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The effect of Sc-microalloying and Y2O3 nano-particles on the microstructure and mechanical properties of as-cast Al-5.5Si alloy is studied by means of optical microscopy, transmission electron microscopy, hardness test and tensile test. The influence of annealing treatment on the microstructure and properties of the Al-Si alloys is also investigated as well. The results show that the addition of Sc and Y2O3 nano-particles could significantly improve the mechanical property of the Al-Si alloy. The ultimate tensile strength and yield strength of Al-Si-Sc/Y2O3 alloy are improved by around 45 and 71%, respectively, when compared to that of the Al-Si alloy. The effect of the nanosized particles (precipitated and added) on strengthening and deformation of Al-Si alloy is analyzed and discussed in detail. The results of annealing treatment indicate that the change in mechanical property of the Al-Si-Sc alloy during annealing treatment is mainly associated with the precipitation of the secondary Si phase.

In this paper, high-strength steel is prepared by different heat-treatment processes. Through split Hopkinson pressure bar experiment, optical microscope, scanning electron microscope and X-ray dif...

In this study, the two-phase flow coordination characteristics between α and β phases of H62 brass made by up-drawing continuous casting are investigated based on the upsetting process. An in situ and new research method for two-phase flow is put forward, and the two-phase flow and grain refinement characteristics are observed under different deformation conditions. The results show that α phase flows fast under 400 °C, β phase is pulled and overridden by α phase under this temperature. When the temperature increases to 500 °C, which is higher than β phase transition temperature, the flow velocity of β phase increases, and the deformation of β phase is found to bulge. The flow of β phase is more sensitive to low deformation rates than α phase. The deformation amount has a more significant impact on β phase than α phase, and the deformation of β phase promotes the grain fragmentation and refinement of α phase accompanied by huge β phase bulging obviously. Under the conditions of high temperature, low deformation rate, and large deformation amount, both phase α and β of up-drawing continuous casting brass alloy are broken and the grains are refined. Based on the two-phase flow characteristic, numerical simulation is used to obtain the optimal continuous extrusion parameters of the H-shaped wire of up-drawing continuous casting H62 brass. Then, the optimized complex cross-section wire is prepared by continuous extrusion experiment. This research aims to provide guidance for the complex processing of two-phase alloys.

Modern industrial development has put forward higher demands on the performance of metallic structural materials, especially in terms of light weight, high strength and corrosion resistance. All of these characteristics are of particular importance in transportation fields. As one of the most representative structural materials, aluminum and alloys have exhibited significant advantages in light weight. Most of the alloys are prominently featured in one specific aspect. The overall performance still needs to be improved. In recent years, researchers have developed Al-Mg-Zn(-Cu) alloy, a new wrought aluminum alloy, whose design strategy is known as “crossover alloying”. This novel alloy is an age-hardened Al-Mg alloy with a T-Mg32(Al, X)49 (X is Zn, Cu) phase as the main strengthening phase. This system of alloys exhibits excellent properties in terms of strength and corrosion resistance, which makes it promising for applications in automotive, marine, aerospace and other fields. This paper summarizes the research progress of Al-Mg-Zn(-Cu) alloy, and analyzes the basic methods of microstructural control in terms of composition design and property research. Finally, the future directions of this alloy are proposed.

Nanostructuring of metals is nowadays considered as a promising strategy towards the development of materials with enhanced electrochemical performance. Porous and fully dense CuNi films were electrodeposited on a Cu plate by electrodeposition in view of their application as electrocatalytic materials for the hydrogen evolution reaction (HER). Porous CuNi film were synthesized using the hydrogen bubble template electrodeposition method in an acidic electrolyte, while fully dense CuNi were electrodeposited from a citrate-sulphate bath with the addition of saccharine as a grain refiner. The prepared films were characterized chemically and morphologically by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD). The Rietveld analysis of the XRD data illustrates that both CuNi films have a nanosized crystallite size. Contact angle measurements reveal that the porous CuNi film exhibits remarkable superhydrophobic behavior, and fully dense CuNi film shows hydrophilicity. This is predominately ascribed to the surface roughness of the two films. The HER activity of the two prepared CuNi films were investigated in 1 M KOH solution at room temperature by polarization measurements and electrochemical impedance spectroscopy (EIS) technique. Porous CuNi exhibits an enhanced catalysis for HER with respect to fully dense CuNi. The HER kinetics for porous film is processed by the Volmer–Heyrovsky reaction, whereas the fully dense counterpart is Volmer-limited. This study presents a clear comparison of HER behavior between porous and fully dense CuNi films.

