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As two important industrial manufacturing materials, ceramics and metals have their own advantages and disadvantages in terms of physical, chemical, and mechanical properties. The field of material manufacturing has witnessed efforts to develop technical processes that can properly combine these two alloys, aiming to effectively use their respective advantages. The welding technology for ceramics and metals, as a research topic with broad prospects, is comprehensively and deeply analyzed in this review. The current research progress in this field is analyzed from different process perspectives such as fusion welding, brazing welding, diffusion welding. By using appropriate intermediate materials between these two materials, the residual stress and brittle intermetallics near the interface of the transition joint can be minimised by solving the thermal expansion mismatch, reducing the bonding temperature and pressure.

Superalloys play a critical role in aerospace applications due to their exceptional mechanical properties at high temperatures. The application of magnetic fields to regulate superalloys presents novel avenues for optimizing microstructures, controlling solidification defects, and enhancing their high-temperature properties. This paper provides a comprehensive review of research findings on the influence of magnetic fields on the microstructure and properties of superalloys. It systematically elucidates the effects of different types and intensities of magnetic fields on alloy solidification. Moreover, this paper extensively explores the effects of various types of magnetic fields on the phase composition, microstructure, and properties of superalloys, including Ni-based and Co-based alloys, as well as high-entropy alloys. The underlying mechanisms behind the impact of magnetic fields on these alloy types are thoroughly analyzed. Finally, the last section offers a brief summary of the current development status and prospects of magnetic field-regulated superalloys.

In this paper, the microstructure and mechanical properties of CoCrFeNiMox (x = 0, 0.1, 0.3, 0.5, 0.7, and 1.0) high-entropy alloys (HEAs) prepared with high-vacuum arc melting method were studied in detail. After Mo-doping, the strengthening mechanism of HEAs mainly included the component segregation strengthening and the second phase strengthening. Cr and Mo elements were enriched at the grain boundary of HEAs, which leaded to the formation of σ phase and strengthens the alloys. The microhardness and strength increased with Mo contents, while the elongation decreased gradually. Among which, the higher microhardness, yield strength, and ultimate tensile strength of CoCrFeNiMo0.3 alloy reach 205.96 HV, 292.22 MPa, and 593.25 MPa, respectively, in compared with other alloys. More importantly, the percentage elongation of which remains 37.36%, and the microhardness distribution was uniform with an average value of 7.4 GPa and an elastic modulus of 263.6 GPa. The research findings presented in this paper could serve as a valuable theoretical basis and practical foundations for the strengthening efforts of face centered cubic (FCC) HEAs.

Multi-wire arc additive manufacturing (MWAAM) enabled customized production with high deposition efficiency and low cost as compared to the common wire arc additive manufacturing (WAAM) technology. In this paper, two titanium alloy components were prepared using the MWAAM technique, and the microstructures, mechanical properties, and wear behaviors of Ti–6Al–4V (TC4) alloy and Ti-6.5A1-3.5Mo-1.5Zr-0.3Si (TC11) alloy were investigated. The results showed that the microstructure distribution of TC11 alloy prepared by MWAAM was more intensive and the length and width of the lamellar α-Ti phase were significantly reduced compared with that of TC4 alloy. The polar densities corresponding to the texture in the two selected regions of the TC4 alloy and the TC11 alloy were 17.30 and 17.69, respectively. The proportion of the HAGBs of the TC4 sample and the TC11 sample were 99.07 % and 99.43 %, respectively. The average microhardness on the X–Y plane of TC4 and TC11 alloys were 316.17 HV and 366.14 HV, respectively, while the average microhardness on the Y-Z plane were 318.18 HV and 358.10 HV, respectively. The average compression yield strengths of TC4 and TC11 alloys were 836.61 MPa and 1088.33 MPa, respectively. The COFs of MWAAM TC4 and TC11 samples were stable at 0.479 and 0.455 under 20 N, respectively. The COFs of MWAAM TC4 and TC11 samples were stable at 0.472 and 0.432 under 60 N, respectively. The average yield strength, average ultimate strength, proportion of HAGBs, and microhardness of TC11 alloy were all higher than that of TC4 alloy. These results indicated that TC11 alloy had advantages over TC4 alloy in terms of mechanical properties and microstructure, with higher strength and deformation resistance. The properties of titanium alloy samples prepared by MWAAM were not lower than those of titanium alloy samples prepared by single wire WAAM, while MWAAM significantly better than single wire WAAM in deposition efficiency. The results obtained in this paper can help to prepare titanium alloy components with excellent mechanical properties more efficiently in MWAAM process.

This paper reports on the successful synthesis of a novel alumina powder with a unique rose-like structure composed of alumina platelets, using the molten salt method. The synthesized powder was then utilized to prepare alumina ceramic with impressive mechanical properties. The influences of the synthesizing temperature of alumina powder on the microstructure and mechanical properties of alumina ceramic are investigated in details. The results indicate that the alumina ceramic prepared using the rose-like powder synthesized at 800 °C exhibits a high relative density of 99.5 %, flexural strength of 408.2 ± 18.7 MPa, and fracture toughness of 6.14 ± 0.63 MPa m1/2. The work presented in this paper will provide a useful guideline for the preparation of high-performance alumina ceramic materials in the future.

In this paper, a novel coaxial continuous-pulsed dual-beam laser was proposed to join TC4 titanium alloy with QP980 high-strength steel, and magnesium alloy containing rare-earth elements (Mg-RE) was creatively as filler. The weld appearance, microstructure and mechanical properties of joints obtained by single-beam and dual-beam laser welding were compared and analyzed. And the evolution of bonding mechanism and the fracture mechanism with laser beam energy density was analyzed. The results showed that the appearance and mechanical strength of the joint obtained by dual-beam laser were better than that by single-beam laser. And the maximum tensile shear load of TC4/QP980 lap joint welded by dual-beam laser reached 303 N/mm, which was 124 % of that of single-beam laser welding. The bonding of Mg-RE with QP980 affected by temperature of laser welding and mainly depended on Gd and Y. They just diffused to QP980 under low power and reacted with Fe under high power. And the inter-diffusion of Zr of Mg-RE with Ti of TC4 produced to the bonding of Mg-RE with TC4. The roles of continuous laser and pulsed laser in dual-beam laser welding were revealed in this paper and it showed a great application potential of coaxial dual-beam laser welding technology in dissimilar metal joining.

Wire and arc additively manufactured aluminum alloys are prone to porosity, leading to poor mechanical properties in samples, which hinders their broad industrial application. Laser and arc hybrid processes have garnered increasing attention for their potential to reduce porosity, stabilize the arc, and enhance deposition efficiency. This paper investigates the porosity, element distribution, microstructure evolution, and mechanical properties of 2319 aluminum alloy produced through the laser and cold metal transfer (laser-CMT) hybrid additive manufacturing process. In comparison with the as-deposited samples, the laser-CMT hybrid process decreases porosity, enhances element distribution, mitigates Cu element segregation, and results in increased θ′′ phase precipitation. Following T6 heat treatment, the ultimate tensile strength (UTS), yield strength (YS), and elongation of the x-direction specimens from the laser-CMT hybrid process are 450.0 MPa, 318.1 MPa, and 10.0%, respectively. These values are 11.27%, 7.03%, and 36.65% higher than those of the as-deposited samples. To validate the findings, a large-scale load-carrying frame for a commercial aircraft was fabricated, demonstrating the efficacy of the process. The paper also presents a detailed analysis of the strengthening mechanism. Samples deposited using the laser-CMT method exhibit reduced porosity and excellent mechanical properties, making this process promising for a wide range of applications.

