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In the case of electrical contact, copper alloys are often unable to withstand arc ablation and premature failure. To solve this issue, Ni-8wt.%Al (Ni–8Al) coatings were successfully prepared on copper substrates utilizing the high-speed laser cladding. In addition, the microstructure evolution, microhardness, electric conductivity and arc ablation resistance of the prepared coatings were investigated in detail. As a result, the achieved Ni–8Al coatings were structurally dense with good metallurgical bonding to the substrate, of which the microstructure showed a bottom-up evolution of fine sub-grain structure. Notably, the microhardness of the coating was 191.7 HV0.2, representing an increase of 82.57% compared to the substrate, and the electrical conductivity was 18.03 %IACS, approaching that of pure nickel. Additionally, the increase in ablation currents led to changes in the ablation behaviors and failure mechanisms of both the substrate and coating. At high currents, a huge arc ablation crater appeared in the center of the substrate due to the reaction force of the anode flame and the difference in surface tension between the liquid metal at the center and the edge of the molten pool. Nevertheless, the coatings showed better arc ablation resistance due to the improvement of molten pool stability during arc ablation by the in situ formed Al2O3 layer on the coating surface.

In the present work, the type, morphology and size of secondary phase particles in a Mg–4Al–2Sn-0.5Ca (ATX420) alloy are tailored through sub-rapid solidification (SRS) and aging treatment before friction stir processing (FSP) to systematically investigate their impact on microstructures and mechanical properties of the FSP ATX420 Mg alloy. The smaller eutectic CaMgSn phase with micro-defects in the as-cast SRS alloy is more likely to be broken during FSP, compared to the as-cast conventional solidification (CS) alloy. Additionally, nano-sized CaMgSn and Mg17Al12 particles precipitate in as-aged SRS alloy due to a high supersaturation solubility of solutes in the as-cast SRS alloy. These densely-distributed nano-sized precipitates in the as-aged SRS alloy increase the processing temperature by 60 °C during FSP, which results in less nano-sized precipitates in the stirring zone and grain growth of the α-Mg matrix. This leads to a decrease in hardness in the FSP-aged-SRS alloy (∼10 HV). Besides, the grain structure evolutions in the stirring zone and transition zone are systematically investigated for understanding the microstructure evolution during FSP in Mg alloys with eutectic phase.

The influence of B and Sb on the microstructure and corrosion behavior of T6-treated Al–Si–Mg alloys has been specifically studied. It is found that the addition of 0.03 wt% B to Al–Si–Mg alloys results in the lowest corrosion rate (0.02451 mm/y) when immersed in 3.5 wt% NaCl solution for 3 days. This improvement can be attributed to the transformation of coarse dendritic α-Al grains into refined equiaxed grains, which is beneficial for the formation of uniform and compact passive film. In contrast, the Al–Si–Mg alloy with addition of 0.2 wt% Sb shows the highest corrosion rate (0.05795 mm/y), which can be attributed to two reasons. First, the addition of Sb contributes to the transformation of rod-like eutectic Si particles into a spherical morphology, increasing the number of micro-galvanic corrosion sites and thus accelerating the corrosion process. Second, the generated Mg3Sb2 phase, being more noble than the eutectic Si phase, strengthens the micro-galvanic corrosion.

In this paper, the hot deformation behavior of Ti65 alloy was investigated over the temperature range of 930–1110 °C with the strain rate of 0.001–1 s−1. According to the stress-strain curves, the constitutive equation was developed to describe the flow behavior of Ti65 alloy. The processing maps were constructed based on the dynastic materials model (DMM) and the perfect formability zone of Ti65 alloy is found under the temperature of 970–1020 °C and the strain rate of 0.001–0.1 s−1. In addition, a three-dimensional nonlinear transient thermo-mechanically coupled finite element model of the multi-dimensional forging (MDF) process of Ti65 alloy was developed. The effects of the forging temperature and forging speed, on the temperature rise, residual stress, and grain refinement were predicted. By analyzing the temperature and stress distribution, the optimum forging temperature and speed for Ti65 alloys were determined to be 1000 °C and 10 mm/s, respectively. Increasing the forging temperature or reducing the forging speed reduces the temperature rise and the maximum tensile stress, thus reducing the risk of cracking. Additionally, the equivalent strain increases as forging speed decreases. Simultaneously, the accumulated strain is more significant for the inside of the forgings. The results of this research are instructive for the optimization of the MDF process.

