In order to describe and predict the kinetic process of discontinuous dynamic recrystallization (DDRX) during hot working for metals with low to medium stacking fault energies quantitatively, a new physically-based model was proposed by considering the characteristics of grain size distribution, capillary effect of initial grain boundaries (GBs) and continuous consumption of GBs. Using Incoloy 028 alloy as a model system, experiments aiming to provide kinetic data (e.g., the size and volume fraction of recrystallized grain) and the associated microstructure were performed. Good agreement is obtained between model predictions and experimental results, regarding flow stress, recrystallized fraction and grain size evolution. On this basis, a thermo-kinetic relationship upon the growth of recrystallized grain was elucidated, i.e., with increasing thermodynamic driving force, the activation energy barrier decreases.

The equi-biaxial tensile test is often required for parameter identification of anisotropic yield function and it demands the special testing technique or device. Instead of the equi-biaxial tensile test, the plane strain test carried out with the traditional uniaxial testing machine is suggested to provide the experimental data for calibration of anisotropic yield function. This simplified method by using plane strain test was adopted to identify the parameters of Yld2000-2d yield function for 5xxx aluminum alloy and AlMgSi alloy sheets. The predicted results of yield stresses, anisotropic coefficients and yield loci by the proposed method were very similar with the experimental data and those by the equi-biaxial tensile test. It is validated that the plane strain test is effective to provide experimental data instead of equi-biaxial tensile test for calibration of Yld2000-2d yield function.

The distribution of stress and strain between adjacent particles in particulate reinforced metal matrix composites was investigated using cohesive zone models. It is found that the strain of the composite is concentrated in the matrix, and there is a region with higher strain along the loading path, which can promote the formation of a void near the particles pole. The stress and strain in matrix near the particles gradually decrease with the increase of the distance between particles. And it is calculated that there is a critical distance within which the stress and strain fields of the neighboring particles can influence with each other. This critical distance increases with the increase of particle size. It is also found that the angle between the tensile direction and the center line of particles plays an important role in the stress and strain distribution. The model with the angle of 0° has the greatest influence on the distribution of stress and strain in the matrix, while the model with the angle of 45° has the least influence on the distribution of stress and strain in the matrix.

A finite element model based on solid mechanics was developed with ABAQUS to study the material flow in whole process of friction stir welding (FSW), with the technique of tracer particles. Simulation results indicate that the flow pattern of the tracer particles around the pin is spiral movement. There are very different flow patterns at the upper and lower parts of the weld. The material on the upper surface has the spiral downward movement that is affected by the shoulder and the lower material has the spiral upward movement that is affected by the pin. The velocity of the material flow on the periphery of the stirring pin is higher than that at the bottom of the stirring pin. The material can be rotated with a stirring pin a few times, agreeing well with the previous experimental observation by tungsten tracer particles.

The pressure distributions generated by vaporizing metal foils were studied. An analytical model which described the dynamic mechanical behavior of a rectangular plate under an impulsive loading was introduced. The formed parts of free bulging tests were analyzed using the optical measurement system. Two measurement methods for pressure distributions were introduced and compared. Both the perforated sheet forming test and the pressure film were found to be effective method to measure pressure distributions. The cost of perforated sheet forming test was cheap and the pressure film was easy to operate. Three different pressure distributions were measured and discussed, namely single pressure distribution, tailored pressure distribution and double-direction pressure distribution. These three pressure distributions could be applied in different metal forming processes.

A new method for determining two key parameters (threshold pressure and permeability) for fabricating metal matrix composites was proposed based on the equation-solving method. An infiltration experimental device was devised to measure the infiltration behavior precisely with controllable infiltration velocity. Two experiments with alloy Pb-Sn infiltrating into Al₂O₃ preform were conducted independently under two different pressures so as to get two different infiltration curves. Two sets of coefficients which are functions of threshold pressure and permeability can be obtained through curve fitting method. By solving the two-variable equation set, two unknown variables were determined. It is shown that the determined threshold pressure and permeability are very close to the calculated ones and are also verified by another independent infiltration experiment. The proposed method is also feasible to determine the key infiltration parameters for other metal matrix composite systems.

