The metastable β' phase is often the most effective hardening precipitate in Mg-Gd based alloys.In this paper,the structural,elastic and electronic properties of the recently identified β'-Mg7Gd precipitate ...The metastable β' phase is often the most effective hardening precipitate in Mg-Gd based alloys.In this paper,the structural,elastic and electronic properties of the recently identified β'-Mg7Gd precipitate in Mg-Gd binary alloys were investigated using first-principles calculations based on density functional theory.The lattice mismatches between the coherent β'-Mg7Gd precipitate and α-Mg matrix are discussed and used to rationalize the experimentally observed morphology of the precipitate.The mechanical properties were investigated through analysis of the single-crystal elastic constants and the polycrystalline elastic moduli.It is found that β'-Mg7Gd is brittle in nature.Strong covalent bonding in β'-Mg7Gd,as inferred from its electronic structure,further explains its mechanical properties.Our theoretical results show good agreement with experimental measurements.展开更多
AA6005 A-T6 aluminum hollow extrusions were friction stir welded at a fixed high welding speed of 2000 mm/min and various rotation speeds.The results showed that the heat-aff ected zone(HAZ)retained the similar grain ...AA6005 A-T6 aluminum hollow extrusions were friction stir welded at a fixed high welding speed of 2000 mm/min and various rotation speeds.The results showed that the heat-aff ected zone(HAZ)retained the similar grain structure as the base material except some grain coarsening,and the density of dislocations andβ′precipitates were almost unchanged,indicating that the high welding speed inhibited the coarsening and dissolution ofβ″precipitates via fast cooling rate.The thermo-mechanically aff ected zone(TMAZ)was characterized by elongated and rotated grains,in which a low density ofβ′precipitates and the highest density of dislocations were observed.The highest heat input and severest plastic deformation occurring in the nugget zone(NZ)resulted in the occurrence of dynamic recrystallization and a high density of dislocations.Hence,all theβ″precipitates and most of theβ′precipitates dissolved into the matrix,and a fewβ′precipitates were transformed intoβprecipitates.The microhardness was controlled by the precipitation and solution strengthening in the HAZ,by the dislocation and precipitation strengthening in the TMAZ,and by the fine-grain and dislocation strengthening in the NZ.With the increase in rotation speed,the peak and the lowest microhardness value increased monotonously.展开更多
基金supported by the National Basic Research Program of China(2007CB613704)the National Natural Science Foundation of China(50874100)
文摘The metastable β' phase is often the most effective hardening precipitate in Mg-Gd based alloys.In this paper,the structural,elastic and electronic properties of the recently identified β'-Mg7Gd precipitate in Mg-Gd binary alloys were investigated using first-principles calculations based on density functional theory.The lattice mismatches between the coherent β'-Mg7Gd precipitate and α-Mg matrix are discussed and used to rationalize the experimentally observed morphology of the precipitate.The mechanical properties were investigated through analysis of the single-crystal elastic constants and the polycrystalline elastic moduli.It is found that β'-Mg7Gd is brittle in nature.Strong covalent bonding in β'-Mg7Gd,as inferred from its electronic structure,further explains its mechanical properties.Our theoretical results show good agreement with experimental measurements.
基金supported by the National Natural Science Foundation of China(Nos.51435004,51175117,U1404502)the National Science and Technology Major Project of China(No.2010ZX04007-011).
文摘AA6005 A-T6 aluminum hollow extrusions were friction stir welded at a fixed high welding speed of 2000 mm/min and various rotation speeds.The results showed that the heat-aff ected zone(HAZ)retained the similar grain structure as the base material except some grain coarsening,and the density of dislocations andβ′precipitates were almost unchanged,indicating that the high welding speed inhibited the coarsening and dissolution ofβ″precipitates via fast cooling rate.The thermo-mechanically aff ected zone(TMAZ)was characterized by elongated and rotated grains,in which a low density ofβ′precipitates and the highest density of dislocations were observed.The highest heat input and severest plastic deformation occurring in the nugget zone(NZ)resulted in the occurrence of dynamic recrystallization and a high density of dislocations.Hence,all theβ″precipitates and most of theβ′precipitates dissolved into the matrix,and a fewβ′precipitates were transformed intoβprecipitates.The microhardness was controlled by the precipitation and solution strengthening in the HAZ,by the dislocation and precipitation strengthening in the TMAZ,and by the fine-grain and dislocation strengthening in the NZ.With the increase in rotation speed,the peak and the lowest microhardness value increased monotonously.