Ni-based bimetallic films with 20 at.% and 45 at.% Cu and mesostructured surfaces were prepared by electrodeposition from an aqueous solution containing micelles of P123 triblock copolymer serving as a structure-directing agent. The pH value of the electrolytic solution had a key effect on both the resulting Cu/Ni ratio and the surface topology. The catalytic activity of the CuNi films toward hydrogen evolution reaction was investigated by cyclic voltammetry (CV) in 1 M KOH electrolyte at room temperature. The Cu45Ni55 film showed the highest activity (even higher than that of a non-mesostructured pure Ni film), which was attributed to the Ni content at the utmost surface, as demonstrated by CV studies, as well as the presence of a highly corrugated surface.

The melt temperature of aluminum alloys plays a significant role in determining the microstructure characteristic during continuous rheo-extrusion. However, it is difficult to measure the actual melt temperature in the roll-shoe gap. In this work, based on the basic theory of heat transfer, a calculation model for heat transfer coefficient of cooling water/roll interface and melt/roll interface is established. In addition, the relationship between the temperature at the melt/roll interface and the velocity of cooling water is investigated. Combined with the CALPHAD calculation, the melt temperature during solidification in the continuous rheo-extrusion process is calculated. Using this model, the cooling rate of an Al–6Mg (wt.%) alloy melt prepared by continuous rheo-extrusion is estimated to be 10.3 K/s. This model used to determine the melt parameters during solidification provides a reference for optimizing the production process of continuous rheo-extrusion technology.

Homogeneous graphene dispersion and suitable interface bonding are two key challenges to realize the high strengthening potential of graphene in metal matrix composites (MMCs). In this study, graphene nanosheets (GNSs) with deposited nickel (Ni) nanoparticles were synthesized to simultaneously overcome the two challenges. Ni-coated-GNS-reinforced aluminum (Al) MMCs were fabricated by graphene synthesis, Ni decoration and subsequent powder metallurgy. It was revealed that Ni-coated GNSs exhibited noticeably enhanced strengthening effect compared with graphene reinforcements in most previous studies. With the addition of 1.5 wt% Ni-coated GNSs, the composites exhibited 132% higher strength than that of unreinforced aluminum. The enhancement in Vickers hardness and Young's modulus further confirmed the remarkable strengthening effect. The high strength and high Young's modulus were examined by strengthening models, and a comparison between experimental and theoretical values was reached. The main strengthening mechanisms in the Ni-coated GNSs/Al composites were clarified as dislocation-related ones.

Al–1Fe (wt%) alloy containing nanosized Al3Fe phase was processed by continuous rheo-extrusion, and subjected to heat treatment at different temperatures. During heat treatment, due to the diffusion of Fe atoms, the nanosized Al3Fe phase was blunted and fragmented along the width direction, and the bluntness and fragmentation resulted in the spheroidization of Al3Fe phase. However, with the extension of heat treatment time, the spheroidized Al3Fe phase became coarse and grew along a particular plane. Then, the morphology of Al3Fe phase transformed into small plate-like. While, the plate-like Al3Fe phase with an average length of 30 µm in the as-cast Al–1Fe (wt%) alloy indicated good thermal stability during heat treatment. The different thermal stability of Al3Fe phases was attributed to their size. The large surface curvature of nanosized Al3Fe phase significantly accelerated the diffusion of Fe atoms. When the heat treatment temperature was 200 ℃ and 300 ℃, the tensile strength and elongation of the rheo-extruded Al–Fe alloy marginally decreased. The decrease of tensile strength and the decrease of elongation increased when the heat treatment temperature was greater than 400 ℃. The tensile strength and elongation of as-cast Al–1Fe (wt%) alloy were insignificantly altered. Though the loss of tensile strength of Al–Fe alloy containing nanosized Al3Fe phase was much greater, its tensile strength was always higher than the tensile strength of the as-cast Al–Fe alloy in the entire heat treatment.