A novel method for testing stress–strain curves of non-metallic materials was presented. The high temperature stress–strain curves of MnS were preliminarily obtained and corrected to account for the influence of friction. Using the finite element method, the influence of deformation parameters on the deformation evolution of MnS inclusions was investigated based on the experimental reference data. The corresponding physical experiment was designed for comparative analysis. The results indicate that the experimental high-temperature deformation data of MnS are highly reliable. In the process of matrix deformation, the shapes of MnS inclusions change from spherical to ellipsoidal and even to lamellar. There are some differences in the morphological deformation of MnS inclusions located at different positions. With the increase in the initial size of MnS inclusions, the risk of failing the inclusion-flaw inspection increases and the forging quality further deteriorates.

To solve the defects of bottom concave appearing in the extrusion experiments of complex hollow aluminium profiles, a 3D finite element model for simulating steady-state porthole die extrusion process was established based on HyperXtrude software using Arbitrary Lagrangian–Eulerian (ALE) algorithm. The velocity distribution on the cross-section of the extrudate at the die exit and pressure distribution at different heights in the welding chamber were quantitatively analyzed. To obtain an uniformity of metal flow velocity at the die exit, the porthole die structure was optimized by adding baffle plates. After optimization, maximum displacement in the Y direction at the bottom of profile decreases from 1.1 to 0.15 mm, and the concave defects are remarkably improved. The research method provides an effective guidance for improving extrusion defects and optimizing the metal flow of complex hollow aluminium profiles during porthole die extrusion.

Nickel-based superalloys are easy to produce low cycle fatigue (LCF) damage when they are subjected to high temperature and mechanical stresses. Fatigue life prediction of nickel-based superalloys is of great importance for their reliable practical application. To investigate the effects of total strain and grain size on LCF behavior, the high temperature LCF tests were carried out for a nickel-based superalloy. The results show that the fatigue lives decreased with the increase of strain amplitude and grain size. A new LCF life prediction model was established considering the effect of grain size on fatigue life. Error analyses indicate that the prediction accuracy of the new LCF life model is higher than those of Manson-Coffin relationship and Ostergren energy method.

Molecular statics was employed to simulate interaction between screw dislocation and twin boundaries (TB) in hexagonal close-packed zirconium. In the moving TB model, the interaction of a moving TB with a static screw dislocation was investigated. Twinning dislocation (TD) nucleation and movement play an important role in the interaction. The screw dislocation passes through the moving TB and changes to a basal one with a wide core. In the moving dislocation model, a moving dislocation passes through the TB, converting into a basal one containing two partial dislocations and an extremely short stacking fault. If the TB changes to the one, the moving prismatic screw dislocation can be absorbed by the static TB and dissociated into two TDs on the TB. Along with the stress-strain relationship, results reveal the complicated mechanisms of interactions between the dislocation and TBs.

Finite element analysis has been carried out to understand the effect of various processing routes and condition on the microscale deformation behavior of Al–4.5Cu–2Mg alloy. The alloy has been developed through four different routes and condition, i.e. conventional gravity casting with and without refiner, rheocasting and SIMA process. The optical microstructures of the alloy have been used to develop representative volume elements (RVEs). Two different boundary conditions have been employed to simulate the deformation behavior of the alloy under uniaxial loading. Finally, the simulated stress-strain behavior of the alloy is compared with the experimental result. It is found that the microstructural morphology has a significant impact on stress and strain distribution and load carrying capacity. The eutectic phase always carries a higher load than the α(Al) phase. The globular α(Al) grains with thinner and uniformly distributed eutectic network provide a better stress and strain distribution. Owing to this, SIMA processed alloy has better stress and strain distribution than other processes. Finally, the simulated yield strength of the alloy is verified by experiment and they have great agreement.

