The semi-solid 7075 alloy melt is different from the traditional liquid alloy
① Semi solid alloy melt has good fluidity, which is regarded as continuous and incompressible fluid, and its fluidity is expressed by apparent viscosity. Bingham model can be used to simulate the alloy fluid because of the high solid rate in semi-solid processing.
② In the semi-solid alloy melt, the solid particles are evenly distributed in the liquid phase matrix, the primary solid particles have smaller diameter, and the density of the solid phase is close to that of the liquid phase, so it can be regarded as a single phase in the simulation process.
③ In rheo squeeze casting, the filling time is very short, the heat conduction time is also very short, and the extrusion mold has been preheated to the appropriate temperature before filling, so the heat transfer of slurry can be ignored in the filling process of semi-solid squeeze casting, which can be regarded as the isothermal flow process of isothermal medium.
④ The apparent viscosity η a of semi-solid metal is related to the melt temperature, shear rate and liquid phase rate, but the solid volume fraction is basically unchanged due to the short filling time and small temperature change in rheo squeeze casting. The apparent viscosity is inversely proportional to the shear rate, and the relationship between the apparent viscosity and the shear rate satisfies the “power” law
η a – apparent viscosity;
K – density;
γ – shear rate;
N – “power” law exponent.