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Surface cracking is one of the common problems in the extrusion process of Al–Li alloys, which seriously affects the surface quality and performance of the profile. In this study, the extrusion experiments of 2195 Al–Li alloy profiles were carried out under different temperatures and speeds to reveal the influence of extrusion parameters on the profile cracking and clarify the cracking mechanism. It was found that the extrusion cracking is closely related to the profile temperature at the die outlet and the plastic work accumulation after the material flows through the die bearing. Cracking occurs when the surface temperature of the profile is too high and the tensile plastic work accumulation exceeds the critical value. Based on the cracking mechanism, a prediction criterion for the extrusion cracking was established by taking into account the influences of deformation temperature and strain rate. The extrusion cracking of the spray-deposited 2195 Al–Li alloy profile was predicted by finite element simulation coupled with the established criteria. The predicted cracking position and degree were in good agreement with the experimental results. Finally, the boundary conditions for safe extrusion without cracking were investigated, and the extrusion limit diagram of the 2195 Al–Li alloy was constructed, which can be conveniently used to guide the selection of extrusion parameters in actual production. [ABSTRACT FROM AUTHOR]

The grains at the longitudinal weld in porthole extrusion profiles are more prone to abnormal growth during solid solution treatment, leading to a decline in mechanical properties. To improve the microstructure and enhance the mechanical properties at the longitudinal weld in profile, the precipitation behavior of the dispersoid in 2195 Al-Li alloy with different homogenization heating rates was studied. The impact of dispersoid morphology and distribution on grain structure and mechanical properties at the longitudinal weld was elucidated. The results indicated that the ramp heating homogenization treatment significantly promoted the precipitation of fine Al 3 Zr dispersoids, which effectively hindered the abnormal growth of grains within the low plastic deformation zone at the longitudinal weld and reduced the width of the coarse grain zone. The tensile strength and elongation of the ramp heating homogenized (RH) profiles after water quenching and aging were higher than those of the fast heating homogenized (FH) profiles. It was also found that the incoherent Al 3 Zr dispersoid within the recrystallized grains of the profile was prone to induce the precipitation of quench-induced phases. Due to the reduction of recrystallization fraction at the longitudinal weld in RH profile, the precipitation of quench-induced phases was inhibited. The strength of the air-quenched and aged RH profile was higher than that of the FH profile. It can be concluded that the extrusion process using the RH billet can improve the microstructure and mechanical properties at the longitudinal weld in 2195 Al-Li alloy profile. • Ramp heating homogenization treatment can promote the precipitation of Al3Zr. • Al3Zr reduces the recrystallization fraction and the width of the coarse grain zone. • Al3Zr inhibits abnormal grain growth within low plastic deformation zone. • RH billet optimizes microstructure, mechanical properties and quenching sensitivity. [ABSTRACT FROM AUTHOR]

The extrusion process of spray deposited 2195 Al–Cu–Li alloy was carried out with a porthole die. The microstructural evolution in the extrusion, especially the welding process in the near-vacuum chamber was characterized. The effect of weld seam on the microstructures and properties of profiles was revealed. It was found that the materials close to bridge is refined obviously and forms a layer of fine grain, while a typical fibrous structure with incomplete recrystallized grains is formed in matrix area. The fine grain layer forms welding area. The welding area mainly contains shear type texture while matrix area mainly has rolling type texture during the welding process. The sufficient recrystallization in the welding area results in the low dislocation density and weakens the work-hardening effect, which further suppresses the precipitation of the strengthening phase Al 2 CuLi. The massive dislocations of matrix area promote the precipitation of Al 2 CuLi, which improves the hardness of matrix area. The "kissing-bond" micro-pores on the welding interface and the massive dense and fine secondary particles in the welding area reduce the tensile properties of the profile with weld seam. • The welding area of profile has fine grains while matrix area has extrusion fibers. • High recrystallization degree in welding area results in the low dislocation density and weakens the work-hardening effect. • The welding area exhibits typical shear texture while matrix area has rolling texture. • The"kissing-bond" micro-voids in the welding interface reduce the tensile strength of profile with weld seam. [ABSTRACT FROM AUTHOR]

