The evolution of the S'precipitate in Al−Cu−Mg alloy was investigated using transmission electron microscopy(TEM),high-angle annular dark-field scanning transmission electron microscopy(HAADF−STEM),molecular dynam...The evolution of the S'precipitate in Al−Cu−Mg alloy was investigated using transmission electron microscopy(TEM),high-angle annular dark-field scanning transmission electron microscopy(HAADF−STEM),molecular dynamics(MD)simulations,and other analytical techniques.The precipitation behavior during different aging stages of the supersaturated solid solution formed after rapid cold punching was focused,which induces rapid dissolution of precipitates.The findings reveal that the precipitation sequence is significantly influenced by aging temperature.At higher aging temperatures,which mitigate lattice distortion in the matrix,the precipitation sequence follows the conventional path.Conversely,at lower aging temperatures,where lattice distortion persists,the sequence deviates,suppressing the formation of Guinier−Preston−Bagaryatsky(GPB)zones.MD simulations confirm that the variations in solute atom diffusion rates at different aging temperatures lead to the differences in the S'phase precipitation sequence.展开更多
X-ray diffraction(XRD),scanning electron microscopy(SEM),energy-dispersive spectroscopy(EDS),electron backscatter diffraction(EBSD),and transmission electron microscopy(TEM)were used to systematically investigate the ...X-ray diffraction(XRD),scanning electron microscopy(SEM),energy-dispersive spectroscopy(EDS),electron backscatter diffraction(EBSD),and transmission electron microscopy(TEM)were used to systematically investigate the impact of rapid cold stamping on microstructural evolution and mechanical properties of spray-formed Al-Zn-Mg-Cu alloys under ambient conditions.The results reveal that the dislocation density increases with successive cold stamping passes,the volume fraction of the secondary phase(Mg(Zn,Cu,Al)_(2))increases from 15.64% to 23.94%,and the average size decreases from 1.41 to 0.75μm.The pinning effect of the secondary phases on dislocations promotes a significant transformation from low-angle grain boundaries to high-angle grain boundaries,resulting in the average grain size decreasing from 5.75 to 0.97μm.The strength and hardness of the samples increase with successive cold stamping passes,which is attributed to the synergistic effects of dislocation strengthening,grain boundary strengthening,and secondary phase strengthening.展开更多
High-resolution transmission electron microscopy(TEM),X-ray diffractometry(XRD),energy dispersive spectroscopy(EDS)and hardness test were used to study the re-dissolution and re-precipitation behavior of nano-precipit...High-resolution transmission electron microscopy(TEM),X-ray diffractometry(XRD),energy dispersive spectroscopy(EDS)and hardness test were used to study the re-dissolution and re-precipitation behavior of nano-precipitates of the spray-formed fine-grained Al-Cu-Mg alloy during rapid cold stamping deformation.Results show that the extruded Al-Cu-Mg alloy undergoes obvious re-dissolution and re-precipitation during the rapid cold-stamping deformation process.The plasticθ′phase has a slower re-dissolution rate than the brittle S′phase.The long strip-shaped S′phases and the acicularθ′phases in Al-Cu-Mg alloy after three passes of cold stamping basically re-dissolved to form a supersaturated solid solution.A large number of fine granular balanceθphases precipitate after four passes of rapid cold-stamping deformation.Rapid cold stamping deformation causes the S′phase andθ′phase to break and promote the nano-precipitate phases to re-dissolve.The high distortion free energy of the matrix promotes the precipitation of the equilibriumθphase,and the hardness of the alloy obviously increases from HB 55 to HB 125 after the rapid cold stamping process.展开更多
