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The industrial sector is the primary source of carbon emissions in China. In pursuit of meeting its carbon reduction targets, China aims to promote resource consumption sustainability, reduce energy consumption, and achieve carbon neutrality within its processing industries. An effective strategy to promote energy savings and carbon reduction throughout the life cycle of materials is by applying life cycle engineering technology. This strategy aims to attain an optimal solution for material performance, resource consumption, and environmental impact. In this study, five types of technologies were considered: raw material replacement, process reengineering, fuel replacement, energy recycling and reutilization, and material recycling and reutilization. The meaning, methodology, and development status of life cycle engineering technology abroad and domestically are discussed in detail. A multidimensional analysis of ecological design was conducted from the perspectives of resource and energy consumption, carbon emissions, product performance, and recycling of secondary resources in a manufacturing process. This coupled with an integrated method to analyze carbon emissions in the entire life cycle of a material process industry was applied to the nonferrous industry, as an example. The results provide effective ideas and solutions for achieving low or zero carbon emission production in the Chinese industry as recycled aluminum and primary aluminum based on advanced technologies had reduced resource consumption and emissions as compared to primary aluminum production.

Upon 98% reduction cold-rolling, a single layer AA3003 foil material of 115 μm thick was intermediately annealed at 300–420 °C/1-8 h, and the preferred temperature and time of the intermediate annealing for the laminated AA4343/AA3003/AA4343 composite foil material were determined. All of these samples were cold rolled by 40% to 70 μm thick and finally annealed at a temperature in the range of 300–550 °C for 1–9 h. Their sagging resistance and microstructure were investigated using simulated brazing treatment, optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). For the single layer AA3003 foil, the sagging distance decreased first and then increased with increasing intermediate annealing temperature, and the lowest sagging distance corresponds to the coarsest grain in the recrystallized sample. After the final annealing for the single layer, the sagging distance decreased monotonously. For the laminated foil subjected to the final annealing, the sagging distance curves decreased first and then increased with increasing annealing temperature and time. The improvement of sagging resistance was attributed to the recovery of two types of materials during annealing process. The deterioration of the sagging resistance in the laminated foils was due to the corrosion in the brazing process, resulted from the Si diffusion from the cladding layer into the core layer. It is the coarse grains, few dislocations and minimal diffusion of Si that are crucial for improving the sagging resistance of the laminated foils.

Aging behavior and phase transformation of Al–5Zn–1Mg–1Cu(-Si) alloys under different isothermal temperatures were investigated using transmission electron microscope (TEM) and mechanical tests. The aging temperature and Si addition significantly influenced to the types of precipitated phases and mechanical properties of the Al–Zn–Mg–Cu alloys. Adding Si in this alloy changed the precipitated phases from T′ and η′ phases to the dual-sized η and GPB-II phases. With increasing isothermal aging temperature, more GPB-II phases formed in alloys with the same composition, effectively improving the microhardness and mechanical properties. When aging at 150 °C, 0.5 wt%Si-containing alloy reached the highest peak hardness of about 150HV and maintained stable hardness, while an alloy without Si only reached 120HV and later declined by 15HV. The tensile strength and yield strength of the 0.5 wt%Si-containing alloy were higher than those of non-Si alloy by 132 MPa and 165 MPa, increasing 51% and 90%, respectively. This result was due to the presence of fine and dispersed 4–8 nm GPB-II phases in 0.5 wt%Si-containing alloy. The GPB-II phase had a core-shell structure, with the core region mainly enriched in Mg and Si, and the shell region mainly enriched in Cu and Zn. Compared with the stability of T′ and η′ phases, this core-shell structure of GPB-II effectively inhibited its growth and beneficially maintained a smaller-sized GPB-II phase. The strengthening effect of GPB-II phase was better than that of η or T phases when aging at 150 °C or 200 °C. The mechanical properties of high Zn/Mg ratios Al–Zn–Mg–Cu alloys can enhanced by adding Si.

The microstructure and grain refinement of Al-4.5Er-1Zr-1.5Ti master alloy were analyzed by the refinement experiment, OM, SEM and XRD. The results show that the grain size of pure aluminum is reduced from 14,000μm to 202μm by Al-4.5Er-1Zr-1.5Ti master alloy, which is mainly due to the nucleation promoted by Ti2Al20Er, Al3Er and Al3Ti. Plastic deformation further improves the refining effect of the material by improving the primary phase size, and the Al-4.5Er-1Zr-1.5Ti −2ARB can refine the pure aluminum from 202 mμm to 150μm, and the refinement was increased by 25.7 %. The master alloy showed a better refinement effect in Al-5Cu alloy than pure aluminum, with a grain size of 92μm and a refinement improvement of 97.8 %.

As a challenge to avoid the strength-ductility trade-off for Ti alloys, strength and ductility are contradictory, especially at a high content of primary α phase. This study proposed a new strategy to evade this trade-off dilemma by designing an 81% primary α phase/ultrafine-grained (UFG) secondary α phase lamellar heterogeneous structure(LPSlow-HS) in near-α Ti alloys. Compared to the bimodal structure, the LPSlow-HS offers a remarkable increase in the ultimate tensile strength(1119 MPa) and yield strength(1069 MPa), respectively, while the elongation (15%) is not sacrificed. Owing to the strong heterogeneous deformation-induced(HDI) strengthening, more number of delamination of interfaces, UFG microstructures and strong strain hardening render the Ti alloys high strength. This strategy may provide a new approach for achieving higher HDI strengthening effects in heterogeneous structures (HS) under high soft phases, and offer a feasible method for producing high strength-ductility Ti alloys under high primary α phase.

