The effect of thixoforming process on morphologies of silicon particles that affect fracture mode of A356 alloy was investigated.Microstructure and fracture surfaces of thixoformed samples were investigated by image a...The effect of thixoforming process on morphologies of silicon particles that affect fracture mode of A356 alloy was investigated.Microstructure and fracture surfaces of thixoformed samples were investigated by image analyzing technique and scanning electron microscopy.A new combination parameter, called silicon density ratio (SDR) index, was introduced.SDR index approximates the collective effects of morphological characteristics of silicon particles on microstructure transparency of alloy in crossing the dislocation.It is suggested that samples with lower SDR index have superior mechanical properties, especially elongation, and consequently intergranular fracture mode.On the contrary, samples with higher SDR index have inferior mechanical properties and fracture path tends to propagate along the cell boundaries leading to transgranular fracture.展开更多
Tensile properties of a thixoforged A356 alloy were measured and compared with those of rheocast and gravity cast alloys with the same composition.In the thixoforging process,A356 rheocast alloy produced by stirring m...Tensile properties of a thixoforged A356 alloy were measured and compared with those of rheocast and gravity cast alloys with the same composition.In the thixoforging process,A356 rheocast alloy produced by stirring method was reheated to 600 °C or 610 °C,held for 10 min,and then 50% deformation was applied.Microstructure,tensile properties and fracture surfaces of produced specimens were then investigated.Results obtained show that tensile strength,yield strength and elongation-to-failure of thixoforged samples formed at lower temperature are higher than those of samples formed at higher temperature.By increasing temperature,in the case of thixoforged samples,tensile fracture path is changed from trans-primary alpha phase to inter-primary alpha phase.Differences observed in the tensile fracture path and improvement in the mechanical properties due to thixoforging process is attributed to microstructural changes as well as morphological aspects of silicon phase.展开更多
Pitting behavior of thixoformed A356 alloy, with different reheating temperatures, was evaluated. Linear sweep voltammetric tests were used to study the pitting behavior of thixoformed, rheocast and gravity-cast A356 ...Pitting behavior of thixoformed A356 alloy, with different reheating temperatures, was evaluated. Linear sweep voltammetric tests were used to study the pitting behavior of thixoformed, rheocast and gravity-cast A356 alloy in a 3.5% NaCl solution. A simulation method was also used in order to identify local galvanic corrosion current density between local galvanic couples. The results obtained show that the resistance to pitting corrosion of the thixoformed samples formed at 600 ℃ is higher than that of the samples formed at 610 ℃ as well as rheocast and gravity-cast samples. These results could be explained by morphological aspects of silicon phase as well as the area effect as related to galvanic corrosion between silicon particles and eutectic aluminum phase.展开更多
文摘The effect of thixoforming process on morphologies of silicon particles that affect fracture mode of A356 alloy was investigated.Microstructure and fracture surfaces of thixoformed samples were investigated by image analyzing technique and scanning electron microscopy.A new combination parameter, called silicon density ratio (SDR) index, was introduced.SDR index approximates the collective effects of morphological characteristics of silicon particles on microstructure transparency of alloy in crossing the dislocation.It is suggested that samples with lower SDR index have superior mechanical properties, especially elongation, and consequently intergranular fracture mode.On the contrary, samples with higher SDR index have inferior mechanical properties and fracture path tends to propagate along the cell boundaries leading to transgranular fracture.
文摘Tensile properties of a thixoforged A356 alloy were measured and compared with those of rheocast and gravity cast alloys with the same composition.In the thixoforging process,A356 rheocast alloy produced by stirring method was reheated to 600 °C or 610 °C,held for 10 min,and then 50% deformation was applied.Microstructure,tensile properties and fracture surfaces of produced specimens were then investigated.Results obtained show that tensile strength,yield strength and elongation-to-failure of thixoforged samples formed at lower temperature are higher than those of samples formed at higher temperature.By increasing temperature,in the case of thixoforged samples,tensile fracture path is changed from trans-primary alpha phase to inter-primary alpha phase.Differences observed in the tensile fracture path and improvement in the mechanical properties due to thixoforging process is attributed to microstructural changes as well as morphological aspects of silicon phase.
文摘Pitting behavior of thixoformed A356 alloy, with different reheating temperatures, was evaluated. Linear sweep voltammetric tests were used to study the pitting behavior of thixoformed, rheocast and gravity-cast A356 alloy in a 3.5% NaCl solution. A simulation method was also used in order to identify local galvanic corrosion current density between local galvanic couples. The results obtained show that the resistance to pitting corrosion of the thixoformed samples formed at 600 ℃ is higher than that of the samples formed at 610 ℃ as well as rheocast and gravity-cast samples. These results could be explained by morphological aspects of silicon phase as well as the area effect as related to galvanic corrosion between silicon particles and eutectic aluminum phase.