High-resolution transmission electron microscopy(TEM),X-ray diffractometer(XRD),and hardness test were used to study the evolution of long plate-shaped S'phase in the spray-formed fine-grained Al−Cu−Mg alloy durin...High-resolution transmission electron microscopy(TEM),X-ray diffractometer(XRD),and hardness test were used to study the evolution of long plate-shaped S'phase in the spray-formed fine-grained Al−Cu−Mg alloy during aging after rapid cold punching deformation.Results show that the long plate-shaped S'phase in the extruded Al−Cu−Mg alloy undergoes evident distortion,brittle failure,separation and redissolution,during rapid cold punching deformation,leading to the transformation of long plate-shaped S'phase into short rod or even redissolution and disappearance,causing the matrix to become a supersaturated solid solution.After the aging treatment,the reprecipitation of the phases occurs,and these aging phases are mainly long plate-shaped and granular.The incompletely dissolved S'phase acts as nucleation core,promoting uphill diffusion of the surrounding solute atoms.The S'phase gradually grows with increasing the aging time.The completely dissolved S'phase forms the incoherent equilibrium phase with the matrix to reduce its free energy.After rapid cold punching,the aging response of the deformed Al−Cu−Mg alloy is accelerated,and the hardness of the alloy is substantially increased.展开更多
The microstructure evolution of spray formed and rapidly solidified Al-Cu-Mg alloy with fine grains during rapid cold punching and recrystallization annealing was investigated by transmission electron microscopy(TEM)....The microstructure evolution of spray formed and rapidly solidified Al-Cu-Mg alloy with fine grains during rapid cold punching and recrystallization annealing was investigated by transmission electron microscopy(TEM). The results show that the precipitates of fine-grained Al-Cu-Mg alloy during rapid cold punching and recrystallization annealing mainly consist of S phase and a small amount of coarse Al6Mn phase. With the increase of deformation passes, the density of precipitates increases, the size of precipitates decreases significantly, and the deformation and transition bands disappear gradually. In addition, the grains are refined and tend to be uniform. Defects introduced by rapid cold punching contribute to the precipitation and recrystallization, and promote nucleation and growth of S phase and recrystallization. Deformation and transition bands in the coarse grains transform into deformation-induced grain boundary during the deformation and recrystallization, which refine grains, obtain uniform nanocrystalline structure and promote homogeneous distribution of S phase.展开更多
Transmission electron microscopy(TEM),X-ray diffraction(XRD),electron backscattered diffraction(EBSD),and tensile tests were used to study the effects of strain rates(0.1,1 and 9.1 s^(-1))on the microstructure and mec...Transmission electron microscopy(TEM),X-ray diffraction(XRD),electron backscattered diffraction(EBSD),and tensile tests were used to study the effects of strain rates(0.1,1 and 9.1 s^(-1))on the microstructure and mechanical properties of spray-formed Al-Cu-Mg alloys during large-strain rolling at 420℃.Results show that during hot rolling,the proportion of high-angle grain boundaries(HAGBs)and the degree of dynamic recrystallization(DRX)initially increase and then decrease,whereas the average grain size and dislocation density show the opposite trend with the increase of the strain rate.In addition,the number of S′phases in the matrix decreases,and the grain boundary precipitates(GBPs)become coarser and more discontinuous as the strain rate increases.When the strain rate increases from 0.1 to 9.1 s^(-1),the tensile strength of the alloy decreases from 492.45 to 427.63 MPa,whereas the elongation initially increases from 12.1%to 21.8%and then decreases to 17.7%.展开更多
The microstructures and interface structures of basalt particle reinforced 7A04 Al matrix composites (BP/7A04 Al) were analyzed by using OM, TEM, SEM and EDS, and the mechanical properties of 7A04 Al alloy were compar...The microstructures and interface structures of basalt particle reinforced 7A04 Al matrix composites (BP/7A04 Al) were analyzed by using OM, TEM, SEM and EDS, and the mechanical properties of 7A04 Al alloy were compared with those of BP/7A04 Al matrix composites. The results show that the basalt particles are dispersed in the Al matrix and form a strong bonding interface with the Al matrix. SiO2 at the edge of the basalt particles is continuously replaced by Al2O3 formed in the reaction, forming a high-temperature reaction layer with a thickness of several tens of nanometers, and Al2O3 strengthens the bonding interface between basalt particles and Al matrix. The dispersed basalt particles promote the dislocation multiplication, vacancy formation and precipitation of the matrix, and the precipitated phases mainly consist of plate-like η(MgZn2) phase and bright white band-shaped or ellipsoidal T (Al2Mg3Zn3) phase. The bonding interface, high dislocation density and dispersion strengthening phase significantly improve the mechanical properties of the composites. The yield strength and ultimate tensile strength of BP/7A04 Al matrix composites are up to 665 and 699 MPa, which increase by 11.4% and 10.9% respectively compared with 7A04 Al alloy without basalt particles.展开更多
