In the scope of this exploration, AZ61 magnesium matrix composites fortified with bimodal size SiC particles were synthesized using ultrasonic-assisted mixing in the semi-solid state, which exhibited optimal grain refinement and exceptional creep resistance. We examined the impact of bimodal SiC particles on the microscopic structure and creep deformation of the resulting composites. Our findings indicated that incorporating bimodal SiC particles resulted in the refinement of the matrix grains and alteration of the morphology of the Mg17Al12 phase. Furthermore, the micron-sized SiC particles exhibited a typical necklace-like particle distribution around the grain boundaries of the bimodal SiC particle/AZ61 composites, while the nano-sized SiC particles were mainly located around the micron-sized particles. As the volumetric percentage of micron SiC particles increased, the quantity of nano-sized particle clusters diminished noticeably. Creep analysis at 200 °C and 50 MPa revealed that the creep life of M−6+N−1 composite was increased by 111.9% compared to the AZ61 alloy. Additionally, the M−6+N−1 combination exhibited a significantly lower steady-state creep rate compared to the matrix alloy, with a reduction of approximately 11 times. These results indicate that the bimodal SiC particle/AZ61 composites have superior creep resistance, which is a consequence of the grain refinement and grain boundary pinning effects of SiC particles.

This study aimed to investigate the impact of corrosion on the microstructure and tensile properties of 7075 high-strength alloy. It involved outdoor exposure tests in an actual marine atmospheric environment in Wanning, Hainan Province. The results showed that the 7075 alloy was corroded rapidly in the marine atmospheric environment, and corrosion pits and intergranular cracks were generated. The intergranular cracks were extended along the grain boundary during corrosion, leading to the exfoliation of the matrix. The cause for the intergranular corrosion was discussed based on the microstructure characteristics of 7075 alloy. The tensile properties of the 7075 alloy gradually deteriorated with the increase of exposure time in the marine atmospheric environment. The ultimate strength and elongation were decreased by about 3.2% and 58.3%, respectively, after 12 months of outdoor exposure.

The mechanical behavior and microstructure evolution of Al-Mg-Li alloys under the effect of electric current was investigated using an electropulsing-assisted uniaxial tensile (EAUT) test combined with microstructure observations. It was found that the localized Joule heating-induced microscale high temperature at the grain boundaries in the necking zone significantly accelerated the grain boundary weakening when necking occurred, which resulted in rapid intergranular fracture and relevant decrease in elongation. Electropulsing induced continuous dynamic recrystallization (CDRX) in the both side layers and the discontinuous dynamic recrystallization (DDRX) in the intermediate layers of the Al-Mg-Li sheet during EAUT testing at 460 degrees C and higher, promoting the formation of newly near-equiaxed recrystallized grains and weakening of beta-fiber texture components. For the conventional high temperature tensile test, only a small amount of recrystallized grains formed along the grain boundaries of the coarse parent grains under the control of DDRX. The occurrence of CDRX during EAUT was substantially attributed to the promoted effect of electropulsing on dislocation glide and climb, which resulted from the combined effect of microscale localized Joule heating around dislocations and the electro-induced enhancement effect on vacancy diffusion. (c) 2021 Elsevier B.V. All rights reserved.

This work analyzed changes in the corrosion morphology and mechanical performance of 7085 aluminum alloy after outdoor exposures for different times in a humid and hot marine atmospheric environment. After one month of exposure, a pronounced corrosion of the alloy was observed. The corrosion product was mainly Al(OH)3, and the corrosion features were mainly pitting corrosion and intergranular corrosion (IGC). With the exposure time extended from 6 months to 12 months, the IGC depth increased from 114 μm to 190 μm. After a 1-year outdoor exposure in a humid and hot marine environment, the alloy's ultimate strength and yield stress remained nearly unchanged, while its elongation and area reduction decreased from the original 6% and 9%, respectively, to 3% and 5%. Moreover, the reasons for IGC and its effect on the mechanical performance was analyzed.