A two-dimensional computational fluid dynamics model was established to simulate the friction stir butt-welding of 6061 aluminum alloy. The dynamic mesh method was applied in this model to make the tool move forward and rotate in a manner similar to a real tool, and the calculated volumetric source of energy was loaded to establish a similar thermal environment to that used in the experiment. Besides, a small piece of zinc stock was embedded into the workpiece as a trace element. Temperature fields and vector plots were determined using a finite volume method, which was indirectly verified by traditional metallography. The simulation result indicated that the temperature distribution was asymmetric but had a similar tendency on the two sides of the welding line. The maximum temperature on the advancing side was approximately 10 K higher than that on the retreating side. Furthermore, the precise process of material flow behavior in combination with streamtraces was demonstrated by contour maps of the phases. Under the shearing force and forward extrusion pressure, material located in front of the tool tended to move along the tangent direction of the rotating tool. Notably, three whirlpools formed under a special pressure environment around the tool, resulting in a uniform composition distribution.

Automotive suspension control arm is used to join the steering knuckle to the vehicle frame. Its main function is to provide stability under fatigue stresses of loading and unloading in accelerating and braking. Conventionally, these parts were made of steel; however, fuel consumption and emission of polluting gases are strongly dependent on car weight. Recently, there is a try to develop and design much lighter and better fatigue resistant metal of semisolid A357 aluminum alloys. This work aims at a better understanding of identifying the fatigue strain-hardening parameters used for determining fatigue characteristics of aluminum suspension control arm using analytical and mathematical modeling. The most judicious method is to perform the fatigue tests on standardized test pieces and then plot two Wohler curves, mainly number of cycles as a function of the stress and as a function of the deformation. From these curves and following a certain mathematical and analytical methods, certain curves are plotted and then all of these coefficients are drawn. The new calculated parameters showed a clear improvement of the fatigue curve towards the experimental curve performed on the samples of aluminum alloy A357 compared with the same analytical curve for the same alloy.

According to inverse heat transfer theory, the evolutions of synthetic surface heat transfer coefficient (SSHTC) of the quenching surface of 7B50 alloy during water-spray quenching were simulated by the ProCAST software based on accurate cooling curves measured by the modified Jominy specimen and temperature-dependent thermo-physical properties of 7B50 alloy calculated using the JMatPro software. Results show that the average cooling rate at 6 mm from the quenching surface and 420-230 °C (quench sensitive temperature range) is 45.78 °C/s. The peak-value of the SSHTC is 69 kW/(m2×K) obtained at spray quenching for 0.4 s and the corresponding temperature of the quenching surface is 160 °C. In the initial stage of spray quenching, the phenomenon called “temperature plateau” appears on the cooling curve of the quenching surface. The temperature range of this plateau is 160-170 °C with the duration about 3 s. During the temperature plateau, heat transfer mechanism of the quenching surface transforms from nucleate boiling regime to single-phase convective regime.

Numerical simulation and experiments were introduced to develop AA4045/AA3003 cladding billets with different clad-ratios. The temperature fields, microstructures and mechanical properties near interface were investigated in detail. The results show that cladding billets with different clad-ratios were fabricated successfully. Si and Mn elements diffused across the bonding interface and formed diffusion layer. With the increase of clad-layer thickness, the interfacial region transforms from semisolid-solid state to liquid-solid state and the diffusion layer increased from 10 to 25 μm. The hardness at interface is higher than that of AA3003 side but lower than that of the other side. The bonding strength increased with the clad-layer thickness, attributing to solution strengthening due to elements diffusion. The cladding billets were extruded into clad pipe by indirect extrusion process after homogenization. The clad pipe remained the interfacial characteristics of as-cast cladding billet and the heredity of clad-ratio during deformation was testified.

An extended continuum mixture model for macrosegregation is applied to predicting Cu and Mg segregation in large-size ingot of 2024 aluminum alloy during direct chill casting (DC). A microsegregation model using the approximate phase diagram data was coupled with macroscopic transport equations for macrosegregation profiles. Then, the impacts of transport mechanisms on the formation of macrosegregation were discussed. It is found that copper and magnesium have a similar segregation configuration from the billet center to surface. Negative segregation is observed in the centerline and subsurface, whereas positive segregation is obtained in the surface and somewhat underestimated positive segregation in the middle radius. Further, the discrepancy between the predicted and experimental results was discussed in detail. The results show that the magnesium to some extent alleviates the copper segregation in ternary alloy, compared with that in binary alloy. The predicted results show good agreement with measured experimental data obtained from literatures.