Aluminum alloys are widely used in the fields like aerospace, automotive and manufacturing industries due to their excellent comprehensive performances and low mass and density. With the rapid development of the industries above mentioned, the requirements of aluminum alloys properties are increasingly raised. Therefore, it is especially significant to choose reasonable treatment methods to upgrade the related performances of aluminum alloys. As a green, low-cost and no pollution new heat treatment process, deep cryogenic treatment (DCT) can significantly improve the microstructures and performances of the metals with little variation in their sizes and shapes. The present paper summarizes the characteristics and mechanisms of the DCT influence on the structure-performance evolutions of aluminum alloys. When the DCT parameters are selected appropriately, ultra-low temperature can lead to refinement and preferred orientation of grains, increase of dislocation density and optimization of secondary phase distribution for aluminum alloys. Besides, mechanical properties, residual stress, corrosion resistance, wear resistance and electrical conductivity of aluminum alloys can be considerably improved due to the various microstructure evolutions induced by DCT. The present paper not only concludes major findings of the previous researches but also suggests future recommendations for aluminum alloys processed by DCT.

Extruded magnesium alloy bars are susceptible to uneven microstructure after the heat treatment process, which is characterised by coarse grain size in the surface, thus affecting the further processing properties of the overall bars. In this paper a new cyclic rotating-bending (CRB) process is proposed to improve the microstructure by achieving a gradient plastic deformation of the bars from the surface to the core. The paper is based on finite element simulations to qualitatively and quantitatively investigate the plastic strain distribution and evolution in the middle radial section of the bar under different CRB processes. In addition, the influence on the microstructure distribution under the processes is also further clarified. The results show that during CRB deformation, the plastic strain in the middle radial section of AZ31B magnesium alloy bars gradually decreases from the surface to the core radially, and the plastic strain in the surface is significantly positively correlated with the bending angle and the period of rotation. When the bending angle reaches 150°–170° and the period of rotation reaches 30 r, the section of the bars is fully plastic deformed. Simultaneously, compared to the initial microstructure, significant twinning deformation occurs in the surface of the bars after different CRB processes, which further promotes grain refinement.

In tribological applications, the degradation of metallic coatings due to oxidation and thermal softening at high temperatures is an issue of increasing concern. Recently, researchers have focused on the development of durable hard coatings that can perform well under elevated temperatures. The alloying of ternary TiAlN coatings with various elements has received considerable attention due to its ability to improve coating properties at high temperatures by solid solution hardening, grain refinement, formation of new phases, diffusion barriers, and self-lubricious tribo-oxides. This paper reviews the microstructure, thermal stability, oxidation behaviour, and mechanical and tribological properties of resultant quaternary TiAlXN coatings (X = Si, Cr, V, Ta and B). The effects of the deposition parameters, chemical composition, high-temperature annealing, and coating architecture on the coating properties are discussed in depth. The properties of quinary TiAlCrSiN coatings are also reviewed to provide a better understanding of the synergistic effects of Si and Cr additions to TiAlN. The maximum hardness and plastic deformation resistance (H/E and H3/E2) of TiAlXN coatings produced by various deposition techniques are compared. This paper provides useful insights into the challenges and future research perspectives of the reviewed coatings.

Nickel-base alloy is a type of metal material with excellent properties and is widely used in many fields. However, in the harsh environment of the acid solution, corrosion causes the reduction of the service life of the alloys, thereby limiting the alloys' use and development. In this paper, the effect of Chromium (Cr) content on the microstructure and corrosion behavior of nickel-based alloys in hydrochloric acid (HCl) was studied by scanning electron microscopy (SEM), energy dispersive spectrum (EDS), electron backscatter diffraction (EBSD) and electrochemical workstation. Meanwhile, X-ray photoelectron spectroscopy (XPS) was used to investigate the composition and properties of the surface passive films. For the Cr20 and Cr30 alloys with a single face-centered cubic (FCC) structure, the Cr2O3 content in the passive films increased with the Cr content, effectively improving the corrosion resistance. As the Cr content continued to increase, the second phases having a body-centered cubic (BCC) lattice were precipitated both in the Cr40 and Cr50 samples, inducing microgalvanic corrosion, thus deteriorating the corrosion resistance. XPS results showed that, in the Cr30 alloy, the relative content of Cr2O3 and the bound water were the highest, indicating that its passive film had the best corrosion resistance. For the passive film, the pitting resistance was related to Cr content, appropriate Cr content improved the corrosion resistance.

For the development of new energy automobile industry and the trend of automobile lightweight have put forward a huge demand for high-strength lightweight materials, so developing high strength aluminum alloys is particularly momentous. As the most widely used aluminum alloy, 6000 series aluminum alloys (Al–Mg–Si alloys) have the advantages such as better mechanical properties, outstanding welding properties, excellent formability and fine processing capability, and therefore have obtained great attention as the structural materials. In addition, the Al–Mg–Si alloys with low density and corrosion resistance not only reduce the total weight of the car, but also extend the service life when subjected to chemical corrosion, which effectively achieve energy saving and emission reduction. This paper summarizes the research progress of 6000 series aluminum alloys, in particular, and reviews the methods of microalloying and particle strengthening, and their effects on the microstructure and properties of the alloy, thus providing a reference for the subsequent development of high-performance aluminum alloys in automobile and aerospace industries.

In general, the Ti–6.5Al–2Zr–1Mo–1V (TA15) components fabricated via laser powder bed fusion (L-PBF) exhibit high strength and low ductility. Herein, we report a novel approach to enhance the comprehensive mechanical properties of L-PBF TA15 alloy by adjusting the laser power. Samples processed using the optimal laser power exhibit a grid structure of alternating wide and narrow prior-β grains (PBGs), the inside of which is composed of a fully martensitic microstructure. The paper discusses in detail the alterations in the microstructure of samples processed at both low and high laser powers, clarifying the relationship between microstructure and mechanical properties. Thinner martensite contributes to higher strength, while a homogenous microstructure improves ductility. These findings provide valuable insights for controlling microstructure and achieving strength-ductility synergy in L-PBF additive manufacturing of titanium alloys.

