The quenching sensitivity of AA7136 alloy was investigated by time−temperature−property(TTP)diagrams,and the heterogeneous precipitation behavior during isothermal holding was investigated using scanning electron micr...The quenching sensitivity of AA7136 alloy was investigated by time−temperature−property(TTP)diagrams,and the heterogeneous precipitation behavior during isothermal holding was investigated using scanning electron microscopy,scanning transmission electron microscopy and high resolution transmission electron microscopy.Based on 99.5%TTP diagram,the nose temperature is determined to be about 346℃ with the transformation time of about 0.245 s.The precipitation ofη(MgZn_(2)),T(Al_(2)Zn_(3)Mg_(3)),S(Al_(2)CuMg)or Cu−Zn-rich Y phases can be found depending on isothermal holding temperature and time,and it is described in a time−temperature−precipitation diagram.The size and area fraction of isothermal holding induced phase particles increase,which results in the decrease of hardness of samples after aging.The quantitative contribution to loss of hardness by grain boundaries/subgrain boundaries and dispersoids in the matrix is discussed based on the amount of heterogeneous precipitation related to them.展开更多
Precipitation during the industrial cool down takes place predominantly above 300 °C in the EN AW 6082 and 6005 alloys. The phase precipitation throughout cooling is equilibrium phase. A considerable capacity is ...Precipitation during the industrial cool down takes place predominantly above 300 °C in the EN AW 6082 and 6005 alloys. The phase precipitation throughout cooling is equilibrium phase. A considerable capacity is retained after the cool down for further precipitation during a subsequent heating cycle. The β-Mg 2 Si is once again the predominant phase that forms during a scan heating cycle employed in exactly the same manner with the industrial billet preheating operation. The precipitation in the 6060 alloy, on the other hand, occurs predominantly below 300 °C with additionally ′-Mg 2 Si particles formed below 200 °C.展开更多
An Al-Mn-Fe-Si model alloy was subjected to two homogenization treatments, to achieve materials with different levels of Mn in solid solution and dispersoid densities, followed by cold rolling and back-annealing. Char...An Al-Mn-Fe-Si model alloy was subjected to two homogenization treatments, to achieve materials with different levels of Mn in solid solution and dispersoid densities, followed by cold rolling and back-annealing. Characterization of homogenization and deformation structures with respect to the effect of different microchemistries and strains on the structures was performed. Time-temperature-transformation （TTT） diagram with respect to precipitation and recrystallisation as a basis for analysis of the degree of concurrent precipitation was established. The TTT-diagram shows a strong effect of Mn concentration in solid solution and dispersoid density on the softening behavior. Recrystallization which finishes without the effect of concurrent precipitation results in an even, fine and equiaxed grain structure. Precipitation prior to or during recrystallization （concurrent） does retard the softening kinetics and leads to a coarse grain structure. However, the effect also depends on the duration of recrystallization and amount of precipitation. Recrystallization proceeding over a long time combined with a large amount of concurrent precipitation has a strong effect, otherwise the effect will be limited. Pre-existing fine and dense dispersoids （mean size 0.1 μm） before back-annealing do also lead to a coarse grain structure after recrystallization no matter whether additional concurrent precipitation occurs.展开更多
Creep ageing forming(CAF)has been widely used in the aerospace engineering,but how to optimize the processing conditions,especially under complex stress state of the CAF process for large-size components produced by f...Creep ageing forming(CAF)has been widely used in the aerospace engineering,but how to optimize the processing conditions,especially under complex stress state of the CAF process for large-size components produced by friction-stir welding is still a great challenge to now.In this work,the creep ageing behaviors and underlying microstructure evolution of a thick friction-stir welded Al-Cu alloy plate after CAF process under different stress levels are systematically investigated.The creep strain and the strength of the joint are both significantly increased when the stress is close to the average yield strength of the initial weld joint.The grain size reduces while the local strain and dislocation density increase from top to bottom of the NZ;hence,the bottom layer of the weld joint exhibits higher creep strain and steady-stage creep strain rate during the CAF process.The results reveal that the gradient microstructures sensitive to the stress level effectively govern the creep-ageing performance from the upper to the bottom layer in a thick friction stir welded Al-Cu alloy plate.Rationally increasing the initial dislocation density of the weld joint can both enhance the tensile properties and promote the creep deformation of the weld joint for CAF process.展开更多
