Billets of A356 aluminum alloy were treated using ultrasonic vibrations during solidification.The billets were reheated to the semisolid state at different routes to optimize the procedure.Billets were,then,thixocast ...Billets of A356 aluminum alloy were treated using ultrasonic vibrations during solidification.The billets were reheated to the semisolid state at different routes to optimize the procedure.Billets were,then,thixocast using a die casting machine.The results showed that the ultrasonic-treated billets exhibited finely distributed α（Al） globules after reheating and thixocasting.The thixocast ultrasonic-treated billets showed higher ultimate tensile strength and elongation compared with the untreated billets.Moreover,the thixocast parts showed a tendency to ductile fracture under tension when made from ultrasonic-treated billets,while those made of untreated billets showed brittle fracture with obvious straight facets.These results revealed the feasibility and competence of ultrasonic melt treatment as a potential route for preparing billets for thixocasting.展开更多
A new technology,semi-solid casting(thixocasting) method,was used to replace the conventional hot forging process to form AISI420 stainless steel air-turbine blade.The power law cut-off(PLCO) material model in Procast...A new technology,semi-solid casting(thixocasting) method,was used to replace the conventional hot forging process to form AISI420 stainless steel air-turbine blade.The power law cut-off(PLCO) material model in Procast software was used to simulate the thixocasting process.The thixocasting process was simulated.The results show that the reasonable technology parameters for air-turbine blade thixocasting process are obtained:billet temperature 1 483-1 485 °C,piston velocity 12-15 m/s and die temperature is about 400 °C.展开更多
Forging is state-of-the-art for producing hand tools on an industrial scale.Due to high demands on the stiffness and the fracture toughness,high-strength forging steels were used to provide cavity-free components with...Forging is state-of-the-art for producing hand tools on an industrial scale.Due to high demands on the stiffness and the fracture toughness,high-strength forging steels were used to provide cavity-free components with high mechanical load capacity.Moreover,forging is a cost-effective mass production process but,in spite of all its advantages,it has its limitations,e.g.in the freedom of designs.However,because of the extreme thermal loading(particularly with regard to permanent moulds) and the frequently unavoidable casting defects,hand tools are not cast.By means of thixocasting steel,technical difficulties can be reduced and new options are provided which allow the manufacturing of components with much higher complexity than that using forging.Through near-net shape production,manufacturing steps and costs can be reduced.Furthermore,steels,which are difficult to forge but nonetheless have high potential for specific applications(such as high strength or corrosion resistant steels),can also be processed.In cooperation with industrial partners,X39CrMo17 stainless steel combination spanners with 17 mm width across flats were thixocast.Forming dies were designed and optimized by simulation,the hot forming X38CrMoV5 tool steel as well as the molybdenum alloy TZM were selected as the tool alloys.The dies were treated by a plasma nitriding process and subsequently coated with crystalline Al2O3 protective coatings by plasma-enhanced chemical vapor deposition(PECVD).During the experiments,combination spanners were successfully cast in the semi-solid state.Cast parts were heat-treated to enhance the toughness of components,which was subsequently measured by a standardized torque test.Moreover,a hypothetical approach of a possible,industrial batch process was carried out using the simulation software MAGMAsoft.展开更多
Tensile fracture behaviors of thixocast, artificially aged thixocast （thixocast＋T6） and as-extruded AA7075 alloys were investigated. The microstructural and fractographic observations were carried out using optical...Tensile fracture behaviors of thixocast, artificially aged thixocast （thixocast＋T6） and as-extruded AA7075 alloys were investigated. The microstructural and fractographic observations were carried out using optical microscope （OM） and scanning electron microscope （SEM）. Experimental studies showed that as-extruded and thixocast＋T6 specimens exhibited considerably more excellent mechanical properties than as-thixocast AA7075 specimen. T6 artificial heat treatment with prolonged