Fine nanostructures of bonding interfaces of weld seams formed by porthole die extrusion in the absence/presence of a gas-pocket behind the bridge of the extrusion die were systematically studied to understand the underlying interfacial bonding mechanisms. Interfacial grain boundaries, nanoscale amorphous layers, and three kinds of new interfacial structures were found. Specifically, it was found that, in the absence of a gas-pocket behind the bridge, there are two distinctly different interfacial structures. For the first kind of bonding interface, interfacial grain boundaries exist in contact areas and micro-voids exist in non-contact areas. For the second kind of bonding interface, there are no interfacial grain boundaries in contact areas and only nanoscale micro-voids exist in non-contact areas. In the presence of a gas-pocket behind the bridge, nanoscale voids and amorphous layers exist at the bonding interface. It was also found that the formation of gas-pockets can be avoided by increasing the depth of the welding chamber, and the increase of the welding chamber's depth and extrusion speed also contributes to the volume reduction of micro-voids and the migration of grain boundaries at the bonding interface, so as to improve the welding quality of weld seams. Based on the experimental findings, two interfacial bonding mechanisms corresponding to the absence/presence of a gas-pocket are proposed. The specific behavior of micro-asperities contact, micro-voids closure, oxide films breaking and interfacial grain boundaries migration are described, and the solid-state bonding process during porthole die extrusion is revealed from the micro-nano scales. [ABSTRACT FROM AUTHOR]

A new type of wrought magnesium alloy Mg-3.0Zn-1.0Sn-0.3Mn-0.3Ca (ZTMX3100) was developed in this work. The effects of extrusion temperature (200–400 °C) on grain structure, second phase particle, texture, and mechanical properties of the alloy were systematically investigated by combining microstructure observations and mechanical properties tests. The results indicated that dynamic recrystallization occurs at 200–400 °C in the alloy. As the extrusion temperature increases, the average grain size increases gradually from 2.6 μm to 17.8 μm due to different degrees of grain growth, the continuous CaMgSn phase bands are gradually broken into discontinuous chain-like or dot-like structures, and the grains and CaMgSn phases distribute more uniformly. The as-extruded alloys exhibit a typical extruding texture with (0001) basal planes parallel to the extrusion direction. The bar extruded at 300 °C presents the optimum comprehensive mechanical properties, which is attributed to the combined effect of relatively small grain size, uniformly distributed discontinuous particles, and weak basal texture. Finally, the quantitative relationship between grain size and Zener-Hollomon parameter and the quantitative relationship between the yield strength of the alloy and extrusion temperature were obtained. [ABSTRACT FROM AUTHOR]

In porthole die extrusion process of aluminum alloy profiles, the formation of longitudinal weld seams (L-seams) is inevitable. Analysis of L-seam defects and investigation of solid-state bonding criteria are important issues for practical production. In this study, a set of modular porthole extrusion dies with different depths of welding chambers were designed and manufactured. The profiles extruded with different depths of welding chambers were obtained by performing extrusion experiments.The welding quality of extruded profiles was characterized by means of microstructure observation, tensile test and fracture analysis. The true stress-strain curves of homogenized AA6063 aluminum alloy with various strain rates and deformation temperatures were obtained by means of isothermal hot compression test. Three-dimensional transient numerical simulation models of the porthole die extrusion processes were established. Flow behaviors of aluminum alloy in porthole die extrusion process were investigated, and the formation processes of L-seams and their defects were revealed. The solid-state bonding processes of metal particles were traced and their welding paths were determined. Finally, based on the plastic deformation and diffusion mechanisms for closure behaviors of micro voids on contact interfaces, a new dimensionless solid-state bonding criterion related to stress triaxiality, effective strain rate, temperature and contact time was proposed. The bonding quality of L-seams of extruded profiles without any macro defect was predicted successfully by using this new criterion. In addition, it was found that the formation of a macro hole in the profile extruded with a shallow welding chamber is attributed to metal flow behavior, and does not relate to solid-state bonding process. [ABSTRACT FROM AUTHOR]

In this paper, the 'trial-and-repair' process of the extrusion die is transferred from the workshop to the computer for a complex hollow aluminum profile used in high-speed trains. Firstly, a finite element (FE) model of the extrusion process is established with the arbitrary Lagrangian-Eulerian code HyperXtrude. To balance the material flow velocity in the die cavity, more than ten baffle plates are used and distributed in the welding chamber. Then, taking the exit velocity uniformity as the evaluating criterion, the initial extrusion die is modified by adjusting the shapes, the layout, and the heights of the baffle plates. Through a series of modifications, the velocity difference in the cross-section of the extrudate decreases significantly from 102.3 mm/s with the initial die to 26.6 mm/s with the final one. The local twisted or bent deformation of the extrudate is well controlled with the optimal die. Finally, a real extrusion die is manufactured and a practical profile is extruded. The difference in the rib thickness of the profile between the experimental measurements and desired dimensions is 0.12 mm, which satisfies the practical requirements. Moreover, the microstructures in the profile and its ribs are examined, and no heat defects are observed in the profile. Therefore, the virtual tryout of the extrusion die in this work are well verified, and the design rules of extrusion dies could provide theoretical guidance for practical repairs of complex extrusion dies in workshop. [ABSTRACT FROM AUTHOR]

