Effects of the extrusion parameters on microstructure,texture and room temperature mechanical properties of extruded Mg-2.49Nd-1.82Gd-0.2Zn-0.2Zr alloy

Microstructure,texture,and mechanical properties of the extruded Mg-2.49Nd-1.82Gd-0.2Zn-0.2Zr alloy were investigated at different extrusion temperatures(260 and 320℃),extrusion ratios(10:1,15:1,and 30:1),and extrusion speeds(3 and 6 mm/s).The experimental results exhibited that the grain sizes after extrusion were much finer than that of the homogenized alloy,and the second phase showed streamline distribution along the extrusion direction(ED).With extrusion temperature increased from 260 to 320℃,the microstructure,texture,and mechanical properties of alloys changed slightly.The dynamic recrystallization(DRX)degree and grain sizes enhanced as the extrusion ratio increased from 10:1 to 30:1,and the strength gradually decreased but elongation(EL)increased.With the extrusion speed increased from 3 to 6 mm/s,the grain sizes and DRX degree increased significantly,and the samples presented the typical<2111>-<1123>rare-earth(RE)textures.The alloy extruded at 260℃ with extrusion ratio of 10:1 and extrusion speed of 3 mm/s showed the tensile yield strength(TYS)of 213 MPa and EL of 30.6%.After quantitatively analyzing the contribution of strengthening mechanisms,it was found that the grain boundary strengthening and dislocation strengthening played major roles among strengthening contributions.These results provide some guidelines for enlarging the industrial application of extruded Mg-RE alloy.

Predictive factors for coronal and sagittal graft extrusion length after using tendon autograft for medial meniscus reconstruction

BACKGROUND Meniscus extrusion occurs in most elderly individuals and most patients after meniscus allograft transplantation.The risk factors and correlative factors of meniscus extrusion have been extensively studied.However,for using tendon autograft for meniscus reconstruction,both graft type and surgical method are different from those in previous studies on meniscus extrusion.AIM To identify predictive factors for coronal and sagittal graft extrusion length after using tendon autograft for medial meniscus reconstruction.METHODS Ten patients who underwent medial meniscus reconstruction with tendon autograft were selected for this retrospective observational study.The graft extrusions and potential factors were measured and correlation and regression analyses were performed to analyze their relationships.RESULTS The medial graft extrusion correlated with the preoperative bilateral hip-kneeankle angle difference,preoperative Kellgren-Lawrence grade,preoperative relative joint space width,and preoperative bilateral medial edge incline angle difference.The anterior graft correlated with the anterior tunnel edge distance at 1 week after operation.The posterior graft extrusion correlated with the preoperative bilateral hip-knee-ankle angle difference,preoperative relative joint space width,and posterior tunnel edge distance at 1 week after operation.The mean graft extrusion correlated with the preoperative bilateral hip-knee-ankle angle difference and preoperative relative joint space width.The preoperative joint space width and anterior and posterior tunnel edge distance at 1 week can be used to predict the medial,anterior,posterior,and mean graft extrusion length.CONCLUSION The preoperative joint space width and tunnel position can be used to predict the coronal and sagittal graft extrusion length after using tendon autograft for medial meniscus reconstruction.

Investigation of high rate mechanical flow followed by ignition for high-energy propellant under dynamic extrusion loading

Investigating the ignition response of nitrate ester plasticized polyether(NEPE) propellant under dynamic extrusion loading is of great significant at least for two cases. Firstly, it helps to understand the mechanism and conditions of unwanted ignition inside charged propellant under accident stimulus.Secondly, evaluates the risk of a shell crevice in a solid rocket motor(SRM) under a falling or overturning scene. In the present study, an innovative visual crevice extrusion experiment is designed using a dropweight apparatus. The dynamic responses of NEPE propellant during extrusion loading, including compaction and compression, rapid shear flow into the crevice, stress concentration, and ignition reaction, have been firstly observed using a high-performance high-speed camera. The ignition reaction is observed in the triangular region of the NEPE propellant sample above the crevice when the drop weight velocity was 1.90 m/s. Based on the user material subroutine interface UMAT provided by finite element software LS-DYNA, a viscoelastic-plastic model and dual ignition criterion related to plastic shear dissipation are developed and applied to the local ignition response analysis under crevice extrusion conditions. The stress concentration occurs in the crevice location of the propellant sample, the shear stress is relatively large, the effective plastic work is relatively large, and the ignition reaction is easy to occur. When the sample thickness decreases from 5 mm to 2.5 mm, the shear stress increases from 22.3 MPa to 28.6 MPa, the critical value of effective plastic work required for ignition is shortened from 1280 μs to 730 μs, and the triangular area is easily triggering an ignition reaction. The propellant sample with a small thickness is more likely to stress concentration, resulting in large shear stress and effective work, triggering an ignition reaction.

