In the present work, scandium elements with a series of contents(0.06 wt.%, 0.10 wt.%, 0.14 wt.%,0.17 wt.%, 0.20 wt.% and 0.25 wt.%) were added in a high Zn-containing Al-Zn-Mg-Cu-Zr alloy and the corresponding as-cas...In the present work, scandium elements with a series of contents(0.06 wt.%, 0.10 wt.%, 0.14 wt.%,0.17 wt.%, 0.20 wt.% and 0.25 wt.%) were added in a high Zn-containing Al-Zn-Mg-Cu-Zr alloy and the corresponding as-cast microstructure characteristics including grains and phases were thoroughly investigated. The results indicated that fine grain boundaries existed in these alloys and fine MgZn2phases discontinuously distributed on them. Besides,AlZnMgCu eutectic phases and Sc, Zr-containing phases with flocculent morphology were observed. As scandium contents vary from 0.06 wt.% to 0.17 wt.%, the average grain size continuously decreased and its equiaxial characteristics were strengthened. Meanwhile, the content of AlZnMgCu eutectic phase showed a decrease trend. When scandium contents were 0.20 wt.% and 0.25 wt.%, no further enhancement on grain refinement was observed, so as to the reduction of AlZnMgCu eutectic phase content. Besides, Sc, Zr-containing phases with blocky morphology were observed and the alloy with a scandium content of 0.25 wt.% possessed a larger amount of blocky Sc, Zr-containing phase than the alloy with a scandium content of 0.20 wt.%. Grain refinement and reduction of AlZnMgCu eutectic phase content associated with scandium addition were discussed.展开更多
The dynamic recrystallization and carbides precipitation of the Cr-Co-Mo-Ni bearing steel were investigated by hot compression tests performed at temperatures ranging from 850 ℃to 1080 ℃ with strain rate of 1-20 s-1...The dynamic recrystallization and carbides precipitation of the Cr-Co-Mo-Ni bearing steel were investigated by hot compression tests performed at temperatures ranging from 850 ℃to 1080 ℃ with strain rate of 1-20 s-1. The activation energy（Q） for the tested steel is calculated to be around 682.99 k J/mol at a deformation strain of 0.6. Microstructural analysis by SEM shows that the dynamic recrystallization（DRX） behavior is dependent sensitively on the deformation strain, temperature and strain rate, while an exponential relationship between DRX grain size and Z parameter is obtained from the computational formula. Moreover, the M6C-type carbides（〈1 μm） act as the main prohibitor of grain coarsening, and the polynomial regression relationship between them is worked out. With electron backscatter diffraction（EBSD） observation, DRX is the main nucleation mechanism responsible for the formation of new grains during hot compression. In conclusion, the interaction between DRX affected by hot deformation parameters and carbides precipitation determines the ultimate grain size refinement.展开更多
Fine-grained 01420 Al-Li alloy sheets were produced by thermo-mechanical processing based on the mechanism of particle stimulated nucleation of recrystallization.The thermo-mechanically processed sheets were observed ...Fine-grained 01420 Al-Li alloy sheets were produced by thermo-mechanical processing based on the mechanism of particle stimulated nucleation of recrystallization.The thermo-mechanically processed sheets were observed to contain layers of different microstructures along the thickness.The precipitate behavior of the second phase particles and their effects on the distribution of dislocations and layered recrystallized grain structure were analyzed by optical microscopy(OM),scanning electron microscopy(SEM),transmission electron microscopy(TEM) and X-ray diffractometry(XRD).The formation mechanism of the gradient particles was discussed.The results show that after aging,a gradient distribution of large particles along the thickness is observed,the particles in the surface layer(SL) are distributed homogeneously,whereas those in the center layer(CL) are mainly distributed parallel to the rolling direction,and the volume fraction of the particles in the SL is higher than that in the CL.Subsequent rolling in the presence of layer-distributed particles results in a corresponding homogeneous distribution of highly strained regions in the SL and a banded distribution of them in CL,which is the main reason for the formation of layered grain structure along the thickness in the sheets.展开更多
