Alloys with large solidification intervals are prone to issues from the disordered growth and defect formation;accordingly, finding ways to effectively optimize the microstructure, further to improve the mechanical pr...Alloys with large solidification intervals are prone to issues from the disordered growth and defect formation;accordingly, finding ways to effectively optimize the microstructure, further to improve the mechanical properties is of great importance. To this end, we couple travelling magnetic fields with sequential solidification to continuously regulate the mushy zones of Al-Cu-based alloys with large solidification intervals. Moreover, we combine experiments with simulations to comprehensively analyze the mechanisms on the optimization of microstructure and properties. Our results indicate that only downward travelling magnetic fields coupled with sequential solidification can obtain the refined and uniform microstructure, and promote the growth of matrix phase -Al along the direction of temperature gradient.Additionally, the secondary dendrites and precipitates are reduced, while the solute partition coefficient and solute solid-solubility are raised. Ultimately, downward travelling magnetic fields can increase the ultimate tensile strength, yield strength, elongation and hardness from 196.2 MPa, 101.2 MPa, 14.5 % and85.1 kg mm-2 without travelling magnetic fields to 224.1 MPa, 114.5 MPa, 17.1 % and 102.1 kg mm-2,and improve the ductility of alloys. However, upward travelling magnetic fields have the adverse effects on microstructural evolution, and lead to a reduction in the performance and ductility. Our findings demonstrate that long-range directional circular flows generated by travelling magnetic fields directionally alter the transformation and redistribution of solutes and temperature, which finally influences the solidification behavior and performance. Overall, our research present not only an innovative method to optimize the microstructures and mechanical properties for alloys with large solidification intervals,but also a detailed mechanism of travelling magnetic fields on this optimization during the sequential solidification.展开更多
Porosity is a major casting defect in alloys with large solidification intervals due to the disordered microstructure and broad mushy zones,which decreases badly the mechanical performance.Hence,finding ways to effect...Porosity is a major casting defect in alloys with large solidification intervals due to the disordered microstructure and broad mushy zones,which decreases badly the mechanical performance.Hence,finding ways to effectively reduce the porosity,further to optimize microstructure and mechanical performance is of great significance.In this regard,the Al-Cu-based alloys with large solidification intervals are continuously processed by coupling the travelling magnetic fields(TMF)with sequential solidification.Additionally,experiments combined with simulations are utilized to comprehensively analyze the mechanism of TMF on the reduction in porosity,including shrinkage porosity and gas porosity,from different perspectives.Current findings determine that downward TMF can effectually optimize together the porosity,microstructure and performance,by inducing the strong long-range directional melt flows,stabilizing the mushy zones,and optimizing the feeding channels and exhaust paths,as well as increasing the driving force of degassing process.Eventually,downward TMF can increase the ultimate tensile strength,yield strength,elongation and hardness from 175.2 MPa,87.5 MPa,13.3%and 80.2 kg mm^(-2) without TMF to 218.6 MPa,109.3 MPa,15.6%and 95.5 kg mm^(-2),while reduce the total porosity from0.95%to 0.18%.However,Up-TMF exerts negative effects on the optimization of porosity,microstructure and performance due to the opposite strong directional magnetic force and melt flows.Overall,our study provides an effective way to optimize together the porosity,microstructure and mechanical performance,and reveals their relationship,as well as details the relevant mechanisms of TMF on the porosity reduction from different perspectives.展开更多
The effects of 1Zn and/or 2Ag additions on the hot tearing susceptibility(HTS)of Mg-14Gd-0.4Zr(wt%)alloy were studied.The HTS was evaluated by both theoretical predictions using Kou's criterion and experimental ob...The effects of 1Zn and/or 2Ag additions on the hot tearing susceptibility(HTS)of Mg-14Gd-0.4Zr(wt%)alloy were studied.The HTS was evaluated by both theoretical predictions using Kou's criterion and experimental observations based on the in situ force-temperature recorded constrained rod casting(ISFTCRC)method.The results show that the order of HTS from high to low is Mg-14Gd-2Ag-1Zn-0.4Zr,Mg-14Gd-2Ag-0.4Zr,Mg-14Gd-1Zn-0.4Zr and Mg-14Gd-0.4Zr.Adding 1Zn and/or 2Ag changes the solidification path and the solidification interval,which affects the hot tearing susceptibility.Alloying elemental 1Zn slightly increases the solidification interval and the temperature range in the square root of the solid phase fraction(f_(s)^(1/2))range of 0.949-0.995,resulting in a slight increase in the hot tearing susceptibility.The addition of 2Ag drastically widens both the solidification interval and the temperature range in the f_(s)^(1/2)range of 0.949-0.995,thus significantly increasing the hot tearing susceptibility.Compared to the addition of 2Ag alone,the broadening degree of both the solidification interval and the temperature range in the f_(s)^(1/2)range of 0.949-0.995 is greater by adding the composite 2Ag/1Zn,which further promotes the occurrence of hot tearing.A narrower solidification interval and a temperature range in the f_(s)^(1/2)range of 0.949-0.995 result in a lower hot tearing susceptibility.展开更多