Magnetic chitosan hydrogel has aroused immense attention in recent years due to their biomedical significance and magnetic responsiveness. Here, A new electrodeposition method is reported for the fabrication of a novel CuNi-based magnetic chitosan freestanding film (MCFF) in an acidic chitosan plating bath containing SDS-modified CuNi NPs. Contrary to chitosan’s anodic and cathodic deposition, which typically involves electrochemical oxidation, the synthetic process is triggered by coordination of chitosan with Cu and Ni ions in situ generated by the controlled surface dissolution of the suspended NPs with the acidic plating bath. The NPs provide not only the ions required for chitosan growth but also become entrapped during electrodeposition, thereby endowing the composite with magnetic properties. The obtained MCFF offers a wide range of features, including good mechanical strength, magnetic properties, homogeneity, and morphological transparency. Besides the fundamental interest of the synthesis itself, sufficient mechanical strength ensures that the hydrogel can be used by either peeling it off of the electrode or by directly building a complex hydrogel electrode. Its fast and easy magnetic steering, separation and recovery, large surface area, lack of secondary pollution, and strong chelating capability could lead to it finding applications as an electrochemical detector or adsorbent.

Multilayer reduced graphene oxide (mrGO) was chemically modified by electroless plating of copper on surface to form mrGO-Cu. The scanning electron microscope (SEM) and transmission electron microscope (TEM) analysis revealed that nano-Cu particles were uniformly dispersed on the surface of mrGO. The mrGO-Cu powders were further utilized as reinforcements for aluminum (Al) matrix and the mrGO-Cu/Al composite was successfully fabricated through clad rolling of milled powder. The tribological properties of the mrGO-Cu/Al composites were explored. The tribological results show that the mrGO-Cu could reduce the friction coefficient and wear loss of mrGO-Cu/Al composites, since the mrGO-Cu participated in lubricating processes due to the formation of a transfer layer on the contact surface. Furthermore, it is found that the composition of mrGO-Cu could significantly influence the tribological properties of the mrGO-Cu/Al composites. The composites with 4% of mrGO-Cu for composites exhibited the best tribological behavior, which transformed from adhesive wear to abrasive wear, due to the formation of a graphite lubricating film.

Thermomechanical treatment consisting of heat treatment and deformation is an effective processing route for precipitation-hardened 6xxx alloy (Al-Mg-Si-Cu system), and precipitates and dislocations produced during the process can significantly change its mechanical and conductive performance. We therefore investigated the microstructural evolution of precipitates in a representative 6xxx alloy during thermomechanical treatment. When the precipitates encountered the accumulated dislocations, the precipitates were bent and broken into dispersed smaller particles. The strength of the alloy was significantly improved by the proliferation of dislocations and precipitates and desired electrical conductivity was obtained as well. Our results prove that peak aging plus cold rotary swaging is an efficient processing route for simultaneously improving the mechanical and conductive performance of 6xxx alloy.

The microstructure and mechanical properties of Al-0.35Fe alloys with a series of different zirconium (Zr) additions from 0.1 to 0.4% are investigated by optical microscopy, scanning electron microscopy, transmission electron microscopy and tensile testing. The as-cast structure of the alloys varies with the Zr content. When the content of Zr is 0.1%, Zr dissolves into the aluminum (Al) matrix completely and iron (Fe) concentrates along the boundary in a network of eutectic Al3Fe. With the increase in Zr content to 0.2% and above, nanoscale Al3Zr particles appear in the alloy. With the Zr content increasing from 0.1 to 0.4%, the grain size of the Al matrix decreases from 73 to 23 μm. The morphology of the eutectic Al3Fe phase changes from short rod-like to an agglomerated structure consisting of finer and shorter rod-like shapes. The tensile and yield strengths increase while the total elongation decreases with increasing Zr content. The strengthening mechanism of the alloy can be attributed to the combination of fine-grain, solution and second-phase strengthening.