The appropriate die design for multi-hole extrusion is still a challenging task because of the complicated circumstances and large material deformation during extrusion process. In the present study, the material flow during multi-hole extrusion process for producing a hollow and thin-walled profile was revealed by means of numerical simulation based on the Arbitrary Lagrangian Eulerian (ALE) method. The effects of eccentricity ratio, shape of the second-step welding chamber, and uneven bearing length on the exit velocity distribution of extrudate were synthetically investigated, and a two-hole porthole die was designed accordingly. The exit velocity and temperature on the extrudate in this optimized die were analyzed and compared with the initial die, and it was found that both of them exhibit better uniformity, which is beneficial for the enhancement of product quality. Through performing the current work, a logical and effective route for designing multi-hole porthole die was proposed as the guidance for die designers. [ABSTRACT FROM AUTHOR]

The extrusion die plays a crucial role in aluminum alloy profile production, which influences product quality and service life of extrusion die directly. In this paper, a profile with irregular shape was taken as an analysis example, and multiobjective optimization for porthole extrusion die based on modern intelligence algorithm was carried out. Aiming at achieving the uniform velocity distribution in the cross-section of the profile as well as decreasing the maximum stress on the extrusion die and the deflection of the mandrel, the angle between port bridges, the position of die orifice, and the height of welding chamber were considered as the design variables. Then Kriging model was established on the basis of Latin hypercube samplings, and above design variables were optimized using Pareto-based genetic algorithm. Finally, an optimal die structure is gained. Compared with the initial scheme, the velocity distribution in the extrudate was more even, and the stress on the die and the deflection of the mandrel were decreased obviously in the optimal scheme. The optimal design method for porthole die has strong commonality, thus, it could give useful guidelines for practical production of the same kind of aluminum profile. [ABSTRACT FROM AUTHOR]

In this article, a subroutine that calculates die wear depth based on modified Archard's wear model was developed and then embedded into DEFORM-3D, with which the extrusion process of an aluminum alloy 7075 rod was simulated. Useful information was obtained from the numerical simulation, including interface pressure, distribution of instantaneous temperature, required extrusion force, die wear depth, etc. The numerical result shows that extrusion parameters have multiple effects on die wear behavior. The severest die wear occurs at the bearing entrance due to the greatest deformation, highest pressure, and temperature in this area. It is found that ram speed has no single tendency on die wear, while die wear depth rises with the elevated initial temperatures of billet and extrusion tooling. In addition, the required extrusion force has strong dependence on extrusion parameters. The extrusion force rises clearly with an increase of ram speed and a decrease of initial temperatures of billet and extrusion tooling, which is totally accordant to practical observation. Therefore, the study in this work could provide useful and helpful guides for selecting reasonable extrusion variables, predicting die life and reducing production cost. [ABSTRACT FROM PUBLISHER]

Abstract: Extrusion stem speed is one of important process parameters during aluminum profile extrusion, which directly influences the profile quality and choice of extrusion equipments. In this paper, the extrusion process of a thin-walled hollow aluminum profile was simulated by means of the HyperXtrude commercial software. Through a serial of numerical simulation, the effects of stem speed on extrusion process, such as metal flow behavior at die exit, temperature distribution, extrusion force, and welding pressure, have been investigated. The numerical results showed that there existed an optimum value of stem speed for flow velocity distribution. With the increasing stem speed, the temperature of the extrudate and required extrusion force increased, and the welding quality of extrudate would be improved. Through comprehensive comparison and analysis, the appropriate stem speed could be determined for practical extrusion production. Thus, the research results could give effective guideline for determining initial billet and die temperature and choosing the proper extrusion press in aluminum profile industry. [Copyright &y& Elsevier]

