The flow stress behavior and microstructure development of Al-5Zn-2Mg （7005） aluminum alloy were studied by hot compression tests at deformation temperatures between 300-500 ＆#176;C and strain rates between 0.05-50...The flow stress behavior and microstructure development of Al-5Zn-2Mg （7005） aluminum alloy were studied by hot compression tests at deformation temperatures between 300-500 ＆#176;C and strain rates between 0.05-50 s-1. The deformed structures of the samples were observed by optical microscopy （OM）, transmission electron microscopy （TEM） and electron backscattering diffraction （EBSD） analysis. The calculated activation energy is 147 kJ/mol, which is very close to the activation energy for lattice self-diffusion in aluminum （142 kJ/mol）. Dynamic recovery is the dominant restoration mechanism during the deformation. At high strain rate of 50 s-1, temperature rise due to deformation heating leads to a significant flow softening. Microstructure observations indicated that the remaining softening after deformation heating correction at high strain rate and the softening observed at high temperature are associated with grain coarsening induced by grain boundary migration during dynamic recovery process.展开更多
Strengthening of aluminium alloys 7xxx through the imposition of severe plastic deformation supplemented by ageing treatments is a challenge due to the limited workability of these alloys in cold deformation regimes.T...Strengthening of aluminium alloys 7xxx through the imposition of severe plastic deformation supplemented by ageing treatments is a challenge due to the limited workability of these alloys in cold deformation regimes.This study aims to comprehensively investigate the strengthening of aluminium alloy 7005 through the imposition of severe plastic deformation supplemented by two different ageing treatments:pre-deformation artificial ageing or postdeformation natural ageing.For this purpose,microstructure evolutions of the alloy processed through mentioned procedures were studied using X-ray diffraction and scanning electron microscopy while the alloy strengthening was evaluated using Vickers hardness measurement.Results show that a superlative strengthening is obtained through the imposition of severe plastic deformation supplemented by post-deformation natural ageing.For instance,the yield strength of the alloy increases to more than 400 MPa,about one-third greater than the counterpart amount after the usual T6 treatment.This superlative strength mainly occurs due to refinement of grains,an increase of dislocation density and an increase of volume fraction of the precipitates that appeared during natural ageing.Considering the applied models,it is inferred that the increase of volume fraction of precipitates that appeared during natural ageing has a determinative role in the strengthening of the alloy.展开更多
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
The compressive deformation behavior of as-quenched 7005 aluminum alloy was investigated at the temperature ranging from 250 °C to 450 °C and strain rate ranging from 0.0005 s-1 to 0.5 s^-1 on Gleeble-1500 t...The compressive deformation behavior of as-quenched 7005 aluminum alloy was investigated at the temperature ranging from 250 °C to 450 °C and strain rate ranging from 0.0005 s-1 to 0.5 s^-1 on Gleeble-1500 thermal-simulation machine. Experimental results show that the flow stress of as-quenched 7005 alloy is affected by both deformation temperature and strain rate, which can be represented by a Zener-Hollomon parameter in an exponent-type equation. By comparing the calculated flow stress and the measured flow stress, the results show that the calculated flow stress agrees well with the experimental result. Based on a dynamic material model, the processing maps were constructed for the strains of 0.1, 0.3 and 0.5. The maps and microstructural examination revealed that the optimum hot working domain is 270-340 °C, 0.05-0.5 s^-1 with the reasonable dynamic recrystallization. The instability domain exhibits adiabatic shear bands and flow localization, which should be avoided during hot working in order to obtain satisfactory properties.展开更多