The impact of cold rolling deformation,which was introduced after solid solution and before aging treatment,on microstructure evolution and mechanical properties of the as-extruded spray formed Al−9.8Zn−2.3Mg−1.73Cu−0...The impact of cold rolling deformation,which was introduced after solid solution and before aging treatment,on microstructure evolution and mechanical properties of the as-extruded spray formed Al−9.8Zn−2.3Mg−1.73Cu−0.13Cr(wt.%)alloy,was investigated.SEM,TEM,and EBSD were used to analyze the microstructures,and tensile tests were conducted to assess mechanical properties.The results indicate that the D1-T6 sample,subjected to 25%cold rolling deformation,exhibits finer grains(3.35μm)compared to the D0-T6 sample(grain size of 4.23μm)without cold rolling.Cold rolling refines the grains that grow in solution treatment.Due to the combined effects of finer and more dispersed precipitates,higher dislocation density and smaller grains,the yield strength and ultimate tensile strength of the D1-T6 sample can reach 663 and 737 MPa,respectively.In comparison to the as-extruded and D0-T6 samples,the yield strength of the D1-T6 sample increases by 415 and 92 MPa,respectively.展开更多
The flow stress behavior of spray-formed Al-9Mg-1.1Li-0.5Mn alloy was studied using thermal simulation tests on a Gleeble-3500machine over deformation temperature range of300-450℃and strain rate of0.01-10s^-1.The mic...The flow stress behavior of spray-formed Al-9Mg-1.1Li-0.5Mn alloy was studied using thermal simulation tests on a Gleeble-3500machine over deformation temperature range of300-450℃and strain rate of0.01-10s^-1.The microstructural evolution of the alloy during the hot compression process was characterized by transmission electron microscopy(TEM)and electron back scatter diffractometry(EBSD).The results show that the flow stress behavior and microstructural evolution are sensitive to deformation parameters.The peak stress level,steady flow stress,dislocation density and amount of substructures of the alloy increase with decreasing deformation temperature and increasing strain rate.Conversely,the high angle grain boundary area increases,the grain boundary is in serrated shape and the dynamic recrystallization in the alloy occurs.The microstructure of the alloy is fibrous-like and the main softening mechanism is dynamic recovery during steady deformation state.The flow stress behavior can be represented by the Zener-Hollomon parameter Z in the hyperbolic sine equation with the hot deformation activation energy of184.2538kJ/mol.The constitutive equation and the hot processing map were established.The hot processing map exhibits that the optimum processing conditions for Al-9Mg-1.1Li-0.5Mn alloy are in deformation temperature range from380to450℃and strain rate range from0.01to0.1s^-1.展开更多
High-angle annular dark-field scanning transmission electron microscopy and selected area electron diffraction techniques were used to study the mechanism that underlies the influence of rapid cold-stamping deformatio...High-angle annular dark-field scanning transmission electron microscopy and selected area electron diffraction techniques were used to study the mechanism that underlies the influence of rapid cold-stamping deformation on the fracture behavior of the elongated nanoprecipitated phase in extruded Al−Cu−Mg alloy.Results show that the interface between the long strip-shaped S′phase and the aluminum matrix in the extruded Al−Cu−Mg alloy is flat and breaks during rapid cold-stamping deformation.The breaking mechanisms are distortion and brittle failure,redissolution,and necking.The breakage of the long strip S′phase increases the contact surface between the S′phase and the aluminum matrix and improves the interfacial distortion energy.This effect accounts for the higher free energy of the S′phase than that of the matrix and creates conditions for the redissolution of solute atoms back into the aluminum matrix.The brittle S′phase produces a resolved step during rapid cold-stamping deformation.This step further accelerates the diffusion of solute atoms and promotes the redissolution of the S′phase.Thus,the S′phase necks and separates,and the long strip-shaped S′phase in the extruded Al−Cu−Mg alloy is broken into a short and thin S′phase.展开更多
