Pressure casting method of magnesium alloy and metal products thereof

Abstract

The present invention provides a pressure casting method of a magnesium alloy. In the method, a molten magnesium alloy is cooled to form a partially molten state containing a solid-phase, and the partially molten state is further cooled to form a solid-phase granularly crystallized solid material. The solid material is partially-melted and pressure cast into a mold by a molding machine. A ratio of primary crystals in said solid material is set to 55 to 65%. The solid material is partially-melted in a solid-phase and liquid-phase coexisting state at a selected heating temperature so that a semi-solid having a thixotropic properties and having the size of a main solid phase of 50 to 250 μm and a solid-phase ratio of 30 to 70% is formed. The semi-solid is pressure cast into a mold through a nozzle while maintaining the semi-solid state to form metal products having a ratio of primary crystals of 20 to 50%.

1 . A pressure casting method of a magnesium alloy comprising the steps of cooling a molten magnesium alloy to form a partially molten state containing a solid-phase, further cooling the partially molten state to form a solid-phase granularly crystallized solid material and partially-melting the solid material to pressure cast it into a mold by a molding machine, 
 wherein a ratio of primary crystals of said solid material is set to 55 to 65%, the solid material is melted to be a semi-solid body having a thixotropic properties in a solid-phase and liquid-phase coexisting state so that the semi-solid having the size of a main solid phase of 50 to 250 μm and a solid-phase ratio of 30 to 70%, and pressure casting the semi-solid into a mold through a nozzle while maintaining the semi-solid state to mold metal products having a ratio of primary crystals of 20 to 50%.    
   
   
       2 . The pressure casting method of a magnesium alloy according to  claim 1 , wherein the temperature of a heating means in a molding machine for holding the semi-solid in said semi-solid state is set at a temperature 5 to 15° C. higher than the temperature of the semi-solid in accordance with time from the starting of melting of the solid material to the pressure casting of the semi-solid.  
   
   
       3 . The pressure casting method of a magnesium alloy according to  claim 1 , wherein said semi-solid is pressure cast from a nozzle having a diameter of 8 to 15 mm into a mold through a gate having a thickness of 1 mm or less.  
   
   
       4 . A metal product of a magnesium alloy molded by the pressure casting method of a magnesium alloy according to  claim 1 , comprising a metal structure whose main primary crystal is spherical and has a diameter of 10 μpm or more.  
   
   
       5 . The metal product of a magnesium alloy according to  claim 4 , wherein said metal product has a wall thickness of 0.4 to 1.5 mm, preferably 0.6 to 1.0 mm.  
   
   
       6 . A metal product of a magnesium alloy molded by the pressure casting method of a magnesium alloy according to  claim 2 , comprising a metal structure whose main primary crystal is spherical and has a diameter of 10 μm or more.  
   
   
       7 . A metal product of a magnesium alloy molded by the pressure casting method of a magnesium alloy according to  claim 3 , comprising a metal structure whose main primary crystal is spherical and has a diameter of 10 μm or more.  
   
   
       8 . The metal product of a magnesium alloy according to  claim 6 , wherein said metal product has a wall thickness of 0.4 to 1.5 mm, preferably 0.6 to 1.0 mm.  
   
   
       9 . The metal product of a magnesium alloy according to  claim 7 , wherein said metal product has a wall thickness of 0.4 to 1.5 mm, preferably 0.6 to 1.0 mm.