Taguchi's design of experiment and numerical simulation were applied in the optimization of an aluminum profile extrusion process. By means of HyperXtrude, the extrusion process was simulated and the effects of process parameters on the uniformity of metal flow and on the extrusion force were investigated with the signal to noise ratio and the analysis of variance. Through analysis, the optimum combination of process parameters for uniform flow velocity distribution was obtained, with the billet diameter of 170 mm, ram speed of 2.2 mm/s, die temperature of 465°C, billet preheated temperature of 480°C, and container temperature of 425°C. Compared with the initial process parameters, the velocity relative difference in the cross-section of extrudate was decreased from 2.81% to 1.39%. In the same way, the optimum process parameters for minimum required extrusion force were gained, with the billet diameter of 165 mm, ram speed of 0.4 mm/s, die temperature of 475°C, billet preheated temperature of 495°C, and container temperature of 445°C. A 24.7% decrease of required extrusion force with optimum process parameters was realized. Through the optimization analysis in this study, the extrusion performance has been greatly improved. Finally, the numerical results were validated by practical experiments, and the comparison showed that the optimization strategy developed in this work could provide the effective guidance for practical production. [ABSTRACT FROM AUTHOR]

The most important way to improve the quality of aluminum profiles is to assure the material flow through die land exit with the same velocity. In this paper, a numerical model was developed to investigate metal flow behavior during aluminum profile extrusion. Firstly, the numerical model for a complex hollow aluminum profile was built based on the arbitrary Lagrangian-Eulerian program HyperXtrude. Then, with the numerical model, metal flow behavior at each stage during the whole extrusion process was analyzed and dead zones in the die cavity were also investigated by means of the particle tracking method. Finally, the numerical results were validated by comparing with the nose ends of two extrudates in practice, and the comparison showed that the numerical model developed in this work could provide the effective guidance for practical production. [ABSTRACT FROM AUTHOR]

Purpose – The paper aims to use the finite volume method widely used in computational fluid dynamics to avoid the serious remeshing and mesh distortion during aluminium profile extrusion processes simulation when using the finite element method. Block-structured grids are used to fit the complex domain of the extrusion. A finite volume method (FVM) model for aluminium extrusion numerical simulation using non-orthogonal structured grids was established. Design/methodology/approach – The influences of the elements' nonorthogonality on the governing equations discretization of the metal flow in aluminium extrusion processes were fully considered to ensure the simulation accuracy. Volume-of-fluid (VOF) scheme was used to catch the free surface of the unsteady flow. Rigid slip boundary condition was applied on non-orthogonal grids. Findings – This paper involved a simulation of a typical aluminium extrusion process by the FVM scheme. By comparing the simulation by the FVM model established in this paper with the ones simulated by the finite element method (FEM) software Deform-3D and the corresponding experiments, the correctness and efficiency of the FVM model for aluminium alloy profile extrusion processes in this paper was proved. Originality/value – This paper uses the FVM widely used in CFD to calculate the aluminium profile extrusion processes avoiding the remeshing and mesh distortion during aluminium profile extrusion processes simulation when using the finite element method. Block-structured grids with the advantage of simple data structure, small storage and high numerical efficiency are used to fit the complex domain of the extrusion. [ABSTRACT FROM AUTHOR]

Currently, the design of extrusion dies is usually carried out on the basis of experience and corrected after a number of trial extrusion runs before becoming usable. Thus, it is difficult to guarantee product quality and productivity when the profile structure is complex, and actual production has to be stopped or postponed, especially for multihole extrusion dies. This work analyzes the design of a multihole extrusion die for producing an aluminum tube and investigates the effects of number and layout of portholes on extrusion process. Firstly, four multihole dies with three, six, seven, and nine portholes are designed, respectively. Then, extrusion processes with different multihole dies are simulated by means of HyperXtrude. Based on the results of the numerical simulation, metal flow, temperature distribution, welding pressure, extrusion load, die stress, etc. are analyzed and compared. Through analysis, Die 1 (with three portholes) is the optimum one among these four dies, where the uniform velocity distribution, maximum welding pressure, minimum required extrusion load, and minimum die stress are obtained. Finally, the design methods for multihole extrusion dies are summarized. [ABSTRACT FROM AUTHOR]