To investigate the feasibility of spinning the welded aluminum alloys, hot spinning tests were conducted on the electron beam welded (EBWed) 2219 aluminum alloy thick plates at 400 °C and successfully obtained a 2.8 mm curved welded-spun plate with a total thickness reduction of 72 %. The abnormal grain growth (AGG) phenomenon of the base material during hot spinning could be observed due to the reduced pinning effect of the θ-Al2Cu phases and static recrystallization, while the fusion zone exhibited homogeneous recrystallized microstructure. After hot spinning, the yield strength of the base material increased from 89.3 MPa to 133.6 MPa and the yield strength of the joint increased from 93.1 MPa to 134.7 MPa. To further optimize the microstructure and improve the mechanical properties of the spun alloy, the subsequent solid solution and aging treatment were conducted. Most of the coarse θ particles dissolved into the matrix and a large quantity of needle-like θ′ precipitates were generated. The yield strengths of the base material and the joint increased to 213.1 MPa and 216.4 MPa, respectively, which was mainly attributed to the precipitation strengthening of the θ′ precipitates. The comparison between the calculated yield stress and the experimental results showed that the contributions of different strengthening mechanisms in strengths were reliable.

AlCrFeNiMoNb high-entropy alloys were successfully coated onto a ZM5 alloy using high-velocity air fuel spray (HVAF). Microcomputed tomography(micro-CT) results revealed that the porosity of the coating was only 0.36%, which demonstrates the coating has a highly dense structure. The average microhardness of high-entropy alloys coating was ＞ 5 times greater than that of the ZM5 alloy substrate. The changes of ZM5 substrate microhardness can be attributed to dynamic recrystallisation. The corrosion potential (Ecorr) of the AlCrFeNiMoNb coating was improved to approximately∼ − 0.998 V and the corrosion current (Icorr) of the coating significantly decreased by two orders of magnitude. The wear volume loss of the coating was ∼15 times lower than that of the ZM5 substrate. This indicates that the coating of the AlCrFeNiMoNb high-entropy alloy on the ZM5 substrate significantly improved the wear resistance of the ZM5 alloy. The ZM5 alloy surface had better corrosion and wear resistance properties owing to the protection offered by the AlCrFeNiMoNb high-entropy alloy.

Residual stress induced by welding easily causes deformation and even fracture failure in welded structures. In this paper, a three-dimensional thermal-mechanical coupling finite element model of friction stir welding (FSW) was developed. The effects of different welding processes, namely conventional friction stir welding (C-FSW), stationary shoulder friction stir welding (SS-FSW), and bobbin tool friction stir welding (BT-FSW), on the temperature, residual stress, and deformation of welded joints were investigated by employing a heat source model and a force model to the welding analysis. The results reveal that a discernible disparity in temperature gradient is observed in the region ahead of the tool and behind it among various welding processes. The peak values of longitudinal residual stress along the surface and bottom paths of SS-FSW are reduced by 35.7% and 34.1%, respectively. In addition, the deformation at the initial end of the weld is slightly larger than that at the final end along the welding direction in three welding processes. Compared with other FSW processes, SS-FSW exhibits the smallest deformation, which is advantageous for improving assembly accuracy and enhancing the load-bearing capacity of weldments. The above results provide an important theoretical reference for the FSW process optimization of Ti62A alloy.

Hot extrusion process can improve the mechanical properties of materials. However, due to the presence of SiC particles, SiCp/Al composites are prone to fracture damage in the extrusion process. To determine the optimal processing parameters, the processing maps of 17 vol.% SiCp/2009Al composite were established using power dissipation rate and Murty instability criterion. Furthermore, taking aluminum canning into consideration, a three-dimensional macroscopic hot extrusion finite element model of SiCp/Al composite was constructed. The influences of initial temperature, canning morphology and canning thickness on extrusion properties were predicted, and verified by comparison of processing maps and experiments. The optimal extrusion parameters for SiCp/2009Al composite are located within the window of temperature, 450–475 °C and strain rate, 0.001–0.004 s−1 or 0.6–1 s−1. Additionally, the properties of the SiCp/Al composite can be greatly improved by hot extrusion with a suitable canning. Of these, the half canning finish the extrusion task faster, but the extrusion properties under the bottom canning are the best. When the ratio of the canning thickness to the diameter of the workpiece is about 0.17, the effective stress, strain and damage are minimum. The work performed in this research, for the first time, provides quantitative evaluations of process parameters on the hot deformation of SiCp/Al composite, which enables to provide useful guides for hot extrusion parameters selection of SiCp/Al composite.