Magnesium alloys have received a lot of attention in aerospace, automotive, electronic communications and other fields due to their low density, high specific strength and damping performance. However, magnesium alloy sheets prepared by conventional thermomechanical processing usually have a strong basal texture, resulting in poor formability. In this paper, Mg–Mn–Ce alloys with good plastic forming ability were prepared by studying and optimizing the annealing process. Under the low-temperature annealing condition, it can promote the static recrystallization and grain refinement of Mg–Mn–Ce alloy, and also eliminate the internal stress. With the increase of annealing temperature, a large amount of dispersed Mg12Ce as a stable second phase effectively hindered the grain boundary migration, while the nanoscale α-Mn forms a fine second phase to inhibit grain growth, and both of them together greatly stabilize the deformation structure of the alloy, and maintain a good grain organization under the condition of annealing temperature of 300 °C and holding time of 30 min. The present work also improves the Arrhenius constitutive equation for the Mg–Mn–Ce alloy with respect to the degree of deviation, which significantly improves the accuracy of the model in predicting the thermoforming behavior. Meanwhile, to address the shortcomings of the traditional forming method of magnesium alloy, the processing process of spreading the centrifugal casting tube flat is proposed, the forming process is simulated, and the location of easy breakage in the forming process is predicted. These findings provide microanalytical support for the improvement of forming properties of magnesium alloys by annealing.

In the global pursuit of energy conservation, reduction in consumption and emissions, as well as lightweighting, 5xxx-series aluminum alloys have emerged as a promising lightweight and high-strength material with a wide range of applications in aerospace, transportation, building structures, medical devices, and more. However, it is worth noting that 5XXX-series aluminum alloys belong to a category of non-heat-treatable reinforced aluminum alloys with limited means of enhancing their properties through heat treatment. Consequently, the development of high-performance 5XXX-series aluminum alloys poses a significant challenge. This paper provides an overview of the research progress on 5xxx-series aluminum alloys while discussing the current state of research regarding the influence of microalloying elements on their microstructure and properties. Furthermore, it elucidates the emerging trends in synergistic regulation between deformation processes and heat treatment processes for enhancing organizational refinement and improving alloy properties. Additionally, this study analyzes the reinforcement mechanism responsible for the exceptional properties exhibited by 5xxx-series aluminum alloys. Lastly, it discusses the exceptional properties exhibited by 5xxx-series alloys along with their primary areas of application. The findings presented herein can serve as a valuable reference for future advancements in advanced high-performance 5xxx-series aluminum alloys.

The demand for lightweight materials, site-specific properties, and customized features drives the need for joining components made from dissimilar materials. However, dissimilar welding poses challenges such as the formation of large heat affected zones and intermetallic compounds at the interface, leading to easy premature failure and cracking. In recent years, additive manufacturing (AM) of dissimilar metallic materials has gained popularity as a solution to these challenges, as evidenced by numerous review articles discussing various aspects of this field. However, a comprehensive review focusing on microstructural analysis at the joint interface of a wide range of materials combinations produced by AM has been lacking. This review aims to address this gap by providing an in-depth examination of microstructures and mechanical properties at the interface for various metal combinations. Furthermore, it delves into different processing approaches and the challenges associated with manufacturing dissimilar structures. This review serves as a valuable resource for beginners in the field, offering a thorough discussion and comparison of the reported results. The paper presents major conclusions and identifies outstanding issues for future investigations. By providing valuable insights crucial for the widespread implementation of dissimilar AM technologies, this analysis will assist current AM processing for dissimilar structures. It is particularly significant for understanding the microstructure at the joint interface of various miscible and immiscible dissimilar structures manufactured using different additive manufacturing techniques.

In recent years, severe plastic deformation has been one of the most popular methods of increasing the mechanical properties of bars. Obtaining an ultra or nanostructure in such bars provides high strength properties, but also reduces plasticity. This paper shows that gradient structure formation in carbon steel bars gives a simultaneous increase in strength properties and some decrease in plastic properties. A new combined technology is proposed for obtaining gradient microstructure. This technology consists of drawing medium carbon steel bars on a radial-shear broaching mill and subsequent drawing. Bars with 30 mm diameter were strained at room temperature to a diameter of 16 mm in 3 passes. As a result, during three straining cycles, the average value of microhardness in the central zone was 2085 MPa, in the neutral zone was 2505 MPa, and in the surface zone was 2915 MPa. This variation of microhardness confirms gradient microstructure availability. Also there was an increase in strength characteristics almost 2 times, plastic characteristics undergo reduction due to gradient microstructure obtained during straining, but remain at a fairly good level for steel AISI 1045. The validity of the results is confirmed by a large number of experiments using a set of standard and modern research methods, such as optical, scanning and transmission microscopy, EBSD analysis, microhardness changes, fractographic method and tensile tests of mechanical properties, as well as by the results reproduction in the joint use of methods.

Refractory high-entropy alloys (RHEAs) have good overall properties and potential high temperature applications, but they are not competitive in terms of light weight and wear and corrosion resistance, which severely limits the wide range of applications. In this paper, novel NbMoZrTi-X (Al, V) light refractory high entropy alloys (LRHEAs) were fabricated and their physical phase composition, microstructure, hardness, and wear and corrosion resistance were systematically investigated. The results show that NbMoZrTi LRHEA and NbMoZrTiV LRHEA are both single BCC structures, while NbMoZrTiAl LRHEA and NbMoZrTiAlV LRHEA are transformed into BCC, B2, and Zr5Al3 phase structures. The hardness increases as the volume fraction of the Zr5Al3 hard phase increases, with NbMoZrTiAl LRHEA having a maximum Vickers hardness of 811.29 HV. Room temperature dry friction tests showed that NbMoZrTiAl LRHEA had the lowest wear and coefficient of friction of 1.5 mg and 0.6713, respectively. Electrochemical tests performed in 3.5 wt% NaCl solution showed that NbMoZrTiAlV LRHEA has excellent corrosion resistance with the highest Ecorr (−0.142 V) and the lowest Icorr (2.149 × 10−7 A/cm2). Therefore, the addition of V and Al to NbMoZrTi-based LRHEA can effectively improve its wear and corrosion resistance due to the increase in hardness and dense passivation film formation. Our study provides a new strategy for designing LRHEAs with a combination of high hardness and excellent wear and corrosion resistance.

Al–Nb–B refiner has been considered as an alternative to Al–Ti–B refiner for hypoeutectic Al–Si alloys due to Si-poisoning effect. In this paper, the effects of Al–Nb–B and Al–Ti–B refiner on the microstructure and mechanical properties in indirect squeeze casting Al–8Si-0.2Mg-0.5Mn alloy were compared. Results show that the grain sizes in the edge chilling layer, segregation band, and the center region of the Al–Nb–B refined alloys were refined by 13.9%, 12.5%, and 17.6% compared to Al–Ti–B refined alloys, respectively. The yield strength, tensile strength, and elongation of Al–Nb–B inoculated alloys were superior to those of the unrefined alloys and Al–Ti–B inoculated alloys. The coexistence of NbAl3 and NbB2 particles in the Al–Nb–B refiner exhibited excellent anti Si-poisoning capability. They significantly decreased the grain size and uniformly distributed the eutectic Si particles and Fe-rich phases, resulting in an increase in the yield strength of the alloy by 16.1% compared to the Al–Ti–B inoculated alloy. The distribution of iron-rich phases in the segregation band was affected by the inoculation. The size of α-Al15(Fe, Mn)3Si2 phase in Al–Ti–B inoculated alloys was refined, and the number significantly increased, resulting in a decrease in tensile strength of 12.82 MPa. In the Al–Nb–B inoculated alloys, the size and number of α-Al15(Fe, Mn)3Si2 phase decreased, and the δ-Al4FeSi2 phase increased, which effectively improved the fracture toughness and ductility. In addition, with the increase in grain refinement (from unrefined to Al–Ti–B to Al–Nb–B inoculated alloy), the fracture behavior changed from trans-granular fracture to intergranular fracture, improving the fracture toughness.

