The 7075 Al alloy was processed by accumulative roll bonding （ARB） at 350 ℃ using 2：1, 3：1 and 4：1 thickness reductions per pass （Rp） up to 8, 6 and 3 passes, respectively. Microstructural examinations of the ...The 7075 Al alloy was processed by accumulative roll bonding （ARB） at 350 ℃ using 2：1, 3：1 and 4：1 thickness reductions per pass （Rp） up to 8, 6 and 3 passes, respectively. Microstructural examinations of the processed samples revealed that ARB leads to a microstructure composed of equiaxed crystallites with a mean size generally lower than 500 nm. It was found that, due to both the stored energy through- out the processing and the particle pinning effect, the alloy is affected by discontinuous recrystallisation during the inter-pass heating stages, the precise microstructural evolution being dependent on Rp. Me- chanical testing of the ARBed samples revealed that the main active deformation mechanism in the ARBed samples in the temperature range from 250 to 350 ℃ at intermediate and high strain rates is grain bound- ary sliding, the superplastic properties being determined by both the microstructure after ARB and its thermal stability.展开更多
The rate of microstructural coarsening of recrystallisation and partial melting (RAP) and cooling slope (CS) processed materials in the semi-solid state is compared with rates found in the literature.The rate of coars...The rate of microstructural coarsening of recrystallisation and partial melting (RAP) and cooling slope (CS) processed materials in the semi-solid state is compared with rates found in the literature.The rate of coarsening depended on the liquid fraction but RAP route 2014 alloy with 37% liquid coarsened slightly more slowly than the CS route 2014 alloy with a lower liquid fraction of 17%, contrary to expectations.For the CS route, an increase in liquid fraction resulted in faster coarsening.A modified 2014 alloy with Fe, Mn and Zn stripped out of the composition gave a relatively high coarsening rate.The coarsening rate was also relatively high for CS 201 alloy in comparison with either RAP 2014 or CS 2014.Low coarsening rates are thought to be associated with the presence of particles which inhibit the migration of liquid film grain boundaries.This could be the result of pinning or of the liquid film impeding diffusion at the boundary.展开更多
Lightweight curved profiles are widely utilised in the transportation industry considering the increasing need for improving aerodynamic efficiency,aesthetics and cutting emissions.In this paper,curved AZ31 Mg alloy p...Lightweight curved profiles are widely utilised in the transportation industry considering the increasing need for improving aerodynamic efficiency,aesthetics and cutting emissions.In this paper,curved AZ31 Mg alloy profiles were manufactured in one operation by a novel process,differential velocity sideways extrusion(DVSE),in which two opposed rams were used.Effects of extrusion temperature and velocity(strain rate) on curvature,microstructure,and mechanical properties of the formed profiles were examined.Profile curvature was found to be more readily controlled by the velocity ratio of the bottom ram v2to the top ram v1,whereas extrusion temperature(T=250,300,350℃)and extrusion velocity(v_(1)=0.1,1 mm/s) slightly affect curvature for a given velocity ratio.A homogeneous microstructure with equiaxed grains(~4.5 μm) resulted from dynamic recrystallisation(DRX),was observed after DVSE(v_(2)/v_(1)=1/2) at 300 ℃ and v_(1)=0.1 mm/s,where the initial billet had an average grain size of ~25 um.Increasing extrusion temperature leads to grain growth(~5 μm) at 350 ℃ and v_(1)=0.1 mm/s.DRX is incomplete at the relatively low temperature of 250℃(v_(1)=0.1 mm/s),and higher strain rate with v1=1mm/s(T=300℃),resulting in inhomogeneous bi-modal necklace pattern grains ranging in size around 1-25 μm for the former and 2-20μm for the latter.Grain refinement is attributed to DRX during the severe plastic deformation(SPD) arising in DVSE,and initiates at the prior boundaries of coarse grains in a necklace-like manner.Compared with the billet,micro-hardness and ultimate tensile strength of the profiles have been enhanced,which is compatible with grain refinement.Also,an obvious increase in tensile ductility was found.However,yield strength slightly decreases except for the complete DRXed case(300℃,v_(1)=0.1 mm/s),where a slightly higher value was found,indicating strengthening by grain refinement is greater than softening caused by texture modification.The initial billet had a strong basal texture wherein the {0002} 展开更多
Magnesium alloys are the lightest structural alloys and have attracted substantial research attention in the past two decades. However, their mechanical properties, including ductility and strength, are limited after ...Magnesium alloys are the lightest structural alloys and have attracted substantial research attention in the past two decades. However, their mechanical properties, including ductility and strength, are limited after forming due to the formation of coarse grains and strong texture. This study proposes and proves a new cryogenic-hot forming process concept. Cryogenic deformation is imposed before the hot deformation. The effect of the cryogenic step has been compared with a conventional direct hot deformation process. The mechanical properties, microstructure,and texture of both the novel and conventional process routes have been compared. The cryogenic-hot deformed sample exhibits the highest ductility and fracture strength(ultimate tensile strength: 321 MPa, ductility: 21%) due to effective grain refinement and texture weakening by cryogenically formed twin-twin interaction induced recrystallisation. The proposed cryogenic-hot forming process can be a potential innovative manufacturing method for producing high-performance magnesium components.展开更多