The isothermal sections of Al-Fe-Sn ternary system at 973 and 593 K were determined experimentally by the equilibriated alloy method using scanning electron microscopy coupled with energy-dispersive spectrometry and X-ray diffractometry. Experimental results show that no ternary compound is found on these two sections. The maximum solubility of Fe in the liquid phase is 1.6% (mole fraction) at 973 K and those of Fe and Al in the liquid phase are 0.6% and 5.1% (mole fraction) at 593 K, respectively. The maximum solubility of Sn in the Fe-Al compounds is 4.2% (mole fraction) at 973 K and 2.3% (mole fraction) at 593 K. All the Fe-Al compounds can be in equilibrium with the liquid phase.

A numerical simulation based on a regularized phase field model is developed to describe faceted dendrite growth morphology. The effects of mesh grid, anisotropy, supersaturation and fold symmetry on dendrite growth morphology were investigated, respectively. These results indicate that the nucleus grows into a hexagonal symmetry faceted dendrite. When the mesh grid is above 640×640, the size has no much effect on the shape. With the increase in the anisotropy value, the tip velocities of faceted dendrite increase and reach a balance value, and then decrease gradually. With the increase in the supersaturation value, crystal evolves from circle to the developed faceted dendrite morphology. Based on the Wulff theory and faceted symmetry morphology diagram, the proposed model was proved to be effective, and it can be generalized to arbitrary crystal symmetries.

Numerical control (NC) warm bending is a proven strategy to form the large diameter thin-walled (LDTW) Ti-6Al-4V tubes, which are typical light-weight and high-performance structural components urgently required in many industries. In virtue of unveiling the thermo-mechanical coupled deformation behaviors, uniaxial tensile tests were conducted on Ti-6Al-4V tube within wide ranges of temperatures (25-600 °C) and strain rates (0.00067-0.1 s-1). Moreover, a modified Johnson-Cook (JC) model is proposed with a consideration of nonlinear strain rate hardening and the interaction between strain hardening and thermal softening. Resultantly, the present model gives more accurate predictions for flow stress over the entire deformation ranges and the maximum error decreases by about 90%. By employing proposed model to NC warm bending, preferable precision is obtained in predicting forming defects including fracture, wrinkling and over thinning. The present work lays foundation for the forming limit prediction and process optimization in NC warm bending of LDTW Ti-6Al-4V tubes.

The forming quality of high-strength TA18 titanium alloy tube during numerical control bending in changing bending angle β, relative bending radius R/D and tube sizes such as diameter D and wall thickness t was clarified by finite element simulation. The results show that the distribution of wall thickness change ratio Δt and cross section deformation ratio ΔD are very similar under different β; the Δt and ΔD decrease with the increase of R/D, and to obtain the qualified bent tube, the R/D must be greater than 2.0; the wall thinning ratio Δto slightly increases with larger D and t, while the wall thickening ratio Δti and ΔD increase with the larger D and smaller t; the Δto and ΔD firstly decrease and then increase, while the Δti increases, for the same D/t with the increase of D and t.

Commercially pure titanium (CP Ti) has been actively used in the plate heat exchanger due to its light weight, high specific strength, and excellent corrosion resistance. However, researches for the plastic deformation characteristics and press formability of the CP Ti sheet are not much in comparison with automotive steels and aluminum alloys. The mechanical properties and hardening behavior evaluated in stress-strain relation of the CP Ti sheet are clarified in relation with press formability. The flow curve denoting true stress-true strain relation for CP Ti sheet is fitted well by the Kim-Tuan hardening equation rather than Voce and Swift models. The forming limit curve (FLC) of CP Ti sheet as a criterion for press formability was experimentally evaluated by punch stretching test and analytically predicted via Hora’s modified maximum force criterion. The predicted FLC by adopting Kim-Tuan hardening model and appropriate yield function shows good correlation with the experimental results of punch stretching test.