Laser welding is widely used for the joining of aluminum alloy in the automotive industry, and the vehicles produced are inevitably subjected to high strain rate loading during their service. Therefore, this paper studied the mechanical properties of 6061-T6 aluminum alloy and its laser welded joint at strain rates between 0.0003 and 1000 s&minus, 1. Results showed that the microstructure of welded material (WM) was much finer than base material (BM), typical columnar crystals grew perpendicularly to the fusion line, and the minimum hardness value (~56 HV) was obtained inside WM. The strength and dynamic factors of BM and WM increased with increasing strain rate, and the strength of WM was less sensitive to strain rate compared with BM. The strain rate effect was not homogenous in the plastic deformation region. The modified Johnson&ndash, Cook (J&ndash, C) model which introduced the term C = C1 + C2&middot, &epsilon, could well describe the dynamic plastic deformation of BM. However, the fitted results of the simplified J&ndash, C model were overall better than the modified J&ndash, C model for WM, especially for high strain rate (1000 s&minus, 1). These findings will benefit the determination of the dynamic deformation behavior of laser welded aluminum alloy under high strain rates, and could provide a better understanding of lightweight and the safety of vehicles.

Low-cost heat-resistant Al-Sc-Zr-Fe conductor wires were successfully manufactured by continuous rheo-extrusion process, and the mechanical and conductive properties of the materials were analyzed and compared after three different thermo-mechanical treatment methods. The coarse plate-shape Al3Fe phase transformed to small sized rod-like phase after solid solution treatment at 630 &deg, C for 21 h. Direct aging treatment at 300 &deg, C for 24 h led to the refinement and spheroidization of Al3Fe phase with a diameter of 200 nm. After the subsequent aging treatment at 300 &deg, C for 24 h, the tensile strength and conductivity of the alloy wire significantly increased due to the homogeneous precipitation of the coherent spherical Al3(Sc, Zr) phase with an average size of 15 nm. The tensile strength, elongation, and conductivity of the alloy conductor wire after optimized thermo-mechanical treatment reached 165.7 MPa, 7.3%, and 60.26% International Annealed Copper Standard (IACS), respectively. The thermal resistance of the present alloy wire was superior to that of standard AT1 type alloy conductor according to IEC international standard.

Novel porous magnetic soft materials (pMSMs) based on a poly (vinyl alcohol) (PVA) porous matrix filled with CuNi nanoparticles (NPs) of around 70 nm were synthesized. Initially, magnetic CuNi NPs were fabricated by the reduction of Ni and Cu ions with hydrazine hydrate in ethylene glycol medium in the absence of other capping agents. The pMSMs are subsequently fabricated by mixing CuNi NPs and PVA through freezing-drying process. The as-obtained pMSMs can respond to a magnetic field, i.e., the compressive modulus increase under a magnetic field of 0.23 T. The experimental results indicate that CuNi NPs can easily move to form chain-like structures under the application of a magnetic field. A combination of direct observation and finite element modeling has shown that under the influence of a magnetic field, chain-like aggregates of CuNi NPs lead to self-reinforcement of the pMSMs and, thus, to the increased compressive modulus. From a technological point of view, these materials with good magnetic responsiveness and moderate mechanical strength have potential applications in artificial muscle, soft actuators and drug release, to name a few.

