According to inverse heat transfer theory, the evolutions of synthetic surface heat transfer coefficient（SSHTC） of the quenching surface of 7B50 alloy during water-spray quenching were simulated by the Pro CAST soft...According to inverse heat transfer theory, the evolutions of synthetic surface heat transfer coefficient（SSHTC） of the quenching surface of 7B50 alloy during water-spray quenching were simulated by the Pro CAST software based on accurate cooling curves measured by the modified Jominy specimen and temperature-dependent thermo-physical properties of 7 B50 alloy calculated using the JMat Pro software. Results show that the average cooling rate at 6 mm from the quenching surface and 420-230 ℃（quench sensitive temperature range） is 45.78℃/s. The peak-value of the SSHTC is 69 kW/（m^2·K） obtained at spray quenching for 0.4 s and the corresponding temperature of the quenching surface is 160 ℃. In the initial stage of spray quenching, the phenomenon called ＂temperature plateau＂ appears on the cooling curve of the quenching surface. The temperature range of this plateau is 160-170℃ with the duration about 3 s. During the temperature plateau, heat transfer mechanism of the quenching surface transforms from nucleate boiling regime to single-phase convective regime.展开更多
Through-thickness heterogeneity in creep properties of 7B50-T7451 aluminum alloy Friction Stir Welding(FSW)joints was investigated.Creep tests for three slices of the FSW joint were conducted at the temperature of 150...Through-thickness heterogeneity in creep properties of 7B50-T7451 aluminum alloy Friction Stir Welding(FSW)joints was investigated.Creep tests for three slices of the FSW joint were conducted at the temperature of 150-200℃ and applied stress of 60-225 MPa.The theta projection method was used to predict creep curves and minimum creep rate.The results show that the minimum creep rate increases and creep rupture life decreases with the increase of creep temperature and applied stress.Creep properties of the FSW joint deteriorate along the thickness direction from the top to the bottom.The threshold stress of all three slices of the FSW joint decreases with the increase of creep temperature and even disappears at 200℃ for the bottom slice.Creep activation energy approaches the activation energy of the lattice self-diffusion of aluminum.The value of true stress exponent for different slices is approximately equal to three.The predominant creep mechanism of the FSW joint is dislocation viscous glide by lattice self-diffusion.What is more,a constitutive model is established based on the theta method to accurately describe creep behavior ofdifferent slices of the FSW joint.展开更多
In the present work,continuous cooling curves were accurately measured by the modified Jominy specimen of 7B50 alloy during water-spray quenching tests.Besides,the time-temperature-properties(TTP) curves of this alloy...In the present work,continuous cooling curves were accurately measured by the modified Jominy specimen of 7B50 alloy during water-spray quenching tests.Besides,the time-temperature-properties(TTP) curves of this alloy were obtained during isothermal treatments.Based on the accurate cooling curves and TTP curves,the hardness distribution along the thickness direction of 7B50 alloy thick plates was predicted by quench factor analysis method.It is found that the quench sensitive temperature range of 7B50 alloy is 240-410℃,the nose temperature is 335℃,and the incubation period at the nose temperature is about 0.87 s.When 7B50 alloy was isothermal treated at 180-400℃ after solid solution treatment(470℃ for 1 h followed by 483℃ for 2 h),the exponent(n) in the Johnson-Mehl-Avrami equation is close to 1 until transformed fraction of new precipitates is up to 60%,indicating that new precipitates first grow into rodlike shape and then coarsen or thicken.When the distance is less than 65 mm from the spray quenching surface of the modified Jominy specimen,the deviation between the predicted and measured hardness is less than 2.7%,confirming the quench factor analysis method as the feasible way to predict the hardness distribution along the thickness direction of 7B50 alloy thick plates.When the distance from the spray quenching surface is 25 mm,the average cooling rate in quench sensitive temperature range is 9.93 ℃·s^-1,while the quench factor(τ) is 9.89 and the corresponding predicted hardness is HV 185.1 equivalent to 97.3% of the maximum measured hardness of 7B50 alloy in T6 temper.展开更多
