Semi-solid molding method

A method of semi-solid molding a high strength metal part within a die cavity defined by a die set mounted on a vertical die cast press, the press including a shot sleeve having a generally vertical axis and enclosing a shot piston movable axially within the sleeve with the sleeve and piston defining a shot chamber above the piston, the method comprising the steps of:

• melting a solid metal to form a molten metal,
• treating the molten metal with a grain refiner,
• transferring the molten metal into the shot chamber,
• cooling the molten metal within the shot chamber to within a predetermined temperature range while the molten metal within the shot chamber has a horizontal width substantially greater than its vertical depth and without stirring the molten metal to form a substantially quiescent and shallow semi-solid slurry having a globular and generally non-dendritic microstructure with a range of 40% to 60% solid,
• forming a downwardly facing annular entrapment recess above the shot chamber and generally in axial alignment with an inner surface of the shot sleeve,
• moving the shot piston upwardly within the shot chamber to inject a central portion of the semi-solid slurry from the shot chamber into the die cavity through a gate opening within a central portion of the shot chamber,
• trapping a more solidified outer portion of the semi-solid slurry adjacent the shot sleeve within the entrapment recess in response to the upward movement of the shot piston, and
• allowing the semi-solid slurry to solidify within the die cavity to form the metal part.