Due to superior mechanical properties and corrosion resistance, aluminum alloys with high magnesium content varying from 3 to 10 wt% have been widely used as aircraft welding wire and automotive materials. However, it remains challenging to produce high magnesium containing aluminum alloys in wire form through conventional casting, extrusion and rolling. Therefore, the present work employs continuous rheo-extrusion to manufacture Al alloy wires with high magnesium contents, which can eliminate the formation of coarse dendrites and thus improve mechanical properties. Microstructures and properties of the alloy wires were investigated by metallurgical microscopy, X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Results show that coarse dendrites were completely converted into equiaxed grains. A solid solution with high solubility of Mg and nanosized Al3Mg2 phases were formed in the alloy due to the high cooling rate in continuous rheo-extrusion. Such microstructural features incurred serrated plastic deformation in tensile tests due to the interactions between the solid solution atoms and dislocations. With increasing magnesium content, ultimate tensile strength increased while the elongation decreased gradually. Ultimate tensile strength and elongation of Al-5Mg (wt%) alloy wires were improved by 73% and 8% than that of conventional casting respectively.

The Mg-3Sn-1Mn-1La alloy sheets were prepared by a continuous rheo-rolling process, and the effects of the solution and aging treatment on the microstructures and mechanical properties of the alloy were studied. The tensile strength and elongation at room temperature and 150 °C of the Mg-3Sn-1Mn-1La alloy sheets were decreased with increasing the solution time. The grain size was increased gradually. The plate-shaped MgSnLa compounds composed of La5Sn3, Mg2Sn and Mg17La2 phases and Mg2Sn phase gradually disappeared. At the same time, new irregular MgSnLa compounds were formed in grains. Aging treatment of the alloy was performed after solution treatment. The new spherical MgSnLa compounds composed of La5Sn3, Mg2Sn and Mg17La2 phase were formed, increased and distributed gradually homogeneously in the matrix with increasing the aging treatment time. Meanwhile, the Mg2Sn phases with spherical, short-rod and lath-shaped were formed in the matrix. After solution treatment at 550 °C for 24 h, aging at 250 °C for 48 h, the tensile strength at room temperature and at 150 °C of the Mg-3Sn-1Mn-1La alloy sheet was increased to 270 MPa and 233 MPa, with 19% and 20% increase, respectively. The elongation at room temperature and 150 °C was increased to 7.9% and 67.5%, with 6% and 4% increase, respectively. The formed spherical MgSnLa compounds and Mg2Sn phases which were coherent with the matrix and effectively pinned the dislocations and grain boundaries were responsible for the enhanced mechanical properties of the alloys.

Al-1Fe (wt%) alloys containing nanosized Al3Fe phase and micrometer-sized Al3Fe phase were prepared by continuous rheo-extrusion and casting, respectively. The yield strength, tensile strength and elongation of Al-1Fe (wt%) alloy containing nanosized Al3Fe phase were 128.2 MPa, 135 MPa and 30%, respectively, while that of Al-1Fe (wt%) alloy containing micrometer-sized Al3Fe phase were 81.6 MPa, 87.1 MPa and 26.8%, respectively. The influence of nanosized Al3Fe phase on the mechanical properties of Al-Fe alloy was investigated by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM), and compared with pure Al. The results suggested that the improvement of yield strength was 80.6 MPa and the reduction of elongation was 4.2% induced by nanosized Al3Fe phase. However, for the micrometer-sized Al3Fe phase, the increment of yield strength was only 32.8 MPa and the loss of elongation was 6.5%. When Al3Fe phase was refined to nanosize, its number density was increased, and the Orowan strengthening effect was significantly better. Micro-cracks around Al3Fe phase gradually grow and connect to one another with the accumulation of stress concentration and incompatible deformation. The rapid propagation of crack led to failure of the alloy. The crack around the hard Al3Fe phase became smaller once Al3Fe phase was refined, and it took a longer time for crack growth to occur. Thus, alloys containing nanosized Al3Fe phase shown superior plasticity. However, the deformation incompatibility between the matrix and the hard Al3Fe phase could not be completely eliminated even when the Al3Fe phase was refined to nanosize.

