Regulating the precipitation behavior of Mg alloys to overcome the strength-ductility trade-off puzzle is a long-thought pursuit in the materials community.With this purpose,external stress has been recently applied d...Regulating the precipitation behavior of Mg alloys to overcome the strength-ductility trade-off puzzle is a long-thought pursuit in the materials community.With this purpose,external stress has been recently applied during aging and shows immense potential in affecting atomic diffusion,and regulating the coherence of the phase boundaries.In this study,elastic tensile(TSA)and compressive stress aging(CSA)of Mg-1.1Gd-0.6Zn-0.3Mn alloy are carried out and the competition of precipitation between multiple precipitates occurs during stress aging.A significant quantity ofβ’precipitates primarily distribute along grain boundaries in conventional peak aging alloy.Whereas high density ofγ’phases rather thanβ’phase precipitate in both TSA and CSA alloys.The first-principle calculations reveal that the application of external stress introduces shear strain,which decreases unstable stacking fault energies,and thereby promoting the precipitation ofγ’phase and impeding the precipitation ofβ’phase.Furthermore,the sequential transformation fromγ’phase to Long Period Stacking Ordered(LPSO)phase occurs in CSA sample,due to the release of elastic local strain at phase boundaries.After subjected to TSA treatment,the sample possesses an ultimate tensile strength of 356 MPa,a yield strength of 294 MPa,and a total elongation of~14.3%.The excellent strength-ductility synergy of TSA sample is primarily contributed to the profuseγ’precipitates hindering the motion of large number of pyramidal(c+a) dislocations during tensile deformation.This study offers new insights on regulating the precipitation behavior of Mg alloys containing multiple types of precipitates through the application of external stress,and extends the potential window for obtaining an excellent strength-ductility synergy in age-hardenable Mg alloys.展开更多
Abrupt near-surface temperature changes in mountainous areas are a special component of the mountain climate system.Fast and accurate measurements of the locations,intensity,and width of the near-surface changes are n...Abrupt near-surface temperature changes in mountainous areas are a special component of the mountain climate system.Fast and accurate measurements of the locations,intensity,and width of the near-surface changes are necessary but highly difficult due to the complicated environmental conditions and instrumental issues.This paper develops a spatial pattern recognition method to measure the near-surface high temperature increase(NSHTI),one of the lesser-attended changes.First,raster window measurement was proposed to calculate the temperature lapse rate using MODIS land surface temperature and SRTM DEM data.It fully considers the terrain heights of two neighboring cells on opposite or adjacent slopes with a moving window of 3×3 cell size.Second,a threshold selection was performed to identify the NSHTI cells using a threshold of-0.65℃/100 m.Then,the NSHTI strips were parameterized through raster vectorization and spatial analysis.Taking Yunnan,a mountainous province in southwestern China,as the study area,the results indicate that the NSHTI cells concentrate in a strip-like pattern along the mountains and valleys,and the strips are almost parallel to the altitude contours with a slight northward uplift.Also,they are located mostly at a 3/5 height of high mountains or within 400 m from the valley floors,where the controlling topographic index is the altitude of the terrain trend surface but not the absolute elevation and the topographic uplift height and cutting depth.Additionally,the NSHTI intensity varies with the geographic locations and the proportions increase with an exponential trend,and the horizontal width has a mean of about 1000 m and a maximum of over 5000 m.The result demonstrates that the proposed method can effectively recognize NSHTI boundaries over mountains,providing support for the modeling of weather and climate systems and the development of mountain resources.展开更多
基金the financial supports from the University Natural Science Research Project of Anhui Province(No.2022AH050316)the National Natural Science Foundation of China,China(No.51901144)the Anhui Provincial Natural Science Foundation,China(No.2108085QE185)。
文摘Regulating the precipitation behavior of Mg alloys to overcome the strength-ductility trade-off puzzle is a long-thought pursuit in the materials community.With this purpose,external stress has been recently applied during aging and shows immense potential in affecting atomic diffusion,and regulating the coherence of the phase boundaries.In this study,elastic tensile(TSA)and compressive stress aging(CSA)of Mg-1.1Gd-0.6Zn-0.3Mn alloy are carried out and the competition of precipitation between multiple precipitates occurs during stress aging.A significant quantity ofβ’precipitates primarily distribute along grain boundaries in conventional peak aging alloy.Whereas high density ofγ’phases rather thanβ’phase precipitate in both TSA and CSA alloys.The first-principle calculations reveal that the application of external stress introduces shear strain,which decreases unstable stacking fault energies,and thereby promoting the precipitation ofγ’phase and impeding the precipitation ofβ’phase.Furthermore,the sequential transformation fromγ’phase to Long Period Stacking Ordered(LPSO)phase occurs in CSA sample,due to the release of elastic local strain at phase boundaries.After subjected to TSA treatment,the sample possesses an ultimate tensile strength of 356 MPa,a yield strength of 294 MPa,and a total elongation of~14.3%.The excellent strength-ductility synergy of TSA sample is primarily contributed to the profuseγ’precipitates hindering the motion of large number of pyramidal(c+a) dislocations during tensile deformation.This study offers new insights on regulating the precipitation behavior of Mg alloys containing multiple types of precipitates through the application of external stress,and extends the potential window for obtaining an excellent strength-ductility synergy in age-hardenable Mg alloys.
基金supported by the National Natural Science Foundation of China (Grant No. 42061004)the Joint Special Project of Agricultural Basic Research of Yunnan Province (Grant No. 202101BD070001093)the Youth Special Project of Xingdian Talent Support Program of Yunnan Province
文摘Abrupt near-surface temperature changes in mountainous areas are a special component of the mountain climate system.Fast and accurate measurements of the locations,intensity,and width of the near-surface changes are necessary but highly difficult due to the complicated environmental conditions and instrumental issues.This paper develops a spatial pattern recognition method to measure the near-surface high temperature increase(NSHTI),one of the lesser-attended changes.First,raster window measurement was proposed to calculate the temperature lapse rate using MODIS land surface temperature and SRTM DEM data.It fully considers the terrain heights of two neighboring cells on opposite or adjacent slopes with a moving window of 3×3 cell size.Second,a threshold selection was performed to identify the NSHTI cells using a threshold of-0.65℃/100 m.Then,the NSHTI strips were parameterized through raster vectorization and spatial analysis.Taking Yunnan,a mountainous province in southwestern China,as the study area,the results indicate that the NSHTI cells concentrate in a strip-like pattern along the mountains and valleys,and the strips are almost parallel to the altitude contours with a slight northward uplift.Also,they are located mostly at a 3/5 height of high mountains or within 400 m from the valley floors,where the controlling topographic index is the altitude of the terrain trend surface but not the absolute elevation and the topographic uplift height and cutting depth.Additionally,the NSHTI intensity varies with the geographic locations and the proportions increase with an exponential trend,and the horizontal width has a mean of about 1000 m and a maximum of over 5000 m.The result demonstrates that the proposed method can effectively recognize NSHTI boundaries over mountains,providing support for the modeling of weather and climate systems and the development of mountain resources.