Compound forging is a promising method for fabricating aluminum-steel bimetal parts. However, metallurgical bonding interfaces, which are important for the mechanical performance, are usually difficult to be obtained due to Al2O3 oxide film. In this work, a thixotropic-core compound forging technology was proposed for fabricating aluminum-steel bimetal parts with a reliable metallurgical bonding interface. 7075 aluminum rods and 304L stainless steel shells were used as billets. Before compound forging, the 7075-T6 alloy and 304L steel were heated to the desired temperatures respectively. The influences of the compression displacement and the initial temperature of steel shell on the formation of metallurgical bonding interface were studied. The results showed that a metallurgical bonding interface was formed in the bimetal part. The interface thickness increased gradually as the initial temperature of steel shell increased. However, if the initial temperature of steel shell was higher than 900 °C, an overgrown interface was formed, resulting in substantially deterioration of the shear strength. An increase in the compression displacement enabled tearing of the oxide film. However, when the compression deformation was excessively large, microcracks could be induced near the interface. When the initial temperature of steel shell and the compression displacement were 900 °C and 20 mm, respectively, the optimal metallurgical bonding interface with a thickness of 3.8 μm and shear strength of 108.2 MPa was obtained.

对一种近β型的两相钛合金Ti12LC进行了热变形实验研究.采用差热实验分析了该合金的相变点温度.通过热模拟压缩实验,研究了变形温度、应变速率和变形量对该合金微观组织的影响.结果 表明,随着温度的变化,初生α相的形态和数量发生改变,当上升到相变温度点以上时,β晶粒的粗化明显;随着应变速率的降低,合金内部动态再结晶充分,晶粒均匀细小,但过低的应变速率又会引起组织粗大;随着变形量的增加,条状α相含量相对增多,组织球化明显,且针状β转变组织含量减少,组织相对更加均匀;在变形量小于75％且不发生变形失稳的缺陷下,通过更大的变形量能获得更好的微观组织.

The mechanisms of dynamic recovery and dynamic recrystallization significantly affect the mechanical behavior and microstructure of the materials deformed at high temperatures. The modified Kocks and Mecking (K–M) model was used to assess the evolution of dislocation density of pure copper under high-temperature compression. The relationship between the deformation conditions and model parameters was derived and verified. The model offers quantitative prediction of flow stress curves, a recrystallized fraction, and recrystallized grain size under different conditions. The model can well integrate the recrystallization mechanism during deformation. The dislocation density and dynamic recrystallization evolution of pure copper provide a basis for optimizing thermomechanical processing in different fields of industry.

Cold extrusion provides manufacturing precision of pure copper arc parts, which requires a reduction in the forming force and elastic deformation. The functional models of constant strain rate and cosine velocity upsetting of pure copper were constructed using its thermomechanical simulation data. They were well verified by FEM, proven to be consistent with experimental stress-strain relations. The potentials of cold extrusion based on the cosine velocity and its application in the manufacturing of pure copper arc parts were presented. The equivalent stress of cold extrusion based on a cosine velocity is reduced as compared to the conventional constantvelocity one. Adequate extrusion conditions were chosen to form a pure copper arc part that fulfilled the design requirements verified by the cold extrusion test, thereby achieving a near-net shape of interior and exterior surfaces.

An isothermal closed-die forming process, including two forging procedures in which the female die of the final forging procedure is split into two parts, was developed, and a very complex component of magnesium alloy called the upper receiver was successfully produced. The obtained forged piece has higher mechanical properties and meets the standard of being safely used in special machines. Based on the FORGE software platform, finite element (FE) simulation was used to determine the preform shape, processing parameters, and forging procedure. A closed-die cavity was formed during the final forging procedure, which can effectively enhance the workability of magnesium alloy, refine the grain sizes, and increase the strength of the component. Importantly, the forged piece has homogeneous microstructures, and the ultimate tensile strength located at the lateral and bottom positions of the upper receiver is greater than 396MPa and the minimum of the elongation ratio at fracture is 15%.

The deformation behavior of pure copper was studied in hot compression tests in the temperature range of 773–1173 K and strain rate interval of 0.001–1.0 s–1, the corresponding flow stress curves were plotted. The new method to calculate critical and saturation stresses was devised, quantitative analysis of strain hardening and dynamic softening was presented, a three-stage constitutive model was constructed to predict the flow stress of pure copper. As predicted and measured flow stress comparison indicate, the physical constitutive model can accurately characterize hot deformation of pure copper. With dynamic recovery and/or recrystallization. Numerical simulation of an upsetting process is carried out by implementing the constitutive model into commercial software. This model can be put to practical use and be quite promising for improving efficiency of a hot forging process for pure copper components.