基金supported by the China Scholarship Council (CSC) Local Cooperation Program (No. 202308430176)the National Natural Science Foundation of China (No. 52271177)the Hunan Provincial Natural Science Foundation Regional Joint Fund, China (No. 2023JJ50173)。
文摘The evolution of the S'precipitate in Al−Cu−Mg alloy was investigated using transmission electron microscopy(TEM),high-angle annular dark-field scanning transmission electron microscopy(HAADF−STEM),molecular dynamics(MD)simulations,and other analytical techniques.The precipitation behavior during different aging stages of the supersaturated solid solution formed after rapid cold punching was focused,which induces rapid dissolution of precipitates.The findings reveal that the precipitation sequence is significantly influenced by aging temperature.At higher aging temperatures,which mitigate lattice distortion in the matrix,the precipitation sequence follows the conventional path.Conversely,at lower aging temperatures,where lattice distortion persists,the sequence deviates,suppressing the formation of Guinier−Preston−Bagaryatsky(GPB)zones.MD simulations confirm that the variations in solute atom diffusion rates at different aging temperatures lead to the differences in the S'phase precipitation sequence.
基金supported by the National Natural Science Foundation of China(No.52271177).
文摘X-ray diffraction(XRD),scanning electron microscopy(SEM),energy-dispersive spectroscopy(EDS),electron backscatter diffraction(EBSD),and transmission electron microscopy(TEM)were used to systematically investigate the impact of rapid cold stamping on microstructural evolution and mechanical properties of spray-formed Al-Zn-Mg-Cu alloys under ambient conditions.The results reveal that the dislocation density increases with successive cold stamping passes,the volume fraction of the secondary phase(Mg(Zn,Cu,Al)_(2))increases from 15.64% to 23.94%,and the average size decreases from 1.41 to 0.75μm.The pinning effect of the secondary phases on dislocations promotes a significant transformation from low-angle grain boundaries to high-angle grain boundaries,resulting in the average grain size decreasing from 5.75 to 0.97μm.The strength and hardness of the samples increase with successive cold stamping passes,which is attributed to the synergistic effects of dislocation strengthening,grain boundary strengthening,and secondary phase strengthening.
基金financially supported by the Major Special Projects in Anhui Province,China(No.202003c08020005)the Key Projects in Hunan Province,China(No.2020GK2045)+1 种基金the Science and Technology Innovation Program of Hunan Province,China(No.2021RC4036)Postgraduate Scientific Research Innovation Project of Hunan Province,China(No.CX20211079)。
基金Project(2019JJ60050) supported by the Natural Science Foundation of Hunan Province,China
文摘High-resolution transmission electron microscopy(TEM),X-ray diffractometry(XRD),energy dispersive spectroscopy(EDS)and hardness test were used to study the re-dissolution and re-precipitation behavior of nano-precipitates of the spray-formed fine-grained Al-Cu-Mg alloy during rapid cold stamping deformation.Results show that the extruded Al-Cu-Mg alloy undergoes obvious re-dissolution and re-precipitation during the rapid cold-stamping deformation process.The plasticθ′phase has a slower re-dissolution rate than the brittle S′phase.The long strip-shaped S′phases and the acicularθ′phases in Al-Cu-Mg alloy after three passes of cold stamping basically re-dissolved to form a supersaturated solid solution.A large number of fine granular balanceθphases precipitate after four passes of rapid cold-stamping deformation.Rapid cold stamping deformation causes the S′phase andθ′phase to break and promote the nano-precipitate phases to re-dissolve.The high distortion free energy of the matrix promotes the precipitation of the equilibriumθphase,and the hardness of the alloy obviously increases from HB 55 to HB 125 after the rapid cold stamping process.
基金financially supported by the Major Special Projects in Anhui Province,China(No.202003c08020005)the Key Projects in Hunan Province,China(No.2020GK2045).
