Study On The Mould-filling Mechanism And Numerical Simulation Of Rheo-diecasting Of Semi-solid Magnesium Alloys

As a near-net shape forming technology with wide application in 21 century, semisolid metal processing technology is catching many researchers'attention in various fields. Magnesium alloy will be more and more applied in electronic, automobile and aviation industries as a green engineering material with many advantages. Up to now, research on semi-solid magnesium alloys is seldom dated. In this paper, the mould filling process of rheo-diecasting of semi-solid magnesium alloy has been studied with rheo-diecasting experiments; the numerical simulation program of rheo-diecasting of semi-solid magnesium alloy has been compiled which combined the viscosity model of semi-solid magnesium alloy with the SOLA-VOF method; and the characteristics of mould filling process of reho-diecasting experiments with different gate system has been analyzed though numerical simulation. The simulation results were in accord with the experimental results. The effects of the ingate velocity on the mould filling process of die-casting and rheo-diecasting were systematically studied. The mould filling process presented the characters of Frommer's conclusion under the high ingate velocity. However, under the low ingate velocity, as kinetic energy of the slurry or liquid metal which plunged into the cavity of die would decrease, the mould filling process showed the characters of Brandt's conclusion. On the premise of mould filling completely, the lower ingate velocity could decrease the air entrapment. Under the same ingate velocity, the semi-solid rheo-diecasting decreased the air entrapment during the mould filling process, and high quality metal castings could be obtained through semi-solid forming technology. The influences of ingate dimension upon the mould filling process of die-casting was investigated. The big ingate area strengthened the characters of Brandt's conclusion in mould filling processes, and the area ratio of ingate area to cross-sectional area of mould was important for decreasing pores in casting. The structural parameters of casting have effects on the mould filling process. It is best to avoid abrupt change of casting width, and avoid liquid metal or semi-solid slurry impacting on the cores directly, as it would result in turbulent convection and air entrapment. The apparent viscosity model of semi-solid slurry of magnesium was established according to the process of reho-diecasting. The numerical simulation program aimed at the mould filling process of reho-diecasting of semi-solid metals was compiled, which combined the viscosity model of magnesium alloy in semi-solid state with SOLA-VOF method. The characters of mould filling process of semi-solid rheo-diecasting were analyzed by the numerical simulation program. The computer simulation results showed that the effects of ingate dimension and ingate location on the rheo-diecasting were relatively small, and the casting process-design was easily to be done. The mould filling processes of experimental sample casting, which changed ingate dimension were simulated by the numerical simulation program, and the simulation results were in accord with the experimental results.