In the present work, an ultrasonic assisted squeeze casting method is proposed for processing wrought aluminum alloys. A frame-shaped part was fabricated to verify the feasibility of ultrasonic assisted squeeze casting technology. The results show that a 2024 alloy part with a complex shape and good surface quality can be produced by the proposed ultrasonic assisted squeeze casting method. As the ultrasonic power increasing, the microstructures of the squeeze cast parts were clearly refined, and the coarse polygonal or dendritic structures evolved to fine and equiaxed grains. Mechanical properties, such as strength and plasticity, were also improved significantly as the ultrasonic power increasing. When the ultrasonic power was 1.8 kW, the UTS, YS and elongation to fracture were 372 MPa, 246 MPa and 8.5%, which were improved by 20.8%, 21.2% and 84.8%, respectively, compared to a conventional squeeze cast part. Finally, the effect of ultrasonic vibration on mold-filling and solidification was analyzed.

The dynamic recrystallization (DRX) behavior of T2 copper was studied by experiments and cellular automaton (CA) simulation during hot compression. The hot compression deformation of T2 copper was performed by isothermal hot compression tests over a wide range of temperatures (400-900 degrees C) and strain rates (0.001-10 s(-1)). The experimental results show that the deformation temperatures and strain rates have a profound influence on the DRX behavior. The characteristic parameters for the DRX behavior of T2 copper were obtained and a DRX kinetics model based on the modified Avrami equation was proposed to describe the DRX behavior of T2 copper. The average DRX grain size of the copper was estimated on the basis of metallography observation, and a power law function of Zener-Hollomon parameter was established to predict the grain size under different deformation conditions. A mesoscopic cellular automaton model was established to simulate the DRX behavior of T2 copper. The comparison between experimental and simulation results indicates that the recrystallization fraction and the average DRX grain size can be accurately predicted by the present CA model. It suggests that the developed CA model can be used to take control of the DRX process for the copper during hot working. (C) 2019 Elsevier B.V. All rights reserved.

Squeeze casting is a near net shaping technology which is advantageous to refining the microstructures and improving the mechanical properties. In the present work, in-situ Al3Ti/2024 Aluminum matrix composites with different amount of Al3Ti reinforcements were successfully fabricated by ultrasonic treatment and subsequent squeeze casting. The effects of specific pressure and the amount of reinforcements on microstructures and mechanical properties were studied. The results show that when the specific pressure is increased from 0 to 150 MPa, the average grain sizes of α-Al matrix are decreased by 39.8%, and the yield strength and compressive strength are increased by 16.8% and 22.9%, respectively. However, severe segregations of eutectic structures were generated under an excessive specific pressure of 200 MPa, which also results in deterioration in the mechanical strength. The mass fraction of Al3Ti phases has significant influence on morphology of eutectic structures. When the mass fraction of Al3Ti phases is increased from 4 to 16 wt%, the eutectic structures was changed from continuous network to dispersed structures gradually. The compressive strength was increased from 611.2 to 712.0 MPa (increased by 16.5%), as the Al3Ti content increasing from 0 to 16 wt%. However, as the mass fraction of Al3Ti phases increased, the variation in the yield strength is not monotonically increasing.

Mg AZ31/Al 7050 laminate was fabricated by co-extrusion directly from the as-cast Mg AZ31 and Al 7050 billets. The influence of annealing temperature and annealing time on microstructure and mechanical behavior of the extruded Mg/Al laminate was systematically studied. Results show that annealing treatments at 250 °C for 3 h or at 350 °C for 3 h do not result in an obvious grain coarsening of Mg layer and cannot remove the heterogeneous structure. Annealing does not vary texture in the Mg layer, a large fraction of <0002>//ND and a small fraction of <0002>//TD, but the intensity of component <0002>//ND weakens to some extent. Lamellar microstructure in the Al layer remains after annealing at 250 °C for 3 h or at 350 °C for 3 h. High fractions of the texture components S and cube exist in the extruded sample, and annealing treatment hardly changes their fractions. Post-annealing treatment will largely reduce yield strength of extruded plate and increase plasticity slightly. The yield strength drops from 302 MPa to 206 MPa after annealing at 250 °C for 3 h and to 141 MPa after annealing at 350 °C for 3 h. The elongation to fracture increases from 1.5% to 5.4% after annealing at 250 °C for 3 h and to 4.8% at 350 °C for 3 h. The corresponding mechanism was discussed.

A back pressure thixoextruding method was proposed to control the liquid segregation during the thixoforming process. The back pressure was provided by disk springs which can apply an elastic force on the deformed alloy to make it in a three-dimensional compression stress state. Thixoextrusion of AZ80 magnesium alloy was conducted to verify the feasibility of the proposed technology. The results show that the suitable partial remelting regime for AZ80 magnesium alloy is isothermal holding at 560 degrees C for 15-25 min. Although the components with good surface qualities can be successfully fabricated by both back pressure thixoextruding and conventional thixoextruding, the distribution of microstructures and mechanical properties are quite different. Severe liquid segregation occurred during the conventional thixoextruding process, and a great amount of liquid-solidified structures were detected in the peripheral area, resulting in lower mechanical properties. By applying a back pressure in the thixoextruding process, the liquid segregation was reduced effectively, and the microstructures and mechanical properties are homogeneous among different positions. Back pressure thixoextruding is an efficient method for controlling the liquid segregation behavior and has great potentiality for commercial application.