Laser powder bed fusion (LPBF) Al–Li alloy technology demonstrates adaptability to the development requirements of structural complexity and functional integration, making it a promising area of research in additive manufacturing for the aerospace, defense industry, and other fields. However, challenges such as microstructure anisotropy and metallurgical defects inevitably arise during the LPBF process of lightweight alloys, significantly impeding further enhancements in their formability properties. Some improvement measures offer a viable solution to enhance the microstructure, mitigate metallurgical defects, and optimize residual stress distribution in additive structures, thereby enabling high–performance Al–Li alloy production by LPBF. This paper first introduces the fundamental principle of LPBF and discusses the process of parameter optimization for LPBF Al–Li alloys. It then describes the typical microstructures and common metallurgical defects of LPBF Al–Li alloys, along with examining the evolution process of microstructures and formation mechanism of metallurgical defects. Specifically, it focuses on discussing the influence of Li element on solidification structure. On this basis, it presents the mechanical properties and anisotropy of mechanical properties for LPBF Al–Li alloys. Afterward, a comprehensive review is provided of the current research status regarding LPBF improvement measures, including powder alloying, heat treatment, and other technologies. Emphasis is placed on improvements in microstructure anisotropy and reductions in metallurgical defects through these improvement measures. Finally, this article summarizes the research progress made in LPBF Al–Li alloys and its improvement measures while also prospecting future research work.

With increasing global research on the recycling of construction waste, the recycling of waste concrete aggregates has gradually attracted attention. Researches have shown that recycled aggregate (RA) has a certain degree of influence on the mechanical properties and durability of recycled aggregate concrete (RAC) owing to its high water absorption, high porosity, and large number of microcracks. Therefore, how to improve the mechanical properties and durability of RAC is a key issue of concern for scholars. Based on the review of related literature and comprehensive analysis, the reinforcement theories and methods such as self-reinforcement of recycled coarse aggregate (RCA), optimization of preparing technology of RAC, and external spiral constraint of RAC were systematically summarized in this paper. The results indicate that the adherent mortar of RCA can be enhanced by carbonation, and weak acid treatment can effectively remove the old adhesion of RCA, which is economical and environmentally friendly. The denseness of RAC can be improved by adding cementitious materials with volcanic ash effect, and the reduction of microcracks in mortar can be improved by adding fibers. The load-bearing capacity and mechanical properties of RAC are significantly improved by the spiral constraint of materials such as fiber reinforced polymer (FRP) and so on. The optimization of the production process not only improves the quality of RAC, but also enhances the production efficiency. The microstructure analysis of RAC was also summarized in this paper. Moreover, the results of this study can provide a technical reference for research on the mechanical strength and durability of RAC, develop the further research ideas, and promote the application of RAC. Finally, some potential opportunities and development directions have been suggested for future research on the improvement methods of RAC.

Recent strides in wire + arc additive manufacturing (WAAM) of aluminum components present unique chances for more enhancements in their properties. More studies were done by controlling manufacturing parameters, the wire properties, arc mode, and applying post-process treatment to regulate the microstructure and mechanical characteristics of the fabricated aluminum parts. In this paper, a wide range of previous late studies has been chosen to research the different attempts leading to an enhancement in the mechanical properties of aluminum components fabricated with WAAM. A discussion of the challenges of applying WAAM for aluminum alloys is also reviewed. The main purpose of this paper is to evolve a detailed understanding of the mechanical characteristics of the deposited aluminum components at various conditions.

This paper investigates the influence of niobium on the thermal stability of ultra-fine bainite microstructures and their mechanical properties by means of an isothermal transformation at 340 °C, followed by tempering in the range of 200–700 °C for two medium-carbon, carbide-free bainitic steels with and without 0.018 wt. % Nb. The results reveal that ultra-fine bainite microstructures, especially film-like retained austenite, is refined, and the average carbon content of retained austenite is also improved as a result of the addition of Nb element. Both of the bainitic steels in this paper exhibit good thermal stability at low temperatures (≤400 °C) and precipitation hardening arising from carbide precipitation following tempering at 500 °C. The precipitation strengthening compensates for the decrease in strength induced by the decrement in the dislocation density and coarsening of the bainitic ferrite plates during tempering process. M23C6- and MC-type carbides are precipitated in Nb-free and Nb steels, respectively, when the tempering temperature exceeds 400 °C. The further coarsening of the carbides and bainitic ferrite plates, and the decrement in the dislocation density in the latter, relate to the decrease in the mechanical properties for both of the tested bainitic steels following tempering at 500 and 600 °C. Compared to those in the bainitic steel without Nb, the larger size and superior thermal stability of MC-type carbides results in greater strength and elongation of the bainitic steel containing 0.018 wt. % of the Nb element, but does harm to its impact toughness after tempering at 700 °C.

This research aims to identify how meltpool temperature is determined by process parameters in Laser-Based Powder Bed Fusion (LB-PBF) and the effect of meltpool temperature and heat treatment temperature on microstructure and tensile properties. The study illustrates how crystallographic features in 316L stainless steel were developed in response to the meltpool temperature and induced energy density of LB-PBF manufacture, and by post manufacture heat treatment. For this research, 25 samples based on a Taguchi Design of Experiments (DoE) with five parameters over five levels were printed. To improve precision, the DoE was repeated three times and a total of 75 samples were produced. A thermophysical-based analytical model was developed to measure the meltpool temperature and subsequently surface tension of the liquid in melting zones. Then, a statistical method was used to identify the effective process parameters in tensile properties including ultimate strength, fracture strain and toughness. The microstructural evaluation and crystallographic features were presented to identify the governing mechanisms for the discussed phenomena. This result verifies that the meltpool temperature is a driving factor for the microstructural evolution and observed crystallographic features. Results showed that samples with lower meltpool temperatures have smaller grain sizes, superior strength and toughness properties. The crystallographic analysis showed the weak texture and anisotropic properties are dominant by the preferred orientation growth. The geometrically necessary boundary values were also found to be a driving factor for fracture strain. The originality of this paper is identifying the effect of process parameters on meltpool temperature using an analytical model that is developed based on the thermophysical properties of the feedstock. Characterizing the effect of meltpool temperature in crystallographic features are also another contribution of this paper.

