Process Innovation And Performance Optimization Of Low-pressure Die Casting Of Aluminum Alloy Engine Cylinder Head

Due to the excellent characteristics such as high specific strength and lower density of Al alloys,the application of Al alloy engine cylinder head has been adapted to the process of automobile lightweight.In the course of production process,raw materials consumptions are reduced,and in the course of its usage,fuel consumptions and vehicle exhaust emissions are reduced.It conforms to the rapid development of emerging industries and the requirements of environmental protection policies for energy conservation and emission reduction.In this paper,a grade AC4 B Al-Si-Cu alloy was selected to be studied,and low-pressure die-casting test bar mold with new structure and shape was designed using Creo software,and the rationality of the structure was subsequently verified using Pro CAST software.As well as,the Al-alloy test bar castings were manufactured with the Low-pressure Diecasting,the Vacuum-assisted Low-pressure Die-casting and the Ultrasonic-assisted Lowpressure Die-casting process,respectively.The mechanical properties and microstructure were analyzed and tested using suitable experiment equipment.Thus,the optimal process parameters were determined.Afterwards,a certain type of engine cylinder head was trialproduced using the above three processes under the best process parameters.The experimental results are as follows.At the same temperature,the properties of casting would be improved maintaining higher holding pressure.As the pouring temperature of melt,its properties increase with the same holding pressure.However,segregation appears into the casting structure when the pouring temperature is controlled too low,which affects the mechanical properties.With the increase of the vacuum degree from-0 bar to-0.6 bar,the castability of the melt increases,and the porosity of the casting simple decreases accordingly.When the vacuum is-0.6 bar,the castabilty is better,and the porosity is the least.With the increase of the ultrasonic power from 0 W to 720 W,the grain size refines,and the mechanical properties increase.When the ultrasonic is 720 W,the grain size is the finest,and the mechanical properties are better.The ultrasonic function plays a major role for performance improvement in the Ultrasonic-assisted Low-pressure Die-casting.Nevertheless,as ultrasonic power increases to 1080 W,the ultrasonic radiation rod resonates with the device,and ultrasonic reflection and cancellation occurs at the mold cavity,decreased mechanical properties and coarsened microstructure.Cylinder head was formed under the Low-pressure Die-casting.Microstructures and properties are deteriorated from far and near according to the position of the gate.A few of castings shows cold shut defects and oxide film,and shrinkage holes appear at the hot joints.The castability of aluminum melt at lower temperatures is improved by vacuum assisting.Defects such as cold shut and short run were not found in the casting.Their microstructures were fine and even,defects such as oxide film did not appear either.When ultrasonic technology was used to low pressure casting,the casting microstructures wre refined and the mechanical properties were increased apparently,especially in the zone of the upper part of the cam,which was prone to shrinkage.