The extrusion die plays a crucial role in the quality control of aluminum alloy profile production. In practice, the extrusion die design mainly depends on the experience and intuition of the die designers. The designed and manufactured dies are usually tested and modified many times before putting into practical extrusion production, and difficult to be guaranteed as optimal ones. In this paper a method of die design based on numerical simulation was proposed in order to optimize the die structure and enhance the level of die design. Firstly, the extrusion process of a large wallboard of high-speed train was simulated by means of HyperXtrude software. It was found that a severe non-uniform velocity distribution emerged in the cross-section of the extrudate and twist deformation occurred, therefore the initial die was not an acceptable one. Then, three times of modifications to the die structure were made to optimize the die structure and improve the product quality. Finally, an optimal die structure with uniform material flow velocity in the cross-section of the die exit was obtained. A sound wallboard extrudate of high-speed train was produced. The die design methods for complex extrusion profiles were summarized and proposed, including the design methods of porthole area of multi-cavity dies, the baffle plate, and the sunken port bridge structure. [ABSTRACT FROM AUTHOR]

The article presents a study on the chemical caloric effects in reactive extrusion processes for free radical polymerization. It discusses the experimentation to analyze polymerization trend, deduce the numerical model of the heat of chemical reaction and obtain relationships among reactive caloric intensity, monomer concentration and fluid temperature. It also looked into optimization of reactive processing conditions.

Al-Li alloys are considered as promising materials for the aircraft and aerospace industries. As an effective way of producing complex profiles, the hot extrusion process has become more attractive. Here, isothermal extrusion of homogenized 2196 Al-Li alloys under the temperature of 703–783 K and extrusion speed of 0.1–1.0 mm/s was implemented. The microstructure and mechanical properties of extruded profiles under different processing conditions were evaluated. The results showed that the homogenization could eliminate the dendritic structure caused by casting and reduce segregation, creating a uniform element distribution. The insoluble intermediate particles composed of Al, Cu, and Fe were distributed on the grain boundaries with blocks and dots. After extrusion, the grains were flattened and elongated into thin fibers. With increasing extrusion temperature and speed, the misorientation of grains was increased, the degree of dynamic recovery and recrystallization were promoted, and the grain size was decreased. Increasing the extrusion speed properly is beneficial to grain refinement and dynamic recrystallization. The main texture components of the extruded profiles were Y, Cube textures with the orientations of <111>, <100>, and other {111} fibers. With the increasing temperature and speed, the texture types were changed from shear texture to recrystallization texture. The intensity of texture was decreased, while the texture diversity was increased. The hardness, tensile strength and yield strength of extruded profile were greatly enhanced, but the elongation was decreased. The tensile fracture morphology exhibited a large number of dimples, which was considered to be ductile fracture. [ABSTRACT FROM AUTHOR]

Abstract A reasonable constitutive model is the key for accurate numerical simulation of extrusion process of aluminum alloy profiles. In this work, 20 material parameters in a fourth-order strain-compensated constitutive model of an Al-Zn-Mg alloy were determined by the inverse analysis method. Firstly, taking the minimization of shape error of specimens under different compression extents (10–60%) at the temperature of 475 °C and the strain rate of 1 s−1 as the optimization objective, the friction coefficient in hot compression test was determined by inverse analysis. Results showed that the friction coefficient was 0.031 and the global error was merely 1.001%, which demonstrated the practical lubrication condition between specimen and tool head could be reflected by the acquired friction coefficient. Then, based on the obtained friction coefficient, the inverse analysis was also used to identify 20 unknown material parameters in the fourth-order strain-compensated constitutive model at once by minimizing the difference between predicted and experimental force-displacement data. The predicted force-displacement curves matched the experimental ones well with the global error of only 6.07%. Finally, the developed constitutive model was applied in simulating the porthole and piercing extrusion for a hollow thin-walled profile and corresponding verified experiments were also carried out. Graphical abstract fx1 Highlights • 20 material parameters were identified at once for AA7N01 by inverse analysis. • The friction coefficient in hot compression was obtained as 0.031 by inverse analysis. • The constitutive model was successfully applied and verified in the profile extrusion. [ABSTRACT FROM AUTHOR]