To understand the synergistic effect of TiAl3 and TiB2 particles on grain refinement of α-Al, equal-channel angular pressing (ECAP) of Al-5Ti-1B (wt%) alloy was carried out. The ECAPed Al-5Ti-1B (wt%) alloy was characterized by X-ray Diffraction (XRD), electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM). The results reveal that α-Al grains and TiAl3 phase of ECAPed Al-5Ti-1B (wt%) alloy were refined, while the average size of TiB2was marginally decreased. The tensile strength was increased from 128 MPa to 218 MPa, and the elongation was reduced from 26% to 20.6%. The transformation from dislocations to low-angle grain boundaries (LAGBs) and high-angle grain boundaries (HAGBs) resulted in continuous dynamic recrystallization (CDRX), which induced grain refinement during ECAP. From 3 to 6 passes of ECAP, CDRX occurred in the alloy, and as ECAP passes increased to 9, the rate of formation of LAGBs and the transformation rate from LAGBs to HAGBs reached a dynamic balance. The present study indicates that the second phase particles promote the formation of LAGBs but prolong complete-recrystallization time, such that complete-recrystallization leads to grain refinement. TiB2 particles are smaller than TiAl3 particles and this is caused by the composition of the alloy and its synthesis method, and compared with TiAl3, TiB2 with a smaller size had a more obvious influence on the formation of LAGBs and grain refinement.

Common strengthening strategies for casting aluminum alloys sacrifice ductility. Herein, the strength-ductility synergy of a rheo-diecasting semi-solid Al–Si–Mg–Cu–Fe–Sr alloy was tailored by optimizing the pouring temperature and subsequent heat treatment. The results demonstrated that with decreasing pouring temperature from 700 °C to 670 °C, the average grain diameter of primary α-Al grains and porosity decreased, while the average shape factor and solid phase fraction increased, resulting in improved mechanical properties of the alloy. After T6 heat treatment, changes in the morphologies of eutectic Si phases and Al3Fe phases were observed, and Mg2Si precipitates were formed, which further enhanced the mechanical properties of the alloy.

In this work, based on the A356 alloy, a novel Al–Si–Mg–Cu–Fe–Sr alloy with good mechanical property and high thermal conductivity was developed. The semi-solid slurry of the alloy was prepared via the vibrating contraction inclined plate. The microstructure evolution and solidification behavior of the alloy were investigated. The results demonstrated that, compared with the A356 alloy, the enhanced property of the Al–Si–Mg–Cu–Fe–Sr alloy was associated with the size of primary α-Al grains and morphology of eutectic Si phases. In addition, the preparation process parameters of semi-solid slurries, including the pouring temperature, inclination angle, and vibration frequency, had a crucial effect on the size and morphology of primary α-Al grains. The optimized pouring temperature, inclination angle, and vibration frequency were 670 °C, 45°, and 60 Hz, respectively. In this condition, for the primary α-Al grains, a minimum grain diameter of 64.31 µm and a maximum shape factor of 0.80 were obtained. This work provides a reference for the application of the alloy with high performance in the field of automobile and communication.

The addition of trace La significantly affected the properties of the Al–Zn–Si coating. Adding La improved the corrosion resistance of the coating. More importantly, it restrained the nucleation of α-Al dendrites consequently leading to coarser grains. Based on the density functional theory calculations, we found that the doping concentration was important to the spontaneous nucleation of the heterogeneous nucleus in liquid metal, and there should be a transition between homogeneous nucleation and heterogeneous nucleation.

Continuous preparation of high-conductivity and high-strength aluminium alloy cable remains a challenge. Here we reveal the scientific significance of high electrical conductivity Al-Ag-Sc-Zr alloy with ultrafine grains prepared by novel processing technologies, the combination of rheo-extrusion and accumulative continuous extrusion forming. Attributed to the continuous dynamic recrystallization during rheo-extrusion, equiaxial microstructure and significantly refined grains (2.8 ± 0.2 μm) were achieved. By means of partially replacing low conductive scandium and zirconium solute atoms with high conductive silver solute atoms, the processed alloy wires exhibit significant higher electrical conductivity (53.5 ± 0.4 %IACS) than the Al-Sc-Zr alloy with similar atomic concentration of alloying elements. Appropriate mechanical properties were also obtained due to the similar solution strengthening effects of silver atoms to scandium and zirconium atoms. These results highlight the potential of this high electrical conductivity Al-Ag-Sc-Zr alloy and its novel processing route.