This paper investigates the impact of pre-precipitated η phases and Al3(Er, Zr) particles on the hot workability and recrystallization behavior of an Al–Zn–Mg–Er–Zr alloy. The optimal pre-precipitation heat treatment prior to hot deformation was obtained by heat treatment under different conditions combined with microstructure analysis. Subsequently, hot compression tests were conducted to establish the processing maps, and the influence of pre-precipitation on the microstructure and the hot workability under various thermal deformation conditions were analyzed. Furthermore, the effect of pre-precipitation of η phases and Al3(Er, Zr) particles on the recrystallization was studied. The results demonstrate that after the optimized pre-precipitation treatment, a multitude of Al3(Er, Zr) particles (∼10 nm) and η phases (∼1 μm) appeared in the alloy. Through this pre-precipitation treatment, the flow stress was significantly reduced, and the hot workability of the alloy was significantly enhanced, particularly at low temperatures and low deformation rates. Moreover, the pre-precipitated η phases facilitated recrystallization, refined grains and hence created a more homogeneous microstructure. Concurrently, during the recrystallization process, the precipitated Al3(Er, Zr) particles impeded grain boundary migration, and thus inhibited the growth of recrystallized grains, contributing to grain refinement.

Abstract Simultaneous improvement of strength and conductivity is urgently demanded but challenging for bimetallic materials. Here we show by creating a self-assembled lamellar (SAL) architecture in W-Cu system, enhancement in strength and electrical conductivity is able to be achieved at the same time. The SAL architecture features alternately stacked Cu layers and W lamellae containing high-density dislocations. This unique layout not only enables predominant stress partitioning in the W phase, but also promotes hetero-deformation induced strengthening. In addition, the SAL architecture possesses strong crack-buffering effect and damage tolerance. Meanwhile, it provides continuous conducting channels for electrons and reduces interface scattering. As a result, a yield strength that doubles the value of the counterpart, an increased electrical conductivity, and a large plasticity were achieved simultaneously in the SAL W-Cu composite. This study proposes a flexible strategy of architecture design and an effective method for manufacturing bimetallic composites with excellent integrated properties.

The effects of Si addition to Fe on the formation and growth of intermetallic compounds (IMC) in Fe/Al composites were studied by Scanning electron microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and electron backscatter diffraction (EBSD) techniques. The results showed that: when annealing time was 1 h, the critical IMC formation temperature of Pure Al/Pure Fe, Pure Al/Fe+0.82Si, Al+0.88Si/Pure Fe and Al+0.88Si/Fe+0.82Si were 440 °C, 480 °C, 520 °C and 620 °C, respectively. The major IMC phase formed in the four composites after heat treatments at 640 °C/1h and 640 °C/24h was the η phase (Fe2Al5), and a large number of θ phase (Fe4Al13) particles were present in the η phase for the Pure Al/Pure Fe sample. When Si element was added to Fe and Al, Fe3Al2Si3 phase and FeAl2Si phase were observed in the η phase. The thickness of the formed IMC layer in the four composites after heat treatment at 640 °C/1h was in the order: Pure Al/Pure Fe ≈ Pure Al/Fe+0.88Si > Al+0.888Si/Pure Fe ≈ Al+0.888Si/Fe+0.88Si. The growth activation energies of the IMC layer in the Pure Al/Pure Fe, Pure Al/Fe+0.82Si, Al+0.88Si/Pure Fe, Al+0.88Si/Fe+0.82Si samples were 76.1 kJ/mol, 276 kJ/mol, 349 kJ/mol and 519.6 kJ/mol, respectively. The effect of Si atoms on the formation of IMC was mainly by the interfacial enrichment mechanism and the new phase inhibition mechanism of FexAlySiz. The enrichment of Si at the interface of Al and Fe increased the growth activation energy and reduce the growth rate of IMC layer thickness. The formation of new FexAlySiz phase can inhibit the rapid growth of IMC phase along the C axis.

In this work, Er–Zr-Sc modified Al–Mg alloy, manufactured by selective laser melting, offers excellent mechanical properties, due to the formation of a desirable microstructure and the synergistic effects of multiple strengthening mechanisms. The microstructure in as-built and aged alloys have been characterized by scanning electron microscopy and transmission electron microscopy. The results show that the microstructure of alloy is composed of equiaxed grains (∼0.7 μm in diameter) along the boundary of molten pool and columnar grains (∼1.46 μm in width) inside the molten pool. Al3(Sc,Zr) particles serve as nucleation sites to promote the nucleation of equiaxed grains, and Al3(Er,M) eutectic phases and other compounds at the grain boundaries inhibit grain growth, both of which greatly refine the grains and bring significant grain boundary strengthening and Orowan strengthening effect. During the aging process, coherent Al3(Er,Zr,Sc) nano-precipitates are dispersedly precipitated from the Al matrix, which plays a key role in improving the mechanical properties of the aged alloy, and then the alloy reaches a yield strength of 530 MPa, a tensile strength of up to 542 MPa, and an elongation of over 12 %. Under the combined addition of Er, Sc, and Zr, and the influence of multi-element interaction, the alloy has high-density secondary phases and extremely fine grains, which are the main sources of reinforcement.