基金financial supports from the National Key Research and Development Program of China (No. 2016YFB0300901)the Scientific Research Project of Inner Mongolia Colleges and Universities, China (No. NJZY21092)。
文摘The quenching sensitivity of AA7136 alloy was investigated by time−temperature−property(TTP)diagrams,and the heterogeneous precipitation behavior during isothermal holding was investigated using scanning electron microscopy,scanning transmission electron microscopy and high resolution transmission electron microscopy.Based on 99.5%TTP diagram,the nose temperature is determined to be about 346℃ with the transformation time of about 0.245 s.The precipitation ofη(MgZn_(2)),T(Al_(2)Zn_(3)Mg_(3)),S(Al_(2)CuMg)or Cu−Zn-rich Y phases can be found depending on isothermal holding temperature and time,and it is described in a time−temperature−precipitation diagram.The size and area fraction of isothermal holding induced phase particles increase,which results in the decrease of hardness of samples after aging.The quantitative contribution to loss of hardness by grain boundaries/subgrain boundaries and dispersoids in the matrix is discussed based on the amount of heterogeneous precipitation related to them.
文摘Precipitation during the industrial cool down takes place predominantly above 300 °C in the EN AW 6082 and 6005 alloys. The phase precipitation throughout cooling is equilibrium phase. A considerable capacity is retained after the cool down for further precipitation during a subsequent heating cycle. The β-Mg 2 Si is once again the predominant phase that forms during a scan heating cycle employed in exactly the same manner with the industrial billet preheating operation. The precipitation in the 6060 alloy, on the other hand, occurs predominantly below 300 °C with additionally ′-Mg 2 Si particles formed below 200 °C.
基金Project (KMB:193179/I40) supported by the Research Council of Norway
文摘An Al-Mn-Fe-Si model alloy was subjected to two homogenization treatments, to achieve materials with different levels of Mn in solid solution and dispersoid densities, followed by cold rolling and back-annealing. Characterization of homogenization and deformation structures with respect to the effect of different microchemistries and strains on the structures was performed. Time-temperature-transformation （TTT） diagram with respect to precipitation and recrystallisation as a basis for analysis of the degree of concurrent precipitation was established. The TTT-diagram shows a strong effect of Mn concentration in solid solution and dispersoid density on the softening behavior. Recrystallization which finishes without the effect of concurrent precipitation results in an even, fine and equiaxed grain structure. Precipitation prior to or during recrystallization （concurrent） does retard the softening kinetics and leads to a coarse grain structure. However, the effect also depends on the duration of recrystallization and amount of precipitation. Recrystallization proceeding over a long time combined with a large amount of concurrent precipitation has a strong effect, otherwise the effect will be limited. Pre-existing fine and dense dispersoids （mean size 0.1 μm） before back-annealing do also lead to a coarse grain structure after recrystallization no matter whether additional concurrent precipitation occurs.
基金Project(2021YFB3400903) supported by the National Key R&D Program of ChinaProject(1053320211480) supported by the Science and Technology Innovation Project of Graduate Students of Central South University,China。
文摘Creep ageing forming(CAF)has been widely used in the aerospace engineering,but how to optimize the processing conditions,especially under complex stress state of the CAF process for large-size components produced by friction-stir welding is still a great challenge to now.In this work,the creep ageing behaviors and underlying microstructure evolution of a thick friction-stir welded Al-Cu alloy plate after CAF process under different stress levels are systematically investigated.The creep strain and the strength of the joint are both significantly increased when the stress is close to the average yield strength of the initial weld joint.The grain size reduces while the local strain and dislocation density increase from top to bottom of the NZ;hence,the bottom layer of the weld joint exhibits higher creep strain and steady-stage creep strain rate during the CAF process.The results reveal that the gradient microstructures sensitive to the stress level effectively govern the creep-ageing performance from the upper to the bottom layer in a thick friction stir welded Al-Cu alloy plate.Rationally increasing the initial dislocation density of the weld joint can both enhance the tensile properties and promote the creep deformation of the weld joint for CAF process.