The extended band structures of as-cold-rolled high Cr steel sheets are recrystallisation-resistant, and tend to become aggregates of the so-called grain colonies as a partially recovered state after final annealing. ...The extended band structures of as-cold-rolled high Cr steel sheets are recrystallisation-resistant, and tend to become aggregates of the so-called grain colonies as a partially recovered state after final annealing. Such band structures diminish formability and become origin of the so-called ridging. A novel processing will be shown here, which involves strain-path change by introducing one-pass ECAP prior to cold-rolling, and facilitates recrystallisation. Indeed, the recrystallisation temperature was reduced by 100℃, compared with cold-rolling alone imposing an equivalent strain. Grain- scale microshear bands introduced during one-pass ECAP perturbed the banded structures in post-ECAP cold-rolling and enhanced the recrystallisation at the final annealing.展开更多
Thermomechanical Controlled Processing (TMCP) including accelerated cooling after the final hot rolling pass is a well-established technology,widely applied in HSLA steel plate production.However,there are still certa...Thermomechanical Controlled Processing (TMCP) including accelerated cooling after the final hot rolling pass is a well-established technology,widely applied in HSLA steel plate production.However,there are still certain limitations,especially for thicker plate.The rolling schedule includes a long holding period (HP) after the roughing stage to allow the temperature to fall sufficiently for optimised TMCP during finishing.Intermediate Forced Cooling (IFC) applied during the HP can increase productivity by decreasing the required hold time,can restrict austenite grain growth,and can also improve the subsequent strain penetration in thick plate with further metallurgical benefits.Multi-pass plane strain compression (PSC) tests have been performed on the thermomechanical compression (TMC) machine at Sheffield University including different severities of IFC.Clearly it is impossible to simulate all aspects of the temperature and strain gradients present in thick plates in laboratory specimens,and most of the tests were conducted at temperatures and strains calculated by Finite Element modelling as relevant to specific positions through the plate thickness.However,some aspects of the gradients were addressed with tests using cold platens.The results have indeed shown that IFC can shorten the HP and reduce austenite grain growth and its variation across thick plate.展开更多
The nucleation,grain growth of 34 coarse grains during annealing were tracked using a quasi-in-situ EBSD method.These 34 coarse grains had different orientations and most grains were non-basal orientated.No preferable...The nucleation,grain growth of 34 coarse grains during annealing were tracked using a quasi-in-situ EBSD method.These 34 coarse grains had different orientations and most grains were non-basal orientated.No preferable grain growth or special types of grain boundaries were identified.Only 9 coarse grains nucleated from deformed grain boundaries due to initial large grain size and limited grain boundary volume fraction.The main nucleation site of 34 coarse grains was dislocation cells or subgrains in deformed grain interiors.Their recrystallisation behaviour can be illustrated by abnormal subgrain growth(As GG)rarely reported in Mg alloys.The coarse basal grains showed no growth advantage in terms of grain size or number over other non-basal grains,leading to a weak basal texture in AZ31B alloy.展开更多
The recrystallized grain structure of Al-（Mn）-Fe-Si alloys after isothermal annealing was studied by electron backscatter diffraction（EBSD） technique. Statistical correlation suggests that the frequency of forming...The recrystallized grain structure of Al-（Mn）-Fe-Si alloys after isothermal annealing was studied by electron backscatter diffraction（EBSD） technique. Statistical correlation suggests that the frequency of forming P-oriented（{011}？566？） grains at a particle larger than the critical diameter（about 1.1 μm） is about 2% when the effect of fine dispersoids and concurrent precipitation is negligible. The overall grain number density is correlated linearly with the number densities of P and Cube（{001}？100？） grains. The grain number densities of typical orientations（P, ND-rotated cube {001}？310？ and Cube） and the overall recrystallized grains increase as rolling strain increases, following a similar exponential law.展开更多
本文采用 X 射线衍射技术研究了3004铝合金板材在中间退火过程中织构的变化及立方织构的形成规律,并用高压透射电镜原位动态观察、内耗测定和金相方法探讨了退火过程微观组织结构的变化。研究结果表明:中间退火可大量地形成立方织构;热...本文采用 X 射线衍射技术研究了3004铝合金板材在中间退火过程中织构的变化及立方织构的形成规律,并用高压透射电镜原位动态观察、内耗测定和金相方法探讨了退火过程微观组织结构的变化。研究结果表明:中间退火可大量地形成立方织构;热轧工艺及第二相粒子的种类、数量、大小与分布等对退火再结晶织构的生长有显著的影响。此外,由 X 射线织构分析和高压透射电镜动态观察,论证了立方织构形成的机理符合定向形核与定向生长的综合机制的理论。展开更多
基金support from the CICYT (Projects Nos. MAT200914452 and MAT2012-38962)
文摘The 7075 Al alloy was processed by accumulative roll bonding （ARB） at 350 ℃ using 2：1, 3：1 and 4：1 thickness reductions per pass （Rp） up to 8, 6 and 3 passes, respectively. Microstructural examinations of the processed samples revealed that ARB leads to a microstructure composed of equiaxed crystallites with a mean size generally lower than 500 nm. It was found that, due to both the stored energy through- out the processing and the particle pinning effect, the alloy is affected by discontinuous recrystallisation during the inter-pass heating stages, the precise microstructural evolution being dependent on Rp. Me- chanical testing of the ARBed samples revealed that the main active deformation mechanism in the ARBed samples in the temperature range from 250 to 350 ℃ at intermediate and high strain rates is grain bound- ary sliding, the superplastic properties being determined by both the microstructure after ARB and its thermal stability.