During multi-pass conventional spinning, roller paths combined with the forward and the backward pass are usually used to improve the material formability. In order to understand the backward spinning process properly, the backward roller paths of hemispherical parts with aluminum alloy 2024-O are analyzed. Finite element model with parameterized conventional spinning roller paths, which are based on quadratic Bezier curves, is developed to explore the evolution of the stress, strain and thinning during the backward processes. Analysis of the simulation results reveals stress and strain features of backward pass spinning. According to the findings, the application of the backward pass can obviously improve the uniformity of wall thickness. Furthermore, references of the parameters in future backward path design are provided.

In order to have a better understanding of the hot deformation behavior of the as-solution-treated Mg-4Zn-2Sn-2Al (ZAT422) alloy, a series of compression experiments with a height reduction of 60% were performed in the temperature range of 498-648 K and the strain rate range of 0.01-5 s-1 on a Gleeble 3800 thermo-mechanical simulator. Based on the regression analysis by Arrhenius type equation and Avrami type equation of flow behavior, the activation energy of deformation of ZAT422 alloy was determined as 155.652 kJ/mol, and the constitutive equations for flow behavior and the dynamic recrystallization (DRX) kinetic model of ZAT422 alloy were established. Microstructure observation shows that when the temperature is as low as 498 K, the DRX is not completed as the true strain reaches 0.9163. However, with the temperature increasing to 648 K, the lower strain rate is more likely to result in some grains’ abnormal growth.

Critical cooling rates for producing metallic glasses were evaluated based on a calculated continuous cooling transformation (CCT) diagram. Temperature distributions of the melt in molten pool in the vertical type twin-roll casting (VTRC) process of metallic glasses were simulated, and cooling rates under different casting conditions were calculated with the simulated results. By comparing the results obtained by CCT diagrams and simulation, the possibility of producing metallic glasses by the VTRC method and influences of casting conditions on cooling rate were discussed. The results reveal that cooling rate with 3 or 4 orders of magnitude by the VTRC process can be attained in producing Mg-based metallic glasses, which is faster than the critical cooling rate calculated by the CCT diagram. One side pouring mode can improve the temperature distributions of casting pool. VTRC process has a good ability in continuous casting metallic glassy thin strips.

Stepped heating treatment has been applied to aluminum alloy thick plate to improve the mechanical performance and corrosion resistance. Accurate temperature control of the plate is the difficulty in engineering application. The heating process, the calculation of surface heat transfer coefficient and the accurate temperature control method were studied based on measured heating temperature for the large-size thick plate. The results show that, the temperature difference between the surface and center of the thick plate is small. Based on the temperature uniformity, the surface heat transfer coefficient was calculated, and it is constant below 300 °C, but grows greatly over 300 °C. Consequently, a lumped parameter method (LPM) was developed to predict the plate temperature. A stepped solution treatment was designed by using LPM, and verified by finite element method (FEM) and experiments. Temperature curves calculated by LPM and FEM agree well with the experimental data, and the LPM is more convenient in engineering application.

To control the tri-modal microstructure and performance, a prediction model of tri-modal microstructure in the isothermal local loading forming of titanium alloy was developed. The staged isothermal local loading experiment on TA15 alloy indicates that there exist four important microstructure evolution phenomena in the development of tri-modal microstructure, i.e., the generation of lamellar α, content variation of equiaxed α, spatial orientation change of lamellar α and globularization of lamellar α. Considering the laws of these microstructure phenomena, the microstructure model was established to correlate the parameters of tri-modal microstructure and processing conditions. Then, the developed microstructure model was integrated with finite element (FE) model to predict the tri-modal microstructure in the isothermal local loading forming. Its reliability and accuracy were verified by the microstructure observation at different locations of sample. Good agreements between the predicted and experimental results suggest that the developed microstructure model and its combination with FE model are effective in the prediction of tri-modal microstructure in the isothermal local loading forming of TA15 alloy.