• The abnormal grains formed during extrusion were Cube orientated, while that formed in solution treatment were random. • The strain-free Cube orientated grains located at the frontier of different textures have growth advantage in extrusion. • The migration and annihilation of dislocations resulted in abnormal grain growth in solution treatment. • The weld seam had higher thermal stability in solution treatment when formed at higher extrusion temperature and speed. • The matrix area kept fine grainsin extrusion and heattreatment due to the flat grain boundaries and many sub-structures. The porthole die extrusion processes of 2196 Al-Cu-Li alloy were carried out at billet temperatures of 420–510 °C and ram speeds of 0.25–5.0 mm/s, then the extruded profiles were subjected to the solution and aging treatment. Abnormal grain growth (AGG) was observed along longitudinal weld of profiles during the extrusion and solution treatment. The fine equiaxed grains with Copper orientation were formed in the welding area when extruded at low temperature and low extrusion speed, and some Copper orientated grains transformed into recrystallization textures with the increase of deformation temperature. When extruded at high temperature and speed, AGG occurred in the junction area of Copper texture and recrystallization textures, and some strain-free Cube orientated grains in this area transformed into AGG structures due to the high growth-driving force and growth priority. During the solution treatment, the migration and annihilation of dislocations were repeated inside the equiaxed grains of the welding area, resulting in the coalescence of the subgrains and the formation of AGG. The abnormal grains formed during extrusion were mainly Cube orientated, while those occurred during solution treatment were randomly orientated. The weld seam had higher thermal stability during solution treatment if profiles were extruded at higher extrusion temperature and speed. In the matrix area, most of the dislocations migrated along the same direction, and the dislocations were hard to meet and annihilate. Besides, little driving force for grain growth could be provided by the flat grain boundaries of the matrix area. Hence, the Brass orientated grains in the matrix area possessed high thermal stability during the extrusion and solution treatment. The AGG structure led to the intergranular fracture and poor elongation of samples in the tensile test. [ABSTRACT FROM AUTHOR]

The extrusion parameters greatly influence the microstructures of aluminum alloys, and further determine the mechanical properties of the final products. In this work, using a self-designed experimental device, a series of extrusion experiments was conducted to investigate the influence of the extrusion parameters on the microstructure, crystallographic texture, and second-phase particles in the Al-Mg-Si aluminum alloy (AA6N01), which is widely applied in the bodies of high-speed trains. Firstly, the billet discard in the press container was taken out for analyzing the material flow and microstructural evolution during the extrusion process. The results showed that continuous dynamic recrystallization occurred, and the initially coarse equiaxed grains in the as-homogenized billet evolved gradually into fine equiaxed grains at the die exit due to their dynamic recovery and dynamic recrystallization. More importantly, coarse grain layers were observed on the surface of the extruded profiles under specific extrusion conditions (460 °C/48 mm/min and 520 °C/48 mm/min). Then, the textures on the surface and at the center of the profiles were analyzed under different extrusion conditions by electron backscatter diffraction. The results showed that the textures of all the extruded profiles were mainly along <100> and <111 > , but the texture intensity was higher at the profile's center than that on the surface under the same extrusion condition. Finally, the second-phase particles in the as-homogenized billet and as-extruded profiles were compared and analyzed. The Fe-rich particles were broken under deformation conditions and their sizes decreased during the extrusion process. However, they were all still distributed on the grain boundaries after deformation, and the composition and content remained unchanged. The Mg 2 Si particles served as the main strengthening phase in AA6N01, and they were greatly aggregated as the extrusion temperature increased and the extrusion speed decreased. [ABSTRACT FROM AUTHOR]

The microstructure and mechanical properties of 1060/6063 Al alloys joint fabricated by porthole die extrusion were investigated. A sound welding interface of 1060/6063 Al alloys was obtained, and the welding quality can be further improved using higher welding chamber. Complete dynamic recrystallization (DRX) occurred during porthole die extrusion, while the DRXed grain size of 6063 Al matrix was always much smaller than that of 1060 Al matrix. The height of welding chamber had an significant effects on the microtexture of the extruded profiles. The profiles extruded using welding chamber with a height of 10 mm exhibited highest tensile strength and elongation. On the contrary, the joining of 1060/6063 Al alloys using flat die is not acceptable, where many cracks appeared at the welding interface and only partial DRX occurred. [ABSTRACT FROM AUTHOR]