Deformation mechanisms and microstructural characteristics of AZ61 magnesium alloys processed by a continuous expansion extrusion approach

The unique continuous extrusion-based severe plastic deformation approaches were proposed recently to process high-performance magnesium (Mg) alloys,while the in-depth deformation mechanisms under such complicated thermomechanical conditions were not well understood In the present work,the fundamental deformation behaviors of AZ61 Mg alloy from 25 to 400°C were firstly examined under uniaxial compression deformation.Then the deformation mechanisms and microstructural characteristics of AZ61 Mg alloy during continuous expansion extrusion forming (CEEF) were systematically investigated by microstructural observations,finite element and cellular automata simulations The results showed that the continuous evolutions of temperature,larger strain level and complex stress state with strain rate range of 0~5.98 s-1during CEEF brought the distinctive dynamic recrystallization behaviors and texture development in AZ61 Mg alloy,which were different to that of uniaxial compression deformation.In details,a remarkable grain refinement was achieved via CEEF processing due to the simultaneous actions of continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX).Gradually enhanced CDRX were observed from center to edge region,which had significant effects on the texture distribution and texture strength.The c-axis of most grains rotated under distinctive shear strain following parabolic metal flow,resulting in stable fiber texture.In addition,the evolution of the internal texture of the alloy led to an obvious increase in the Schmid factor for the activation of basal(c+a)slip system.©2022 Chongqing University.Publishing services provided by Elsevier B.V.on behalf of Ke Ai Communications Co.Ltd.

Extrusion 3D printing of carbon nanotube-assembled carbon aerogel nanocomposites with high electrical conductivity

Carbon nanotubes(CNTs)with high aspect ratio and excellent electrical conduction offer huge functional improvements for current carbon aerogels.However,there remains a major challenge for achieving the on-demand shaping of carbon aerogels with tailored micro-nano structural textures and geometric features.Herein,a facile extrusion 3D printing strategy has been proposed for fabricating CNT-assembled carbon(CNT/C)aerogel nanocomposites through the extrusion printing of pseudoplastic carbomer-based inks,in which the stable dispersion of CNT nanofibers has been achieved relying on the high viscosity of carbomer microgels.After extrusion printing,the chemical solidification through polymerizing RF sols enables 3D-printed aerogel nanocomposites to display high shape fidelity in macroscopic geometries.Benefiting from the micro-nano scale assembly of CNT nanofiber networks and carbon nanoparticle networks in composite phases,3D-printed CNT/C aerogels exhibit enhanced mechanical strength(fracture strength,0.79 MPa)and typical porous structure characteristics,including low density(0.220 g cm^(-3)),high surface area(298.4 m^(2)g^(-1)),and concentrated pore diameter distribution(~32.8nm).More importantly,CNT nanofibers provide an efficient electron transport pathway,imparting 3D-printed CNT/C aerogel composites with a high electrical conductivity of 1.49 S cm^(-1).Our work would offer feasible guidelines for the design and fabrication of shape-dominated functional materials by additive manufacturing.

Modeling of recrystallization behaviour of AA6xxx aluminum alloy during extrusion process

An innovative approach was introduced for the development of a AA6063 recrystallization model.This method incorporated a regression-based technique for the determination of material constants and introduced novel equations for assessing the grain size evolution.Calibration and validation of this methodology involved a combination of experimentally acquired microstructural data from the extrusion of three different AA6063 profiles and results from the simulation using the Qform Extrusion UK finite element code.The outcomes proved the agreement between experimental findings and numerical prediction of the microstructural evolution.The trend of the grain size variation based on different process parameters was accurately simulated,both after dynamic and static recrystallization,with an error of less than 25% in almost the whole sampling computations.

