In the present research, semisolid billet of 7005 aluminum alloy was fabricated by using recrystallization and partial remelting（RAP）, then thixoformed at different isothermal temperatures, preheating temperatures a...In the present research, semisolid billet of 7005 aluminum alloy was fabricated by using recrystallization and partial remelting（RAP）, then thixoformed at different isothermal temperatures, preheating temperatures and load routes. Mechanical properties and microstructure of the thixoformed product were investigated. The results showed that microstructure achieved by three-step induction heating warm extruded 7005 aluminum alloy consists of a uniform and spheroidal microstructure suitable for thixoforming.Preheating temperature of the die affected significantly the filling status of semisolid billet of 7005 aluminum alloy. Complete filling status with good surface quality was obtained at a preheating temperature of 365 ℃. Thixoformed microstructures consisting of relatively spheroidal grains illustrate the dependence of filling process on the sliding and rotating of solid grains rather than plastic deformation of solid grains. A non-uniform distribution of liquid phase was found in the different regions of the thixoformed product due to the slower adjustable velocity of solid grains as compared with liquid phase. Increase of isothermal temperatures led to a slight decrease of mechanical properties of the thixoformed product due to coarsening of solid grains. The highest yield strength, ultimate tensile strength and elongation of thixoformed components with T6 heat treatment are 237 MPa, 361 MPa and 16.8%, respectively, which were achieved at the isothermal temperature of 605℃. Load route has a significant effect on mechanical properties and microstructure of the thixoformed product. Defects, such as crack and microporosity occurred in the microstructure of the thixoformed product obtained under load route 2. It led to an obvious reduction of mechanical properties as compared with route 1. A better compatibility of deformation caused by more liquid fraction at the isothermal temperature of 612℃ is beneficial to reducing nonuniformity of liquid phase in the different regions of the thixoformed product.展开更多
Semisolid billet of AZ80 magnesium alloy was prepared by new strain induced melt activated (new SIMA) process and thixoforging experiment was performed.The results show that after as-cast AZ80 magnesium alloy is proce...Semisolid billet of AZ80 magnesium alloy was prepared by new strain induced melt activated (new SIMA) process and thixoforging experiment was performed.The results show that after as-cast AZ80 magnesium alloy is processed by equal channel angular extrusion, microstructure is refined well due to heavy dynamic recrystallization occurring in severe plastic deformation.Compared with semisolid isothermal treatment and conventional SIMA, semisolid billet with fine and spheroidal grains are achieved in new SIMA.Thixoforging process of semisolid billet prepared by new SIMA has many advantages such as good surface quality of final component, high ability to fill cavity and net-shape.The fine and spheroidal grains and high mechanical properties such as tensile strength of 298 MPa and elongation of 28% can be developed in final part thixoforged.展开更多
The experiments for rheologic behaviors of semisolid continuous casting billets of A356 alloy in semisolid state had been carried out with a multifunctional rheometer. The results show that the deformation rate increa...The experiments for rheologic behaviors of semisolid continuous casting billets of A356 alloy in semisolid state had been carried out with a multifunctional rheometer. The results show that the deformation rate increases with loading time, the maximum strain reaches to 120％ (which is one time larger than that of traditional mold casting billet) and the strain can be rapidly eliminated to 10％ after unloading. Moreover, there is a critic stress for billet deformation even in semisolid state, which is named as critic shear stress. This stress increases with the decreasing of heating time. The theologic behaviors can be expressed by five elements mechanical model (H_2- [N_1|H_2]-[N_2|S]) and can be modified with the increasing of heating time.展开更多
基金supported by the National Natural Science Foundation of China(NSFC)under Grant No.51375112Science and Technology Innovation Talents Special Fund of Harbin under Grant No.2015RAQXJ012
文摘In the present research, semisolid billet of 7005 aluminum alloy was fabricated by using recrystallization and partial remelting（RAP）, then thixoformed at different isothermal temperatures, preheating temperatures and load routes. Mechanical properties and microstructure of the thixoformed product were investigated. The results showed that microstructure achieved by three-step induction heating warm extruded 7005 aluminum alloy consists of a uniform and spheroidal microstructure suitable for thixoforming.Preheating temperature of the die affected significantly the filling status of semisolid billet of 7005 aluminum alloy. Complete filling status with good surface quality was obtained at a preheating temperature of 365 ℃. Thixoformed microstructures consisting of relatively spheroidal grains illustrate the dependence of filling process on the sliding and rotating of solid grains rather than plastic deformation of solid grains. A non-uniform distribution of liquid phase was found in the different regions of the thixoformed product due to the slower adjustable velocity of solid grains as compared with liquid phase. Increase of isothermal temperatures led to a slight decrease of mechanical properties of the thixoformed product due to coarsening of solid grains. The highest yield strength, ultimate tensile strength and elongation of thixoformed components with T6 heat treatment are 237 MPa, 361 MPa and 16.8%, respectively, which were achieved at the isothermal temperature of 605℃. Load route has a significant effect on mechanical properties and microstructure of the thixoformed product. Defects, such as crack and microporosity occurred in the microstructure of the thixoformed product obtained under load route 2. It led to an obvious reduction of mechanical properties as compared with route 1. A better compatibility of deformation caused by more liquid fraction at the isothermal temperature of 612℃ is beneficial to reducing nonuniformity of liquid phase in the different regions of the thixoformed product.
基金Project(50605015) supported by the National Natural Science Foundation of ChinaProject(HITQNJS.2008.012) supported by Development Program for Outstanding Young Teachers in Harbin Institute of Technology,China+1 种基金Projects(20090460884,20080440849) supported by China Postdoctoral Science FoundationProject(LBH-Q08104) supported by the Postdoctoral Foundation of Heilongjiang Province,China
文摘Semisolid billet of AZ80 magnesium alloy was prepared by new strain induced melt activated (new SIMA) process and thixoforging experiment was performed.The results show that after as-cast AZ80 magnesium alloy is processed by equal channel angular extrusion, microstructure is refined well due to heavy dynamic recrystallization occurring in severe plastic deformation.Compared with semisolid isothermal treatment and conventional SIMA, semisolid billet with fine and spheroidal grains are achieved in new SIMA.Thixoforging process of semisolid billet prepared by new SIMA has many advantages such as good surface quality of final component, high ability to fill cavity and net-shape.The fine and spheroidal grains and high mechanical properties such as tensile strength of 298 MPa and elongation of 28% can be developed in final part thixoforged.
文摘The experiments for rheologic behaviors of semisolid continuous casting billets of A356 alloy in semisolid state had been carried out with a multifunctional rheometer. The results show that the deformation rate increases with loading time, the maximum strain reaches to 120％ (which is one time larger than that of traditional mold casting billet) and the strain can be rapidly eliminated to 10％ after unloading. Moreover, there is a critic stress for billet deformation even in semisolid state, which is named as critic shear stress. This stress increases with the decreasing of heating time. The theologic behaviors can be expressed by five elements mechanical model (H_2- [N_1|H_2]-[N_2|S]) and can be modified with the increasing of heating time.