Hardfacing is done to increase the service life of structural components. Hardfacing is widely done in nuclear and petrochemical industries, mining and sugar refineries. Hardfacing is done on farming equipment to extend their service life as they are prone to impact, abrasion and corrosion. Generally, Ni-base, Co-base and Fe-base alloys are used for hardfacings. Among them, Ni-base alloys are preferred to Co-base and Fe-base alloys as these alloys can retain its hardness even at the elevated temperatures. Colmonoy alloys are predominantly used in nuclear reactor as the dose rate of these alloys is 1/265th that of Co-base alloys. Plasma Transferred Arc (PTA), Gas Tungsten Arc (GTA) and Laser are the major hardfacing processes. The hardfacing process governs the four major aspects of the coating, viz. microstructure, substrate dilution, wear and mechanical properties. This paper provides an in-depth understanding of various research works carried out on Ni alloy hardfacings by different processes on different substrates in those four domains. The outcome of this paper would be beneficial to present and future researchers on Ni alloy hardfacings and also to many hardfacing industries.

Magnesium alloys, acknowledged as the environmentally-friendly engineering material of the 21st century, are ideally suited to fulfill the requirements of lightweight manufacturing. However, the poor plasticity of magnesium alloys hampers their further application. Subsequently, development of nanoparticle-reinforced magnesium matrix composites has been proven to be a promising way to enhance the comprehensive performance of magnesium alloys. The exceptional performance achieved even by very small number of reinforcements stimulated innovation in preparation techniques and in-depth analysis of reinforcement mechanisms. This paper provides a review on key challenges related to their processing, the profound impact of different micro-nanoparticle reinforcements on the microstructure and properties of magnesium matrix composites during solidification and subsequent deformation machining. Additionally, the reinforcement mechanisms of the excellent mechanical performance of the composites are also discussed. This study can provide valuable insights for the understanding of the selection of appropriate reinforcements and processing to optimize the performance nanoparticle-reinforced magnesium matrix composites.

In order to solve the existing problem of low efficiency of multi-layer and multi-pass welding methods for thick stainless steel clad plate (SSCP), this paper proposes high-power laser-arc hybrid welding (HP-LAHW) single-pass weld thick SSCP. The effects of wire feeding rate (WFR) on the weld's composition distribution, microstructure and mechanical properties were investigated. The weld morphology is nail-shaped, consisting of a wide arc zone (ArcZ) within the stainless steel layer and a long narrow laser zone (LaserZ), mainly in the carbon steel layer. With the increase of WFR, the dilution rate of the carbon steel layer to the ArcZ decreases first and then increases. The influence of WFR on the microstructure and mechanical properties of the weld is observed mainly in the ArcZ. When the WFR reaches 6 m/min, the composition of the microstructure within the ArcZ will change from martensite, ferrite, and a small amount of granular austenite to ferrite and a small amount of austenite, resulting in the microhardness of the ArcZ decreasing rapidly from 398 HV to 210 HV. The solidification type and microstructure transformation mechanisms within the weld were elucidated based on quantitative calculations of the chromium and nickel equivalent ratios. The microstructure of the LaserZ in all welds is predominantly martensitic due to the rapid cooling rate, which makes the tensile properties of the weld higher than the base metal (BM). The results of this study provide technical support for realizing high-efficiency and high-performance single-pass HP-LAHW of thick SSCP.

This paper is the first attempt to fabricate eutectic high entropy alloy (EHEA) using dual-wire arc additive manufacturing (D-WAAM) technology with twisted wire + single wire. Using CoFeNi twisted wire and Al single wire as raw materials, the eutectic point was determined by adjusting the Al content over a wide range by adjusting the speed of the Al single wire. We designed and fabricated Al19Co25Fe25Ni31 hypo-eutectic, Al20Co22Fe30Ni28 eutectic, and Al21Co22Fe29Ni28 hyper-eutectic high entropy alloys, and conducted in-depth research on their mechanical properties and microstructure. With increasing Al content, the microstructural changes from hypo-eutectic to hyper-eutectic, the strength of the alloy increases, and the plasticity of the alloy decreases. The fabricated Al20Co22Fe30Ni28 EHEA shows the best strength-plastic balance. This characteristic is mainly attributed to the eutectic alloy exhibiting a dual-phase lamellar microstructure consisting of an ordered face-centered cubic (FCC) L12 phase with a volume fraction of 56.9% and an ordered body-centered cubic (BCC) B2 phase with a volume fraction of 43.1%. Because the alloy contains both the hard B2 phase and the tough L12 phase, the room temperature tensile strength reaches 1041 MPa, and the plasticity reaches 14.9%, which is higher than those of other EHEAs fabricated by casting and arc melting. The excellent strength and plasticity of these materials show great potential in engineering applications. This approach not only expands the existing additive manufacturing technology but also provides new ideas for the additive manufacturing of EHEAs.

Niobium carbide (NbC) is often used as a reinforcing phase to improve the mechanical properties of composite coatings, but its low thermal conductivity makes the flow of molten pool poor, and the cladding layer is prone to defects such as non-fusion and slag inclusion. Therefore, in this paper, Ni60–NbC composite coatings with different NbC content were prepared by laser cladding technology, and the 10 vol% graphene-20 vol% NbC-70 vol% Ni60 composite coatings were prepared under the optimal NbC component. The effects of the addition of NbC and graphene on the microstructure and microhardness of the coating were systematically discussed. The results show that the microhardness of 20 vol% NbC composite coating is increased from 680.1 HV to 882.9 HV compared with Ni60 coating without NbC.The composite coating with both NbC and graphene has a microhardness of up to 1048HV, which is 18% higher than the composite coating with only 20 vol% NbC. The mechanism is that the addition of graphene promotes the formation of chromium carbide (Cr23C6, Cr7C3) and increases the fluidity of the molten pool, which causes small niobium carbide particles to dissolve and recondense to form large particles. Large niobium carbide particles and chromium carbide jointly inhibit the excessive growth of other grains. This study provides a new idea for laser cladding of nickel-based composite coatings.

Wire and arc additive manufacturing (WAAM) has been developed to be a highly efficient technique for making large Ti-alloy products. However, the deposition of metal by this method causes coarse texture, which limits its application. To address this, the study utilizes a wire and pulsed arc additive manufacturing (WPAAM) process for making TA15 alloy. Compared with the WAAM method, this WPAAM method inducts several current/voltage-impulse cycles under different pulse frequencies, which makes grains tiny and improves tensile strength. The study then uses a VOF model to discuss the effect of impulse cycles on the solidification process. The findings suggested that the impulse cycles deform the molten pool and influence the vibration in the solid/liquid interface. This makes the coarse columnar grains tiny and forms diminutive α laths. This paper further discusses the correlation between the microstructure and the mechanical properties. The results show that the CBGs and the α laths play a joint contribution to yield strength in the WAAMed TA15 alloy. This study provides a reference for optimizing the microstructure of WAAM titanium alloys by adjusting pulse frequencies and provides a theoretical basis for strengthening WAAMed Ti-alloy.