An Al-3Ti-0.2C-1RE grain refiner was prepared by in-situ reaction method.The microstructure was investigated by optical microscopy(OM),scanning electron microscopy(SEM) equipped with energy-dispersive spectrometry(EDS...An Al-3Ti-0.2C-1RE grain refiner was prepared by in-situ reaction method.The microstructure was investigated by optical microscopy(OM),scanning electron microscopy(SEM) equipped with energy-dispersive spectrometry(EDS) and X-ray diffraction(XRD).The results show that the Al-3Ti-0.2C-1RE grain refiner is composed of α-Al,TiAl3,TiC and Ti2 Al20 Ce phases.Compared with Al-3Ti-0.2C refiner,the morphology of TiAl3 phase is changed and Ti2 Al20 Ce phases form with the addition of RE.Accordingly,the refining performance is improved.The phase forming process of the refiner is as follows: Blocky Ti2 Al20 Ce and fine blocky TiAl3 form in the melt at the initial stage of reaction,then the fine blocky TiAl3 gradually disappears,and the blocky Ti2 Al20 Ce grows bigger with the increase of holding time.The predominant mechanism to synthesize TiC particles is the reaction between high concentration of solute Ti atoms and graphite particles.展开更多
The experiment of ultrasonic treatment of roll casting aluminum strip on plane twin-roll cast-roller with double-heads ultrasonic tools was carried out, and the metallographic structure of the roll casting aluminum st...The experiment of ultrasonic treatment of roll casting aluminum strip on plane twin-roll cast-roller with double-heads ultrasonic tools was carried out, and the metallographic structure of the roll casting aluminum strip treated by ultrasonic was studied. The results show that ultrasonic treatment can refine the grain of the roll casting aluminum strips and make the structure of the strips more homogeneous. The effect is the best when the power of ultrasonic is 300 W and the incident angle of the guide rod is 45、. The mechanism of acoustic cavitations and acoustic flow on grain refinement was also discussed. The heat effect of intensity ultrasonic was studied. The present problems during ultrasonic roll casting process, such as the imperfect cooling system, the inaccurate calculation of ultrasonic energy, and the shape and position of the guide rod to be improved were pointed out.展开更多
The effect of an ultrasonic field on the microstructure and mechanical properties of 7085 aluminum alloy during solidification was investigated by optical microscopy, Vickers hardness test, tensile test, scanning elec...The effect of an ultrasonic field on the microstructure and mechanical properties of 7085 aluminum alloy during solidification was investigated by optical microscopy, Vickers hardness test, tensile test, scanning electron microscopy （SEM） with energy dispersive X-ray spectrometry, and electron probe micro-analysis （EPMA）. The results showed that the grains of aluminum alloy were significantly refined and secondary phases were dispersed and distributed uniformly at the grain boundaries, due to ultrasonic treatment （UST）. By EPMA, it was observed that the distribution of the main elements A1, Zn, Mg and Cu was more homogeneous in alloys with UST, than in alloys without UST. The mechanical properties of the aluminum alloy also significantly improved. As demonstrated by the SEM fractography of the fractured faces of several castings, fracture of the unrefined specimens occurred in a brittle manner, whereas the cracks of the refined specimens showed quasi-cleavage fracture.展开更多
In order to prolong the service life of aircraft skin made from AA2524, the effects of laser shock peening(LSP) on fatigue crack growth(FCG) rate and fracture toughness(K_(c)) of AA2524 were investigated. Multiple LSP...In order to prolong the service life of aircraft skin made from AA2524, the effects of laser shock peening(LSP) on fatigue crack growth(FCG) rate and fracture toughness(K_(c)) of AA2524 were investigated. Multiple LSP treatment was performed on compact tension(CT) specimen from single side and double sides. The surface integrity was measured with Vickers hardness tester, X-ray diffractometer and confocal laser scanning microscope, respectively. FCG rate test and fracture toughness test under plane stress were carried out after LSP treatment. The microstructure features of cross-sections were observed with scanning electron microscope. The results showed that the micro-hardness and residual stress of CT specimens were increased dramatically after LSP treatment. Compared to the base metal(BM), the fatigue life was prolonged by 2.4 times and fracture toughness was increased by 22% after multiple LSP.展开更多
