| For ZL205 A alloy,its mechanical properties at indoor temperature is prominent,is one of the high strength casting aluminum alloy in industrial production.Because of excellent machining,welding and other comprehensive performance,it is widely used in large load-bearing structure.In casting process,the heat transfer coefficient of casting mold interface mainly influences the whole solidification process and temperature field,and also determines the internal quality of the casting.therefore,It is very important to establish an effective calculation model and determine the heat transfer coefficient for the optimization of 205 A alloy casting process.After comprehensive study on Fourier thermal partial differential equation,the heat transfer inverse model under cylindrical coordinate system and cartesian coordinate system is established,and the inverse calculation program is written.The difficulty of calculating interfacial heat transfer coefficient experiment is to locate the thermocouple accurately.Therefore,a accurate positioning method of thermocouple in sand mold and casting was improved,and the temperature field in casting mold was obtained.The interfacial heat transfer coefficient under the corresponding conditions is obtained by putting the temperature field measured into the inverse modelWhen metal liquid enters the casting mold,the casting-model interface heat transfer coefficient at increases immediately due to the large temperature difference between metal liquid at the interface and the casting mold.With the decrease of temperature difference between casting surface temperature and casting surface temperature,the heat transfer coefficient of casting-casting interface changes from rising to falling.The solidification and crystallization occurred in the liquid metal after the liquid metal temperature entered the liquid phase line,and the heat transfer coefficient of casting-model interface began to increase with the solidification process.When the temperature of metal liquid reaches eutectic point,eutectic reaction occurs and releases a large amount of heat,resulting in a large increase in the heat transfer coefficient in a short time.When the wall thickness of casting is 4mm,12 mm and 18 mm,the peak heat transfer coefficient of mold-casting interface is 14652 W m ?K,716 W m2 ?K and 4312 W m ?K respectively.When the wall thickness of the casting increases,the more obvious the solidification and contraction phenomenon is,the greater the air gap formed at the interface.When the solidification pressure is 0KPa,20 KPa,60KPa and 80 KPa,the interfacial heat transfer coefficient reaches the peak value of 7422 W m ?K,10522 W m ?K,2080 W m2 ?K and 2150 W m2 ?K.The peak of interfacial heat transfer coefficient increases with the increase of solidification pressure.The temperature field of the casting solidification process was simulated by using the interfacial heat transfer coefficient of temperature function obtained by the inverse algorithm and the single value interfacial heat transfer coefficient found in the literature.During solidification pressure of 20 KPA,simulation results analysis found that when using the interface heat transfer coefficient of temperature function,the temperature difference between the simulated and measured temperature than using a single value of average interface heat transfer coefficient is sm all.When the thickness of the casting wall is 18 mm,when the interfacial heat transfer coefficient of temperature function is used,the mean value of the temperature difference between simulated temperature and measured temperature is smaller than that of the single value interfacial heat transfer coefficient.It can be seen that the calculation precision is improved when the interfacial heat transfer coefficient of temperature function is used to simulate the temperature field... |
PDF Full Text Request