An equal channel reciprocating extrusion(ECRE)was proposed first to obtain a severe plastic deformation(SPD)of 7005 alloy.The microstructure and mechanical properties of one-pass ECREed(ECRE processed)7005 alloy were ...An equal channel reciprocating extrusion(ECRE)was proposed first to obtain a severe plastic deformation(SPD)of 7005 alloy.The microstructure and mechanical properties of one-pass ECREed(ECRE processed)7005 alloy were investigated.The results show that SPD occurring in ECRE leads to a mixed microstructure.ECREed 7005 alloy exhibits a significant improvement of ultimate tensile strength(UTS)and elongation.Mechanical properties in the region undergoing a complete ECRE process are higher than those in the region undergoing an incomplete ECRE process due to larger dislocation strengthening effect.Yield strength(YS)and UTS first decrease and then increase with an increase of extrusion temperature.The YS of 359.2 MPa,UTS of 490 MPa and elongation of 17.7%are obtained after T6 treatment.Fine-grain strengthening,dislocation strengthening and precipitation strengthening in the T6-treated ECREed sample all play important roles in improving the mechanical properties.展开更多
High temperature pre-precipitation （HTPP）took place in7005 alloy at various temperatures after solution treatment and itsinfluence on mechanical properties, corrosion behaviors and microstructure of the alloy was in...High temperature pre-precipitation （HTPP）took place in7005 alloy at various temperatures after solution treatment and itsinfluence on mechanical properties, corrosion behaviors and microstructure of the alloy was investigated using tensile test, intergranular corrosion （IGC） test, slow strain rate testing （SSRT）, together with microstructural examinations. It is found that Vickers hardness of the aged alloy decreases gradually with decreasing the HTPP temperature, and almost a reverse trend of electrical conductivity is found compared to the hardness changes. Depending on the changes, two HTPP temperaturesof 440 and 420℃ were chosen for comparative study. Results reveal that HTPP alloy tempers exhibit higher resistance to stress corrosion cracking （SCC） and IGC than none pre-precipitate one with an acceptable strength loss due to the substantial enhancement of distribution discontinuity of the coarse grain boundary precipitates （GBPs）, and the coarsening and interspacing effect on GBPs becomes more obvious with decreasing the pre-precipitation temperature.展开更多
利用力学性能测试等手段研究了淬火方式以及时效条件对6005A合金力学性能的影响,确定了6005A的合金的TTP(time temperature properties)曲线,发现其鼻尖温度在370℃左右。研究了7005合金的双级时效过程,该合金淬火后,经105℃,8h+155℃,5...利用力学性能测试等手段研究了淬火方式以及时效条件对6005A合金力学性能的影响,确定了6005A的合金的TTP(time temperature properties)曲线,发现其鼻尖温度在370℃左右。研究了7005合金的双级时效过程,该合金淬火后,经105℃,8h+155℃,5h的双级时效,可获得HB为116的高硬度。展开更多
基金Project(51075132)supported by the National Natural Science Foundation of ChinaProject(20090161110027)supported by the Doctoral Fund of Ministry of Education of ChinaProject(2011BAG03B02)supported by National Key Technology R&D Program during the 12th Five-Year Plan Period,China
文摘The flow stress behavior and microstructure development of Al-5Zn-2Mg （7005） aluminum alloy were studied by hot compression tests at deformation temperatures between 300-500 ＆#176;C and strain rates between 0.05-50 s-1. The deformed structures of the samples were observed by optical microscopy （OM）, transmission electron microscopy （TEM） and electron backscattering diffraction （EBSD） analysis. The calculated activation energy is 147 kJ/mol, which is very close to the activation energy for lattice self-diffusion in aluminum （142 kJ/mol）. Dynamic recovery is the dominant restoration mechanism during the deformation. At high strain rate of 50 s-1, temperature rise due to deformation heating leads to a significant flow softening. Microstructure observations indicated that the remaining softening after deformation heating correction at high strain rate and the softening observed at high temperature are associated with grain coarsening induced by grain boundary migration during dynamic recovery process.
基金the research board of Ferdowsi University of Mashhad(FUM)for the financial support and the provision of research facilities used in this work through grant No.3/41681.