Method of fabricating artificial rock specimens based on extrusion free forming(EFF)3D printing

Three-dimensional(3D)printing technology has been widely used to create artificial rock samples in rock mechanics.While 3D printing can create complex fractures,the material still lacks sufficient similarity to natural rock.Extrusion free forming(EFF)is a 3D printing technique that uses clay as the printing material and cures the specimens through high-temperature sintering.In this study,we attempted to use the EFF technology to fabricate artificial rock specimens.The results show the physico-mechanical properties of the specimens are significantly affected by the sintering temperature,while the nozzle diameter and layer thickness also have a certain impact.The specimens are primarily composed of SiO_(2),with mineral compositions similar to that of natural rocks.The density,uniaxial compressive strength(UCS),elastic modulus,and tensile strength of the printed specimens fall in the range of 1.65–2.54 g/cm3,16.46–50.49 MPa,2.17–13.35 GPa,and 0.82–17.18 MPa,respectively.It is capable of simulating different types of rocks,especially mudstone,sandstone,limestone,and gneiss.However,the simulation of hard rocks with UCS exceeding 50 MPa still requires validation.

Improving the ductility and toughness of nano-TiC/AZ61 composite by optimizing bimodal grain microstructure via extrusion speed

In this study,the nano-TiC/AZ61 composites with different heterogeneous bimodal grain(HBG)structures and uniform structure are obtained by regulating the extrusion speed.The effect of HBG structure on the mechanical properties of the composites is investigated.The increasing ductility and toughening mechanism of HBG magnesium matrix composites are carefully discussed.When the extrusion speed increases from 0.75 mm/s to 2.5 mm/s or 3.5 mm/s,the microstructure transforms from uniform to HBG structure.Compared with Uniform-0.75 mm/s composite,Heterogeneous-3.5 mm/s composite achieves a 116.7%increase in ductility in the plastic deformation stage and almost no reduction in ultimate tensile strength.This is mainly because the lower plastic deformation inhomogeneity and higher strain hardening due to hetero-deformation induced(HDI)hardening.Moreover,Heterogeneous-3.5 mm/s composite achieves a 108.3%increase in toughness compared with the Uniform-0.75 mm/s composite.It is mainly because coarse grain(CG)bands can capture and blunt cracks,thereby increasing the energy dissipation for crack propagation and improving toughness.In addition,the CG band of the Heterogeneous-3.5 mm/s composite with larger grain size and lower dislocation density is more conducive to obtaining higher strain hardening and superior blunting crack capability.Thus,the increased ductility and toughness of the Heterogeneous-3.5 mm/s composite is more significant than that Heterogeneous-2.5 mm/s composite.

Force analysis and experimental study of pure aluminum and Al-5%Ti-1%B alloy continuous expansion extrusion forming process

The deformation zone of CONFORM extrusion was divided into primary gripping zone,gripping zone,conical expansion chamber zone,cylindrical zone and sizing zone of die,and corresponding force equilibrium equations were established using the Slab method.The deformation force formulae of CONFORM machine at any wrapping angle with an expansion chamber were obtained.Experiment on pure aluminum and Al-5%Ti-1%B alloy was conducted on the CONFORM machine self-designed.The resistance to deformation of Al-5%Ti-1%B alloy at the deformation temperature of 400℃ and the strain rate of 3.07 s-1 was measured to be 50 MPa using Gleeble-1500 thermal simulation machine.The calculation results of deformation forces for CONFORM process with an expansion chamber for pure aluminum and Al-5%Ti-1%B alloy were given.The experimental CONFORM radial force is in agreement with the radial force obtained by theoretical formula.

Effect of process parameters on sheath forming of continuous extrusion sheathing of aluminum

The effect of flow passage length in the die cavity and extrusion wheel velocity on the shape of aluminum sheath during the continuous extrusion sheathing process was analyzed by using finite element methods based on software DEFORM 3D and experimentally validated. The results show that by increasing the flow passage length, the velocity of metal at the cross-section of sheath tends toward uniformity, the values of the bending angles of sheath gradually approach the ideal value of zero and the cross-section exhibits a better shape. The extrusion wheel velocity has negligible effects on the bending shape and cross-section of the sheath product when a long flow passage is used.

