Isothermal forging Modelling of aluminium based metal matrix composites

摘要

The modern automotive industry, due to pressures from government regulations, continuously requires reduction in fuel consumption and the associated reduction in harmful engine emissions. Light metals such as aluminium alloys are desirable to replace traditional materials. However, aluminium alloys are not sufficiently stiff or strong to be used in many situations and so reinforcement is necessary. Discontinuously reinforced aluminium alloy matrix composites (Al-MMCs) seem to be promising candidate materials for this purpose. Unfortunately, such materials are difficult to form due the presence of ceramic phases, usually SiC or Al_2O_3 particles. Forming conditions can be more easily optimised if finite element models (FEM) are developed. The isothermal forging was experimentally simulated by hot torsion and compression tests. The results were used to individuate the optimal "processing window" in terms of temperature and strain rate according to the dynamic material model. The study has analysed the constitutive equations that relate flow stress, temperature and strain rates and correlated mechanical response to microstructure in terms of damage, microstructural changes occurring under dynamic and static restoration of the material. FEM studies, using DEFORM~(TM) 3-D code, have been carried out on the isothermal forged components in order to model the mechanical behaviour of the material during deformation. The simulations have been carried out at the temperatures of 450 and 500 ℃ and initial strain rates of 10~(-2) and 10~(-1) s~(-1). The stress and strain distribution have been mapped in different points of the component in order to evaluate the differences in deformation of the component due to the complex geometry. True stress vs. true strain data were obtained by hot compression tests. The DEFORM~(TM) then calculated the constitutive equations of the material to model the hot forming behaviour during deformation. Light microscopy observations were performed on different sections of the isothermal forged components in order to quantify the damage in terms of fracture of the particles and voids formation at the interface between the particles and the matrix and the microstructural evolutions of the materials.