The macro-galvanic effect in friction stir welding (FSW) joints is contributive for accelerating the localized corrosion of 7xxx aluminum alloy weldment. A process route, solid solution treating→FSW→T76 ageing (SSW-T76), was developed to weak the macro-galvanic effect. The microstructure and corrosion of joints prepared from SSW-T76 route and the conventional route (T76→FSW, T76W) were comparatively investigated. It was found that both precipitate coarsening and solute segregation were effectively suppressed when the route was changed from T76W to SSW-T76. The discrepancy in microstructure, micochemistry and corrosion potential between the base material (BM), the heat-affected zone (HAZ) and the nugget zone (NZ) was narrowed, leading to suppressed macro-galvanic effect and thereafter to decreased pitting and IGC.

In this paper, the Arrhenius-type constitutive equation based on strain compensation was developed, and the constants of the constitutive equation were determined by linear fitting to construct the material models of Ti62A alloy. Meanwhile, the creep parameters of Ti62A alloy at high temperature were corrected by existing experiments, and the Norton creep model during post weld heat treatment (PWHT) was established. The sequential coupling finite element method was used to calculate the residual stress distribution in the welding and PWHT processes of Ti62A alloy plates. The effects of PWHT parameters on the residual stress relief of welded joints were revealed, such as creep, heating rate, and heat treatment temperature. The results reveal that the creep has an important influence on residual stress relief during PWHT. Compared with longitudinal residual stress, the effects of heating rate and heat treatment temperature on transverse residual stress are more significant. A lower heating rate or higher heat treatment temperature will be beneficial for releasing residual stress. The results of this paper will contribute to a better understanding of PWHT mechanisms and provide a good theoretical guidance for optimizing process parameters.

Residual stress significantly affects the performance of the welded joints and the tensile residual stress easily leads to the joint fracture and failure. A three dimensional nonlinear transient thermo-mechanically coupled finite element model of Ti62A alloy electron beam welding (EBW) with filler wire was established. The influence of the welding parameters, such as welding power, groove angles and number of welding layers on the temperature and residual stress evolutions was predicted and verified against existing literature data. The calculated results indicate that the high tensile stress of heat affected zone is very likely to induce the failure of the welded joints. When the welding power is 2600 W, the longitudinal residual stress along the welding direction is more symmetrical on both sides, and the force and deformation of the weldment will be more uniform. As the groove angle decreases, the transverse residual compressive stress on the joint surface becomes larger, which results in the low risk for cracking tendency of the joint. Increasing the number of welding layers reduces the weld reinforcement and the residual stress. In addition, the decline magnitude of residual stress decreases with the increase in the number of welding layers. Both the smaller groove angle and the multi-layer welding can effectively reduce the residual stress of weldments and improve the joint performance. The findings of this study will provide a good theoretical basis for optimizing welding process.

Understanding the structure of the plastic deformation region is important for improving the mechanical property of amorphous alloys. What kind of structure is conducive to the formation of deformation zone is however still unclear yet. The uniaxial compression of amorphous Cu64.5Zr35.5 has been conducted by a large-scale molecular dynamics simulation. The structure characteristics of the system, especially the deformation regions are systematically investigated based on the newly developed topologically close-packed cluster (TCP) method and the shear transformation zone theory. Results indicate that the deformation process is divided into three stages that can be reasonably explicated by the population and heredity of the 30 top largest standard clusters (LaSCs). It is also found that the response of topologically close-packed (TCP) atoms to strain is closely related with the bond number connected to icosahedra atoms, and the densely packed TCP atoms are more prone to non-affine displacement than the loosely packed ones, which act as the carrier of accommodating plastic deformation. In addition, the plastic deformation units are composed of various types of LaSCs, and the region with local translational symmetry is observed. These findings greatly improve the understanding of the relationship of microstructure and deformation of metallic glasses.