Influences of electric-hydraulic chattering on backward extrusion process of 6061 aluminum alloy

The possibility of the electric-hydraulic chattering technology and its application in the cold extrusion were presented.The conventional and electric-hydraulic chattering assisted backward extrusion processes were performed on 6061 aluminum alloy billets at room temperature.The experimental results showed that 5.65% reduction in the extrusion load was attained if the die and ejector were vibrated at a frequency of 100 Hz and amplitude of 0.013 mm in the longitudinal direction.The friction coefficient at the billet and tool system interface determined from the finite element analysis（FEA） decreased from 0.2 without chattering to 0.1 with application of electric-hydraulic chattering.The higher values of instantaneous velocity and direction change of material flow were achieved during the chattering assisted backward extrusion process.The strain distribution of the chattering assisted backward extrusion billet revealed lower maximum strain and smoother strain distribution in comparison with that produced by the conventional extrusion method.

Extrusion force analysis of aluminum pipe fabricated by CASTEX using expansion combination die

To determine the extrusion force of pipe fabricated by continuous casting and extrusion (CASTEX) using an expansion combination die, the metallic expansion combination die was divided into diversion zone, expansion zone, flow dividing zone, welding chamber, and sizing zone, and the corresponding stress formulae in various zones were established using the slab method. The deformation zones of CASTEX groove were divided into liquid and semisolid zone, solid primary gripping zone, and solid gripping zone, and the formulae of pipe extrusion forces were established. Experiments were carried out on the self-designed CASTEX machine to obtain the aluminum pipe and measure its extrusion force using the expansion combination die. The experimental results of radial extrusion force for aluminum pipe are in good agreement with the calculated ones.

Continuous extrusion and rolling forming velocity of copper strip

A new copper strip production technology combined with continuous extrusion and rolling technology was proposed. The roll velocity must first be matched with the continuous extrusion velocity to achieve continuous extrusion and roll forming. The bite condition of continuous extrusion was determined, and the compatibility equation between the roll velocity and parameters such as the extrusion wheel velocity, reduction, and strip size was established through mechanical by plastic theoretical calculations. The finite element model of continuous extrusion and rolling was then established by using the TLJ400 continuous extrusion machine with a roll diameter of 200 mm. The relationship between the continuous extrusion and rolling velocities was determined through numerical simulations by software DEFORM-3D, and the accuracy of compatibility equation of velocity was verified.

Microstructure and mechanical properties of AM60B magnesium alloy prepared by cyclic extrusion compression

The cyclic extrusion compression （CEC） process was introduced into the AM60B magnesium alloy. The use of the CEC process was favorable for producing finer microstructures. The results show that the microstructure can be effectively refined with increasing the number of CEC passes. Once a critical minimum grain size was achieved, subsequent passes did not have any noticeable refining effect. As expected, the fine-grained alloy has excellent mechanical properties. The micro-hardness, yield strength, ultimate tensile strength and elongation to failure of two-pass CEC formed alloy are 72.2, 183.7 MPa, 286.3 MPa and 14.0%, but those of as-cast alloy are 62.3, 64 MPa, 201 MPa and 11%, respectively. However, there is not a clear improvement of mechanical properties with further increase in number of CEC passes in AM60B alloy. The micro-hardness, yield strength, ultimate tensile strength and elongation to failure of four-pass CEC formed alloy are 73.5, 196 MPa, 297 MPa and 16%, respectively.

Oxide distribution and microstructure in welding zones from porthole die extrusion

The oxide distribution and microstructure in longitudinal and transverse welding zones during the billet-to-billet extrusion process through porthole die were adequately investigated by means of finite element method,scanning electron microscopy and optical microscopy.The results indicate that the oxides exist at the interface between the matrix and transverse welding zone rather than longitudinal welding seam.The longitudinal welding zone reveals a darker band including the largest grain with irregular shape due to the abnormal grain growth under the heavy shear deformation and high temperature.The transverse welding zone consists of equiaxed recrystallized grains which are a little finer than those in the longitudinal welding seam.