基金Project(2016YFB0300801)supported by the National Key Research and Development Program of ChinaProject(51371045)supported by the National Natural Science Foundation of China
文摘According to inverse heat transfer theory, the evolutions of synthetic surface heat transfer coefficient（SSHTC） of the quenching surface of 7B50 alloy during water-spray quenching were simulated by the Pro CAST software based on accurate cooling curves measured by the modified Jominy specimen and temperature-dependent thermo-physical properties of 7 B50 alloy calculated using the JMat Pro software. Results show that the average cooling rate at 6 mm from the quenching surface and 420-230 ℃（quench sensitive temperature range） is 45.78℃/s. The peak-value of the SSHTC is 69 kW/（m^2·K） obtained at spray quenching for 0.4 s and the corresponding temperature of the quenching surface is 160 ℃. In the initial stage of spray quenching, the phenomenon called ＂temperature plateau＂ appears on the cooling curve of the quenching surface. The temperature range of this plateau is 160-170℃ with the duration about 3 s. During the temperature plateau, heat transfer mechanism of the quenching surface transforms from nucleate boiling regime to single-phase convective regime.
基金financially supported by the National Natural Science Foundation of China(No.52075450)the Fundamental Research Funds for the Central Universities,China(No.D5000220503).
文摘Through-thickness heterogeneity in creep properties of 7B50-T7451 aluminum alloy Friction Stir Welding(FSW)joints was investigated.Creep tests for three slices of the FSW joint were conducted at the temperature of 150-200℃ and applied stress of 60-225 MPa.The theta projection method was used to predict creep curves and minimum creep rate.The results show that the minimum creep rate increases and creep rupture life decreases with the increase of creep temperature and applied stress.Creep properties of the FSW joint deteriorate along the thickness direction from the top to the bottom.The threshold stress of all three slices of the FSW joint decreases with the increase of creep temperature and even disappears at 200℃ for the bottom slice.Creep activation energy approaches the activation energy of the lattice self-diffusion of aluminum.The value of true stress exponent for different slices is approximately equal to three.The predominant creep mechanism of the FSW joint is dislocation viscous glide by lattice self-diffusion.What is more,a constitutive model is established based on the theta method to accurately describe creep behavior ofdifferent slices of the FSW joint.
基金financially supported by the National Key Research and Development Program of China(No.2016YFB0300801)the National Natural Science Foundation of China(No.51371045)
文摘In the present work,continuous cooling curves were accurately measured by the modified Jominy specimen of 7B50 alloy during water-spray quenching tests.Besides,the time-temperature-properties(TTP) curves of this alloy were obtained during isothermal treatments.Based on the accurate cooling curves and TTP curves,the hardness distribution along the thickness direction of 7B50 alloy thick plates was predicted by quench factor analysis method.It is found that the quench sensitive temperature range of 7B50 alloy is 240-410℃,the nose temperature is 335℃,and the incubation period at the nose temperature is about 0.87 s.When 7B50 alloy was isothermal treated at 180-400℃ after solid solution treatment(470℃ for 1 h followed by 483℃ for 2 h),the exponent(n) in the Johnson-Mehl-Avrami equation is close to 1 until transformed fraction of new precipitates is up to 60%,indicating that new precipitates first grow into rodlike shape and then coarsen or thicken.When the distance is less than 65 mm from the spray quenching surface of the modified Jominy specimen,the deviation between the predicted and measured hardness is less than 2.7%,confirming the quench factor analysis method as the feasible way to predict the hardness distribution along the thickness direction of 7B50 alloy thick plates.When the distance from the spray quenching surface is 25 mm,the average cooling rate in quench sensitive temperature range is 9.93 ℃·s^-1,while the quench factor(τ) is 9.89 and the corresponding predicted hardness is HV 185.1 equivalent to 97.3% of the maximum measured hardness of 7B50 alloy in T6 temper.