文摘High-resolution transmission electron microscopy(TEM),X-ray diffractometer(XRD),and hardness test were used to study the evolution of long plate-shaped S'phase in the spray-formed fine-grained Al−Cu−Mg alloy during aging after rapid cold punching deformation.Results show that the long plate-shaped S'phase in the extruded Al−Cu−Mg alloy undergoes evident distortion,brittle failure,separation and redissolution,during rapid cold punching deformation,leading to the transformation of long plate-shaped S'phase into short rod or even redissolution and disappearance,causing the matrix to become a supersaturated solid solution.After the aging treatment,the reprecipitation of the phases occurs,and these aging phases are mainly long plate-shaped and granular.The incompletely dissolved S'phase acts as nucleation core,promoting uphill diffusion of the surrounding solute atoms.The S'phase gradually grows with increasing the aging time.The completely dissolved S'phase forms the incoherent equilibrium phase with the matrix to reduce its free energy.After rapid cold punching,the aging response of the deformed Al−Cu−Mg alloy is accelerated,and the hardness of the alloy is substantially increased.
基金Project(2019JJ60050)supported by the Natural Science Foundation of Hunan Province,China
文摘The microstructure evolution of spray formed and rapidly solidified Al-Cu-Mg alloy with fine grains during rapid cold punching and recrystallization annealing was investigated by transmission electron microscopy(TEM). The results show that the precipitates of fine-grained Al-Cu-Mg alloy during rapid cold punching and recrystallization annealing mainly consist of S phase and a small amount of coarse Al6Mn phase. With the increase of deformation passes, the density of precipitates increases, the size of precipitates decreases significantly, and the deformation and transition bands disappear gradually. In addition, the grains are refined and tend to be uniform. Defects introduced by rapid cold punching contribute to the precipitation and recrystallization, and promote nucleation and growth of S phase and recrystallization. Deformation and transition bands in the coarse grains transform into deformation-induced grain boundary during the deformation and recrystallization, which refine grains, obtain uniform nanocrystalline structure and promote homogeneous distribution of S phase.
基金financially supported by the Major Special Projects in Anhui Province,China(No.202003c08020005)the Key Projects in Hunan Province,China(No.2020GK2045)。
文摘Transmission electron microscopy(TEM),X-ray diffraction(XRD),electron backscattered diffraction(EBSD),and tensile tests were used to study the effects of strain rates(0.1,1 and 9.1 s^(-1))on the microstructure and mechanical properties of spray-formed Al-Cu-Mg alloys during large-strain rolling at 420℃.Results show that during hot rolling,the proportion of high-angle grain boundaries(HAGBs)and the degree of dynamic recrystallization(DRX)initially increase and then decrease,whereas the average grain size and dislocation density show the opposite trend with the increase of the strain rate.In addition,the number of S′phases in the matrix decreases,and the grain boundary precipitates(GBPs)become coarser and more discontinuous as the strain rate increases.When the strain rate increases from 0.1 to 9.1 s^(-1),the tensile strength of the alloy decreases from 492.45 to 427.63 MPa,whereas the elongation initially increases from 12.1%to 21.8%and then decreases to 17.7%.
基金Projects(2019JJ60050,2018JJ3121) supported by the Natural Science Foundation of Hunan Province,ChinaProject(KFBM20170004) supported by the Jiangsu Province Key Laboratory of Materials Surface Science and Technology,China
文摘The microstructures and interface structures of basalt particle reinforced 7A04 Al matrix composites (BP/7A04 Al) were analyzed by using OM, TEM, SEM and EDS, and the mechanical properties of 7A04 Al alloy were compared with those of BP/7A04 Al matrix composites. The results show that the basalt particles are dispersed in the Al matrix and form a strong bonding interface with the Al matrix. SiO2 at the edge of the basalt particles is continuously replaced by Al2O3 formed in the reaction, forming a high-temperature reaction layer with a thickness of several tens of nanometers, and Al2O3 strengthens the bonding interface between basalt particles and Al matrix. The dispersed basalt particles promote the dislocation multiplication, vacancy formation and precipitation of the matrix, and the precipitated phases mainly consist of plate-like η(MgZn2) phase and bright white band-shaped or ellipsoidal T (Al2Mg3Zn3) phase. The bonding interface, high dislocation density and dispersion strengthening phase significantly improve the mechanical properties of the composites. The yield strength and ultimate tensile strength of BP/7A04 Al matrix composites are up to 665 and 699 MPa, which increase by 11.4% and 10.9% respectively compared with 7A04 Al alloy without basalt particles.