基金the UK Engineering and Physical Sciences Research Council (EPSRC Grant GR/M89096) and the University of Leicester for financial support
文摘The rate of microstructural coarsening of recrystallisation and partial melting (RAP) and cooling slope (CS) processed materials in the semi-solid state is compared with rates found in the literature.The rate of coarsening depended on the liquid fraction but RAP route 2014 alloy with 37% liquid coarsened slightly more slowly than the CS route 2014 alloy with a lower liquid fraction of 17%, contrary to expectations.For the CS route, an increase in liquid fraction resulted in faster coarsening.A modified 2014 alloy with Fe, Mn and Zn stripped out of the composition gave a relatively high coarsening rate.The coarsening rate was also relatively high for CS 201 alloy in comparison with either RAP 2014 or CS 2014.Low coarsening rates are thought to be associated with the presence of particles which inhibit the migration of liquid film grain boundaries.This could be the result of pinning or of the liquid film impeding diffusion at the boundary.
基金financial support provided by the UK EPSRC (EP/S019111/1 and EP/R001715/1)。
文摘Lightweight curved profiles are widely utilised in the transportation industry considering the increasing need for improving aerodynamic efficiency,aesthetics and cutting emissions.In this paper,curved AZ31 Mg alloy profiles were manufactured in one operation by a novel process,differential velocity sideways extrusion(DVSE),in which two opposed rams were used.Effects of extrusion temperature and velocity(strain rate) on curvature,microstructure,and mechanical properties of the formed profiles were examined.Profile curvature was found to be more readily controlled by the velocity ratio of the bottom ram v2to the top ram v1,whereas extrusion temperature(T=250,300,350℃)and extrusion velocity(v_(1)=0.1,1 mm/s) slightly affect curvature for a given velocity ratio.A homogeneous microstructure with equiaxed grains(~4.5 μm) resulted from dynamic recrystallisation(DRX),was observed after DVSE(v_(2)/v_(1)=1/2) at 300 ℃ and v_(1)=0.1 mm/s,where the initial billet had an average grain size of ~25 um.Increasing extrusion temperature leads to grain growth(~5 μm) at 350 ℃ and v_(1)=0.1 mm/s.DRX is incomplete at the relatively low temperature of 250℃(v_(1)=0.1 mm/s),and higher strain rate with v1=1mm/s(T=300℃),resulting in inhomogeneous bi-modal necklace pattern grains ranging in size around 1-25 μm for the former and 2-20μm for the latter.Grain refinement is attributed to DRX during the severe plastic deformation(SPD) arising in DVSE,and initiates at the prior boundaries of coarse grains in a necklace-like manner.Compared with the billet,micro-hardness and ultimate tensile strength of the profiles have been enhanced,which is compatible with grain refinement.Also,an obvious increase in tensile ductility was found.However,yield strength slightly decreases except for the complete DRXed case(300℃,v_(1)=0.1 mm/s),where a slightly higher value was found,indicating strengthening by grain refinement is greater than softening caused by texture modification.The initial billet had a strong basal texture wherein the {0002}
基金the financial support from the President’s PhD Scholarship of Imperial College Londonthe funding support by EPSRC under the Grant Agreement EP/R001715/1 on “Light Form: Embedding Materials Engineering in Manufacturing with Light Alloys”。
文摘Magnesium alloys are the lightest structural alloys and have attracted substantial research attention in the past two decades. However, their mechanical properties, including ductility and strength, are limited after forming due to the formation of coarse grains and strong texture. This study proposes and proves a new cryogenic-hot forming process concept. Cryogenic deformation is imposed before the hot deformation. The effect of the cryogenic step has been compared with a conventional direct hot deformation process. The mechanical properties, microstructure,and texture of both the novel and conventional process routes have been compared. The cryogenic-hot deformed sample exhibits the highest ductility and fracture strength(ultimate tensile strength: 321 MPa, ductility: 21%) due to effective grain refinement and texture weakening by cryogenically formed twin-twin interaction induced recrystallisation. The proposed cryogenic-hot forming process can be a potential innovative manufacturing method for producing high-performance magnesium components.
