Study On The Constitutive Relationship And Simulation In Thixotropic Forming Of SiC_p/AZ61 Composites

Compared with traditional metal materials, particulate reinforced metal matrix composites ( PMMCs) possesses lots of advantages, such as high specific stiffness, high specific strength, good resistance to high temperature, wear and fatigue and good steadiness to chemical and dimension. The development of the semi-solid technology is providing bright futures for the fabrication process and the shaping process of metal matrix composites.In this paper, excellent semi-solid SiC_p/AZ61 composites were fabricated by the method of stir-casting and isothermal heat treatment. Then the billets with different SiC volumes were compressed by Thermecmastor-Z dynamic material testing machine at different deformation temperatures and different deformation rates. The relation- ships between stress and strain were analyzed in different deformation conditions. The influences of the different deformation temperatures, different deformation rates and the volume of SiC particulate were anyalysised. The results indicate that the true stress of semi-solid SiC_p/AZ61 composites was sensitive to temperature and strain rates. The ture stress is higher with the increasing of the volume of SiC particulate. The results show that the deformation force was required mainly to overcome particle sliding and particle plastic deformation in thixotropic compression process of high solid phase fraction for semi-solid SiC_p/AZ61 composites, in which the sliding between solid particles and plastic deformation of solid particles mechanisms were dominant.A new constitutive model for semi-solid composites was detived by analyzing constitutive relationships of semi-solid metal and composites. Parameters in the constitutive model were resoved based on semi-solid SiC_p/AZ61 composites thixotropic compression data. The total semi-solid SiC_p/AZ61 composites thixotropic plastic forming constitutive model isσ=exp(-8.27366+50.158f_p-296.555f_p²+14253.359/T)·ε^-0.053·(?)^0.242·[1-βf_L]^2.316·[1+(α(?))^0.242f_p]^-0.505The shape of calculated curves and experimental curves resembled very well. The instruction of the constitutive model provides conveniences for the thixo-forming simulation and machine process of SiC_p/AZ61 composites.A viscoplastic finite element calculation by DEF0RM-2D software has been performed to simulate the thixo-extrusion. The influence of extrusion speeds for the forming process was analyzed. And some extrusion experiments were processed. The results show that the loads of the mold are more with the higher speeds and higher temperature. Experimental results tally with simulation results. These prove that the constitutive relationships for the semi-solid SiC_p/AZ61 composites can be used to guidance the composites' thixo-forming practice.