mechanical properties, provided that volume exchanges originating from its formation do not cause widespread formation of voids in the structure. Mechanical properties varied as a function of aluminum and titanium crystallite and particle sizes and amount of Al 3 Ti phase and voids in the final samples. Aluminum crystallites growth during heat treatment reduces the hardness and increases the matrix ductility, and reinforcement particles growth brings faster failure for the samples. [ABSTRACT FROM AUTHOR]