Ultrafine-grained(UFG) high purity aluminum exhibits a variety of attractive mechanical properties and special deformation behavior. Equal channel angular pressing(ECAP) process can be used to easily and effectively r...Ultrafine-grained(UFG) high purity aluminum exhibits a variety of attractive mechanical properties and special deformation behavior. Equal channel angular pressing(ECAP) process can be used to easily and effectively refine metals. The microstructure and microtexture evolutions and grain boundary characteristics of the high purity aluminum(99.998%) processed by ECAP at room temperature are investigated by means of TEM and EBSD. The results indicate that the shear deformation resistance increases with repeated EACP passes, and equiaxed grains with an average size of 0.9 μm in diameter are formed after five passes. Although the orientations distribution of grains tends to evolve toward random orientations, and microtextures(80°, 35°, 0°),(40°, 75°, 45°) and(0°, 85°, 45°) peak in the sample after five passes. The grain boundaries in UFG aluminum are high-angle geometrically necessary boundaries. It is suggested that the continuous dynamic recrystallization is responsible for the formation of ultrafine grains in high purity aluminum. Microstructure evolution in the high purity aluminum during ECAP is proposed.展开更多
In current research,the interactive effects of different parameters such as melt overheating temperature,the location of gating system and incorporation of the grain refiner in bar and micro-powder form on the mechani...In current research,the interactive effects of different parameters such as melt overheating temperature,the location of gating system and incorporation of the grain refiner in bar and micro-powder form on the mechanical and structural characteristics of commercially pure aluminium are examined.Results show that increasing the melt temperature as well as employing a gating system with higher heat transfer rate increases the ultimate tensile strength(UTS)of the pure aluminium by 7%.Also,the introduction of 2wt%Al–5Ti–1B grain refiner in bar form into the overheated melt enhances the UTS values by two times,while incorporating 2wt%Al–5Ti–1B grain refiner in micro-powder form leads to achieving 32%higher UTS compared to the samples with grain refiner in the bar form due to the elimination of Al3Ti brittle phase,as confirmed by XRD patterns and SEM fracture surface images.展开更多
基金Projects(2020YFB0311400ZL, 2020YFF0218202) supported by the National Key R&D Program of ChinaProject supported by Youth Fund Project of GRINM Group Co.,Ltd.,China。
文摘In the present work, scandium elements with a series of contents(0.06 wt.%, 0.10 wt.%, 0.14 wt.%,0.17 wt.%, 0.20 wt.% and 0.25 wt.%) were added in a high Zn-containing Al-Zn-Mg-Cu-Zr alloy and the corresponding as-cast microstructure characteristics including grains and phases were thoroughly investigated. The results indicated that fine grain boundaries existed in these alloys and fine MgZn2phases discontinuously distributed on them. Besides,AlZnMgCu eutectic phases and Sc, Zr-containing phases with flocculent morphology were observed. As scandium contents vary from 0.06 wt.% to 0.17 wt.%, the average grain size continuously decreased and its equiaxial characteristics were strengthened. Meanwhile, the content of AlZnMgCu eutectic phase showed a decrease trend. When scandium contents were 0.20 wt.% and 0.25 wt.%, no further enhancement on grain refinement was observed, so as to the reduction of AlZnMgCu eutectic phase content. Besides, Sc, Zr-containing phases with blocky morphology were observed and the alloy with a scandium content of 0.25 wt.% possessed a larger amount of blocky Sc, Zr-containing phase than the alloy with a scandium content of 0.20 wt.%. Grain refinement and reduction of AlZnMgCu eutectic phase content associated with scandium addition were discussed.