The microstructure and mechanical properties have a significant impact on the service performance of materials. This paper compared the microstructure and mechanical properties of 2024 aluminum alloy subjected to turning and ultrasonic surface rolling process (USRP). It was found that both turning and USRP can cause grain refinement and increased microhardness. The grain refinement induced by USRP was attributed to dislocation proliferation and T-phase fragmentation; At the same time, a quantitative relationship model between microhardness and microstructure during turning and USRP was constructed. The results showed that precipitation had the greatest impact on the microhardness induced by turning, while dislocations and grain refinement had the greatest impact on the microhardness induced by USRP; In addition, the mechanical performance response mechanism of the materials after turning and USRP was elucidated, and it was found that USRP can significantly enhance the yield strength of the materials.

Vacuum laser welding of titanium alloys is currently being explored for use in UAVs and military-related fields, but the impact of post-weld heat treatment has been seldom studied. In this paper, the Ti–6Al–4V titanium alloy was welded by vacuum laser welding(VLW)with IPG 50 kW fiber laser, and analyze the microstructure and properties of the welds in as-welded state and post-welding heat treatment (850 °C/2h/FC(FC:furnace cooling)and 980 °C/10min/FC+720 °C/2h/FC).The results show that the microstructure of the as-welded weld is composed of primary columnar crystal (primary β phase) and grain boundary martensite (α′), and the microstructure of primary columnar crystal is composed of α'+ (α'+β). The proportion of high-angle grain boundary(HAGB) is 92.3%. The tensile strength is 1009 MPa, and the elongation is 9.3%. The average impact toughness at room temperature is 13J. The weld microstructure at 850 °C/2h/FC is composed of the acicular α phase and the α+β between the acicular α phases, the primary columnar crystals basically disappear, and the acicular α phases criss-cross weave into the net basket structure.The proportion of HAGB is 97.4%.The tensile strength is 988.3 MPa,and the elongation is 14.8%. The average impact toughness is 17J. The microstructure of the weld at 980 °C/10min/FC+720 °C/2h/FC is composed of the coarser acicular α phase and the (α+β) between the coarser acicular α phases. The proportion of HAGB is about 83.2%. The tensile strength is 586 MPa, and the elongation is 1.6%. The average impact toughness is 1.4J.

Laser Powder Bed Fusion (LPBF) presents novel opportunities for the processing and manufacturing of magnesium (Mg) alloys. However, Mg alloys consistently face challenges with poor corrosion resistance. Consequently, it becomes imperative to delve into the corrosion behavior and mechanisms of Mg alloys formed through LPBF. This paper investigated the electrochemical corrosion behavior, the distribution of corrosion products, and the corrosion mechanism of LPBF ZK60 Mg alloy. The results show that the corrosion current density (Icorr) value of LPBF ZK60 Mg alloy is 3.76 μA∙cm−2. The hydrogen evolution in Hank's solution steadily increases with immersion time and reaches a stable state after 24 h. The corrosion rates calculated based on hydrogen evolution and weight loss are 2.1 mm/y and 2.4 mm/y, respectively. The corrosion resistance of LPBF ZK60 Mg alloy is predominantly affected by three factors: uneven microstructure, internal crack defects, and precipitate phases. The melt pool boundary is identified as a corrosion-vulnerable zone, which extends into the columnar crystal zone after corrosion. Crevice corrosion occurs at microcracks, and the precipitate phases within the grains and matrix induces galvanic corrosion. These findings suggest that the corrosion resistance of LPBF ZK60 Mg alloy may be regulated through targeted measures, such as eliminating cracks, achieving microstructure homogenization, and controlling the precipitate phases (including quantity, composition, and distribution).

Recently, the Mg–Ag binary alloy has gained much attention as an antibacterial biomaterial. However, the relationships between the extrusion parameters, microstructure, and mechanical properties of Mg–Ag alloys haven't been clearly established. Therefore, in this paper, the effects of silver (Ag) content (0, 3, 6 wt%) and extrusion (as cast, extrusion ratio (ER) 7.1 and 72.2) on the microstructure and mechanical properties of Mg–Ag alloys are systematically investigated. The results indicate that for the Mg–Ag alloys with the same extrusion ratio, as the Ag increased from 0 to 3 wt%, Mg4Ag and Mg54Ag17 precipitated, leading to significant precipitation strengthening and an increase in the yield strength by over 137%. As the Ag increased to 6 wt%, the yield strength increased by only ∼20%, attributable to Ag promoting dynamic recrystallization, resulting in less grain refinement, a slower amount increase and a smaller size reduction of the precipitate. For the Mg–Ag alloys with the same Ag content, as the extrusion ratio increased to 7.1, the yield strength increased significantly by over 37%, since the grain boundary strengthening and precipitation strengthening were significantly enhanced as the grains were refined, a large number of precipitates appeared, and their sizes significantly reduced. When the extrusion ratio increased to 72.2, the yield strength increased by only ∼10%, due to the weakening of both grain boundary strengthening and precipitation strengthening as the recrystallization further improved, leading to an increase in grain sizes, the redissolution of precipitates, and a lesser reduction in their sizes.

In this paper, three kinds of Cu–Cr2O3 composites with different particle sizes were prepared from Cu-0.67 wt%Cr atomized alloy powder by supercritical water liquid phase in-situ oxidation (SW-LIO) through reduction and spark discharge plasma sintering (SPS). The structure and properties of the composites were systematically analyzed by X-ray diffractometer (XRD), scanning electron microscope (SEM), energy spectrometer, transmission electron microscope, electron backscattering diffraction, universal material testing machine, microhardness tester, eddy current conductometer, friction and wear testing machine, etc. The results show that Cr2O3 particles are evenly distributed in Cu matrix composites. The hardness of composites improved by 19% as the particle size decreased, while the tensile strength and electrical conductivity first increased as the particle size is refined. Meanwhile, the deformation behavior research is carried out, and the mechanical properties and electrical conductivity of composites are enhanced as the deformation amount increases.

Using the planar flow casting method to prepare ultra-thin silicon steel ribbons is an eco-friendly and efficient production method. However, the poor wettability between silicon steel and copper result in difficulties in formability by planar flow casting, which limits its application in production of silicon steel ultra-thin ribbons. The process parameters of planar flow casting are the key factors affecting the formability and magnetic properties of non-oriented silicon steel ribbons, in which the wheel speed determines the solidification rate of the silicon steel melt, which has an important influence on the surface quality and magnetic properties of silicon steel ultra-thin ribbons. Therefore, in this paper, the effect of wheel speed on microstructures and magnetic properties of Fe-3.0 wt %Si alloy are systematically investigated. The results indicate that as the wheel speed increases, the grain size and thickness gradually decrease. When the wheel speed is between 10 and 15 m/s, the surface of the ribbons is relatively flat. As the wheel speed increases, the surface quality of ribbons gradually deteriorates. The ribbons were in fragment with the wheel speed of 35 m/s. Compared with the ribbons before annealing, the magnetic induction B50 increased significantly and the iron losses P1.0/400 decreased sharply at 400 Hz after annealing. The magnetic induction of the ribbons after annealing with the wheel speed of 10 m/s reaches to 1.628 T as the wheel speed is 10 m/s with the corresponding iron loss is 16.171 W/kg. The lower lamination factor and micropores of the ribbons may cause the poorer magnetic properties.