The depth profiling of the element content and precipitation phase distribution of the AA4045/AA3003mod (Al-1.5Mn-0.35Cu alloy)/AA4045 brazed sheets were investigated by optical microscope observation, electron probe microanalysis (EPMA), focused ion beam-scanning transmission electron microscopy (FIB-STEM). The electrochemical test and sea water acetic acid test (SWAAT) were performed to obtain the evolution of electrochemical responses and corrosion forms of brazed sheet. EPMA results showed that a diffusion layer with the thickness of approximately 50 μm existed between the clad layer and core layer, where the Cu diffused from the core layer and Si diffused from the clad layer. It was found that brazing led to a significant low elements solid solution area at the end of the Si diffusion path, where the open circuit potential was lower by 25 mV comparing to the unaffected region. Thus the diffusion zone can provide effective cathodic protection to the unaffected region as sacrificial anode by the potential gradient. The SWAAT analysis revealed the corrosion mechanism of the residual cladding was pitting and intergranular corrosion. This area with high density of intermetallic compounds and Si particles increased sensitivity to localized attacks. These results demonstrated the successful application of the FIB-STEM system in illustrating the electrochemical responses and corrosion propagation by an accurate in-depth characterization of intermetallic particles and the matrix solid solution.

The effects of Sc, Mg and Si elements in an Al-Cu alloy have been studied by means of hardness tests and transmission electron microscopy analysis. The experimental results show that additions of Sc, Mg and Si can improve the heat resistance of the Al-Cu alloy. The Sc/Mg/Si segregation-sandwiched structure is the most stable, when compared with Sc segregation or Si/Sc co-segregation at the interface of θ′/Al. The additions of Si and Mg promote the aging–hardening response of the Al-Cu alloy. Mg is a micro-alloying element with great potential in stabilizing the size of θ′ phases, which further promotes the number density greatly. Consequently, the Al-Cu alloy achieves a high strength, matched with excellent thermal stability, due to the microalloying of Sc/Mg/Si solutes.

The influence of grain size on the corrosion behavior of pure aluminum and the defect density and diffusion coefficient of surface passive films were investigated using electron backscatter diffraction (EBSD) and electrochemical testing techniques, based on the point defect model (PDM). Samples with three different grain sizes (23 ± 11, 134 ± 52, and 462 ± 203 μm) were obtained by annealing at different temperatures and times. The polarization curves and electrochemical impedance spectroscopy results for the pure aluminum in the 3.5% NaCl solution showed that with decreasing grain size, the corrosion current (icorr) decreased monotonously, giving rise to a noble corrosion potential and a large polarization resistance. The Motte–Schottky results showed that the passive films that formed on pure aluminum with fine grains of 23 ± 11 μm had a low density (3.82 × 1020 cm−3) of point defects, such as oxygen vacancies and/or metal interstitials, and a small diffusion coefficient (1.94 × 10−17 cm2/s). The influence of grain size on corrosion resistance was discussed. This work demonstrated that grain refinement could be an effective approach to achieving high corrosion resistance of passive metals.

The challenge of fabricating nanostructured W–Cu composites by powder metallurgy has been solved by means of modulated phase separation. A hierarchically nanostructured (HN) W–Cu composite was prepared using intermediary Al through sluggish asynchronous phase separation. In addition to a dual network composed of a Cu phase and the W–Cu nanostructure, dense Al-containing nanoprecipitates with a body-centered cubic (bcc) structure are distributed in the W matrix. Compared with a pristine W/Cu interface, the newly formed W/Cu interfaces modulated by Al and the coherent W/Al-containing particle interfaces possess lower energy and enhanced bonding strength due to efficient electron transfer and strong coupling interactions. With a large number of stable heterogeneous interfaces and a “self-locking” geometry, the HN W–Cu composite exhibits excellent resistance against plastic deformation. The combination of the presented composite’s hardness and compressive strength outperforms all other sintered W–Cu composites with the same Cu content. Under a reciprocating sliding load, the reactive Al prevents excessive oxidation. The excellent synergy of the hardness and toughness of the friction-induced surface endows the HN composite with high abrasion resistance. This study provides a new strategy to modulate the structure and energy state of interfaces in metallic composites containing immiscible components in order to achieve high mechanical performance.

The printability of Al6SiMg0·5Er1·0Zr alloy at various laser power, scan speed, and hatch spacing was investigated. The optimal processing window was determined. The relationship between hatch spacing and lack of fusion (LOF) defects and microstructure is discussed. Hatch spacing significantly affects the cellular size, which is formed by eutectic Si network, and medium hatch spacing can achieve the finest microstructure. Samples with high densities and fine microstructures were investigated more carefully. The grain and cellular boundaries have many Al3(Er,Zr) phases. The grain size was refined to 2.64 μm, and the epitaxial growth of columnar crystals was completely suppressed. The cellular structure has been significantly improved. Get the equiaxed - ultrafine equiaxed - columnar multi-cellular structure with dramatically enhanced mechanical properties. The yield strength, tensile strength, and elongation were 373 Mpa, 480 MPa, and 5.5%, respectively. Grain boundary strengthening and Orowan strengthening was the main strengthening mechanisms.

