In this study, the ultrafine grained （UFG） 6061 Al alloys fabricated by cold rolling were friction stir welded （FSW） with different rotation rates under both air cooling and rapid cooling in water. Low-heat-input ...In this study, the ultrafine grained （UFG） 6061 Al alloys fabricated by cold rolling were friction stir welded （FSW） with different rotation rates under both air cooling and rapid cooling in water. Low-heat-input parameters of 400 rpm rotation rate in water （400-Water） could effectively inhibit the coarsening of recrystallized grains, reduce the precipitation rate, and retain more dislocations of the UFG 6061 Al parent metal. 400-Water joint showed high lowest-hardness value, narrow low-hardness zone, and high tensile strength, attributing to the effect of dislocation, grain boundary, solid-solution, and precipitation hardening. This work provides an effective strategy to fabricate large-sized bulk UFG AI alloy by cold rolling with large deformation and low-heat-input FSW.展开更多
The spheroidization of the Widmanstätten structure through thermo-mechanical processes,leading to the formation of fine recrystallized and sub-grain structures,is crucial for achieving a balance between strength ...The spheroidization of the Widmanstätten structure through thermo-mechanical processes,leading to the formation of fine recrystallized and sub-grain structures,is crucial for achieving a balance between strength and plasticity.This study systematically examined the spheroidization mechanism of the Widmanstätten structure in Ti-25Zr-4Al-1.5Mn(wt.%,TiZrAlMn)alloy under varying rolling temperatures and its influence on microstructure and mechanical properties.After rolling at 900℃,the specimen exhibited a mixed morphology of Widmanstätten and Basket-weave structures,with a high yield strength of approximately 1038 MPa but low plasticity(∼5.2%).While the rolling temperature was reduced to 850℃,the specimen exhibited refined prior-β grains,discontinuous grain boundaries and a small amount of equiaxed α grains,which collectively enhanced plasticity(∼12.4%)while preserving yield strength.As the rolling temperature further decreased,the dynamic recrystallization mechanism shifted from the discontinuous dynamic recrystallization(DDRX)to continuous dynamic recrystallization(CDRX).Specimens rolled at 800℃ and 750℃ showed excellent strength-plasticity synergy,with yield strengths of 1070 MPa and 1110 MPa,respectively,and total elongations of 15%and 18%,respectively.The enhanced yield strength is attributed to both fine-grain and sub-grain strengthening.Furthermore,the lower degree of recrystallization in the 750-AC specimen preserved a relatively high dislocation density,offering additional strengthening.The favorable plasticity results from a combination of equiaxedαgrains,“soft”barrier sub-grains,and a small number of twins.Additionally,the 750-AC specimen retained 6.4%of the fine β grains and the weak basal texture.These characteristics contribute to the enhanced plasticity.Therefore,750℃is the optimal rolling temperature for achieving the best strength-plasticity synergy in the hot-rolled TiZrAlMn alloy.These findings demonstrate that selecting the appropriate temperature during thermomechanical processing to optimize recrystallized grains and sub-grain content ensures excellent plasticity at high yield strength.This offers valuable guidance for developing near-α Ti alloys with superior mechanical properties.展开更多
基金funded by the National Natural Science Foundation of China(No.51601045)the Guangxi Natural Science Foundation(No.2015GXNSFBA139238)+2 种基金the Guangxi ‘Bagui’ Teams for Innovation and Researchthe National Basic Research Program of China(No.2013CB733000)the Collaborative Innovation Center for Exploration of Hidden Nonferrous Metal Deposits and Development of New Materials in Guangxi
文摘In this study, the ultrafine grained （UFG） 6061 Al alloys fabricated by cold rolling were friction stir welded （FSW） with different rotation rates under both air cooling and rapid cooling in water. Low-heat-input parameters of 400 rpm rotation rate in water （400-Water） could effectively inhibit the coarsening of recrystallized grains, reduce the precipitation rate, and retain more dislocations of the UFG 6061 Al parent metal. 400-Water joint showed high lowest-hardness value, narrow low-hardness zone, and high tensile strength, attributing to the effect of dislocation, grain boundary, solid-solution, and precipitation hardening. This work provides an effective strategy to fabricate large-sized bulk UFG AI alloy by cold rolling with large deformation and low-heat-input FSW.
基金financially supported by the National Natural Science Foundation of China(Nos.52125405,52127808,52071278,U22A20108 and 52471148)the Science Research Project of Hebei Education Department(No.KJZX202201)+2 种基金Natural Science Foundation of Hebei Province(No.242Q9906Z/E2021402002)Basic Research Project of Shijiazhuang City for Universities in Hebei Province(No.241791027A)the Hebei Provincial Department of Education Funding Project for Cultivating Innovative Ability of Graduate Students(Grant no.CXZZBS2025057/CXZZBS2025056).
文摘The spheroidization of the Widmanstätten structure through thermo-mechanical processes,leading to the formation of fine recrystallized and sub-grain structures,is crucial for achieving a balance between strength and plasticity.This study systematically examined the spheroidization mechanism of the Widmanstätten structure in Ti-25Zr-4Al-1.5Mn(wt.%,TiZrAlMn)alloy under varying rolling temperatures and its influence on microstructure and mechanical properties.After rolling at 900℃,the specimen exhibited a mixed morphology of Widmanstätten and Basket-weave structures,with a high yield strength of approximately 1038 MPa but low plasticity(∼5.2%).While the rolling temperature was reduced to 850℃,the specimen exhibited refined prior-β grains,discontinuous grain boundaries and a small amount of equiaxed α grains,which collectively enhanced plasticity(∼12.4%)while preserving yield strength.As the rolling temperature further decreased,the dynamic recrystallization mechanism shifted from the discontinuous dynamic recrystallization(DDRX)to continuous dynamic recrystallization(CDRX).Specimens rolled at 800℃ and 750℃ showed excellent strength-plasticity synergy,with yield strengths of 1070 MPa and 1110 MPa,respectively,and total elongations of 15%and 18%,respectively.The enhanced yield strength is attributed to both fine-grain and sub-grain strengthening.Furthermore,the lower degree of recrystallization in the 750-AC specimen preserved a relatively high dislocation density,offering additional strengthening.The favorable plasticity results from a combination of equiaxedαgrains,“soft”barrier sub-grains,and a small number of twins.Additionally,the 750-AC specimen retained 6.4%of the fine β grains and the weak basal texture.These characteristics contribute to the enhanced plasticity.Therefore,750℃is the optimal rolling temperature for achieving the best strength-plasticity synergy in the hot-rolled TiZrAlMn alloy.These findings demonstrate that selecting the appropriate temperature during thermomechanical processing to optimize recrystallized grains and sub-grain content ensures excellent plasticity at high yield strength.This offers valuable guidance for developing near-α Ti alloys with superior mechanical properties.