Stress corrosion cracking (SCC) of welded joints is a significant issue that affects the widespread application of multimetal welded structures in aerospace, transportation, and other fields. This paper investigates the effect of laser shock peening (LSP) on the SCC of TC4/2A14 friction stir welded (FSW) joints with dissimilar metals. The microstructural evolution, mechanical properties, and corrosion behavior with and without LSP treatment were investigated using optical microscopy, transmission electron microscopy, X-ray analysis, electrochemical testing, and slow strain rate tensile testing (SSRT). The results showed that the LSP significantly refined the grains and induced work-hardening on the near-surface of the material. After LSP, the compressive residual stresses on the surface of the titanium and aluminium sides were −817.6 MPa and −153.6 MPa for the joint, respectively. Corrosion resistance was also improved, with the self-corrosion current density on the Al side of the joints reduced by 77% and the SCC susceptibility index (Issrt) reduced from 0.140 to 0.121. The enhanced SCC resistance of the LSP-treated TC4/2A14 dissimilar metal FSW joints is primarily due to grain refinement, work-hardening effect, and high-level compressive residual stress. These factors not only enhance the material strength and improve the pitting resistance of the joints but also prevent the initiation and propagation of SCC.

Ultrasonic Impact Treatment (UIT) is a surface treatment method that uses ultrasound to create high-frequency, high-intensity impact loads on the surface of metallic materials to improve material properties and durability. The current state of research on the numerical simulation of UIT is reviewed in this paper. Firstly, the working principle of UIT strengthening is introduced, which includes the application of high-intensity UIT to the surface of metallic materials. The UIT strengthening technology has achieved significant success in the industrial field, resulting in plastic deformation, surface compression and residual stress, thereby significantly improving material properties. Secondly, the influence of UIT on the microstructure is reviewed. It is found that the grain refinement and dislocation are successfully predicted by finite element simulation and other methods. The influence of UIT on residual stress is reviewed. It is found that UIT can effectively transform harmful tensile stress into compressive stress, and it has been found that it can be used to guide the industrial practice of welding, laser cladding and additive manufacturing. In general, UIT technology shows important potential in metal material processing, which is of great significance for improving material properties and promoting industrial practice.

The ultra-precision Ti–6Al–4V alloy parts are growing used in medical and aerospace industries, and which always work in the extreme working conditions such as high temperature, high pressure, and variable load. Thus, the requirements for machining accuracy and surface quality of parts are getting higher and higher. The ultrasonic elliptical vibration assisted cutting (UEVC) technology has been proved to be an effective method for the ultra-precision machining of Ti–6Al–4V alloy. However, in the UEVC process, the evolution mechanism of microstructure and microhardness, which directly affect the service performance and life, is unrevealed. In this paper, the comprehensive investigations of microstructural plastic deformation, grain refinement, phase transformation and microhardness of machined surface layer under conventional cutting (CC) and UEVC processes are carried out. The experimental results indicated that, due to the effects of UEVC technology, the plastic deformation area show obvious compression deformation, the depth of plastic deformation is less than 10 μm, there is no obvious phase transformation on the machined surface layer material, and the hardening rate of machined surface is more than 20%. These findings show the UEVC technology has a unique influence on the microstructure and microhardness of Ti–6Al–4V alloy, which have important implications for the cutting parameter design of ultra-precision Ti–6Al–4V alloy parts.

Ti and its alloys have been widely applied in various fields of national economy due to their excellent combinations of specific mechanical properties and outstanding corrosion behavior. Among Ti alloys, Ti–1Al–8V–5Fe (Ti-185) alloy is a metastable and low-cost β-Ti alloy, and owns extremely outstanding mechanical performance. In the paper, to overcome the issue of β flecks associated with Fe segregation in conventional ingot metallurgy process, Ti-185 alloy was prepared by electrostatic levitation (ESL) technique at various supercoolings, and its solidification behavior and dendrite growth were systematically analyzed. Moreover, the thermophysical parameters of liquid Ti-185 alloy were tested, and the microstructure, hardness and compressive property were compared to that of cast ingot. Results shown that the maximum supercooling of 311 K in the liquid Ti-185 alloy can be achieved, and a noticeable recalescence phenomenon appears during ESL process. The density and the ratio of specific heat to emissivity of liquid Ti-185 alloy increases linearly with temperature decreasing. Once the crystal nucleus is formed, the nonfacted interface will advance promptly. Moreover, the dendritic growth velocity (v) exhibits an exponential relationship with the supercooling (ΔT), and can be depicted as the equation of v = 1.59·ΔT1.65 mm s−1. Additionally, at a supercooling of 229 K or above, single crystal can be formed using ESL technique. Furthermore, the microhardness, elastic modulus and compressive strength of as-levitated Ti-185 alloy are hardly affected by the supercooling, but the plasticity of as-levitated sample is obviously higher than that of as-cast one.

This paper reviews the use of Recycled Aggregate (RA) that is collected from construction demolition waste in the production of concrete. The paper primarily focuses on the possibility of using RA in High Performance Concrete (HPC). By analytically reviewing previous work, this study reports the mechanical and physical properties of HPC prepared using RA. The study summarizes the results of workability, water absorption, dry density, compressive strength, tensile strength, and flexural strength of HPC prepared with RA as reported in previous works. The paper also addresses the microstructure and durability performance of this concrete. Using RA in concrete production is an environmentally friendly solution to the continuous depletion of natural aggregates. RA could improve the cement matrix mechanical properties. Due to the porosity of RA, they have lower unit weigh than natural aggregates. For the same reason, RA can significantly decrease the workability of concrete. It is reported that using RA increases compressive strength of HPC. Both splitting and flexural strengths are increased with RA, however, they are decreased when the ratios of replacement are increased. The use of RA in the production of HPC seems to be promising. This paper presents some recommendations to further study this topic.

With the development of aerospace, Mg-Gd-Y-Zn-Zr alloy as a high-performance light alloy has attracted much attention. In this paper, the Mg-8.8Gd-3.9Y-0.85Zn-0.45Zr (wt%, GWZ941) alloy single-pass multilayer components fabricated by cold metal transfer wire and arc additive manufacturing (CMT-WAAM) in CMT mode, CMT-P mode and CMT-Advance mode. Studying the effects of the three CMT characteristics on voltage and current waveforms and metal transfer behaviors of the deposition processes for the GWZ941 alloy. The macro morphology, defect distribution, microstructure, and mechanical properties of the three as-deposited samples were compared. The GWZ941 alloy deposit fabricated by CMT-WAAM exhibits a uniform equiaxed grain structure whose average grain size of the three samples was 11.9 μm, 13.9 μm, and 7.9 μm, with the porosity less than 0.01%. The UTS and EL of the three GWZ941 alloy samples were 257 ± 4 MPa and 7.5 ± 1%, 230 ± 8 MPa and 3.5 ± 1%, 253 ± 2 MPa and 7.0 ± 0.3%, respectively. In the presence of oxide particles in the GWZ941 alloy formed by CMT-WAAM, the oxide content is less than 0.08%, which is the main influencing factor for the reduced strength and plasticity of the GWZ941 alloy.