To control the superplastic flow and fracture and examine the variation in deformation energy, the stress and grain size of Mg-7.28Li-2.19Al-0.091Y alloy were obtained using tensile testing and microstructure quantification, and new high temperature deformation energy models were established. Results show that the grain interior deformation energy increases with increasing the strain rate and decreases with increasing the temperature. The variation in the grain boundary deformation energy is opposite to that in the grain interior deformation energy. At a given temperature, critical cavity nucleation energy decreases with increasing strain rate and cavity nucleation becomes easy, whereas at a given strain rate, critical cavity nucleation energy increases with increasing temperature and cavity nucleation becomes difficult. The newly established models of the critical cavity nucleation radius and energy provide a way for predicting the initiation of microcrack and improving the service life of the forming parts.

Tensile stress-strain curves of five metallic alloys, i.e., SKH51, STS316L, Ti-6Al-4V, Al6061 and Inconel600 were analyzed to investigate the working hardening behavior. The constitutive parameters of three constitutive equations, i.e., the Hollomon, Swift and Voce equations, were compared by using different methods. A new working hardening parameter was proposed to characterize the working hardening behavior in different deformation stages. It is found that Voce equation is suitable to describe stress-strain curves in large strain region. Meanwhile, the predicting accuracy of ultimate tensile strength by Voce equation is the best. The working hardening behavior of SKH51 is different from the other four metallic alloys.

The influences of process parameters on mechanical properties of AA6082 in the hot forming and cold-die quenching (HFQ) process were analysed experimentally. Transmission electron microscopy was used to observe the precipitate distribution and to thus clarify strengthening mechanism. A new model was established to describe the strengthening of AA6082 by HFQ process in this novel forming technique. The material constants in the model were determined using a genetic algorithm tool. This strengthening model for AA6082 can precisely describe the relationship between the strengths of formed workpieces and process parameters. The predicted results agree well with the experimental ones. The Pearson correlation coefficient, average absolute relative error, and root-mean-square error between the calculated and experimental hardness values are 0.99402, 2.0054%, and 2.045, respectively. The model is further developed into an FE code ABAQUS via VUMAT to predict the mechanical property variation of a hot-stamped cup in various ageing conditions.

True stress-true strain curves of Incoloy028 alloy at high temperature and strain rate were investigated by hot compression test. These curves show that the maximum flow stress decreases with the increase in temperature and the decrease in strain rate. FEM simulation was employed to investigate the influence of temperature, extrusion speed and friction coefficient on the extrusion load, stress, strain and strain rate in the extrusion process. The increase of extrusion temperature results in decrease of load and deformation resistance, but has little influence on strain and strain rate. When extrusion speed changes between 200 and 350 mm/s, no obvious change about extrusion load can be found. Sharp peak value up to 42500 kN emerges in the extrusion load curve and the extrusion process becomes unstable seriously when extrusion speed rises up to 400 mm/s. Both stress and strain rate increase with the raise of extrusion speed. When friction coefficient is between 0.02 and 0.03, deformation resistance is about 160 MPa and the strain rate can be limited below 70 s-1. Successful production of Incoloy028 tube verifies the optimized parameters by FEM simulation analysis, and mechanical tests results of the products meet the required properties.

Al-Mg alloys are considered to have potentials to form twins during deformation because Mg can reduce the intrinsic stacking fault energy g_ISFE of Al. Nevertheless, twinning has rarely been found in Al-Mg alloys even subjected to various severe plastic deformation (SPD) techniques. In order to probe the twinning propensity of Al-Mg alloys, first-principles calculations were carried out to investigate the effects of Mg and vacancies on the generalized planar fault energy (GPFE) of Al. It is found that both Mg and vacancies exhibit a Suzuki segregation feature to the stacking fault, and have the influence of decreasing the g_ISFE of Al. However, g_ISFE does not decrease and the twinnability parameter τ_a of Al does not increase monotonically with increasing Mg concentration in the alloy. On the basis of τ_a evaluated from the calculated GPFE of Al-Mg alloys, we conclude that deformation twinning is difficult for Al-Mg alloys even with a high content of Mg. Besides, the decrease of g_ISFE caused by the introduction of Mg and vacancies is supposed to have the effect of improving the work-hardening rate and facilitating the formation of band structures in Al-Mg alloys subjected to SPD.

