AZ31 Mg alloy plates with bimodal grain structures were fabricated via conventional extrusion under varying temperatures and speeds to investigate the mechanisms governing dynamic recrystallization(DRX)and texture evo...AZ31 Mg alloy plates with bimodal grain structures were fabricated via conventional extrusion under varying temperatures and speeds to investigate the mechanisms governing dynamic recrystallization(DRX)and texture evolution.Although all samples exhibited similar DRXed grain sizes(5.0–6.5μm)and fractions(76%–80%),they developed distinct c-axis orientations and mechanical properties.The P1 sample(350℃,0.1 mm/min)exhibited the lowest yield strength(∼192 MPa)but the highest elongation(∼18.2%),whereas the P3 sample(400℃,0.6 mm/min)showed the highest yield strength(∼241 MPa)and the lowest elongation(∼14.2%).The P2 sample(400℃,0.1 mm/min)demonstrated intermediate behavior(∼226 MPa,∼17.7%).These variations were primarily attributed to differences in c-axis orientations,particularly their alignment with respect to the normal direction(ND)and their slight deviation from the extrusion direction(ED).Microstructural analysis revealed that distinct DRX mechanisms were activated under different extrusion conditions.P1 predominantly exhibited twinning-induced dynamic recrystallization(TDRX)and continuous dynamic recrystallization(CDRX),whereas P3 primarily showed CDRX and discontinuous dynamic recrystallization(DDRX).These DRX mechanisms,in combination with the activated slip systems governed by the evolving local stress state,collectively contributed to orientation rotation and texture development.During the early stage of extrusion,tensile strain along the ED promoted basalslip,rotating the c-axes toward the ND.As deformation progressed,compressive strain along the ND became dominant.In P1,basalslip remained active,aligning the c-axes along the ND and forming a smaller angle with the ED.In contrast,P3 exhibited predominant pyramidal<c+a>slip,resulting in a pronounced deviation of the c-axes from the ND and a slightly larger angle relative to the ED.The P2 sample exhibited a transitional texture state between those of P1 and P3.展开更多
Constructing bimodal grain structure is a promising approach to achieve the high strength-ductility syn-ergy in Mg alloy.Formation of bimodal grain is closely related to the dynamic and/or static recrystal-lization pr...Constructing bimodal grain structure is a promising approach to achieve the high strength-ductility syn-ergy in Mg alloy.Formation of bimodal grain is closely related to the dynamic and/or static recrystal-lization process,which has not been fully understood in the typical Mg-RE based alloy.In this work,it is claimed for the first time that the minor Ce addition(∼0.3 wt%)into Mg matrix significantly pro-motes the pyramidal<c+a>and non-basal<a>dislocations at the early stage of extrusion,which con-sequently enhances the formation of sub-grain boundaries via the movement and recovery of pyramidal II-type<c+a>dislocations.At this stage,fine sub-grain lamellae are widely observed predominantly due to the low migration rate of sub-grain boundary caused by the limited mobility of<c+a>dislocations.At the later stage,the sub-grains continuously transform into dynamic recrystallized(DRXed)grains that have10¯10Taylor axis and also strong fiber texture,indicating substantial activation of pyramidal II-type<c+a>dislocation.The low mobility of<c+a>dislocations,accompanied with the solute drag from grain boundary(GB)segregation and pinning from nano-phases,cause a sluggish DRX process and thus a bimodal microstructure with ultra-fined DRXed grains,∼0.51μm.The resultant texture hardening and grain refinement hardening effects,originated from bimodal microstructure,result in a yield strength of∼352 MPa,which is exceptional in Mg-Ce dilute alloy.This work clarifies the critical role of Ce addition in tuning recrystallization behavior and mechanical property of magnesium,and can also shed light on designing the other high-performance Mg alloys.展开更多
Although Cu was studied extensively,the Hall-Petch relationship was mainly reported in the coarsegrained regime.In this work,fully recrystallized Cu specimens with a wide grain size regime of 0.51–14.93μm manifest a...Although Cu was studied extensively,the Hall-Petch relationship was mainly reported in the coarsegrained regime.In this work,fully recrystallized Cu specimens with a wide grain size regime of 0.51–14.93μm manifest a two-stage Hall-Petch relationship.There is a critical grain size of 3μm that divides stagesⅠandⅡwhere the Hall-Petch slope k value are quite different.The stageⅡis supposed to be validified down to 100 nm at least by comparing with a Cu-Ag alloy.The critical grain size varies in different materials systems,and the underline mechanisms are discussed based on the dislocation glide modes.展开更多