In this study, the micro-alloying of rare-earth yttrium (Y) was employed to improve the fracture behavior and work-hardening ability of H13 die steel. The improved work-hardening ability was attributed to modification of Cr23C6 and VC carbides by the addition of Y. The strip-typed Cr23C6 carbides originally distributed along the grain boundary were interrupted and tended to spheroidize with increasing Y content. Compared with 0Y–H13 steel, the quantity of spherical VC carbides significantly increased in 0.013Y–H13 steel. A higher-density dislocations and intensive interaction between precipitates and dislocation led to a higher work-hardening exponent. Additionally, fractographic studies revealed that the fracture mode transition from cleavage failure to ductile rupture with increasing Y content. Moreover, excess Y content (0.044%) resulted in the appearance of inclusion clusters in dimples, which were detrimental to fracture and work-hardening behavior.

Grains of Al–1Si(wt%) alloy were refined by accumulative continuous extrusion forming (ACEF). Electron backscatter diffraction and transmission electron microscopy were used to analyze the microstructure evolution of the Al–1Si(wt%) alloy. The grain size of the alloy decreased from 54.36 to 2.59 μm after four passes of ACEF. The grain refinement was attributed to continuous dynamic recrystallization (CDRX). The enhanced effect of nanosized precipitates on CDRX was pronounced. Nanosized eutectic Si precipitates retained a high density of dislocations in the alloy by promoting their generation and pile-up, resulting in an increase in the driving force for CDRX and a consequent promotion of grain refinement. After 4 ACEF passes, the tensile yield strength of the alloy at room temperature increased from 102 MPa to 117 MPa. Further, the elongation of the alloy at room temperature decreased from 38 to 17 % after 3 ACEF passes and subsequently increased to 23 % after 4 ACEF passes.

In this paper, the precipitation and dynamic softening behavior of Al–Fe–Zr alloys were investigated by transmission electron microscopy (TEM), electron back scattering diffraction (EBSD), and the precipitation thermodynamics was studied by JmatPro software. Results show that the optimizing temperature of Al3Zr precipitates was 350 °C and the fraction of butterfly-shaped Al3Zr and rod-shaped Al3Fe reached a peak at ~350 °C. With the increase of Zr content, the fraction of Al3Zr increased, whereas its size and morphology had almost no change. The fraction and morphology of Al3Fe showed less variation with Zr content. Dynamic recovery and dynamic recrystallization occurred during extrusion. The two kinds of precipitation particles in aluminum matrix pinned the dislocations and inhibited dynamic recrystallization effectively. As the Zr content went up from 0.1 to 0.4 wt%, the inhibition got stronger and the fraction of recrystallized grains decreased from 44.2% to 86.9%. As a consequence of the dynamic recrystallization suppression, dynamic recovery became the major softening mechanism.

In this research, the effect of several heat treatments on the microstructure and microhardness of TC4 (Ti6Al4V) titanium alloy processed by selective laser melting (SLM) is studied. The results showed that the original acicular martensite &alpha, &prime, phase in the TC4 alloy formed by SLM is converted into a lamellar mixture of &alpha, + &beta, for heat treatment temperatures below the critical temperature (T0 at approximately 893 &deg, C). With the increase of heat treatment temperature, the size of the lamellar mixture structure inside of the TC4 part gradually grows. When the heat treatment temperature is above T0, because the cooling rate is relatively steep, the &beta, phase recrystallization transforms into a compact secondary &alpha, phase, and a basketweave structure can be found because the primary &alpha, phase develop and connect or cross each other with different orientations. The residence time for TC4 SLM parts when the treatment temperature is below the critical temperature has little influence: both the &alpha, phase and the &beta, phase will tend to coarsen but hinder each other, thereby limiting grain growth. The microhardness gradually decreases with increasing temperature when the TC4 SLM part is treated below the critical temperature. Conversely, the microhardness increases significantly with increasing temperature when the TC4 SLM part is treated above the critical temperature.

