The appearance of macroscopic segregation in ZL205A alloy castings bears a super resemblance to theappearance of shrinkage porosity, and the chemical composition of the segregation is Al2Cu whose microstructure isin t...The appearance of macroscopic segregation in ZL205A alloy castings bears a super resemblance to theappearance of shrinkage porosity, and the chemical composition of the segregation is Al2Cu whose microstructure isin the form of dentrite or skeleton crystal. According to the characteristic of nebulous segregation, the formationprocess could be divided into two steps by the eutectic temperature of Al2Cu. Then a criterion for each of the twosteps is brought forward on the basis of the shrinkage porosity criterion of low pressure casting.展开更多
The mold filling behavior of gradual expansion structure in low pressure casting was studied by two phase flow model using the Volume of Fluid method, and was verified by water simulation with a Plexiglas mold. To get...The mold filling behavior of gradual expansion structure in low pressure casting was studied by two phase flow model using the Volume of Fluid method, and was verified by water simulation with a Plexiglas mold. To get smooth mold filling process and provide a guide for the pressurizing speed design in the producing practice, the mathematical model with the pressurizing speed, expansion angle and height of the gradual expansion structure was established. For validation experiments, ZL205 A alloy castings were produced under two different pressurizing speeds. Weibull probability plots were used to assess the fracture mechanisms under different pressurizing speeds. Mechanical properties of ZL205 A alloy were applied to assess the entrainment of oxide film. The results show that the filling process of a gradual expansion structure in a low pressure casting can be divided into the spreading stage and filling stage by gate velocity. The gate velocity continues to increase in the gradual expansion structure, and increases with the increase of pressurizing speed or expansion angle. Under the effect of the falling fluid raised by the jet flow along the sidewall, the fluid velocity decreases in the jet zone from ingate to free surface. As such, oxide film entrainment does not occur when the gate velocity is greater than the critical velocity, andthe gate velocity no longer reflects the real state of the free surface. The scatter of the mechanical properties is strongly affected by the entrainment of oxide films.展开更多
The burst feeding behavior of ZL205 A casting under mechanical vibration and low pressure was investigated by casting experiment and physical model. Experimental results indicated that the burst feeding appeared repea...The burst feeding behavior of ZL205 A casting under mechanical vibration and low pressure was investigated by casting experiment and physical model. Experimental results indicated that the burst feeding appeared repeatedly during solidification and left a shrinkage cavity with layered structure under mechanical vibration. The castings with less shrinkage and higher density could be achieved through the vibration. The calculation results of physical model showed that the burst feeding could perform spontaneously under vibration while difficultly without vibration in low-pressure die casting. The obstruction of a casting could be broken and the grains could be rearranged by the vibration. And the obstruction could be carried away due to the inner and outer pressure difference, causing a burst feeding.展开更多
The effect of excitation current intensity on the mechanical properties of ZL205 A castings solidified under a traveling magnetic field was studied. The results of the experiment indicate that the excitation current i...The effect of excitation current intensity on the mechanical properties of ZL205 A castings solidified under a traveling magnetic field was studied. The results of the experiment indicate that the excitation current intensity of the traveling magnetic field has a great influence on the mechanical properties of the ZL205 A castings. When the excitation current intensity is 15 A, the tensile strength and elongation of ZL205 A alloy castings increase 27.2% and 67.7%, respectively, compared with those of the same alloy solidified under gravity. The improvement of mechanical properties is attributed to the decrease of micro-porosity in the alloy. Under the traveling magnetic field, the feeding pressure in the alloy melt before solidification can be enhanced due to the electromagnetic force. Moreover, the melt flow induced by the traveling magnetic field can decrease the temperature gradient. The feeding resistance will be increased because the temperature gradient decrease. So traveling magnetic field has an optimum effect on feeding.展开更多
文摘The appearance of macroscopic segregation in ZL205A alloy castings bears a super resemblance to theappearance of shrinkage porosity, and the chemical composition of the segregation is Al2Cu whose microstructure isin the form of dentrite or skeleton crystal. According to the characteristic of nebulous segregation, the formationprocess could be divided into two steps by the eutectic temperature of Al2Cu. Then a criterion for each of the twosteps is brought forward on the basis of the shrinkage porosity criterion of low pressure casting.
文摘The mold filling behavior of gradual expansion structure in low pressure casting was studied by two phase flow model using the Volume of Fluid method, and was verified by water simulation with a Plexiglas mold. To get smooth mold filling process and provide a guide for the pressurizing speed design in the producing practice, the mathematical model with the pressurizing speed, expansion angle and height of the gradual expansion structure was established. For validation experiments, ZL205 A alloy castings were produced under two different pressurizing speeds. Weibull probability plots were used to assess the fracture mechanisms under different pressurizing speeds. Mechanical properties of ZL205 A alloy were applied to assess the entrainment of oxide film. The results show that the filling process of a gradual expansion structure in a low pressure casting can be divided into the spreading stage and filling stage by gate velocity. The gate velocity continues to increase in the gradual expansion structure, and increases with the increase of pressurizing speed or expansion angle. Under the effect of the falling fluid raised by the jet flow along the sidewall, the fluid velocity decreases in the jet zone from ingate to free surface. As such, oxide film entrainment does not occur when the gate velocity is greater than the critical velocity, andthe gate velocity no longer reflects the real state of the free surface. The scatter of the mechanical properties is strongly affected by the entrainment of oxide films.
基金Projects(51475120,U1537201) supported by the National Natural Science Foundation of China
文摘The burst feeding behavior of ZL205 A casting under mechanical vibration and low pressure was investigated by casting experiment and physical model. Experimental results indicated that the burst feeding appeared repeatedly during solidification and left a shrinkage cavity with layered structure under mechanical vibration. The castings with less shrinkage and higher density could be achieved through the vibration. The calculation results of physical model showed that the burst feeding could perform spontaneously under vibration while difficultly without vibration in low-pressure die casting. The obstruction of a casting could be broken and the grains could be rearranged by the vibration. And the obstruction could be carried away due to the inner and outer pressure difference, causing a burst feeding.
基金financially supported by the National Basic Research Program of China(2011CB610406)the Natural Science Foundation of Hei Longjiang Province(JC201209)the National Natural Science Foundation of China(51425402)
文摘The effect of excitation current intensity on the mechanical properties of ZL205 A castings solidified under a traveling magnetic field was studied. The results of the experiment indicate that the excitation current intensity of the traveling magnetic field has a great influence on the mechanical properties of the ZL205 A castings. When the excitation current intensity is 15 A, the tensile strength and elongation of ZL205 A alloy castings increase 27.2% and 67.7%, respectively, compared with those of the same alloy solidified under gravity. The improvement of mechanical properties is attributed to the decrease of micro-porosity in the alloy. Under the traveling magnetic field, the feeding pressure in the alloy melt before solidification can be enhanced due to the electromagnetic force. Moreover, the melt flow induced by the traveling magnetic field can decrease the temperature gradient. The feeding resistance will be increased because the temperature gradient decrease. So traveling magnetic field has an optimum effect on feeding.