基金Project(2012AA03A503) supported by the National High Technology Research and Development Program of China
文摘The dynamic recrystallization and carbides precipitation of the Cr-Co-Mo-Ni bearing steel were investigated by hot compression tests performed at temperatures ranging from 850 ℃to 1080 ℃ with strain rate of 1-20 s-1. The activation energy（Q） for the tested steel is calculated to be around 682.99 k J/mol at a deformation strain of 0.6. Microstructural analysis by SEM shows that the dynamic recrystallization（DRX） behavior is dependent sensitively on the deformation strain, temperature and strain rate, while an exponential relationship between DRX grain size and Z parameter is obtained from the computational formula. Moreover, the M6C-type carbides（〈1 μm） act as the main prohibitor of grain coarsening, and the polynomial regression relationship between them is worked out. With electron backscatter diffraction（EBSD） observation, DRX is the main nucleation mechanism responsible for the formation of new grains during hot compression. In conclusion, the interaction between DRX affected by hot deformation parameters and carbides precipitation determines the ultimate grain size refinement.
基金Project(2006DFA53250) supported by the International Science and Technology Cooperation Program of ChinaProject(2005CB623706) supported by the Major State Basic Research Development Program of China
文摘Fine-grained 01420 Al-Li alloy sheets were produced by thermo-mechanical processing based on the mechanism of particle stimulated nucleation of recrystallization.The thermo-mechanically processed sheets were observed to contain layers of different microstructures along the thickness.The precipitate behavior of the second phase particles and their effects on the distribution of dislocations and layered recrystallized grain structure were analyzed by optical microscopy(OM),scanning electron microscopy(SEM),transmission electron microscopy(TEM) and X-ray diffractometry(XRD).The formation mechanism of the gradient particles was discussed.The results show that after aging,a gradient distribution of large particles along the thickness is observed,the particles in the surface layer(SL) are distributed homogeneously,whereas those in the center layer(CL) are mainly distributed parallel to the rolling direction,and the volume fraction of the particles in the SL is higher than that in the CL.Subsequent rolling in the presence of layer-distributed particles results in a corresponding homogeneous distribution of highly strained regions in the SL and a banded distribution of them in CL,which is the main reason for the formation of layered grain structure along the thickness in the sheets.
基金Project(51174177)supported by the National Natural Science Foundation of China
文摘An Al-3Ti-0.2C-1RE grain refiner was prepared by in-situ reaction method.The microstructure was investigated by optical microscopy(OM),scanning electron microscopy(SEM) equipped with energy-dispersive spectrometry(EDS) and X-ray diffraction(XRD).The results show that the Al-3Ti-0.2C-1RE grain refiner is composed of α-Al,TiAl3,TiC and Ti2 Al20 Ce phases.Compared with Al-3Ti-0.2C refiner,the morphology of TiAl3 phase is changed and Ti2 Al20 Ce phases form with the addition of RE.Accordingly,the refining performance is improved.The phase forming process of the refiner is as follows: Blocky Ti2 Al20 Ce and fine blocky TiAl3 form in the melt at the initial stage of reaction,then the fine blocky TiAl3 gradually disappears,and the blocky Ti2 Al20 Ce grows bigger with the increase of holding time.The predominant mechanism to synthesize TiC particles is the reaction between high concentration of solute Ti atoms and graphite particles.
基金Projects(IRT0549) supported by Program for Changjiang Scholars and Innovative Research Team in University, China
文摘The experiment of ultrasonic treatment of roll casting aluminum strip on plane twin-roll cast-roller with double-heads ultrasonic tools was carried out, and the metallographic structure of the roll casting aluminum strip treated by ultrasonic was studied. The results show that ultrasonic treatment can refine the grain of the roll casting aluminum strips and make the structure of the strips more homogeneous. The effect is the best when the power of ultrasonic is 300 W and the incident angle of the guide rod is 45、. The mechanism of acoustic cavitations and acoustic flow on grain refinement was also discussed. The heat effect of intensity ultrasonic was studied. The present problems during ultrasonic roll casting process, such as the imperfect cooling system, the inaccurate calculation of ultrasonic energy, and the shape and position of the guide rod to be improved were pointed out.