This work aims to study the influence of laser power on the microstructural evolution of novel Ti–6Zr–5Fe alloy fabricated by selective laser melting (SLM). The microstructural evolutions of all top surfaces in SLM Ti–6Zr–5Fe alloy samples fabricated from 80 W to 140 W were investigated in depth. The microstructure in SLM Ti–6Zr–5Fe alloy includes α phase and β phase, the size of the β phase and α phase increases with the increase of laser power due to the decrease of cooling rate. Meanwhile, the melt pool overlapping width increases with the increase of melt pool width due to the increase of laser power. The increase of melt pool overlapping causes the re-heating or re-melting of SLM Ti–6Zr–5Fe alloy. Moreover, as the laser power increases from 80 W to 140 W, the change of the melt pool greatly influenced the size, morphology, crystallographic orientation of the β phase, and their distributions. The increase of laser power causes adequate precipitation of the α phase, which improves the microhardness from 466 HV to 533 HV. The laser power can effectively regulate and control the microstructure and microhardness of SLM Ti alloys.

The Al–Mn alloy heat exchanger fin production process includes a brazing treatment at s high temperature of 600 °C, in which coarse grains are preferred for their high resistance to deformation at elevated temperatures by decreasing the grain boundary sliding. In this study, Al-1.57Mn-1.57Zn-0.58Si-0.17Fe alloy foils cold rolled by 81.7% (1.1 mm in thickness) and 96.5% (0.21 mm in thickness) were annealed at 100–550 °C for 1 h to investigate their recrystallization behavior, grain sizes, and precipitates by increasing the annealing temperature, using micro-hardness measurement, electron back-scattered diffraction (EBSD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques. The micro-hardness results showed that the recrystallization finishing temperatures for the two samples were almost the same, 323 ± 2 °C. The EBSD results showed that when the annealing temperature decreased from 550 to 400 °C, the recrystallized grain sizes of the two samples were nearly identical—both increased slightly. Further decreasing the annealing temperature from 400 to 330 °C caused the grain sizes to increase more, with the thinner foil sample having a more significant increase. The SEM and TEM observations showed that the micron-sized primary-phase remained unchanged during the annealing process. The nano-sized secondary phase precipitates formed during the hot-rolling process experienced a coarsening and dissolving process upon annealing. The particle size of the secondary phase increased from 32 nm to 44 nm and the area fraction decreased from 4.2% to 3.8%. The nucleation analysis confirmed that the large primary-phase could act as a nucleation site through particle stimulated nucleation (PSN) mode. The relatively dense secondary phase precipitates with small sizes at lower temperatures could provide higher Zener drag to the grain boundaries, leading to fewer nuclei and thereafter coarser grains. The coarsening of the recrystallized grains in the foils could be implemented through thickness reduction and/or precipitation processes to form densely distributed nano-sized precipitates.

In order to improve the mechanical properties of Al–Si alloys fabricated by selective laser melting process, the microstructure and mechanical properties of Er/Zr modified A357 (Al–7Si-0.6 Mg) alloy in as-built and stress relief annealing conditions were studied. The results show that adding 0.15 wt.% Er helps to refine the cellular size, which is formed by eutectic Si network. The (Al,Si)3(Er,Zr) phases were precipitated during the solidification of Er–Zr composite modified sample, which could act as inoculants to promote the formation of equiaxed grains and refine the grain size. The average grain size of 0.8Er-0.4Zr sample was only 3.1 ± 1.4 μm. The yield strength, tensile strength and elongation reached 333 ± 2 MPa, 454 ± 1 MPa and 12.5 ± 1%, respectively. After stress relief annealing, eutectic Si was spheroidized and its size was increased, resulting in a decrease of strength and an increase of elongation. At the same time, the nano-sized L12-structure particles were precipitated in the Er–Zr composite modified sample, which would make up for the loss of strength and level it up to a certain extent. Therefore, Er–Zr composite modification could be an effective method to improve the comprehensive mechanical properties of SLM processed Al–Si alloys.

Isothermal hot compression experiments of homogenized Al–Mg–Si–Er–Zr alloy were conducted at temperatures ranging from 350 to 500 °C and strain rates of 0.01–10 s−1 on a Gleeble-3500 thermal simulation tester. The hot deformation behavior and optimum processing parameters of the alloy were determined by analyzing the flow curves and processing maps. Characterization of the microstructures of the deformed specimens was done using electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM), and the geometrically necessary dislocation (GND) density was used based on the kernel average misorientation (KAM). The results showed that the GND density decreased with a decrease in the strain rate and with an increase in the deformation temperature. Dynamic recovery and continuous dynamic recrystallization were the main softening mechanisms during hot deformation, and dynamic recovery was dominant. It was found that the capacity for dynamic recovery was reduced, while dynamic recrystallization was prevented in the Al–Mg–Si–Er–Zr alloy. This was a result of hindered dislocations and sub-grain boundary movement caused by the pinning of dislocations and sub-grain boundaries from the Mg2Si, Al(MnFe)Si, and Al3(Er, Zr) particles. The addition of Er and Zr resulted in an increase in the activation energy, which can be attributed to the formation of Al3(Er, Zr) particles.