A two-dimensional mathematical model based on volume-of-fluid method is proposed to investigate the heat transfer, fluid flow and keyhole dynamics during electron beam welding (EBW) on 20 mm-thick 2219 aluminum alloy plate. In the model, an adaptive heat source model tracking keyhole depth is employed to simulate the heating process of electron beam. Heat and mass transport of different vortexes induced by surface tension, thermo-capillary force, recoil pressure, hydrostatic pressure and thermal buoyancy is coupled with keyhole evolution. A series of physical phenomena involving keyhole drilling, collapse, reopening, quasi-stability, backfilling and the coupled thermal field are analyzed systematically. The results indicate that the decreased heat flux of beam in depth can decelerate the keyholing velocity of recoil pressure and promote the quasi-steady state. Before and close to this state, the keyhole collapses and complicates the fluid transport of vortexes. Finally, all simulation results are validated against experiments.

In order to simulate the microstructure evolution during hot compressive deformation, models of dynamic recrystallization (DRX) by cellular automaton (CA) method for 7055 aluminum alloy were established. The hot compression tests were conducted to obtain material constants, and models of dislocation density, nucleation rate and recrystallized grain growth were fitted by least square method. The effects of strain, strain rate, deformation temperature and initial grain size on microstructure variation were studied. The results show that the DRX plays a vital role in grain refinement in hot deformation. Large strain, high temperature and small strain rate are beneficial to grain refinement. The stable size of recrystallized grain is not concerned with initial grain size, but depends on strain rate and temperature. Kinetic characteristic of DRX process was analyzed. By comparison of simulated and experimental flow stress–strain curves and metallographs, it is found that the established CA models can accurately predict the microstructure evolution of 7055 aluminum alloy during hot compressive deformation.

Rigid-viscoplastic 3D finite element simulations (3D FEM) of the equal channel angular pressing (ECAP), the combination of ECAP + extrusion with different extrusion ratios, and direct extrusion of pure aluminum were performed and analyzed. The 3D FEM simulations were carried out to investigate the load-displacement behavior, the plastic deformation characteristics and the effective plastic strain homogeneity of Al-1080 deformed by different forming processes. The simulation results were validated by microstructure observations, microhardness distribution maps and the correlation between the effective plastic strain and the microhardness values. The 3D FEM simulations were performed successfully with a good agreement with the experimental results. The load-displacement curves and the peak load values of the 3D FEM simulations and the experimental results were close from each other. The microhardness distribution maps were in a good conformity with the effective plastic strain contours and verifying the 3D FEM simulations results. The ECAP workpiece has a higher degree of deformation homogeneity than the other deformation processes. The microhardness values were calculated based on the average effective plastic strain. The predicted microhardness values fitted the experimental results well. The microstructure observations in the longitudinal and transverse directions support the 3D FEM effective plastic strain and microhardness distributions result in different forming processes.

A new method of quantitative pre-corrosion damage of aviation aluminium (Al-Cu-Mg) alloy was proposed, which regarded corrosion pits as equivalent semi-elliptical surface cracks. An analytical model was formulated to describe the entire region of fatigue crack propagation (FCP). The relationship between the model parameters and the fatigue testing data obtained in the pre-corroded experiments, crack propagation experiments and S-N fatigue experiments was discussed. The equivalent crack sizes and the FCP equation were used to calculate the fatigue life through numerical integration based on MATLAB/GUI. The results confirm that the sigmoidal curve fitted by the FCP model expresses the whole change from Region I to Region III. In addition, the predicted curves indicate the actual trend of fatigue life and the conservative result of fatigue limit. Thus, the new analytical method can estimate the residual life of pre-corroded Al-Cu-Mg alloy, especially smooth specimens.