A conventional multi-pass rolling is designed to form different microstructures in a Mg-2Ag alloy.The relationship between microstructure and mechanical property is investigated.The result shows that twin-induced nucl...A conventional multi-pass rolling is designed to form different microstructures in a Mg-2Ag alloy.The relationship between microstructure and mechanical property is investigated.The result shows that twin-induced nucleation plays a prominent role for the dynamic recrystallization(DRX)behavior of the rolled Mg-2Ag alloys.The DRXed grains distributed around elongated grains have random orientations but gradually turn to the concentrated orientation with strong basal texture when the rolling pass increases.The yield strength and ultimate tensile strength of rolled Mg-2Ag alloy gradually increase with increasing rolling pass.The elongation of rolled sample is gradually improved when the rolling pass increases from one to three,while a significant drop of elongation shows in the four-pass rolling sample.The strong basal texture,refined grains,high-density dislocations,and Ag segregation along grain boundaries are suggested to play a prominent role for enhancing the strength of Mg-Ag alloys,while the low-density dislocations,homogeneously fine-grained microstructure,and weak texture are critical for improving the ductility.展开更多
基金supported by National Key Research&Development Program of China(Grant no.2022YFE0110600)National Natural Science Foundation(Grant no.52220105003)+3 种基金the State Key Laboratory of Advanced Welding and Joining,Harbin Institute of Technology(Grant no.XNDCQQ2910201124)the National Natural Science Foundation for Young Scientists of China(Grant nos.51801042 and 51704088)Natural Science Foundation of Heilongjiang Province-Outstanding Youth Fund(Grant no.YQ2020E006)JSPS KAKENHI(Grant no.JP21H01669).
文摘AZ31 Mg alloy plates with bimodal grain structures were fabricated via conventional extrusion under varying temperatures and speeds to investigate the mechanisms governing dynamic recrystallization(DRX)and texture evolution.Although all samples exhibited similar DRXed grain sizes(5.0–6.5μm)and fractions(76%–80%),they developed distinct c-axis orientations and mechanical properties.The P1 sample(350℃,0.1 mm/min)exhibited the lowest yield strength(∼192 MPa)but the highest elongation(∼18.2%),whereas the P3 sample(400℃,0.6 mm/min)showed the highest yield strength(∼241 MPa)and the lowest elongation(∼14.2%).The P2 sample(400℃,0.1 mm/min)demonstrated intermediate behavior(∼226 MPa,∼17.7%).These variations were primarily attributed to differences in c-axis orientations,particularly their alignment with respect to the normal direction(ND)and their slight deviation from the extrusion direction(ED).Microstructural analysis revealed that distinct DRX mechanisms were activated under different extrusion conditions.P1 predominantly exhibited twinning-induced dynamic recrystallization(TDRX)and continuous dynamic recrystallization(CDRX),whereas P3 primarily showed CDRX and discontinuous dynamic recrystallization(DDRX).These DRX mechanisms,in combination with the activated slip systems governed by the evolving local stress state,collectively contributed to orientation rotation and texture development.During the early stage of extrusion,tensile strain along the ED promoted basalslip,rotating the c-axes toward the ND.As deformation progressed,compressive strain along the ND became dominant.In P1,basalslip remained active,aligning the c-axes along the ND and forming a smaller angle with the ED.In contrast,P3 exhibited predominant pyramidal<c+a>slip,resulting in a pronounced deviation of the c-axes from the ND and a slightly larger angle relative to the ED.The P2 sample exhibited a transitional texture state between those of P1 and P3.
基金supported by National Key Research and De-velopment Program of China(No.2021YFB3701002)National Nat-ural Science Foundation of China(No.U2167213,51971053)+1 种基金and funded by the Project of Promoting Talents in Liaoning province(No.XLYC1808038).H.C.Pan acknowledges the financial assistance from Young Elite Scientists Sponsorship Program by CAST(2019-2021QNRC001,2019-2021QNRC002,2019-2021QNRC003)the fund from the Fundamental Research Funds for the Central Univer-sities(N2202020).