Microstructural evolution and its effect on microhardness and Young's modulus of Ti–6Zr–4Fe alloy solution and aging treated at different temperatures were studied. The α phase transformed into β phase completely at 860 °C, meanwhile, the athermal ω phase was found at 860 °C and it resulted in a higher Young's modulus. The ω phase content increased from 250 °C to 400 °C, and the content decreased with further increase of aging temperature, there were only α phase and β phase at 600 °C. The phase transformation sequence was β → ω + β → ω + α + β → α + β during aging treatment. The microhardness increased from 315 HV to 492 HV due to the element solution strengthening and phase transformation strengthening. The peak microhardness of Ti–6Zr–4Fe alloy aged at 400 °C reached 652 HV. The formation of ω phase resulted in the increase of microhardness and Young's modulus in Ti–6Zr–4Fe alloy.

The Al–7Si–0.6 Mg alloy with added rare earth erbium (Er) was prepared by laser powder bed fusion (LPBF) technology, and the effect of heat treatment on the microstructure and mechanical properties was studied. The addition of Er introduces Al3Er to the molten pool, which can effectively hinder the epitaxial growth of the columnar crystal. The effect of rapid cooling and the addition of Er can also modify eutectic Si particles, resulting in an ultrafine eutectic network cellular structure. Moreover, the as-built samples have an excellent tensile strength exceeding 438 MPa and a ductility of over 8%; furthermore, such excellent mechanical properties are associated with small grains, a continuous Si network, and extremely oversaturated solid solubility. After heat treatment, LPBF-processed alloy samples exhibit superior mechanical properties, especially after direct age treatment, which can mainly be attributed to the precipitation strengthening effect introduced by nanosized precipitates.

Al–Sn–Si alloys have been widely used as bearing alloys in automotive engines. In those alloys, β(Sn) phase serves as the solid lubricant and Si particles are used to improve the hardness, fatigue resistance as well as seizure resistance. With the development of machinery, bearing alloys with higher load-carrying capacity and better tribological properties are demanded to meet the application under severe conditions. Adding appropriate Mg to the Al–Sn–Si alloy can effectively optimize the tribological properties. In this paper, the microstructure, mechanical properties and tribological properties of the Al–12Sn–4Si-xMg (x = 0, 0.5, 1, 1.5, all in wt.%) alloys were studied. The Al–12Sn–4Si-1.5 Mg alloy had the smallest grain size and more uniform microstructure than other specimens. The Al–12Sn–4Si-1.5 Mg alloy showed significantly better wear resistance than the Al–12Sn–4Si alloy at 2 N–70 N. The volume wear rates and friction coefficients at 15 N–70 N were lower than those at 2 N–8 N. The evolution of volume wear rate and friction coefficient with load was related to the evolution of tribolayer with load. The wear mechanism of the alloys was mainly oxidation wear, adhesive wear and fatigue wear, accompanied with abrasive wear.

A novel Al-Mg-Si aluminum alloy with the addition of the micro-alloying element Er and Zr that was promptly quenched after extrusion has been studied. The solid solution and aging treatment of the novel alloy are studied by observing the microstructure, mechanical properties, and strengthening mechanism. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques are employed to examine the changes in the microstructure resulting from various solid solution treatments and aging treatments. The best strengthening effect can be achieved when the solubility of the MgSi phase and precipitate β″ (Mg2Si phase) is at their maximum. The addition of Er and Zr elements promotes the precipitation of the β″ phase and makes the b″ phase more finely dispersed. The aging strengthening of alloys is a comprehensive effect of the dislocation cutting mechanism and bypass mechanism, the joint effect of diffusion strengthening of Al3(Er,Zr) particles and the addition of Er and Zr elements promoting the precipitation strengthening of β″ phases. In this paper, by adding Er and Zr elements and exploring the optimal heat treatment system, the yield strength of the alloy reaches 437 MPa and the tensile strength reaches 453 MPa after solid solution treatment at 565 °C/30 min and aging at 175 °C/10 h.

The nucleation and growth processes of pure Fe/pure Al intermetallic compounds (IMCs) during heat treatment at 380 °C and 520 °C were observed through in situ scanning electron microscopy (SEM). The size of the IMCs were statistically analyzed using image analysis software. The types and distribution of IMCs were characterized using transmission electron microscopy (TEM) and electron backscattering diffraction (EBSD). The results showed that: at 380 °C, the primary phase of the Fe/Al composite intermetallic compounds was Fe4Al13, formed on the Fe side and habituated with Fe. The IMC was completely transformed from the initial Fe4Al13 to the most stable Fe2Al5, and the Fe2Al5 was the habitus with Fe during the process of holding at 380 °C for 15 min to 60 min. At 380 °C, the initial growth rate of the IMC was controlled by reaction, and the growth rate of the thickness and horizontal dimensions was basically the same as 0.02–0.17 μm/min. When the IMC layer thickness reached 4.5 μm, the growth rate of the thickness changed from reaction control to diffusion control and decreased to 0.007 μm/min. After heat treatment at 520 °C (≤20 min), the growth of IMC was still controlled by the reaction, the horizontal growth rate was 0.53 μm/min, the thickness growth rate was 0.23 μm/min, and the main phase of the IMC was the Fe2Al5 phase at 520 °C/20 min.

