The influence of temperature on the flow behavior and rheological characteristics of an A356 alloy in the semi-solid state was investigated using backward extrusion process.Experiments were performed at 5 temperatures...The influence of temperature on the flow behavior and rheological characteristics of an A356 alloy in the semi-solid state was investigated using backward extrusion process.Experiments were performed at 5 temperatures and 4 different wall thicknesses.Viscosities were determined using the force-displacement graphs obtained form back extrusion tests.As observed experimentally,at a constant temperature,the increase of shear rate results in the decrease of alloy viscosity exponentially.Raising the temperature increases the liquid fraction hence reduces the semi-solid alloy viscosity.Metallographic and image analyses show that,because of low forming speed,liquid has time to escape from solid phase forward the sample wall.This condition is the main reason for the segregation phenomenon seen in the base and walls.Vickers hardness test on samples reveals that the hardness increases with the decrease of temperature and wall thickness.展开更多
Near net-shape production of complex parts with higher mechanical properties is one of the most important final goals of the recent researches on the semi-solid processing.Having the knowledge of the influence of ever...Near net-shape production of complex parts with higher mechanical properties is one of the most important final goals of the recent researches on the semi-solid processing.Having the knowledge of the influence of every parameter on the properties of final parts is the key in the production of high quality complex parts.Among these parameters forming temperature and velocity,and reheating and holding times have the greatest effects on the final mechanical properties of the parts.The influence of the parameters of non-dendritic billet production,forming speed,temperature and holding time on the properties of semi-solid extruded parts were investigated.Cooling-slope method was employed in order to produce non-dendritic billets.The material used was A356 aluminum alloy.Since the number of the parameters influencing the final properties of the parts was high(these parameters include:cooling slope angle,ram velocity,temperature and holding time),the final number of the experiments required would be n4,in which n is the number of the states of the parameters(5 in our case).In order to reduce this amount,design of experiments Tachuchi method was employed(design L25).Using this method the number of required experiments was reduced to 25.For the experiments the prepared semi-solid samples were extruded under isothermal condition and with 5 different ram speeds.Standard tensile tests were conducted on the extruded parts and the mechanical properties of the parts were determined.The obtained results analyzed with MiniTab and the influence of each of the parameters and also the percentage of its influence were calculated.Finally an optimum region for the parameters was determined.The temperature,ram speed,slope angle and holding time have more important effects descendingly.展开更多
文摘The influence of temperature on the flow behavior and rheological characteristics of an A356 alloy in the semi-solid state was investigated using backward extrusion process.Experiments were performed at 5 temperatures and 4 different wall thicknesses.Viscosities were determined using the force-displacement graphs obtained form back extrusion tests.As observed experimentally,at a constant temperature,the increase of shear rate results in the decrease of alloy viscosity exponentially.Raising the temperature increases the liquid fraction hence reduces the semi-solid alloy viscosity.Metallographic and image analyses show that,because of low forming speed,liquid has time to escape from solid phase forward the sample wall.This condition is the main reason for the segregation phenomenon seen in the base and walls.Vickers hardness test on samples reveals that the hardness increases with the decrease of temperature and wall thickness.
文摘Near net-shape production of complex parts with higher mechanical properties is one of the most important final goals of the recent researches on the semi-solid processing.Having the knowledge of the influence of every parameter on the properties of final parts is the key in the production of high quality complex parts.Among these parameters forming temperature and velocity,and reheating and holding times have the greatest effects on the final mechanical properties of the parts.The influence of the parameters of non-dendritic billet production,forming speed,temperature and holding time on the properties of semi-solid extruded parts were investigated.Cooling-slope method was employed in order to produce non-dendritic billets.The material used was A356 aluminum alloy.Since the number of the parameters influencing the final properties of the parts was high(these parameters include:cooling slope angle,ram velocity,temperature and holding time),the final number of the experiments required would be n4,in which n is the number of the states of the parameters(5 in our case).In order to reduce this amount,design of experiments Tachuchi method was employed(design L25).Using this method the number of required experiments was reduced to 25.For the experiments the prepared semi-solid samples were extruded under isothermal condition and with 5 different ram speeds.Standard tensile tests were conducted on the extruded parts and the mechanical properties of the parts were determined.The obtained results analyzed with MiniTab and the influence of each of the parameters and also the percentage of its influence were calculated.Finally an optimum region for the parameters was determined.The temperature,ram speed,slope angle and holding time have more important effects descendingly.