Artificial aging plays important roles on the final performances of the manufactured components of Al matrix composites, and it is of great importance to find the appropriate aging parameters to obtain a good combination of mechanical properties and corrosion resistance. In this study, the Si 3 N 4 particle reinforced 6061Al (Si 3 N 4 /6061Al) composite was produced by sintering and hot extrusion, and both single and two-step aging were carried out to examine the precipitation behavior. It was found that the grain structure of Si 3 N 4 /6061Al and 6061Al did not show a notable change after solution treatment, while Mg element inclined to concentrate at the Si 3 N 4 /6061Al interface. The compounds containing Mg and Cu formed at Si 3 N 4 /6061Al interface during aging process, and β″ and β′ phases precipitated after peak and two-step aging, respectively. β″ phase contributed to improving the hardness, strength and wear resistance, while β′ phase caused an opposite trend. The Si 3 N 4 particles could also enhance the mechanical properties due to the load transfer and dislocation strengthening. The samples treated by solution exhibited the best corrosion resistance, while the peak-aged ones were sensitive to intergranular corrosion owing to the continuously distributed precipitates and the precipitate free zones at grain boundaries, and two-step aging could alleviate the intergranular corrosion susceptibility. Due to the preferential dissolutions of Mg element in Mg-containing layers and Mg/Cu-containing phases, the Al matrix around Si 3 N 4 particles was seriously corroded. [Display omitted] • Si 3 N 4 particles evenly distributed and were well bonded with Al matrix during the whole processes. • Addition of 6 wt% Si 3 N 4 particles did not change the precipitation behavior of 6061Al matrix. • The segregation of Mg and Mg/Cu-rich compounds were found at Si 3 N 4 /6061Al interface. • Al matrix around Si 3 N 4 particle was seriously corroded, and IGC was alleviated by two-step aging. • Si 3 N 4 particle contributed to better mechanical properties due to load transfer and dislocation strengthening. [ABSTRACT FROM AUTHOR]

[Display omitted] • An approach to control morphology of PTFE in PP was proposed. • Fibrosis mechanism of PP/PTFE microfibril reinforced composites was elucidated. • Crystallization of PP/PTFE composites with different morphology was studied. • PP/PTFE microfibril reinforced composites showed superior mechanical properties. In-situ fibrillary PTFE was usually developed by melt blending to enhance the melt strength and processability of PP. However, the fibrosis mechanism and the morphology evolution of PTFE during in-situ fibrillation process is still unclear. In this study, both in-situ PP/fibril-PTFE and PP/spherical-PTFE composites were prepared by one-step extrusion process. DSC, XRD, SEM, AFM, as well as O-PTIR analysis were conducted to elucidate the fibrosis mechanism of PTFE. The main reason for the in-situ fibrillation of PTFE-3800 could be ascribed to the chain-extended crystal structure. Furthermore, the acrylate layer of PTFE-3800 can also help PTFE to develop into fibrils. Shear rate was the key parameter in affecting the morphology evolution of PTFE, while processing time could also affect the morphology of PTFE to a certain extent. Interestingly, the SEM analysis showed that reticular crystals are generated in the presence of PTFE fibrils, while spherulites were generated in the presence of PTFE particles. Simultaneous enhancements in the strength, modulus and rigidity were achieved for in-situ fibrillary PTFE reinforced PP composites. [ABSTRACT FROM AUTHOR]

Accurate prediction of the texture evolution of aluminium alloys during hot extrusion process plays an important role in the die design and determination of process parameters. In this work, the deformation textures of aluminium alloys under three-dimensional deformation path are investigated numerically and experimentally. Firstly, the extrusion process of a helical profile is simulated with HyperXtrude and the deformation history under three-dimensional deformation path of the profile is extracted. Then the deformation modes in the different positions on the profile are analyzed and the velocity gradients are imported respectively into FC-Taylor, ALAMEL and ALAMEL III models to predict the extrusion deformation textures. Finally, a specially-designed helical extrusion die is manufactured and the extrusion experiment are carried out. The textures are analyzed by EBSD to verify the predicted results by three crystal plasticity models. The results show that there are significant differences in the deformation modes from the centre to surface of the extruded profile and the three crystal plasticity models differ greatly in the prediction accuracy of textures. For the deformation texture of the helical profile, the FC-Taylor model gives better prediction at the centre position and the ALAMEL-type model predicts better at the surface position of the profile. • A specially-designed helical extrusion die was manufactured and the extrusion experiments were conducted. • The deformation texture under three-dimensional path was well predicted by coupling the FEM simulation and the crystal plastic models. • The deformation mode was close to uniaxial tension in the center of the profile and the texture was a typical duplex fibre one. • The texture gradually rotated when approaching to the surface resulted from the corresponding shear deformation. • FC-Taylor model was the better model for the deformation texture prediction under three-dimensional path. [ABSTRACT FROM AUTHOR]