A series of Al-6Si-3Cu-(0.3-2)Mg alloys were produced by a conventional casting process.Cooling slope technique wasemployed to produce feedstocks before they were thixoformed at50%liquid fraction.The effect of Mg on t...A series of Al-6Si-3Cu-(0.3-2)Mg alloys were produced by a conventional casting process.Cooling slope technique wasemployed to produce feedstocks before they were thixoformed at50%liquid fraction.The effect of Mg on the microstructure ofAl-Si-Cu aluminium alloys under as-cast and semisolid conditions was investigated.It was found that by adding Mg to Al-Si-Cualloy,some of the Al2Cu phase and silicon were consumed to form Al5Cu2Mg3Si5and Mg2Si phases.The needle-likeβ-Al5FeSi phasetransformed to Chinese-script-likeπ-Al8Mg3FeSi6with the addition of Mg.In the as-cast alloys,the primaryα(Al)was dendritic,butas the Mg content increased,the phase became less dendritic.Moreover,the Mg addition considerably modified the size of theα(Al)phase,but it had no significant effect on the silicon morphology.In the thixoformed alloys,the microstructure showed a fine globularprimary phase surrounded by uniformly distributed silicon and fragmented intermetallic phases.The eutectic silicon was modifiedfrom a flaky and acicular shape to fine fibrous particles.The effect of Mg on eutectic silicon during semisolid processing wasevident.The primary Mg2Si particles were modified from big polygonal particles to become smaller and more globular,whereas themorphology of the Chinese-script-likeπ-Al8Mg3FeSi6changed to a compact shape.The results also exhibit that as the Mg content inthe A319alloy increased,the hardness,yield strength and ultimate tensile strength of the thixoformed alloys significantly improved,but the elongation to fracture dropped.展开更多
The effects of Cu content on the microstructure and mechanical properties of thixoformed Al-6Si-xCu-0.3Mg(x= 3,4,5and 6,mass fraction,%) alloys were studied.The samples were thixoformed at 50%liquid content and severa...The effects of Cu content on the microstructure and mechanical properties of thixoformed Al-6Si-xCu-0.3Mg(x= 3,4,5and 6,mass fraction,%) alloys were studied.The samples were thixoformed at 50%liquid content and several of the samples were treated with the T6 heat treatment.The samples were then examined by optical microscopy(OM),scanning electron microscopy(SEM),energy dispersive X-ray(EDX) spectroscopy and X-ray diffraction(XRD) analysis,as well as hardness and tensile tests.The results show that the cooling slope casting and thixoforming process promote the formation of very fine and well distributed intermetallic compounds in the aluminium matrix and the mechanical properties of the alloys increase considerably compared with the permanent mould casting.The results also reveal that as the Cu content in the alloy increases,the hardness and tensile strength of the thixoformed alloys also increase.The ultimate tensile strength,yield strength and elongation to fracture of the thixoformed heat-treated Al-6Si-3Cu-0.3Mg alloy are 298 MPa,201 MPa and 4.5%,respectively,whereas the values of the thixoformed heat-treated alloy with high Cu content(6%) are 361 MPa,274 MPa and 1.1%,respectively.The fracture of the thixoformed Al-6Si-3Cu-0.3Mg alloy shows a dimple rupture,whereas in the alloy that contains the highest Cu content(6%),a cleavage fracture is observed.展开更多
Thixoforming is a processing method that deforms metal in a semisolid state.The advantages of this process include the production of parts with good surface finish,fine microstructures and superior mechanical properti...Thixoforming is a processing method that deforms metal in a semisolid state.The advantages of this process include the production of parts with good surface finish,fine microstructures and superior mechanical properties.However,the process mostly produces parts from aluminium cast grades,thereby not fully utilising the true potential of this method.Hence,thermodynamic modelling can be used to formulate alloy compositions that favour this processing method.Here,the effects of reducing copper content and increasing silicon and magnesium contents on the thixoformability of aluminium alloy 2014 were presented.The work consists of both the modelling and experimental validation.Results showed that by increasing Si and decreasing Cu content in the alloy,the solidification interval temperature was decreased and the temperature working window between the stipulated liquid fractions was widened,two of the characteristics favouring the process.A high solid-solution temperature employed resulted in the dissolution of unfavourable Mg2Si compound.An increase in Mg content used also resulted in the formation of the compactπ-Al8FeMg3Si6 phase and the decrease in the amount of the sharp and plate-like structure of theβ-Al5FeSi phase,improving the strength of the modified alloy.Subsequent T6 heat treatment successfully further increased the strength of the modified alloy.展开更多