文摘Constructing bimodal grain structure is a promising approach to achieve the high strength-ductility syn-ergy in Mg alloy.Formation of bimodal grain is closely related to the dynamic and/or static recrystal-lization process,which has not been fully understood in the typical Mg-RE based alloy.In this work,it is claimed for the first time that the minor Ce addition(∼0.3 wt%)into Mg matrix significantly pro-motes the pyramidal<c+a>and non-basal<a>dislocations at the early stage of extrusion,which con-sequently enhances the formation of sub-grain boundaries via the movement and recovery of pyramidal II-type<c+a>dislocations.At this stage,fine sub-grain lamellae are widely observed predominantly due to the low migration rate of sub-grain boundary caused by the limited mobility of<c+a>dislocations.At the later stage,the sub-grains continuously transform into dynamic recrystallized(DRXed)grains that have10¯10Taylor axis and also strong fiber texture,indicating substantial activation of pyramidal II-type<c+a>dislocation.The low mobility of<c+a>dislocations,accompanied with the solute drag from grain boundary(GB)segregation and pinning from nano-phases,cause a sluggish DRX process and thus a bimodal microstructure with ultra-fined DRXed grains,∼0.51μm.The resultant texture hardening and grain refinement hardening effects,originated from bimodal microstructure,result in a yield strength of∼352 MPa,which is exceptional in Mg-Ce dilute alloy.This work clarifies the critical role of Ce addition in tuning recrystallization behavior and mechanical property of magnesium,and can also shed light on designing the other high-performance Mg alloys.
基金supported financially by the Fundamental Research Funds for the Central Universities(No.N180204015)supported by Chinese Academy of Sciences(CAS)and Japan Society for the Promotion of Science(JSPS)through the Bilateral Program(No.GJHZ1774)supported by Ministry of Education,Culture,Sports,Science and Technology(MEXT),Japan,through the Elements Strategy Initiative for Structural Materials(ESISM)Project and the Grant-in-Aid for Scientific Research(S)(No.15H05767)。
文摘Although Cu was studied extensively,the Hall-Petch relationship was mainly reported in the coarsegrained regime.In this work,fully recrystallized Cu specimens with a wide grain size regime of 0.51–14.93μm manifest a two-stage Hall-Petch relationship.There is a critical grain size of 3μm that divides stagesⅠandⅡwhere the Hall-Petch slope k value are quite different.The stageⅡis supposed to be validified down to 100 nm at least by comparing with a Cu-Ag alloy.The critical grain size varies in different materials systems,and the underline mechanisms are discussed based on the dislocation glide modes.
基金supported by the National Natural Science Foundation of China(Nos.52171121,51971151,and 51971053)the Liao Ning XingLiao Program(No.XLYC1907083)+4 种基金the Science Research Project of Liaoning Province Education Department(No.LQ2019002)the Fundamental Research Funds for the Central Universities(No.N2202020)the Science Research Project of Liaoning Province Education Department(No.LJ2020015)Natural Science Foundation of Liaoning Province of China(2022-NLTS-18-01)the Open Foundation of Key Laboratory of Superlight Materials&Surface Technology of Ministry of Education(HEU10202205).
文摘A conventional multi-pass rolling is designed to form different microstructures in a Mg-2Ag alloy.The relationship between microstructure and mechanical property is investigated.The result shows that twin-induced nucleation plays a prominent role for the dynamic recrystallization(DRX)behavior of the rolled Mg-2Ag alloys.The DRXed grains distributed around elongated grains have random orientations but gradually turn to the concentrated orientation with strong basal texture when the rolling pass increases.The yield strength and ultimate tensile strength of rolled Mg-2Ag alloy gradually increase with increasing rolling pass.The elongation of rolled sample is gradually improved when the rolling pass increases from one to three,while a significant drop of elongation shows in the four-pass rolling sample.The strong basal texture,refined grains,high-density dislocations,and Ag segregation along grain boundaries are suggested to play a prominent role for enhancing the strength of Mg-Ag alloys,while the low-density dislocations,homogeneously fine-grained microstructure,and weak texture are critical for improving the ductility.