By the research in the thermodynamic simulation of a new kind of low-cost Titanium alloy-Ti8LC, The temperature, speed and degree were studied to prove what infection it take to the Micro-structure. The test make clear that the influence of temperature was the most important parameter to the alloy, when it under 1000℃, it appears two-state structure, it is propitious to the combination properties, and when it above 1000℃, it appears lamellar structure, holds high strength but low extensibility. Comprehensive consideration with the resistance to deformation, the velocity in the deformation cannot take too fast, and the degree adapted to 40％～60 ％. This can gain favorable capability.

The hot deformation behavior of a high strength aluminum alloy (Al-Zn-Mg-Cu) was studied by isothermal hot compression tests performed over a range of temperatures (350-490 degrees C) and strain rates (0.001-1 s(-1)). A constitutive equation was established using experimental results to predict the flow stress of the alloy under elevated temperature. In the work hardening-dynamic recovery regime, a physically-based constitutive equation for the flow stress was obtained from the stress-dislocation relation. In the subsequent dynamic recrystallization region, the flow stress after the peak was predicted by employing the kinematics of the dynamic recrystallization in the constitutive model. The stress-strain curves of the alloy predicted by the established models were in good agreement with experimental results. The results indicate that the proposed physically-based constitutive equation can accurately predict the flow behavior of the Al-Zn-Mg-Cu alloy. (c) 2018 Elsevier B.V. All rights reserved.

In the present work, in-situ Al3Ti/2024Al composites with different amount of Al3Ti reinforcements were fabricated by ultrasonic casting method. The effects of solution and subsequent aging treatment on the microstructures and mechanical properties were studied. The results show that solution at 500 degrees C for 6 h is suitable for in-situ A1(3)T1/2024Al composites with mass fractions of reinforcements between 4 wt% and 16 wt%. The aging kinetics of Al3Ti/2024Al composites was promoted by the Al3Ti reinforcements. When the mass fraction of Al3Ti is increased from 0% to 16%, the peak hardness is increased by 20.3%, and the time required to reach the peak hardness is shortened by 66.7%. The microstructures of peak-aged Al3Ti/2024Al composites consist of equiaxed alpha-Al grains and evenly distributed reinforcing particles. As the mass fraction of Al3Ti increasing, the compression and tensile strengths were both increased gradually at the sacrifice of plasticity.

A compound forming technology of functional integration of plastic deformation and thixoformation was proposed. The feasibility of the proposed forming technology was verified by near net shaping of empennage-shape component with complex geometric shape including a handle and 6 blades with a small thickness of 1.5mm. The handle and the blades were formed by plastic deformation and thixotropic deformation, respectively. 7075 alloy slurries with gradient microstructure containing thermoplastic, transition, and semisolid regions were obtained by gradient induction heating. The effect of heating rate during gradient induction heating on recrystallization of 7075 alloy was investigated. When the temperature of semisolid region was controlled in a suitable processing window between 590 and 630°C with a heating rate of 4°C/s, and empennage-shape component with homogenous distribution of hardness could be formed successfully by the compound forming technology.

The evolution of the microstructure and texture in copper has been studied during repetitive extrusion-upsetting (REU) to a total von Mises strain of 4.7 and during subsequent annealing at different temperatures. It is found that the texture is significantly altered by each deformation pass. A duplex 〈001〉+〈111〉 fiber texture with an increased 〈111〉 component is observed after each extrusion pass, whereas the 〈110〉 fiber component dominates the texture after each upsetting pass. During REU, the microstructure is refined by deformation-induced boundaries. The average cell size after a total strain of 4.7 is measured to be ∼0.3μm. This refined microstructure is unstable at room temperature as is evident from the presence of a small number of recrystallized grains in the deformed matrix. Pronounced recrystallization took place during annealing at 200°C for 1h with recrystallized grains developing predominantly in high misorientation regions. At 350°C the microstructure is fully recrystallized with an average grain size of only 2.3μm and a very weak crystallographic texture. This REU-processed and subsequently annealed material is considered to be potentially suitable for using as a material for sputtering targets.