Due to the dynamic evolution of precipitates during thermomechanical processing, the intricate effects of second-phase particles on recrystallization behavior are still far from being clear. In this work, the relevance between static recrystallization and pre-aging precipitates in AZ61 (Mg–6Al–1Zn) alloy was systematically investigated. Our results reveal that the presence of pre-aging precipitates increases stored deformation energy by facilitating the generation of dislocations, thus accelerating the recrystallization rate during the initial recrystallization stage. Besides, these uniform distributed dislocations could act as heterogeneous nucleation sites and promote precipitation of fine dispersoids during the subsequent annealing stage. These dispersoids hinder the movement of dislocations and grain boundaries, leading to the increase of Zener pinning pressure. Therefore, the effect of pre-aging particles on recrystallization kinetics gradually transforms from acceleration to retardation as the annealing time prolongs. This work demonstrates that manipulating the features of precipitates through pre-aging treatment is an applicable strategy to control the static recrystallization behavior of Mg alloys.

A356-SiCp/A356 cladding composite materials were prepared by vacuum solid–liquid casting. The interfacial bonding, microstructure, and mechanical properties of this cladding composite material were investigated. The microstructures indicated that there was a good metallurgical combination interface between A356 and SiCp/A356 of the cladding composite material. The tensile tests showed that the bonding strength of the interface was lower than that of the two materials, but fracture occurred on the A356 side as the macrointerface perpendicular to load, while the tensile strength of A356 was higher than that of the cladding composite material. This fracture phenomenon could be explained by the remelt mechanism and grain coarsing mechanism. As a result of the topmost layer of the A356 alloy in contact with the SiCp/A356 composite slurry being remelted when the SiCp/A356 composite slurry was poured, an inseparable metallurgical combination interface was formed, and α-Al grains and eutectic Si on the A356 side near the interface were coarser than those on the interface. The results of this research can provide a reference for manufacturing automotive brake discs with cladding composite materials.

The glass-forming ability (GFA) of metallic glasses can be enhanced by adding trace elements, but it is difficult to explain the reasons from microcosmic viewpoint due to the limitation of experimental conditions. Therefore, in order to reveal the effects of trace elements on GFA, the rapid solidification process of Mg65Cu(35-x)Yx (x = 5,10,15,20,25) ternary alloys are simulated by molecular dynamics (MD) in this paper, then the short- and medium-range order, thermodynamics and dynamics are investigated. The average atomic potential energy shows that the GFA becomes stronger monotonically with the increase of Y element. S433 and S544 can evolve into S555 with higher fivefold symmetry and packing density during solidification, which the topologically close-packed (TCP) clusters are mainly composed of S555. And the higher TCP clusters system has stronger GFA, because TCP clusters are easy to connect with each other to form large-sized nanoclusters, and the larger size nanoclusters have a smaller average displacement, which hinders the crystallization. As TCP atoms with slower dynamic characteristics than other atoms, the dynamics with higher Y element becomes slower with the increase of TCP clusters, and thus adding Y element plays a promoting role for GFA.

Friction stir welding based on bobbin tool was studied for the joining of ZK60 Mg alloy. Sound joints with the ultimate tensile strength reaching 91.0–94.9% of that of the parent metal can be obtained under the appropriate welding parameters. The welding causes dynamic segregation of Zr-rich precipitates in the stirred zone followed by development of a bimodal recrystallized grain structure with distributed bands of 0.6–1.5 μm ultra-fine grains and 4.4–9.5 μm coarser equiaxed grains. Extensive softening occurred in the stirred zone owing to dissolution of the Mg-Zn based precipitate particles. With the increase in tool rotational speed, the average grain size in the stirred zone increases while the tensile properties are not declined as the enhanced complicated type of plasticized metal flow at the high tool rotational speed produces relatively randomized {0001} textures. The joint produced at the 600 rpm tool rotational speed exhibits the weakest isotropy of {0001} texture and the best combination of strength and ductility. The randomized {0001} textures alleviated the inhomogeneity of plastic deformation during the tensile test, which hindered the joint fracturing with low elongation.

Al/steel dissimilar welds were obtained by friction stir lap welding (FSLW) with an Al interlayer, which was fabricated by friction surfacing (FS). In present study, the tool pin was totally plunged into the Al plate and interlayer without stirring steel, which avoided the tool wear. The Al plate and interlayer were remarkably intermixed as pin length increased. A diffusion layer, instead of the intermetallic layer, was found at the Al/steel interface, indicating the enhanced atomic migration and related interfacial bonding. The maximum failure load of the joints of 2.8 kN was reached when the 2.5 mm pin tool was used. The heterogeneous microstructure, which was caused by the intermixing, was responsible for the fracture, according to the fracture profiles. Necking and dimples were depicted from the fractographies, indicating that the joints were failed by plastic fracture. Keywords: Al/steel dissimilar joining, Friction surfacing, Friction stir welding, Microstructure, Mechanical properties