基金Project(2016GK1004)supported by the Science and Technology Major Project of Hunan Province,China
文摘The effect of an ultrasonic field on the microstructure and mechanical properties of 7085 aluminum alloy during solidification was investigated by optical microscopy, Vickers hardness test, tensile test, scanning electron microscopy （SEM） with energy dispersive X-ray spectrometry, and electron probe micro-analysis （EPMA）. The results showed that the grains of aluminum alloy were significantly refined and secondary phases were dispersed and distributed uniformly at the grain boundaries, due to ultrasonic treatment （UST）. By EPMA, it was observed that the distribution of the main elements A1, Zn, Mg and Cu was more homogeneous in alloys with UST, than in alloys without UST. The mechanical properties of the aluminum alloy also significantly improved. As demonstrated by the SEM fractography of the fractured faces of several castings, fracture of the unrefined specimens occurred in a brittle manner, whereas the cracks of the refined specimens showed quasi-cleavage fracture.
基金Project(52075552) supported by the National Natural Science Foundation of ChinaProject(kq2007085) supported by Changsha Municipal Natural Science Foundation,China。
文摘In order to prolong the service life of aircraft skin made from AA2524, the effects of laser shock peening(LSP) on fatigue crack growth(FCG) rate and fracture toughness(K_(c)) of AA2524 were investigated. Multiple LSP treatment was performed on compact tension(CT) specimen from single side and double sides. The surface integrity was measured with Vickers hardness tester, X-ray diffractometer and confocal laser scanning microscope, respectively. FCG rate test and fracture toughness test under plane stress were carried out after LSP treatment. The microstructure features of cross-sections were observed with scanning electron microscope. The results showed that the micro-hardness and residual stress of CT specimens were increased dramatically after LSP treatment. Compared to the base metal(BM), the fatigue life was prolonged by 2.4 times and fracture toughness was increased by 22% after multiple LSP.
基金Project(12JJ2028)supported by the Hunan Provincial Natural Science Foundation of ChinaProject(201308430093)supported by the China Scholarship CouncilProjects(201012200006,2013zzts185,2012zzts066)supported by the Freedom Explore Program of Central South University,China
文摘Ultrafine-grained(UFG) high purity aluminum exhibits a variety of attractive mechanical properties and special deformation behavior. Equal channel angular pressing(ECAP) process can be used to easily and effectively refine metals. The microstructure and microtexture evolutions and grain boundary characteristics of the high purity aluminum(99.998%) processed by ECAP at room temperature are investigated by means of TEM and EBSD. The results indicate that the shear deformation resistance increases with repeated EACP passes, and equiaxed grains with an average size of 0.9 μm in diameter are formed after five passes. Although the orientations distribution of grains tends to evolve toward random orientations, and microtextures(80°, 35°, 0°),(40°, 75°, 45°) and(0°, 85°, 45°) peak in the sample after five passes. The grain boundaries in UFG aluminum are high-angle geometrically necessary boundaries. It is suggested that the continuous dynamic recrystallization is responsible for the formation of ultrafine grains in high purity aluminum. Microstructure evolution in the high purity aluminum during ECAP is proposed.
文摘In current research,the interactive effects of different parameters such as melt overheating temperature,the location of gating system and incorporation of the grain refiner in bar and micro-powder form on the mechanical and structural characteristics of commercially pure aluminium are examined.Results show that increasing the melt temperature as well as employing a gating system with higher heat transfer rate increases the ultimate tensile strength(UTS)of the pure aluminium by 7%.Also,the introduction of 2wt%Al–5Ti–1B grain refiner in bar form into the overheated melt enhances the UTS values by two times,while incorporating 2wt%Al–5Ti–1B grain refiner in micro-powder form leads to achieving 32%higher UTS compared to the samples with grain refiner in the bar form due to the elimination of Al3Ti brittle phase,as confirmed by XRD patterns and SEM fracture surface images.