The effects of Mg content on the microstructure and tensile properties of thixoformed A319 alloys were studied. The samples were thixoformed at 50% liquid content and some of the thixoformed samples were subjected to ...The effects of Mg content on the microstructure and tensile properties of thixoformed A319 alloys were studied. The samples were thixoformed at 50% liquid content and some of the thixoformed samples were subjected to the T6 heat treatment. The samples were then examined by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy and X-ray diffraction (XRD) analysis as well as tensile tests. The results showed that magnesium was able to refine the eutectic silicon in the samples. It was also observed that a compact Al9FeMg3Si5 phase was formed when the magnesium content was 1.0% and 1.5%. The results also revealed that as the magnesium content in the alloy increases, the tensile strengths of the thixoformed alloys also increase. The ultimate tensile strength, yield strength and elongation to fracture of the thixoformed A319 heat treated alloy were 298 MPa, 201 MPa and 4.5%, respectively, whereas the values of the thixoformed heat treated alloy with 1.5% Mg content were 325 MPa, 251 MPa and 1.4%, respectively. Thixoformed A319 alloy showed a dimple fracture behaviour, while thixoformed A319 alloys with 1.5% Mg showed a mixed mode fracture behaviour, where dimple and cleavage ruptures were seen on the fracture surface of the samples.展开更多
Magnetic nozzle appears to be a practical solution for prolonged space missions.For efficient handling of the spaceship,an in-flight solution to customize the thrust from the magnetic nozzle is essential.Here a new co...Magnetic nozzle appears to be a practical solution for prolonged space missions.For efficient handling of the spaceship,an in-flight solution to customize the thrust from the magnetic nozzle is essential.Here a new concept of three-thick coils system is proposed for tailoring the magnetic field in-flight in accordance with electron pressure distribution.The role of peak position of the pressure and its axial gradient is also uncovered for realizing higher thrust.About three-fold increase in thrust is observed when the electron temperature is raised to w2.5 times of its original value at the exit plane.The set-up is optimized for its best performance and efficient use in the electric space propulsion sector with thrust approaching 5 mN.In particular,this can contribute to the attitude control or the precision pointing of the spacecraft,the technology for removal of space debris and manipulating the ion momentum flux lost to a wall or unsteady laser produced plasma flow in a magnetic nozzle.展开更多
A concept for plasma detachment in a magnetic nozzle is developed based on the detachment region which is found to decrease with the taper angle of the coils employed in the proposed flexible three coil setup.On taper...A concept for plasma detachment in a magnetic nozzle is developed based on the detachment region which is found to decrease with the taper angle of the coils employed in the proposed flexible three coil setup.On tapering the coils while resulting in the same crosssectional area,the plasma plume outside the throat grows radially that leads to an enhancement in the thrust from 2.67 mN to 5 mN at the final detachment plane for a rise in the taper angle from 0 to 13.The maximum thrust can reach about 9 mN when the middle coil is shifted closer to the right coil along with increasing middle-to-outer-coil diameter(inner)ratio from 1 to 3.Proposed three-tapered-coils arrangement for a magnetic nozzle turns out to be a robust candidate for space propulsion offering the ability to control plasma detachment and tune thrust in-flight simply via mechanical movements without changing the current.展开更多
基金Universiti Kebangsaan Malaysia(UKM)and the Ministry of Higher Education(MOHE),Malaysia,for financial support under research grants AP-2012-014 and FRGS/1/2014/TK01/UKM/01/2
文摘A series of Al-6Si-3Cu-(0.3-2)Mg alloys were produced by a conventional casting process.Cooling slope technique wasemployed to produce feedstocks before they were thixoformed at50%liquid fraction.The effect of Mg on the microstructure ofAl-Si-Cu aluminium alloys under as-cast and semisolid conditions was investigated.It was found that by adding Mg to Al-Si-Cualloy,some of the Al2Cu phase and silicon were consumed to form Al5Cu2Mg3Si5and Mg2Si phases.The needle-likeβ-Al5FeSi phasetransformed to Chinese-script-likeπ-Al8Mg3FeSi6with the addition of Mg.In the as-cast alloys,the primaryα(Al)was dendritic,butas the Mg content increased,the phase became less dendritic.Moreover,the Mg addition considerably modified the size of theα(Al)phase,but it had no significant effect on the silicon morphology.In the thixoformed alloys,the microstructure showed a fine globularprimary phase surrounded by uniformly distributed silicon and fragmented intermetallic phases.The eutectic silicon was modifiedfrom a flaky and acicular shape to fine fibrous particles.The effect of Mg on eutectic silicon during semisolid processing wasevident.The primary Mg2Si particles were modified from big polygonal particles to become smaller and more globular,whereas themorphology of the Chinese-script-likeπ-Al8Mg3FeSi6changed to a compact shape.The results also exhibit that as the Mg content inthe A319alloy increased,the hardness,yield strength and ultimate tensile strength of the thixoformed alloys significantly improved,but the elongation to fracture dropped.