Refill friction stir spot welding (RFSSW) was applied to join the 2A12-T4 aluminum alloy successfully, and effects of the tool rotational speed on weld formation, microstructure evolution and mechanical properties of the RFSSW joint were investigated in detail. There existed macrostructure characteristics of bonding ligament and hook associated to the plasticized metal flow in the joint. The microstructure of the joint exhibited variations in the grain size, precipitates distribution and substructure in the width direction. A softened region existed in all the RFSSW joints and its formation could be attributed to the coarsening and dissolution of the S precipitates. Liquation cracks associated to the localized melting of S were observed in the stir zone of the joint produced at the highest rotational speed. The tensile-shear properties of the RFSSW joints were dependent on the hook geometry, distribution of the bonding ligament and hardness of the stir zone. With increasing the rotational speed from 900 to 1300 mm, the hook height increased, the bonding ligament at the weld periphery got more dispersed and the hardness of the stir zone decreased. The optimized RFSSW joint was obtained when the rotational speed was 1300 rpm, and the corresponding tensile-shear failure load was 10,030 N. Two different fracture modes, i.e. the shear fracture mode and shear-plug fracture mode, were identified in the tensile-shear tests. Keywords: Refill friction stir spot welding, Aluminum alloy, Precipitates evolution, Liquation cracks, Mechanical properties

Auxetic materials are a class of materials that expand transversely when stretched longitudinally. Recently, auxetic materials are gaining special interest in wide range of applications mainly due to their attractive mechanical behavior. In this study, we focus on the compressive properties of new three-component auxetic composite-filled tubes including empty tubes, auxetic lattice structures and polymer fillers. The compressive behavior of three-component auxetic composite-filled tubes, auxetic composites and empty tube was investigated by means of finite element analysis (FEA) and experimental method. The results indicated that the auxetic composite-filled tubes exhibit superior behavior compared with both the empty tube and auxetic composites, even significantly higher stress than the sum of total thereof. This feature is related to the interaction effect and additional support between the three components. The energy absorption characteristics and deformation modes of the auxetic composite-filled tubes and empty tube were also ascertained. It was concluded that inserting auxetic composite as a filler material inside the empty tube significantly improved its energy absorption, as well as delaying crack initiation and propagation in the empty tube.

1060 aluminum–T2 copper dissimilar lap joints were produced by friction stir spot welding (FSSW) with various dwell time. All the joints possess a Cu hook extruded upward from the lower Cu plate into the upper Al plate with intermetallic compounds (IMCs) developed on its interface. Increasing the dwell time produced an increase in the heat input during welding and promoted IMC growth. At short dwell time, the interface was characterized by the interruptedly distributed CuAl2 layer partially mingled with CuAl phase. However, continuous CuAl2–CuAl–Al4Cu9 laminated layer developed at the interface at longer dwell time. IMC formation sequence for CuAl2, CuAl and Al4Cu9 were determined by thermodynamic principles. Microhardness was quite different in different zones. Hardness values in the stir zone (SZ) were much higher due to the dispersively distributed IMC particles and the refined grains. Joints with better tensile properties have a higher penetration depth of the hook into the upper Al plate as well as a continuous IMC layer at the hook interface. Results of fracture path analysis indicated that all the fracture initiated at the CuAl2–CuAl or CuAl2–Al interface and then extended along the IMC layer at the hook interface. The dispersed IMC particles in the SZ provided an alternative path for crack extension when strong metallurgical bonding was achieved at the hook interface. Keywords: Friction stir spot welding, Aluminum/copper dissimilar metals, Microstructure evolution, Mechanical properties, Fracture path.

Micro friction stir welding (μFSW) was successfully performed to join the ultra-thin 6061-T4 sheet with the thickness of 0.5 mm. The optimum plunging depth of 0.05 mm was obtained and reduction ratio was lower than 0.2%. Based on better dynamic flow induced by the triflat pin, the good surface appearance at the wider process window was obtained, while the grain size at the nugget zone was finer than that by the taper pin. Increasing welding speed caused that tensile property increased firstly and then decreased with high welding speed than 500 mm/min. The maximum values of tensile strength and elongation of the μFSW joint using the triflat pin reached 220.3 MPa and 11.7%, which were 91.9% and 54.4% of base material, respectively. Keywords: Micro friction stir welding, Ultra-thin sheet, 6061-T4 alloy, Microstructure, Mechanical property