Semisolid slurry of A356 aluminum alloy was prepared by Self-Inoculation Method, and the secondary solidification behavior during rheo-diecasting forming process was researched. The results indicate that the component with non-dendritic and uniformly distributed microstructures can be produced by Rheo-Diecasting (RDC) process (combining Self-inoculation Method (SIM) with High Pressure Die Casting (HPDC)). The isothermal holding time of the slurry has large effect on primary particles, but has little effect on secondary particles. Growth rate of the primary particles in the isothermal holding process conforms to the dynamic equation of Dt3 − D03 = Kt. The suitable holding time for rheo-diecasting of A356 aluminum alloy is 3 min. During filling process, the nucleation occurs throughout the entire remaining liquid, and nuclei grow stably into globular particles with the limited grain size of 6.5μm firstly, then both α1 and α2 particles appear unstable growth phenomenon due to the existence of constitutional undercooling. The average particle sizes and shape factors of both α1 and α2 are decreasing with the increase of filling distance due to different cooling rate in different positions. The growth rate of the eutectic in RDC is 4 times faster than HPDC, which is mainly due to the limitation of α2 particles in RDC process. The average eutectic spacings are decreasing with the increase of filling distance.

The solidification and tensile deformation behaviors of rheo-cast AZ91-Sn alloys were revealed to study the effects of Sn alloying on improvement of AZ91 alloy&rsquo, s mechanical properties. Two kinds of Mg17Al12 phases precipitated from the supersaturated magnesium matrix during rheo-solidification were observed: coarse discontinuous precipitates (DP) at grain boundaries and small-sized continuous precipitates (CP) inside grains. With increasing Sn content, the amount of Mg17Al12 phases was increased whilst the amount of Al atoms in the matrix was decreased. Due to the higher melting point of Mg2Sn than Mg17Al12, Mg2Sn precipitated earlier from the melt, and therefore provided heterogeneous nuclei for Mg17Al12 during the eutectic reaction. Due to grain refinement and solid solution strengthening, AZ91-2.4Sn (mass%) gained 52% increase in tensile strength and 93% increase in elongation compared with pure AZ91 alloy. The higher-density twins and microcracks induced by Sn alloying relaxed stress concentration during plastic deformation, so the fracture mode was transformed from cleavage fracture of pure AZ91 alloy to ductile fracture of AZ91-Sn alloys.

A self-designed setup of modified sloping cooling/shearing process was made to prepare the semisolid Al-3wt%Mg alloy. A three-dimensional simulation model was established for the analysis of preparing the semisolid Al-3wt%Mg alloy. Through simulation and experiment, it is shown that the sloping angle of the plate greatly affects temperature and velocity distributions, and the temperature and velocity of the alloy at the exit of the sloping plate increase with the increase of the sloping angle. The alloy temperature decreases linearly from the pouring mouth to the exit. The alloy temperature at the exit increases obviously with the increase of pouring temperature. To prepare the semisolid Al-3wt%Mg alloy with good quality, the sloping angle θ=45°C is reasonable, and the pouring temperature is suggested to be designed above 650–660°C but under 700°C.

A novel method, powder thixoforming, for net-shape forming of the particle-reinforced Aluminum matrix composites in semi-solid state has been proposed based on powder metallurgy combining with thixoforming technology. The microstructural evolution and phase transformations have been investigated during partial remelting of the 2024 bulk alloy, prepared by cold pressing of atomized alloy powders to clarify the mechanisms of how the consolidated powders evolve into small and spheroidal primary particles available for thixoforming. The effect of heating temperature on the resulting semisolid microstructure has also been discussed. The results indicate that the microstructural evolution includes three stages—the initial rapid coarsening of the fine grains within the powders, the formation of continuous liquid layer on the primary particle surface (the original powder), and the final coarsening—that result from the phase transformations of θ→α, α→L, and α→L and L→α, respectively. The coarsening rate of the primary particles is low, and one original powder always evolves into one spheroidal particle with a continuous liquid layer surface. Properly raising the heating temperature is beneficial for obtaining an ideal semisolid microstructure.