基金Universiti Teknikal Malaysia Melaka (UTeM) and the Ministry of Education Malaysia for financial support of this studyUniversiti Kebangsaan Malaysia (UKM) for the financial support under research grants GUP-2012-040 and AP-2012-014
文摘The effects of Cu content on the microstructure and mechanical properties of thixoformed Al-6Si-xCu-0.3Mg(x= 3,4,5and 6,mass fraction,%) alloys were studied.The samples were thixoformed at 50%liquid content and several of the samples were treated with the T6 heat treatment.The samples were then examined by optical microscopy(OM),scanning electron microscopy(SEM),energy dispersive X-ray(EDX) spectroscopy and X-ray diffraction(XRD) analysis,as well as hardness and tensile tests.The results show that the cooling slope casting and thixoforming process promote the formation of very fine and well distributed intermetallic compounds in the aluminium matrix and the mechanical properties of the alloys increase considerably compared with the permanent mould casting.The results also reveal that as the Cu content in the alloy increases,the hardness and tensile strength of the thixoformed alloys also increase.The ultimate tensile strength,yield strength and elongation to fracture of the thixoformed heat-treated Al-6Si-3Cu-0.3Mg alloy are 298 MPa,201 MPa and 4.5%,respectively,whereas the values of the thixoformed heat-treated alloy with high Cu content(6%) are 361 MPa,274 MPa and 1.1%,respectively.The fracture of the thixoformed Al-6Si-3Cu-0.3Mg alloy shows a dimple rupture,whereas in the alloy that contains the highest Cu content(6%),a cleavage fracture is observed.
基金the National University of Malaysia (Universiti Kebangsaan Malaysia, UKM)the Ministry of Education (MOE) of Malaysia for the financial support received under research grant DIP-2016-007
文摘Thixoforming is a processing method that deforms metal in a semisolid state.The advantages of this process include the production of parts with good surface finish,fine microstructures and superior mechanical properties.However,the process mostly produces parts from aluminium cast grades,thereby not fully utilising the true potential of this method.Hence,thermodynamic modelling can be used to formulate alloy compositions that favour this processing method.Here,the effects of reducing copper content and increasing silicon and magnesium contents on the thixoformability of aluminium alloy 2014 were presented.The work consists of both the modelling and experimental validation.Results showed that by increasing Si and decreasing Cu content in the alloy,the solidification interval temperature was decreased and the temperature working window between the stipulated liquid fractions was widened,two of the characteristics favouring the process.A high solid-solution temperature employed resulted in the dissolution of unfavourable Mg2Si compound.An increase in Mg content used also resulted in the formation of the compactπ-Al8FeMg3Si6 phase and the decrease in the amount of the sharp and plate-like structure of theβ-Al5FeSi phase,improving the strength of the modified alloy.Subsequent T6 heat treatment successfully further increased the strength of the modified alloy.
基金the Universiti Teknikal Malaysia Melaka (UTeM)the Ministry of Education, Malaysia for being financial sponsorsUniversiti Kebangsaan Malaysia (UKM) for the financial support under research grants GUP-2012-040 and AP-2012-014
文摘The effects of Mg content on the microstructure and tensile properties of thixoformed A319 alloys were studied. The samples were thixoformed at 50% liquid content and some of the thixoformed samples were subjected to the T6 heat treatment. The samples were then examined by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy and X-ray diffraction (XRD) analysis as well as tensile tests. The results showed that magnesium was able to refine the eutectic silicon in the samples. It was also observed that a compact Al9FeMg3Si5 phase was formed when the magnesium content was 1.0% and 1.5%. The results also revealed that as the magnesium content in the alloy increases, the tensile strengths of the thixoformed alloys also increase. The ultimate tensile strength, yield strength and elongation to fracture of the thixoformed A319 heat treated alloy were 298 MPa, 201 MPa and 4.5%, respectively, whereas the values of the thixoformed heat treated alloy with 1.5% Mg content were 325 MPa, 251 MPa and 1.4%, respectively. Thixoformed A319 alloy showed a dimple fracture behaviour, while thixoformed A319 alloys with 1.5% Mg showed a mixed mode fracture behaviour, where dimple and cleavage ruptures were seen on the fracture surface of the samples.
文摘Magnetic nozzle appears to be a practical solution for prolonged space missions.For efficient handling of the spaceship,an in-flight solution to customize the thrust from the magnetic nozzle is essential.Here a new concept of three-thick coils system is proposed for tailoring the magnetic field in-flight in accordance with electron pressure distribution.The role of peak position of the pressure and its axial gradient is also uncovered for realizing higher thrust.About three-fold increase in thrust is observed when the electron temperature is raised to w2.5 times of its original value at the exit plane.The set-up is optimized for its best performance and efficient use in the electric space propulsion sector with thrust approaching 5 mN.In particular,this can contribute to the attitude control or the precision pointing of the spacecraft,the technology for removal of space debris and manipulating the ion momentum flux lost to a wall or unsteady laser produced plasma flow in a magnetic nozzle.
文摘A concept for plasma detachment in a magnetic nozzle is developed based on the detachment region which is found to decrease with the taper angle of the coils employed in the proposed flexible three coil setup.On tapering the coils while resulting in the same crosssectional area,the plasma plume outside the throat grows radially that leads to an enhancement in the thrust from 2.67 mN to 5 mN at the final detachment plane for a rise in the taper angle from 0 to 13.The maximum thrust can reach about 9 mN when the middle coil is shifted closer to the right coil along with increasing middle-to-outer-coil diameter(inner)ratio from 1 to 3.Proposed three-tapered-coils arrangement for a magnetic nozzle turns out to be a robust candidate for space propulsion offering the ability to control plasma detachment and tune thrust in-flight simply via mechanical movements without changing the current.