Tungsten has poor processing performance and its brittleness often leads to defects. The effect of grain size on rotary swaging of the sintered rod was investigated to improve the quality of the destination part. Three different grain sizes of sintered rods were selected to research the physical and mechanical properties, microstructure, and texture. The texture evolution of the sintered rods and the effect of qualification rate of destination parts were studied. It was found that the {111} texture existed in the sintered samples along with the γ fiber. With the increase of grain size, the hardness decreased gradually, the intensity of {111} became weak, and γ fiber was no longer complete. Meanwhile, this work investigated the evolution of sintered texture on subsequent processing. The results showed that the sintered texture evolved into {111} after rotary swaging, and the fiber texture of became the main texture after drawing. The {111} texture formed in the sintered process was not beneficial to ductility. The increment of grain size has advantages for the processing technology within a certain range.

This paper centers on high-strength Al-Mg-Mn-Er-Zr alloy, which was developed through the addition of Er, a cheap rare earth element, and suitable for additive manufacturing (3D printing). The microstructure and mechanical properties of Al-Mg-Mn-Er-Zr alloy of as-built and heat treated samples have been characterized, which shows: the precipitation of Al3Zr primary phase at the boundary of molten pool promotes heterogeneous nucleation and refines the grains, which suppresses the formation of solidification cracking in Al-Mg alloy. To bring the Er-Zr synergistic effect into play during the aging heat treatment, the nano-scale precipitation phase of Al3Er that diffuses nucleation at an earlier stage promotes the precipitation of Zr, leading to the formation of Al3(Er,Zr) core-shell structure and enhancing precipitation strengthening effect. Under the combined effects of multiple strengthening mechanisms, the yield strength could reach 440 ± 3 MPa; tensile strength, 520 ± 2 MPa and elongation 15.5 ± 1.0 %.

The hot deformation behavior of Al-Zn-Mg-Er-Zr alloy was investigated through an isothermal compression experiment at a strain rate ranging from 0.01 to 10 s−1 and temperature ranging from 350 to 500 °C. The constitutive equation of thermal deformation characteristics based on strain was established, and the microstructure (including grain, substructure and dynamic precipitation) under different deformation conditions was analyzed. It is shown that the steady-state flow stress can be described using the hyperbolic sinusoidal constitutive equation with a deformation activation energy of 160.03 kJ/mol. Two kinds of second phases exist in the deformed alloy; one is the η phase, whose size and quantity changes according to the deformation parameters, and the other is spherical Al3(Er, Zr) particles with good thermal stability. Both kinds of particles pin the dislocation. However, with a decrease in strain rate or increase in temperature, η phases coarsen and their density decreases, and their dislocation locking ability is weakened. However, the size of Al3(Er, Zr) particles does not change with the variation in deformation conditions. So, at higher deformation temperatures, Al3(Er, Zr) particles still pin dislocations and thus refine the subgrain and enhance the strength. Compared with the η phase, Al3(Er, Zr) particles are superior for dislocation locking during hot deformation. A strain rate ranging from 0.1 to 1 s−1 and a deformation temperature ranging from 450 to 500 °C form the safest hot working domain in the processing map.

Rare earth elements and transition elements are widely used in aluminum alloys, magnesium alloys and copper alloys due to their unique microalloying effects. With regard to in-depth research on the grain refinement characteristics of rare earth elements and transition elements, the combination of grain refinement and microalloying in the master alloys has a great impact on the theories and technical research of refinement, and the broadening of the application field of master alloys. This paper first summarizes the grain refinement mechanisms and analyzes the effects of rare earth elements and transition elements on the grain refinement of aluminum and aluminum alloys, and summarizes the elements suitable for the preparation of Al-M master alloys and their refinement mechanism.

With the rapid development of the machinery industry, bearing materials with better tribological properties are demanded. Al alloys containing Erbium (Er) and Zirconium (Zr) have better comprehensive performance, whose tribological properties have hardly been reported before. In this work, dry sliding wear tests were performed on the Al–Sn and Al–Sn–Er–Zr alloys in two different annealing states to study the effect of trace Er, Zr on the tribological properties of the Al–Sn alloys. The Al–Sn–Er–Zr alloys showed better wear resistance than the Al–Sn alloys, which was mainly due to the higher hardness and strength of the Al–Sn–Er–Zr alloys. The wear losses of the alloys annealed at 375 °C for 100 h at the load of 70 N were significantly lower than those of the alloys annealed at 300 °C for 4 h. The wear coefficient K of the alloys annealed at 375 °C for 100 h decreased with the increasing load. The Al–Sn–Er–Zr alloys showed smoother worn surfaces than the Al–Sn alloys. With the load increasing, the wear mechanism changed from abrasive wear, mild adhesive wear and slight delamination wear to severe adhesive wear and delamination wear. The wear scars of different samples under the same load were similar, indicating that the addition of trace Er, Zr and annealing process did not change the wear mechanism. All samples experienced cracks and voids in the tribolayers. And oxygen accumulated in these defects. Most wear debris were lamellar, which was related to the adhesive wear and consist with the delamination theory.