Hot extrusion of SiC_p/AZ91 Mg matrix composites

SiC particles reinforced AZ91 Mg matrix composites （SiCp/AZ91） with SiC volume fractions of 5%, 10% and 15% were fabricated by stir casting. After T4 treatment, these composites were extruded at 350 °C with an extrusion ratio of 12：1. In the as-cast composite, particles segregated at a microscopic scale within the intergranular regions. Hot extrusion almost eliminated this particle aggregation and improved the particle distribution of the composites. In addition, extrusion refined the grains of matrix. The results show that hot extrusion significantly improves the mechanical properties of the composites. In the as-extruded composite, with the increase of SiCp contents, the grain size of the extruded composites decreases, the strength and elastic modulus increase but the elongation decreases.

Simulation of temperature field and metal flow during continuous semisolid extending extrusion process of 6201 alloy tube

A continuous semisolid extending extrusion （CSEP） method was proposed. Temperature field and metal flow during continuous semisolid extending extrusion process of 6201 alloy tube were studied. During the process, the temperature in the roll-shoe cavity decreases gradually, and the isothermal lines of the alloy deviate from the shoe side to the work roll side in the roll–shoe gap. Metal flow velocity decreases gradually from the surface of the work roll to the surface of the shoe. In the extrusion mould, alloy temperature decreases gradually from the entrance to the exit and from the center to the sidewall of the mould. The extending cavity is radially filled with the alloy. The flow lines in the tube corresponding to the centers of the splitflow orifices and the welding gaps are dense, and the corresponding harness values are high; there are 8 transitional bands between them. In order to prepare 6201 alloy tubes with good surface quality, the pouring temperature from 750 ℃ to 780 ℃ was suggested.

Finite element analysis of strain distribution in ZK60 Mg alloy during cyclic extrusion and compression

Finite element method was used to study the strain distribution in ZK60 Mg alloy during multi-pass cyclic extrusion and compression （CEC）. In order to optimize the CEC processing, the effects of friction condition and die geometry on the distribution of total equivalent plastic strain were investigated. The results show that the strain distributions in the workpieces are inhomogeneous after CEC deformation. The strains of the both ends of the workpieces are lower than that of the center region. The process parameters have significant effects on the strain distribution. The friction between die and workpiece is detrimental to strain homogeneity, thus the friction should be decreased. In order to improve the strain homogeneity, a large corner radius and a low extrusion angle should be used.

DRX rules during extrusion process of large-scale thick-walled Inconel 625 pipe by FE method

A thermal-mechanical and micro-macro coupled finite element（FE） model for the hot extrusion process of large-scale thick-walled Inconel 625 pipe was developed based on the DEFORM-2D platform.Then,the influence rules of the key extrusion parameters on the average grain size and grain uniformity of the extruded pipe were revealed.The results show that with the increase of initial billet temperature,extrusion speed and friction coefficient,the grain uniformity is firstly improved and then deteriorated.Larger extrusion ratio leads to more uniform grain distribution.With the increase of initial billet temperature,the average grain size of the pipe first decreases and then increases.Additionally,larger extrusion ratio can bring smaller average grain size.The extrusion speed and friction coefficient have slight effects on the average grain size of the extruded pipe.

Microstructural evolution of AZ91 magnesium alloy during extrusion and heat treatment

Microstructural evolution of AZ91 magnesium alloy was investigated during homogenizing annealing treatment, hot extrusion and ageing treatment, respectively. The results exhibited that both the divorced eutectic β-Mg17Al12 and the precipitated β-Mg17Al12 phases appeared in the as-cast alloy. The β-Mg17Al12 phase dissolved into α-Mg matrix mostly and the structure kept fine after the optimized homogenization treatment at 380 °C for 15 h. Dynamic recrystallization and consequent grain refinement occurred during extrusion. The banded β-Mg17Al12 precipitates paralleled to the extrusion direction were observed after ageing treatment. The banded precipitation should be attributed to the solidification segregation which was elongated during the subsequent extrusion. Furthermore, the effects of temperature, holding time of homogenization and ageing treatment, and extrusion processing parameters on the microstructural evolution of AZ91 alloy were also discussed in details according to the experimental results.