Process Optimization,Microstructure And Defects Control Of Aluminum Alloy Die Casting For Automobile

With the rapidly development of automobile material lightweight,die casting technology and tough die-casting aluminum alloy is still one of the hot research areas,which are attractive for the application of automobile key components.It is of great importance for enhancement the quality of the production of the aluminum alloys to systematically study on the relationship between the die-cast processes parameters and the mechanical properties of the specimens,the microstructure characteristics influenced on the properties as well as the defects control,and the heat treatment procedures effected on the die-castings' microstructure and their mechanical properties.Combining with the characteristics of pressure casting,the effects of the processing parameters on the die-castings' microstructure characteristics,mechanical properties and the defect of aluminum alloy specimens have been analyzed.With the orthogonal experiment design and analysis method,this paper discusses the relationship between microstructure and mechanical properties of ADC 12 alloy from changing the values of the different parameters,pouring temperature,switch position of fast velocity and fast shot velocity.The results show that mechanical properties of castings are mainly affected by pouring temperature,flollowed by shot velocity and switch position of fast velocity.Minimun porosity and fine microstructure in the castings can be obtained with pouring temperature at 680?,switch position of fast velocity at 440 mm and shot velocity of 3.0 m/s,exhibiting desirable properties.The primary a-Al phase in die castings are small and fine.The density of alloy reaches the maximum value of 2.73 g/cm3,and the ultimate tensile strength is 235.5 MPa and elongation is 2.8%,which is better than the standard of mechanical properties for as-cast ADC 12 alloy.From the analysis of the fractography characteristics of the tensile specimen,the brittle fracture mode is the main fracture mechanism.Super slow shot die casing are discussed in this dissertation,in order to further control the defects of die-casting and to improve mechanical properties.Considering the combination of die casting machine,die casting and die casting alloy,the AC4CH alloy can match the techniacal parameters of die casting machine and the mould.And there are less defects and better mechanical properties in the castings of AC4CH alloy than of ADC 12 alloy.So the effects of the melt-treatment and shot velocity on the die-castings' microstructure characteristics,mechanical properties and the defect control in the die-casting of AC4CH alloy have been analysied as follows.The experiment data indicate that it could obtain a high quality aluminum alloy melt with the addition of 0.3 wt%,while the holding time for the melt is 30 minutes.And the hydrogen content of melt under the value of 0.30 ml/100 g.After optimizing the process parameters,the fine and densified microstructure was found in the castings,while porosity could be reduced significantly.In addtion,the ultimate tensile strength is 267.5 MPa and elongation is 15.4%of as-cast castings.The optimization of solution and aging treatment of the super slow shot die-casting AC4CH alloy is studied in this paper.The result shows that the ultimate tensile strength and elongation of species increase to 334.7 MPa and 9.5%in heat treatment(510?×3 h+170?×3 h).At the same time,this heat treatment reduces greatly the blister defect of castings and increases the rate of good product.