文摘Strengthening of aluminium alloys 7xxx through the imposition of severe plastic deformation supplemented by ageing treatments is a challenge due to the limited workability of these alloys in cold deformation regimes.This study aims to comprehensively investigate the strengthening of aluminium alloy 7005 through the imposition of severe plastic deformation supplemented by two different ageing treatments:pre-deformation artificial ageing or postdeformation natural ageing.For this purpose,microstructure evolutions of the alloy processed through mentioned procedures were studied using X-ray diffraction and scanning electron microscopy while the alloy strengthening was evaluated using Vickers hardness measurement.Results show that a superlative strengthening is obtained through the imposition of severe plastic deformation supplemented by post-deformation natural ageing.For instance,the yield strength of the alloy increases to more than 400 MPa,about one-third greater than the counterpart amount after the usual T6 treatment.This superlative strength mainly occurs due to refinement of grains,an increase of dislocation density and an increase of volume fraction of the precipitates that appeared during natural ageing.Considering the applied models,it is inferred that the increase of volume fraction of precipitates that appeared during natural ageing has a determinative role in the strengthening of the alloy.
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(2011CB612200)supported by the National Basic Research Program of China
文摘The compressive deformation behavior of as-quenched 7005 aluminum alloy was investigated at the temperature ranging from 250 °C to 450 °C and strain rate ranging from 0.0005 s-1 to 0.5 s^-1 on Gleeble-1500 thermal-simulation machine. Experimental results show that the flow stress of as-quenched 7005 alloy is affected by both deformation temperature and strain rate, which can be represented by a Zener-Hollomon parameter in an exponent-type equation. By comparing the calculated flow stress and the measured flow stress, the results show that the calculated flow stress agrees well with the experimental result. Based on a dynamic material model, the processing maps were constructed for the strains of 0.1, 0.3 and 0.5. The maps and microstructural examination revealed that the optimum hot working domain is 270-340 °C, 0.05-0.5 s^-1 with the reasonable dynamic recrystallization. The instability domain exhibits adiabatic shear bands and flow localization, which should be avoided during hot working in order to obtain satisfactory properties.
基金This work is supported by the National Natural Science Foundation of China(51875124).
文摘An equal channel reciprocating extrusion(ECRE)was proposed first to obtain a severe plastic deformation(SPD)of 7005 alloy.The microstructure and mechanical properties of one-pass ECREed(ECRE processed)7005 alloy were investigated.The results show that SPD occurring in ECRE leads to a mixed microstructure.ECREed 7005 alloy exhibits a significant improvement of ultimate tensile strength(UTS)and elongation.Mechanical properties in the region undergoing a complete ECRE process are higher than those in the region undergoing an incomplete ECRE process due to larger dislocation strengthening effect.Yield strength(YS)and UTS first decrease and then increase with an increase of extrusion temperature.The YS of 359.2 MPa,UTS of 490 MPa and elongation of 17.7%are obtained after T6 treatment.Fine-grain strengthening,dislocation strengthening and precipitation strengthening in the T6-treated ECREed sample all play important roles in improving the mechanical properties.
基金Project(51301209)supported by the National Natural Science Foundation of China
文摘High temperature pre-precipitation （HTPP）took place in7005 alloy at various temperatures after solution treatment and itsinfluence on mechanical properties, corrosion behaviors and microstructure of the alloy was investigated using tensile test, intergranular corrosion （IGC） test, slow strain rate testing （SSRT）, together with microstructural examinations. It is found that Vickers hardness of the aged alloy decreases gradually with decreasing the HTPP temperature, and almost a reverse trend of electrical conductivity is found compared to the hardness changes. Depending on the changes, two HTPP temperaturesof 440 and 420℃ were chosen for comparative study. Results reveal that HTPP alloy tempers exhibit higher resistance to stress corrosion cracking （SCC） and IGC than none pre-precipitate one with an acceptable strength loss due to the substantial enhancement of distribution discontinuity of the coarse grain boundary precipitates （GBPs）, and the coarsening and interspacing effect on GBPs becomes more obvious with decreasing the pre-precipitation temperature.
文摘利用力学性能测试等手段研究了淬火方式以及时效条件对6005A合金力学性能的影响,确定了6005A的合金的TTP(time temperature properties)曲线,发现其鼻尖温度在370℃左右。研究了7005合金的双级时效过程,该合金淬火后,经105℃,8h+155℃,5h的双级时效,可获得HB为116的高硬度。