文摘The extended band structures of as-cold-rolled high Cr steel sheets are recrystallisation-resistant, and tend to become aggregates of the so-called grain colonies as a partially recovered state after final annealing. Such band structures diminish formability and become origin of the so-called ridging. A novel processing will be shown here, which involves strain-path change by introducing one-pass ECAP prior to cold-rolling, and facilitates recrystallisation. Indeed, the recrystallisation temperature was reduced by 100℃, compared with cold-rolling alone imposing an equivalent strain. Grain- scale microshear bands introduced during one-pass ECAP perturbed the banded structures in post-ECAP cold-rolling and enhanced the recrystallisation at the final annealing.
基金Tata Steel Europe Research Development & Technology for their financial and technical support
文摘Thermomechanical Controlled Processing (TMCP) including accelerated cooling after the final hot rolling pass is a well-established technology,widely applied in HSLA steel plate production.However,there are still certain limitations,especially for thicker plate.The rolling schedule includes a long holding period (HP) after the roughing stage to allow the temperature to fall sufficiently for optimised TMCP during finishing.Intermediate Forced Cooling (IFC) applied during the HP can increase productivity by decreasing the required hold time,can restrict austenite grain growth,and can also improve the subsequent strain penetration in thick plate with further metallurgical benefits.Multi-pass plane strain compression (PSC) tests have been performed on the thermomechanical compression (TMC) machine at Sheffield University including different severities of IFC.Clearly it is impossible to simulate all aspects of the temperature and strain gradients present in thick plates in laboratory specimens,and most of the tests were conducted at temperatures and strains calculated by Finite Element modelling as relevant to specific positions through the plate thickness.However,some aspects of the gradients were addressed with tests using cold platens.The results have indeed shown that IFC can shorten the HP and reduce austenite grain growth and its variation across thick plate.
基金the UKRI MRC Future Leaders Fellowship,MR/T019123/1funded through EPSRC grants EP/R00661X/1,EP/S019367/1,EP/P02470X/1 and EP/P025285/1,for JSM-7900F FESEM/EBSD kit access at The University of Sheffield。
文摘The nucleation,grain growth of 34 coarse grains during annealing were tracked using a quasi-in-situ EBSD method.These 34 coarse grains had different orientations and most grains were non-basal orientated.No preferable grain growth or special types of grain boundaries were identified.Only 9 coarse grains nucleated from deformed grain boundaries due to initial large grain size and limited grain boundary volume fraction.The main nucleation site of 34 coarse grains was dislocation cells or subgrains in deformed grain interiors.Their recrystallisation behaviour can be illustrated by abnormal subgrain growth(As GG)rarely reported in Mg alloys.The coarse basal grains showed no growth advantage in terms of grain size or number over other non-basal grains,leading to a weak basal texture in AZ31B alloy.
基金Project(20160520116JH)support by the Science and Technology Development Program of Jilin Province,ChinaProject supported by Key Laboratory of Automobile Materials(Ministry of Education),Jilin University,China+1 种基金Project supported by PX group EPFL,SwitzerlandProject(193179/I40)supported by the Research Council of Norway
文摘The recrystallized grain structure of Al-（Mn）-Fe-Si alloys after isothermal annealing was studied by electron backscatter diffraction（EBSD） technique. Statistical correlation suggests that the frequency of forming P-oriented（{011}？566？） grains at a particle larger than the critical diameter（about 1.1 μm） is about 2% when the effect of fine dispersoids and concurrent precipitation is negligible. The overall grain number density is correlated linearly with the number densities of P and Cube（{001}？100？） grains. The grain number densities of typical orientations（P, ND-rotated cube {001}？310？ and Cube） and the overall recrystallized grains increase as rolling strain increases, following a similar exponential law.
文摘本文采用 X 射线衍射技术研究了3004铝合金板材在中间退火过程中织构的变化及立方织构的形成规律,并用高压透射电镜原位动态观察、内耗测定和金相方法探讨了退火过程微观组织结构的变化。研究结果表明:中间退火可大量地形成立方织构;热轧工艺及第二相粒子的种类、数量、大小与分布等对退火再结晶织构的生长有显著的影响。此外,由 X 射线织构分析和高压透射电镜动态观察,论证了立方织构形成的机理符合定向形核与定向生长的综合机制的理论。
