Effect Of Low Pressure Process On Microstructure And Properties Of ADC12 Alloy

As an advanced processing technology,squeeze casting technology has a series of advantages such as simple casting process,low cost,high product performance and reliability.Usually,the purpose of applying pressure in the extrusion casting process is to provide certain feeding force during the molding process of the casting,and the pressure value is high(the pressure value is generally greater than 60 MPa).If a small pressure value is used,the pressure value required for the metal liquid feeding can be satisfied,and a product with a high yield rate can be obtained,which can greatly reduce the equipment cost,thereby improving the medium and low pressure squeeze casting technology in the automobile industry.The most commonly used alloy system in the squeeze casting process is Al-Si alloys.These alloys have excellent casting properties and mechanical properties,making them widely used in automotive parts.In this thesis,ADC12 alloy was taken as the research object,and the Al alloy step-like castings for automobile engine block were prepared by low pressure squeeze casting technology.Firstly,ProCAST software was used to simulate the results of filling and solidification process under different gating systems,so as to obtain the optimal gating system.On the basis of this system,the effect of corresponding process parameters on casting defects was predicted by simulating the filling and solidification process of castings under different casting process parameters.According to the simulation results,the influence of different low pressure process parameters(coating type and thickness,pressure value,mold temperature,casting temperature,etc.)on the microstructure and mechanical properties of the casting is further guided.After that,the best heat treatment process parameters are optimized.The main conclusions are as follows:(1)According to the analysis results of metal liquid filling stability,exhaust gas,sequential solidification and casting defects(entrapping air,cold insulation,etc.)in the simulation process,the optimal pouring system scheme was obtained.(2)By simulating the effect of different pressure valueson the quality of the casting,it was obtained that the internal gas of the casting increases with the increase of pressure.The content of shrinkage cavities is significantly reduced.But after the pressure increases to certain extent,the content of the shrinkage cavities is little affected by the pressure.In conclusion,the effective pressure value ranges from 0.8 to 2 MPa.(3)The effects of process parameters on the microstructures ans mechanical properties of the low pressure squeeze cast ADC12 alloys were systematically studied by means of OM,SEM,X-ray inspection,room temperature mechanical stretching and density.The results are as follows: the use of a thickness of 60 ?m for the No.3 coating is beneficial to reduce the defects such as shrinkage and shrinkage of the casting,and is more in line with the production needs.(4)The comprehensive performance of the casting under 2MPa pressure is optimal.The tensile strength of the thickest 21 mm step is 246 MPa,and the elongation is 2.63%.(5)Comparing the microstructures and properties of the alloy under different heat treatment conditions,the optimal heat treatment process is 540 °C × 6h + 175 °C × 8h.The tensile properties at room temperature are: tensile strength is 345 MPa and elongation is 4.02%.