The formation and growth of Kirkendall voids in a binary alloy system during deformation process were investigated by phase field crystal model. The simulation results show that Kirkendall voids nucleate preferentially at the interface, and the average size of the voids increases with both the time and strain rate. There is an obvious coalescence of the voids at a large strain rate when the deformation is applied along the interface under both constant and cyclic strain rate conditions. For the cyclic strain rate applied along the interface, the growth exponent of Kirkendall voids increases with increasing the strain rate when the strain rate is larger than 1.0×10^-6, while it increases initially and then decreases when the strain rate is smaller than 9.0×10^-7. The growth exponent of Kirkendall voids increases initially and then decreases gradually with increasing the length of cyclic period under a square-wave form constant strain rate.

Combining the design of experiments (DOE) and three-dimensional finite element (3D-FE) method, a sequential multi- objective optimization of larger diameter thin-walled (LDTW) Al-alloy tube bending under uncertainties was proposed and implemented based on the deterministic design results. Via the fractional factorial design, the significant noise factors are obtained, viz, variations of tube properties, fluctuations of tube geometries and friction. Using the virtual Taguchi’s DOE of inner and outer arrays, considering three major defects, the robust optimization of LDTW Al-alloy tube bending is achieved and validated. For the bending tools, the robust design of mandrel diameter was conducted under the fluctuations of tube properties, friction and tube geometry. For the processing parameters, considering the variations of friction, material properties and manufacture deviation of mandrel, the robust design of mandrel extension length and boosting ratio is realized.

To describe the relationship between the whole material deformation behavior and each grain deformation behavior in micro-forming, experimental and numerical modelling methods were employed. Tensile test results reveal that contrary to the value of flow stress, the scatter of flow stress decreases with the increase of thickness-to-grain diameter (T/d) ratio. Microhardness evaluation results show that each grain owns unique deformation behavior and randomly distributes in each specimen. The specimen with less number of grains would be more likely to form an easy deformation zone and produce the concentration of plastic deformation. Based on the experiment results, a size-dependent model considering the effects of grain size, geometry size, and the deformation behavior of each grain was developed. And the effectiveness and practicability of the size-dependent model were verified by experimental results.

The wear behavior of multi-walled carbon nano-tubes (MWCNTs) reinforced copper metal matrix composites (MMCs) processed through powder metallurgy (PM) route was focused on and further investigated for varying MWCNT quantity via experimental, statistical and artificial neural network (ANN) techniques. Microhardness increases with increment in MWCNT quantity. Wear loss against varying load and sliding distance was analyzed as per L16 orthogonal array using a pin-on-disc tribometer. Process parameter optimization by Taguchi’s method revealed that wear loss was affected to a greater extent by the introduction of MWCNT; this wear resistant property of newer composite was further analyzed and confirmed through analysis of variance (ANOVA). MWCNT content (76.48%) is the most influencing factor on wear loss followed by applied load (12.18%) and sliding distance (9.91%). ANN model simulations for varying hidden nodes were tried out and the model yielding lower MAE value with 3-7-1 network topology is identified to be reliable. ANN model predictions with R value of 99.5% which highly correlated with the outcomes of ANOVA were successfully employed to investigate individual parameter’s effect on wear loss of Cu-MWCNT MMCs.

The hot deformation behavior of Al-6.2Zn-0.70Mg-0.30Mn-0.17Zr alloy was investigated by isothermal compression test on a Gleeble-3500 machine in the deformation temperature range between 623 and 773 K and the strain rate range between 0.01 and 20 s^-1. The results show that the flow stress decreases with decreasing strain rate and increasing deformation temperature. Based on the experimental results, Arrhenius constitutive equations and artificial neural network (ANN) model were established to investigate the flow behavior of the alloy. The calculated results show that the influence of strain on material constants can be represented by a 6th-order polynomial function. The ANN model with 16 neurons in hidden layer possesses perfect performance prediction of the flow stress. The predictabilities of the two established models are different. The errors of results calculated by ANN model were more centralized and the mean absolute error corresponding to Arrhenius constitutive equations and ANN model are 3.49% and 1.03%, respectively. In predicting the flow stress of experimental aluminum alloy, the ANN model has a better predictability and greater efficiency than Arrhenius constitutive equations.