solution treatment significantly improved the tensile properties of the thixocast AA7075 alloy. The tensile properties of as-extruded and thixocast＋T6 specimens were close to each other. In as-thixocast specimen having remarkable micro-cracks, fracture was intergranular brittle type. The ductile fracture surfaces were observed in as-extruded and thixocast＋T6 specimens. In as-thixocast specimens, decohesion started between the eutectic-matrix interfaces and propagated through grains. Micro-void coalescence was the dominant form of fracture in thixocast＋T6 heat treated specimens. The micro-voids nucleation was initiated at the interface between the matrix and multinary eutectic structure.展开更多
Abstract： The demand for high performance cast aluminum alloy components is often disturbed by increasing impurity elements, such as iron accumulated from recycled scraps. It is strongly required that coarse plate-li...Abstract： The demand for high performance cast aluminum alloy components is often disturbed by increasing impurity elements, such as iron accumulated from recycled scraps. It is strongly required that coarse plate-like iron compound of β-Al5FeSi turns into harmless form without the need for applying refining additives or expensive virgin ingots. The microstructural modification of Al-7mass%Si alloy billets with different iron contents was examined by applying ultrasonic vibration during the solidification. Ultrasonically melt-treated billets were thixocast right after induction heating up to the semisolid temperature of 583 ℃, the microstructure and tensile properties were evaluated in the thixocast components. Globular primary reAl is required to fill up a thin cavity in thixocasting, so that the microstructural modification by ultrasonic melt-treatment was firstly confirmed in the billets. With ultrasonic melt-treatment in the temperature range of 630 ℃ to 605 ℃, the primary α-AI transforms itself from dendrite into fine globular in morphology. The coarse plate-like β-AIsFeSi compound becomes markedly finer compared with those in non-treated billets. Semisolid soaking up to 583 ℃, does not appreciably affect the size of β-AIsFeSi compounds; however, it affects the solid primary reAl morphology to be more globular, which is convenient for thixocasting. After thixocasting with preheated billets, eutectic silicon plates are extremely refined due to the rapid solidification arising from low casting temperature. The tensile strength of thixocast samples with different iron contents does not change much even at 2mass% of iron, when thixocast with ultrasonically melt-treated billets. However, thixocast AI-7mass%Si-2mass%Fe alloy with non-treated billets exhibits an inferior strength of 80 MPa, compared with 180 MPa with ultrasonically melt-treated billets. The elongation is also improved by about a factor of two in thixocastings with ultrasonically melt-treated billets for all iron contents of AI-7mass%Si alloys, for example, the elongation of 11% in thixocast of AI-7mass%Si-0.5mass%Fe alloy with ultrasonically melt-treated billets, 5% in that with non-treated billets.展开更多
文摘Billets of A356 aluminum alloy were treated using ultrasonic vibrations during solidification.The billets were reheated to the semisolid state at different routes to optimize the procedure.Billets were,then,thixocast using a die casting machine.The results showed that the ultrasonic-treated billets exhibited finely distributed α（Al） globules after reheating and thixocasting.The thixocast ultrasonic-treated billets showed higher ultimate tensile strength and elongation compared with the untreated billets.Moreover,the thixocast parts showed a tendency to ductile fracture under tension when made from ultrasonic-treated billets,while those made of untreated billets showed brittle fracture with obvious straight facets.These results revealed the feasibility and competence of ultrasonic melt treatment as a potential route for preparing billets for thixocasting.
基金Project(50375117) supported by the National Natural Science Foundation of China
文摘A new technology,semi-solid casting(thixocasting) method,was used to replace the conventional hot forging process to form AISI420 stainless steel air-turbine blade.The power law cut-off(PLCO) material model in Procast software was used to simulate the thixocasting process.The thixocasting process was simulated.The results show that the reasonable technology parameters for air-turbine blade thixocasting process are obtained:billet temperature 1 483-1 485 °C,piston velocity 12-15 m/s and die temperature is about 400 °C.
