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
The actual effective partition coefficients of Mg and Cr in a cross-section of a dendrite arm in a direct-chill(DC)-casting ingot of 7475 aluminum alloy are obtained.Meanwhile,by analyzing the microstructure,the mecha...The actual effective partition coefficients of Mg and Cr in a cross-section of a dendrite arm in a direct-chill(DC)-casting ingot of 7475 aluminum alloy are obtained.Meanwhile,by analyzing the microstructure,the mechanism of the heterogeneous distribution of E(Al_(18)Mg_(3)Cr_(2))dispersoids in this DC ingot is revealed.The results show that the actual effective partition coefficients of Mg and Cr are 0.650 and 1.392,respectively,and they describe the heterogeneous distributions of Mg and Cr along the direction of radius of the cross-section of the dendrite arm of the alloy.After homogenization treatment at 470℃ for 24 h,Mg diffuses uniformly,but Cr hardly diffuses.Both the concentrations of Mg and Cr and the sites of heterogeneous nucleation in the alloy are the determinants of the formation of E dispersoids simultaneously.The heat treatment at 250℃ for 72 h provides a large number of the sites of heterogeneous nucleation of the formation of fine E dispersoids that will be formed in the center of the cross-section during the subsequent heat treatment at higher temperature.展开更多
The effects of Si content on the microstructure and yield strength of Al-(1.44-12.40)Si-0.7 Mg(wt.%)alloy sheets under the T4 condition were systematically studied via laser scanning confocal microscopy(LSCM),DSC,TEM ...The effects of Si content on the microstructure and yield strength of Al-(1.44-12.40)Si-0.7 Mg(wt.%)alloy sheets under the T4 condition were systematically studied via laser scanning confocal microscopy(LSCM),DSC,TEM and tensile tests.The results show that the recrystallization grain of the alloy sheets becomes more refined with an increase in Si content.When the Si content increases from 1.44 to 12.4 wt.%,the grain size of the alloy sheets decreases from approximately 47 to 10μm.Further,with an increase in Si content,the volume fraction of the GP zones in the matrix increases slightly.Based on the existing model,a yield strength model for alloy sheets was proposed.The predicted results are in good agreement with the actual experimental results and reveal the strengthening mechanisms of the Al-(1.44-12.40)Si-0.7 Mg alloy sheets under the T4 condition and how they are influenced by the Si content.展开更多
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.
基金financially supported by the National Natural Science Foundation of China(No.51871043)Fundamental Research Funds for the Central Universities of China(No.N180212010)Liaoning Natural Science Foundation of China(No.2019-MS-113)。
文摘The actual effective partition coefficients of Mg and Cr in a cross-section of a dendrite arm in a direct-chill(DC)-casting ingot of 7475 aluminum alloy are obtained.Meanwhile,by analyzing the microstructure,the mechanism of the heterogeneous distribution of E(Al_(18)Mg_(3)Cr_(2))dispersoids in this DC ingot is revealed.The results show that the actual effective partition coefficients of Mg and Cr are 0.650 and 1.392,respectively,and they describe the heterogeneous distributions of Mg and Cr along the direction of radius of the cross-section of the dendrite arm of the alloy.After homogenization treatment at 470℃ for 24 h,Mg diffuses uniformly,but Cr hardly diffuses.Both the concentrations of Mg and Cr and the sites of heterogeneous nucleation in the alloy are the determinants of the formation of E dispersoids simultaneously.The heat treatment at 250℃ for 72 h provides a large number of the sites of heterogeneous nucleation of the formation of fine E dispersoids that will be formed in the center of the cross-section during the subsequent heat treatment at higher temperature.
基金Project(2016YFB0300801)supported by the National Key Research and Development Program of ChinaProject(51871043)supported by the National Natural Science Foundation of ChinaProject(N180212010)supported by the Fundamental Research Funds for the Central Universities of China。
文摘The effects of Si content on the microstructure and yield strength of Al-(1.44-12.40)Si-0.7 Mg(wt.%)alloy sheets under the T4 condition were systematically studied via laser scanning confocal microscopy(LSCM),DSC,TEM and tensile tests.The results show that the recrystallization grain of the alloy sheets becomes more refined with an increase in Si content.When the Si content increases from 1.44 to 12.4 wt.%,the grain size of the alloy sheets decreases from approximately 47 to 10μm.Further,with an increase in Si content,the volume fraction of the GP zones in the matrix increases slightly.Based on the existing model,a yield strength model for alloy sheets was proposed.The predicted results are in good agreement with the actual experimental results and reveal the strengthening mechanisms of the Al-(1.44-12.40)Si-0.7 Mg alloy sheets under the T4 condition and how they are influenced by the Si content.