基金the support from the National Natural Science Foundation of China(No.52271177)the Science and Technology Innovation Leaders Projects in Hunan Province,China(No.2021RC4036).
文摘The impact of cold rolling deformation,which was introduced after solid solution and before aging treatment,on microstructure evolution and mechanical properties of the as-extruded spray formed Al−9.8Zn−2.3Mg−1.73Cu−0.13Cr(wt.%)alloy,was investigated.SEM,TEM,and EBSD were used to analyze the microstructures,and tensile tests were conducted to assess mechanical properties.The results indicate that the D1-T6 sample,subjected to 25%cold rolling deformation,exhibits finer grains(3.35μm)compared to the D0-T6 sample(grain size of 4.23μm)without cold rolling.Cold rolling refines the grains that grow in solution treatment.Due to the combined effects of finer and more dispersed precipitates,higher dislocation density and smaller grains,the yield strength and ultimate tensile strength of the D1-T6 sample can reach 663 and 737 MPa,respectively.In comparison to the as-extruded and D0-T6 samples,the yield strength of the D1-T6 sample increases by 415 and 92 MPa,respectively.
基金Project (2017JJ2073) supported by the Natural Science Foundation of Hunan Province,China
文摘The flow stress behavior of spray-formed Al-9Mg-1.1Li-0.5Mn alloy was studied using thermal simulation tests on a Gleeble-3500machine over deformation temperature range of300-450℃and strain rate of0.01-10s^-1.The microstructural evolution of the alloy during the hot compression process was characterized by transmission electron microscopy(TEM)and electron back scatter diffractometry(EBSD).The results show that the flow stress behavior and microstructural evolution are sensitive to deformation parameters.The peak stress level,steady flow stress,dislocation density and amount of substructures of the alloy increase with decreasing deformation temperature and increasing strain rate.Conversely,the high angle grain boundary area increases,the grain boundary is in serrated shape and the dynamic recrystallization in the alloy occurs.The microstructure of the alloy is fibrous-like and the main softening mechanism is dynamic recovery during steady deformation state.The flow stress behavior can be represented by the Zener-Hollomon parameter Z in the hyperbolic sine equation with the hot deformation activation energy of184.2538kJ/mol.The constitutive equation and the hot processing map were established.The hot processing map exhibits that the optimum processing conditions for Al-9Mg-1.1Li-0.5Mn alloy are in deformation temperature range from380to450℃and strain rate range from0.01to0.1s^-1.
基金Project(19A131)supported by Key Scientific Research Project of Hunan Province,ChinaProject(2019JJ60050)supported by the Natural Science Foundation of Hunan Province,China。
文摘High-angle annular dark-field scanning transmission electron microscopy and selected area electron diffraction techniques were used to study the mechanism that underlies the influence of rapid cold-stamping deformation on the fracture behavior of the elongated nanoprecipitated phase in extruded Al−Cu−Mg alloy.Results show that the interface between the long strip-shaped S′phase and the aluminum matrix in the extruded Al−Cu−Mg alloy is flat and breaks during rapid cold-stamping deformation.The breaking mechanisms are distortion and brittle failure,redissolution,and necking.The breakage of the long strip S′phase increases the contact surface between the S′phase and the aluminum matrix and improves the interfacial distortion energy.This effect accounts for the higher free energy of the S′phase than that of the matrix and creates conditions for the redissolution of solute atoms back into the aluminum matrix.The brittle S′phase produces a resolved step during rapid cold-stamping deformation.This step further accelerates the diffusion of solute atoms and promotes the redissolution of the S′phase.Thus,the S′phase necks and separates,and the long strip-shaped S′phase in the extruded Al−Cu−Mg alloy is broken into a short and thin S′phase.