基金the German Research Foundation (DFG),which supports this work within the framework of the collaborative research centre SFB 289
文摘Forging is state-of-the-art for producing hand tools on an industrial scale.Due to high demands on the stiffness and the fracture toughness,high-strength forging steels were used to provide cavity-free components with high mechanical load capacity.Moreover,forging is a cost-effective mass production process but,in spite of all its advantages,it has its limitations,e.g.in the freedom of designs.However,because of the extreme thermal loading(particularly with regard to permanent moulds) and the frequently unavoidable casting defects,hand tools are not cast.By means of thixocasting steel,technical difficulties can be reduced and new options are provided which allow the manufacturing of components with much higher complexity than that using forging.Through near-net shape production,manufacturing steps and costs can be reduced.Furthermore,steels,which are difficult to forge but nonetheless have high potential for specific applications(such as high strength or corrosion resistant steels),can also be processed.In cooperation with industrial partners,X39CrMo17 stainless steel combination spanners with 17 mm width across flats were thixocast.Forming dies were designed and optimized by simulation,the hot forming X38CrMoV5 tool steel as well as the molybdenum alloy TZM were selected as the tool alloys.The dies were treated by a plasma nitriding process and subsequently coated with crystalline Al2O3 protective coatings by plasma-enhanced chemical vapor deposition(PECVD).During the experiments,combination spanners were successfully cast in the semi-solid state.Cast parts were heat-treated to enhance the toughness of components,which was subsequently measured by a standardized torque test.Moreover,a hypothetical approach of a possible,industrial batch process was carried out using the simulation software MAGMAsoft.
基金the financial supports of the State Planning Organization of Turkey (DPT Project Number: 2003K120470-27)Gazi University Scientific Research Fund (GUBAP Project Number: 07/2013-01)
文摘Tensile fracture behaviors of thixocast, artificially aged thixocast （thixocast＋T6） and as-extruded AA7075 alloys were investigated. The microstructural and fractographic observations were carried out using optical microscope （OM） and scanning electron microscope （SEM）. Experimental studies showed that as-extruded and thixocast＋T6 specimens exhibited considerably more excellent mechanical properties than as-thixocast AA7075 specimen. T6 artificial heat treatment with prolonged solution treatment significantly improved the tensile properties of the thixocast AA7075 alloy. The tensile properties of as-extruded and thixocast＋T6 specimens were close to each other. In as-thixocast specimen having remarkable micro-cracks, fracture was intergranular brittle type. The ductile fracture surfaces were observed in as-extruded and thixocast＋T6 specimens. In as-thixocast specimens, decohesion started between the eutectic-matrix interfaces and propagated through grains. Micro-void coalescence was the dominant form of fracture in thixocast＋T6 heat treated specimens. The micro-voids nucleation was initiated at the interface between the matrix and multinary eutectic structure.
基金financially supported by the Grants-in Aid for Scientific Research from the Ministry of Education,Science,Sports and Culture (No.23560898)
文摘Abstract： The demand for high performance cast aluminum alloy components is often disturbed by increasing impurity elements, such as iron accumulated from recycled scraps. It is strongly required that coarse plate-like iron compound of β-Al5FeSi turns into harmless form without the need for applying refining additives or expensive virgin ingots. The microstructural modification of Al-7mass%Si alloy billets with different iron contents was examined by applying ultrasonic vibration during the solidification. Ultrasonically melt-treated billets were thixocast right after induction heating up to the semisolid temperature of 583 ℃, the microstructure and tensile properties were evaluated in the thixocast components. Globular primary reAl is required to fill up a thin cavity in thixocasting, so that the microstructural modification by ultrasonic melt-treatment was firstly confirmed in the billets. With ultrasonic melt-treatment in the temperature range of 630 ℃ to 605 ℃, the primary α-AI transforms itself from dendrite into fine globular in morphology. The coarse plate-like β-AIsFeSi compound becomes markedly finer compared with those in non-treated billets. Semisolid soaking up to 583 ℃, does not appreciably affect the size of β-AIsFeSi compounds; however, it affects the solid primary reAl morphology to be more globular, which is convenient for thixocasting. After thixocasting with preheated billets, eutectic silicon plates are extremely refined due to the rapid solidification arising from low casting temperature. The tensile strength of thixocast samples with different iron contents does not change much even at 2mass% of iron, when thixocast with ultrasonically melt-treated billets. However, thixocast AI-7mass%Si-2mass%Fe alloy with non-treated billets exhibits an inferior strength of 80 MPa, compared with 180 MPa with ultrasonically melt-treated billets. The elongation is also improved by about a factor of two in thixocastings with ultrasonically melt-treated billets for all iron contents of AI-7mass%Si alloys, for example, the elongation of 11% in thixocast of AI-7mass%Si-0.5mass%Fe alloy with ultrasonically melt-treated billets, 5% in that with non-treated billets.