A new electrochemical method for efficient and green recovery of cemented carbide in a molten salt is described. Tungsten powder is the main product when recovering cemented carbide by molten salt electrolysis. However, the main purpose of tungsten powder is to make tungsten carbide. Based on this, a new method for preparing tungsten carbide by in situ reduction was developed. Pure tungsten carbide powder was successfully prepared in situ by pulse electrolysis in a NaF–KF molten salt system at 1073 K. This not only effectively recovers the spent cemented carbide, but also enriches the product system and optimizes the method for preparation of tungsten carbide powder.

The hot compression experiment of homogenized Al−5.2Mg−0.6Mn−0.29Zn−0.16Er–0.12Zr alloy was carried out by the Gleeble-3500 thermal simulation testing system. The deformation behavior in temperatures of 350~500 ℃ and deformation rates of 0.01~10 s−1 was studied. The relationship between stress and strain rate and deformation temperature was analyzed. The constitutive equation of alloy high-temperature deformation was constructed by the Zener–Hollomon method, and the hot working diagram with the true strain of 0.2 and 0.5 was constructed according to the dynamic material model. The research results show that flow stress has a positive correlation with strain rate and a negative correlation with temperature. The steady flow stress during deformation can be described by a hyperbolic sinusoidal constitutive equation. Adding Er and Zr into Al−Mg alloy can not only refine grains and strengthen precipitation but also form a core–shell Al3(Er, Zr) phase. In the deformation process, Al3(Er, Zr) precipitates can pin dislocations and inhibit dynamic recrystallization (DRX). Dynamic recovery (DRV) is dominant during hot deformation. The mechanism of dynamic recovery is dislocation motion. At high temperatures, Al3(Er, Zr) can also inhibit grain coarsening. The average hot deformation activation energy of the alloy is 203.7 kJ/mol. This high activation energy can be due to the pinning effect of Er and Zr precipitates. The processing map of the alloy was analyzed and combined with the observation of microstructure, the hot deformation instability zone of the alloy was determined, and the suitable process parameters for hot deformation were obtained, which were 450~480 °C, and the strain rate is 0.01~0.09 s−1.

A novel Al-Cu-Zr alloy is designed in this paper, which provides a method for further improving the strength of Al-Cu alloys. In this paper, the addition of the micro-alloying element Zr in Al-Cu alloy was studied. The effect of aging treatment on the mechanical properties and precipitation behavior of the alloy was studied. With the addition of Zr, Al3Zr phases were formed in the alloy, which acts as obstacles to dislocation motion. In addition, Al3Zr phases can be used as the nucleation site of θ′ phases to promote precipitation. All this can improve the strength of Al-Cu alloys. After one-step aging, corresponding to the highest hardness, the largest amount of θ′ phases were observed in the alloy matrix. By contrast, after two-step aging, the θ′ phases were finer, and a large amount of Guinier–Preston (GP) zones formed during the pre-aging step, which were transformed into denser and finer θ′ phases in the secondary aging step. After the same solution treatment (540 °C/12 h), undergoing 120 °C/4 h + 175 °C/10 h two-step aging, the ultimate tensile strength, yield strength, and elongation of the Al-Cu-Zr alloy were 398.7 MPa, 313.3 MPa, and 7.9%, respectively.

The recycling of WC–Co hard metal scraps has been taken into consideration in the literature, due to the release of toxic substances and long recovery process. In this study, the recovery of tungsten process, based on the molten salt electrolysis treatment of WC–Co hard metal scraps, was developed. The anode polarization curves were applied to investigate the dissolution of the WC–Co hard metal scrap. Then, the electrochemical behavior of tungsten and cobalt ions dissolved from WC–Co scrap anode, was studied by cyclic voltammetry (CV) and square wave voltammetry (SWV). The results demonstrated that the reduction of tungsten and cobalt ions occurred through a one-step process involving the transfer of two electrons. This process was achieved by the diffusion of tungsten and cobalt ions in the melts. Finally, the parameters, such as the electrolysis current, the electrolysis duration and temperatures, were applied to analyze the effect of different electrolysis conditions on the composition of recycled products. The results demonstrated that the electrolysis current and the electrolysis temperature, compared to electrolysis duration, have significant effects on the selectivity of tungsten recycling. Furthermore, the analysis of cathode products demonstrated that a tungsten powder of approximately 500 nm could be selectively recovered from WC–Co hard metal scrap with the electrolysis condition of 60 mA for 4 h at 1073 K in NaF–KF molten salt. Keywords: WC–Co scrap, Electrochemical recovery, Tungsten