基金supported by the National Key Research and Development Program of China[2017YFA0403804]National Natural Science Foundation of China[51425402,51671073]。
文摘Alloys with large solidification intervals are prone to issues from the disordered growth and defect formation;accordingly, finding ways to effectively optimize the microstructure, further to improve the mechanical properties is of great importance. To this end, we couple travelling magnetic fields with sequential solidification to continuously regulate the mushy zones of Al-Cu-based alloys with large solidification intervals. Moreover, we combine experiments with simulations to comprehensively analyze the mechanisms on the optimization of microstructure and properties. Our results indicate that only downward travelling magnetic fields coupled with sequential solidification can obtain the refined and uniform microstructure, and promote the growth of matrix phase -Al along the direction of temperature gradient.Additionally, the secondary dendrites and precipitates are reduced, while the solute partition coefficient and solute solid-solubility are raised. Ultimately, downward travelling magnetic fields can increase the ultimate tensile strength, yield strength, elongation and hardness from 196.2 MPa, 101.2 MPa, 14.5 % and85.1 kg mm-2 without travelling magnetic fields to 224.1 MPa, 114.5 MPa, 17.1 % and 102.1 kg mm-2,and improve the ductility of alloys. However, upward travelling magnetic fields have the adverse effects on microstructural evolution, and lead to a reduction in the performance and ductility. Our findings demonstrate that long-range directional circular flows generated by travelling magnetic fields directionally alter the transformation and redistribution of solutes and temperature, which finally influences the solidification behavior and performance. Overall, our research present not only an innovative method to optimize the microstructures and mechanical properties for alloys with large solidification intervals,but also a detailed mechanism of travelling magnetic fields on this optimization during the sequential solidification.
基金supported by the National Key Research and Development Program of China [2017YFA0403804]National Natural Science Foundation of China [51425402,51671073]
文摘Porosity is a major casting defect in alloys with large solidification intervals due to the disordered microstructure and broad mushy zones,which decreases badly the mechanical performance.Hence,finding ways to effectively reduce the porosity,further to optimize microstructure and mechanical performance is of great significance.In this regard,the Al-Cu-based alloys with large solidification intervals are continuously processed by coupling the travelling magnetic fields(TMF)with sequential solidification.Additionally,experiments combined with simulations are utilized to comprehensively analyze the mechanism of TMF on the reduction in porosity,including shrinkage porosity and gas porosity,from different perspectives.Current findings determine that downward TMF can effectually optimize together the porosity,microstructure and performance,by inducing the strong long-range directional melt flows,stabilizing the mushy zones,and optimizing the feeding channels and exhaust paths,as well as increasing the driving force of degassing process.Eventually,downward TMF can increase the ultimate tensile strength,yield strength,elongation and hardness from 175.2 MPa,87.5 MPa,13.3%and 80.2 kg mm^(-2) without TMF to 218.6 MPa,109.3 MPa,15.6%and 95.5 kg mm^(-2),while reduce the total porosity from0.95%to 0.18%.However,Up-TMF exerts negative effects on the optimization of porosity,microstructure and performance due to the opposite strong directional magnetic force and melt flows.Overall,our study provides an effective way to optimize together the porosity,microstructure and mechanical performance,and reveals their relationship,as well as details the relevant mechanisms of TMF on the porosity reduction from different perspectives.
基金Project supported by the National Natural Science Foundation of China(U2037601,52074183)Shanghai Sailing Program(23YF1417100)。
文摘The effects of 1Zn and/or 2Ag additions on the hot tearing susceptibility(HTS)of Mg-14Gd-0.4Zr(wt%)alloy were studied.The HTS was evaluated by both theoretical predictions using Kou's criterion and experimental observations based on the in situ force-temperature recorded constrained rod casting(ISFTCRC)method.The results show that the order of HTS from high to low is Mg-14Gd-2Ag-1Zn-0.4Zr,Mg-14Gd-2Ag-0.4Zr,Mg-14Gd-1Zn-0.4Zr and Mg-14Gd-0.4Zr.Adding 1Zn and/or 2Ag changes the solidification path and the solidification interval,which affects the hot tearing susceptibility.Alloying elemental 1Zn slightly increases the solidification interval and the temperature range in the square root of the solid phase fraction(f_(s)^(1/2))range of 0.949-0.995,resulting in a slight increase in the hot tearing susceptibility.The addition of 2Ag drastically widens both the solidification interval and the temperature range in the f_(s)^(1/2)range of 0.949-0.995,thus significantly increasing the hot tearing susceptibility.Compared to the addition of 2Ag alone,the broadening degree of both the solidification interval and the temperature range in the f_(s)^(1/2)range of 0.949-0.995 is greater by adding the composite 2Ag/1Zn,which further promotes the occurrence of hot tearing.A narrower solidification interval and a temperature range in the f_(s)^(1/2)range of 0.949-0.995 result in a lower hot tearing susceptibility.