Characterization of the mechanical properties plays an essential role in the post-processing and evaluation of the functionality of the additively manufactured metallic parts. A number of studies have been focused on the tensile properties of additively manufactured metals. However, the quasi-static compression test of the additively manufactured 316L blocks with different heat-treatment conditions and scanning strategies seems to be overlooked in the literature. This paper aims to provide a comprehensive study of compressive mechanical response in plastic deformation of SS316L fabricated by selective laser melting (SLM). The mechanical response and microstructures in compressive deformation is analyzed for three printing strategies with 0°-, 90°- and 67.5°- scanning and three heat treatment conditions (450 °C for 3 h, 1100 °C for 1 h with furnace cool and 1100 °C for 1 h with water quenching) for selective laser melted (SLMed) stainless steel 316L in comparison with wrought stainless steel 316L in this work. Alteration of mechanical properties, microstructure evolution and compressive deformation mechanism is studied. Melt pool features are not significantly affected by low-temperature heat treatment (450 °C for 3 h) but fully dissolved through high-temperature heat treatment (1100 °C for 1 h). High-temperature heat treatment provides a higher resistance to compressive plastic deformation for SLMed 316L compared with the low-temperature heat-treated and as-built samples where more twinnings are observed. The compressive plastic deformation mechanism of 90°- and 67.5°-scanning samples is similar, which mainly results from twinning-induced plasticity. For 0°-scanning samples, the strong crystallographic texture is the main cause of anisotropic deformation. Modelling and simulation have been conducted to explain the anisotropic deformation mechanism of the 0°-scanning strategy. Simulation results suggest that the morphology difference of laser-scanning tracks and melt pools, which leads to material flow along the laser scanning direction, explains the anisotropic deformation mechanism.

In this work, the Mg97Y2Zn (at%) alloys have been processed by the rotary-die (RD) ECAP technique under different temperature or pass conditions to tailor the microstructure and mechanical properties. The results reveal that the DRX ratio (VDRX) increases with the increase of ECAP pass or temperature, weakening the texture intensity. The refinement of DRXed grains saturates after 9 passes of ECAP at 350 °C, while the size of DRXed grains (dDRX) monotonically decreases with the reduction of temperature from 400 °C to 300 °C in the case of the same pass number (9P). The combination of fine dDRX, large VDRX, and directionally arranged LPSO phases along the extrusion direction endows the 350 °C–9P alloy with the optimum strength and ductility synergy, exhibiting the tensile yield strength (TYS) of 267 MPa, ultimate tensile strength (UTS) of 318 MPa, and elongation of 10.3%. However, the larger VDRX, weaker texture, less low-angle grain boundaries combine to improve the elongation (14.7%) of the 400 °C–9P alloy at the expense of the TYS (231 MPa) and UTS (303 MPa). This paper provides useful information to optimize the RD-ECAP parameters for the fabrication of high-performance Mg97Y2Zn alloys.

In this paper, the differences of the impact toughness and microstructure of specimens with (IA specimen) and without intercritical annealing (OIA specimen) after welding thermal simulation were compared to illustrate the effect of intercritical annealing. The results show that after welding thermal simulation, the impact energy of IA specimen is 96.6 J, which is much higher than 5.7 J of OIA specimen. This is because after welding thermal simulation, the high-angle (≥45°) grain boundary density of IA specimen is 0.079 μm−1, which is nearly twice as high as that of OIA specimen. On the other hand, the small-sized M-A constituents (maximum 1 μm) and more retained austenite in IA specimen can effectively deflect or prevent the propagation of the crack, helping to obtain high impact toughness.

In this paper, the microstructure and tensile mechanical properties of Mg-8.5Gd-4.5Y-0.8Zn-0.4Zr rare-earth (RE) magnesium alloy in the as-cast state and its solid solution state were investigated by means of optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron backscatter diffraction (EBSD), X-ray diffraction (XRD), differential scanning calorimeter (DSC) and the first-principles simulation. The results show that the mechanical properties were improved after solution treatment. The CS520-12 alloy, treated at 520 °C for 12 h, exhibited excellent mechanical properties, possessing an ultimate tensile strength (UTS) of 343 ± 5 MPa and an elongation of 18.9 ± 0.8 %. These main reasons for the improving of mechanical properties was attributed the formation of I1 stacking faults (SFs) and accumulated-dislocations. The Y element, originating from the melt of the eutectic phase during solution treatment, resulted in a reduction in stacking faults energy (SFE) and facilitated the formation of I1 faults. The presence of numerous SFs hindered dislocation slip. The other key factors for elongation improving were that the weaken of texture, and geometrically necessary dislocation (GND) density decreased from 1.52 × 1013m−2 to 1.22 × 1013m−2. 14H-LPSO phase played an important role in the improving mechanical properties for CS480-12, CS480-24 and CS520-24 alloys. The higher elastic modulus of LPSO compared to Mg matrix, according to the first-principles calculated results, enabled its function as a short-fiber, thus strengthened the mechanical properties. Block-shaped 14H-LPSO in CS480-12 alloys, distributed at the grain boundaries (GBs), suppressed the grow of cracks. The lamellar 14H-LPSO within the grains of CS480-24 and CS520-24 alloys were parallel to the dislocations, which compared with SFs of CS520-12 alloy, can't effectively inhibit the movement of dislocations.

Aluminum is the world's largest production of non-ferrous metals, with light weight, high specific strength, excellent electrical and thermal conductivity and other characteristics. With the continuous development of aerospace, precision electronic instruments, photovoltaic semiconductors and other emerging strategic industries, the demand for high-performance materials of aluminum alloys has become increasingly strong. This paper reviews the research progress of aluminum alloy melt refinement treatment, summarizes the development history of grain refinement, and evaluates the advantages and disadvantages of various types of refining agents, such as Al–Ti–B, Al–Ti–C, Al–Ti–B/C–Re, etc. The article points out the shortcomings of the current research on the melt refinement treatment of aluminum alloys, and looks forward to the future research direction.

In this paper, the 14 μm single-mode laser oscillation welding technique was adopted to achieve high-quality welding of 2A12 aluminum alloy. Specifically, its influence on the microstructure and mechanical properties of the joint and the formation mechanism were investigated. The results showed that the ultra-small spot laser (28 μm) was able to achieve sequential oscillation of the molten pool with small amplitude (0.1 mm). The increased frequency caused the average grain size to decrease and the grain boundary length increased in the fusion zone. Meanwhile, the average grain orientation difference increased, and the growth orientation was more dispersed and homogeneous. While reducing weld morphology defects and refining grain microstructure, there was little influence on the penetration and width morphology of the weld. Finally, successfully prepared welds with tensile strength up to 410.4 MPa and elongation simultaneously increased to 4.065 % at 200 Hz. Furthermore, the influence of keyhole oscillation on the molten pool flow at small amplitude was explained by high-speed camera observation, which explored the mechanism of grain growth in the oscillating joints and provided new ideas for the welding of 2xx aluminum alloys.