Since the automotive industry has many possible applications for semi-solid metal (SSM)-high-pressure die casting (HPDC) parts, the newly developed heat treatment cycles, as well as the traditional heat treatment cycl...Since the automotive industry has many possible applications for semi-solid metal (SSM)-high-pressure die casting (HPDC) parts, the newly developed heat treatment cycles, as well as the traditional heat treatment cycles, were applied to A356 brake calipers cast using a LK DCC630 HPDC machine.Vickers hardness measurements at a cross section of the brake calipers were performed, indicating that similar values can be obtained when using the significantly shorter heat treatment cycles.Finally, the typical tensile properties that can be obtained for SSM-HPDC A356 brake calipers are compared with those manufactured by gravity die casting.Results indicate that the differences in microstructures (globular or dendritic) do not have a noteworthy effect on the heat treatment response.This implies that the short heat treatment cycles originally developed for globular SSM-HPDC A356 castings can be successfully applied to dendritic liquid A356 castings too.展开更多
The microstructures and tensile properties of semi-solid metal high pressure die cast(SSM-HPDC) F357 alloys with low and high levels of Fe,Ni and Cr were compared in different temper conditions.ThermoCalc software was...The microstructures and tensile properties of semi-solid metal high pressure die cast(SSM-HPDC) F357 alloys with low and high levels of Fe,Ni and Cr were compared in different temper conditions.ThermoCalc software was used to predict the different intermetallics that can be expected in the alloys,and scanning electron microscopy(SEM) with energy dispersive spectroscopy(EDS) was used to investigate the actual intermetallics that formed.The influence of these intermetallics on tensile properties was quantified.The results show that lower strength is obtained in the alloy with high Fe,Ni and Cr levels.This is attributed mainly to the formation of more π-Al8FeMg3Si6 phase,which removes strengthening Mg atoms from solid solution.Also,the ductility of the high Fe,Ni and Cr levels alloy is decreased significantly due to microcracking of the higher volume fraction π-Al8FeMg3Si6 and Al9FeNi phases.The combination of lower strength and ductility results in a decrease of the quality index of this alloy compared with the alloy with low levels of Fe,Ni and Cr.展开更多
Thermodynamic calculation of the two-phase Ti alloy was completed using Compu Therm Pandat? and Ti data base, followed by isothermal compression of Ti6 Al4 V(Grade 5), with an initial colony lamellar structure that wa...Thermodynamic calculation of the two-phase Ti alloy was completed using Compu Therm Pandat? and Ti data base, followed by isothermal compression of Ti6 Al4 V(Grade 5), with an initial colony lamellar structure that was performed in the(α+β) and β-phase field. Microstructural evolution and phase transformation were investigated using X-ray diffraction, scanning and transmission electron microscopy. The presence of the Ti3 Al or α2(hcp), the phase stability and transition temperatures were predicted by the Gibbs free energy-temperature and phase fraction-temperature diagrams. The isothermal compression in the(α+β)-phase field is characterized by reorientation and localized kinking of α/β lamellae, and cracking at α/β interphase regions. While in the α→β-phase transformation area, deformation in β-phase and at α/β interphase boundaries, extensive transformation of α into β-phase, martensitic transformation and spheroidization of α-laths mainly characterize this isothermal compression. A complete transformation of α into β single phase occurs in the β-phase field. Ti3 Al or α2(hcp),β(bcc) and α(hcp)-phase, and additional hcp α’ and orthorhombic α' phases in a deformed Ti6 Al4 V are revealed. The flow stress level, the dynamic recovery and dynamic globularization are affected by deformation temperature.展开更多
文摘Since the automotive industry has many possible applications for semi-solid metal (SSM)-high-pressure die casting (HPDC) parts, the newly developed heat treatment cycles, as well as the traditional heat treatment cycles, were applied to A356 brake calipers cast using a LK DCC630 HPDC machine.Vickers hardness measurements at a cross section of the brake calipers were performed, indicating that similar values can be obtained when using the significantly shorter heat treatment cycles.Finally, the typical tensile properties that can be obtained for SSM-HPDC A356 brake calipers are compared with those manufactured by gravity die casting.Results indicate that the differences in microstructures (globular or dendritic) do not have a noteworthy effect on the heat treatment response.This implies that the short heat treatment cycles originally developed for globular SSM-HPDC A356 castings can be successfully applied to dendritic liquid A356 castings too.
文摘The microstructures and tensile properties of semi-solid metal high pressure die cast(SSM-HPDC) F357 alloys with low and high levels of Fe,Ni and Cr were compared in different temper conditions.ThermoCalc software was used to predict the different intermetallics that can be expected in the alloys,and scanning electron microscopy(SEM) with energy dispersive spectroscopy(EDS) was used to investigate the actual intermetallics that formed.The influence of these intermetallics on tensile properties was quantified.The results show that lower strength is obtained in the alloy with high Fe,Ni and Cr levels.This is attributed mainly to the formation of more π-Al8FeMg3Si6 phase,which removes strengthening Mg atoms from solid solution.Also,the ductility of the high Fe,Ni and Cr levels alloy is decreased significantly due to microcracking of the higher volume fraction π-Al8FeMg3Si6 and Al9FeNi phases.The combination of lower strength and ductility results in a decrease of the quality index of this alloy compared with the alloy with low levels of Fe,Ni and Cr.
基金The funding of this project by the South African Department of Science and Technology (DST)
文摘Thermodynamic calculation of the two-phase Ti alloy was completed using Compu Therm Pandat? and Ti data base, followed by isothermal compression of Ti6 Al4 V(Grade 5), with an initial colony lamellar structure that was performed in the(α+β) and β-phase field. Microstructural evolution and phase transformation were investigated using X-ray diffraction, scanning and transmission electron microscopy. The presence of the Ti3 Al or α2(hcp), the phase stability and transition temperatures were predicted by the Gibbs free energy-temperature and phase fraction-temperature diagrams. The isothermal compression in the(α+β)-phase field is characterized by reorientation and localized kinking of α/β lamellae, and cracking at α/β interphase regions. While in the α→β-phase transformation area, deformation in β-phase and at α/β interphase boundaries, extensive transformation of α into β-phase, martensitic transformation and spheroidization of α-laths mainly characterize this isothermal compression. A complete transformation of α into β single phase occurs in the β-phase field. Ti3 Al or α2(hcp),β(bcc) and α(hcp)-phase, and additional hcp α’ and orthorhombic α' phases in a deformed Ti6 Al4 V are revealed. The flow stress level, the dynamic recovery and dynamic globularization are affected by deformation temperature.