As a kind of volatile organic compound (VOC), methyl tert-butyl ether (MTBE) is hazardous to human health and destructive to the environment if not handled properly. MTBE should be removed before the release of wastewater. The present work supported the methyl-modified silica layer (MSL) on porous α-Al2O3 ceramic membranes with methyltrimethoxysilane (MTMS) as a precursor and pre-synthesized mesoporous silica microspheres as dopants by the sol-gel reaction and dip-coating method. MTMS is an environmentally friendly agent compared to fluorinated alkylsilane. The MSL-supported Al2O3 ceramic membranes were used for MTBE/water separation by pervaporation. The NMR spectra revealed that MTMS evolves gradually from an oligomer to a highly cross-linked methyl-modified silica species. Methyl-modified silica species and pre-synthesized mesoporous silica microspheres combine into hydrophobic mesoporous MSL. MSL makes the α-Al2O3 ceramic membranes transfer from amphiphilic to hydrophobic and oleophilic. The MSL-supported α-Al2O3 ceramic membranes (MSL-10) exhibit an MTBE/water separation factor of 27.1 and a total flux of 0.448 kg m−2 h−1, which are considerably higher than those of previously reported membranes that are modified by other alkylsilanes via the post-grafting method. The mesopores within the MSL provide a pathway for the transport of MTBE molecules across the membranes. The presence of methyl groups on the external and inner surface is responsible for the favorable separation performance and the outstanding long-term stability of the MSL-supported porous α-Al2O3 ceramic membranes.

The intergranular corrosion and β phase evolution of 5083 aluminum alloy containing Er and Zr during annealing at 100–230 °C were studied using mass loss tests and transmission electron microscopy. The mass loss curves showed that when annealing temperature changed from 200 to 220 °C, the alloy was subjected to a transition from sensitized state to stabilized state, corresponding to the change of nucleation position of β precipitates from grain boundaries to triple junctions. Particularly, when the annealing temperature was at 210 °C, this transition could also happen when the annealing time was increased from 0.5-10 h to 15-24 h, associated with the change in the shape of β precipitates. The classical nucleation analysis with the consideration of Mg segregation showed the nucleation rates at grain boundary and triple junction were 1013 and 1011 m−3 s−1 at sensitization temperature 150 °C, but 109 and 1010 m−3 s−1 at stabilization temperature 220 °C, suggesting the change of nucleation site with increasing temperature. The analysis of diffusion flux of Mg around β precipitate suggested that the shape change of β precipitates from elongate to spheroidal at 210 °C was attributed to the dominant interface diffusion over the grain boundary diffusion with the increase of time. Keywords: Aluminum alloy, Microstructure, Corrosion, Classical nucleation theory, Diffusion

The thermodynamics of five Al3Er compounds were investigated through first-principles density-functional theory (DFT) and experimental analysis. The Al3Er compounds with Al3Ho.hR20 (prototype Al3Ho, Pearson symbol hR20), Cu3Au.cP4, AlNd3.hP8, Ni3Ti.hP16 and Al3Gd.hR12 structures exhibited formation energies of −0.412(−0.417), −0.411(−0.416), −0.400(−0.413), −0.399(−0.345) and −0.342(−0.345) meV/atom when using DFT with “standard” potential (“frozen core” potential) of Er. The results indicated that the Al3Ho.hR20 structure was the thermodynamic stable phase and the other structures were metastable. The formation energy of Cu3Au.cP4 structure was only 1 meV/atom less than that of Al3Ho.hR20. Experimentally, the Al-30 wt.% Er alloys were cooled from 900 °C to 500 °C at the rate of 5 ± 2 °C/h and 60 ± 2 °C/h, respectively. The corresponding XRD analysis showed that the Al3Ho.hR20 was formed at the cooling rate of 5 ± 2 °C/h and the Cu3Au.cP4 was formed at the cooling rate of 60 ± 2 °C/h, which indicated that the Al3Ho.hR20 was in a thermodynamic stable phase and the Cu3Au.cP4 was in a metastable phase with high stability. The structural analysis indicated that the tiny energy difference between Al3Ho.hR20 and Cu3Au.cP4 might be attributed to a similar structure with varied stacking sequences.

Spherical CoCO3 powder with a small particle size and high density was successfully prepared using a continuous carbonate liquid precipitation method with a raw material of cobalt chloride solution, a precipitant of NH4HCO3, and without a template. The effects of the concentration of ammonium carbonate, process pH, and feeding rate on the tap density and apparent density of cobalt carbonate were investigated. It was found that the apparent and tap density values of 4.4 µm of cobalt carbonate were 1.27 g/cm3 and 1.86 g/cm3, respectively, when the initial concentration of NH4HCO3 solution was 60 g/L, the pH was 7.15−7.20, and the feeding rate of cobalt chloride was 2 L/h. The anisotropic growth process of the crystal lattice plane of CoCO3 under the aforementioned optimal conditions were studied. The results demonstrated that the crystal grew fastest along the (110) facet orientation, which was the dominant growth surface, determining the final morphology of the primary particles. The scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HR-TEM) results demonstrated that the primary particle morphology of the cobalt carbonate was a nanosheet. The unit cell of cobalt carbonate, of a hexagonal structure in the horizontal direction, grew horizontally along the (110) facet orientation, while 20−35 unit cells of the carbon carbonate were stacked along the c-axis in the thickness direction. Finally, the sheet-shaped particles were agglomerated into dense spherical secondary particles, as presented through the crystal re-crystallization model.