Method for manufacturing a cast bar and tube made of a magnesium alloy

A method for manufacturing a cast bar and tube made of a magnesium alloy, said method comprising:

• preparing a manufacturing device including,
• a molten metal furnace holding a casting material as a molten metal therein, the casting material being made of the magnesium alloy,
• a hollow tube including an opening through which the molten metal enters into the hollow tube from the molten metal furnace, and a cylindrical part in which the molten metal that enters through the opening is received, the hollow tube being freely inserted into and withdrawn from the molten metal furnace at one end portion thereof,
• a vacuum chamber connected to the hollow tube at another end portion thereof,
• a depressurization device connected to the vacuum chamber, and generating a negative pressure in the vacuum chamber,
• a connection member connecting the hollow tube and the vacuum chamber,
• an open/close valve member installed on the connection member to control a gas flow between the hollow tube and the vacuum chamber,
• a cooling device connected to the hollow tube and cooling the hollow tube to solidify the molten metal in the hollow tube,
• a vibrating device installed on the hollow tube and vibrating the hollow tube to uniformly mix the molten metal in the hollow tube, and
• a heating device arranged outside the hollow tube and heating a vicinity of the opening of the hollow tube,
• depressurizing the vacuum chamber through the depressurization device while the valve member is closed to generate the negative pressure in the vacuum chamber;
• heating the vicinity of the opening of the hollow tube with the heating device before inserting the opening of the hollow tube into the molten metal furnace;
• inserting the opening of the hollow tube into the molten metal held in the molten metal furnace;
• switching the valve member to be open to introduce the molten metal into the cylindrical part from the molten metal furnace;
• introducing the molten metal into the cylindrical part from the molten metal furnace through the opening with a suction force generated by a pressure difference between the hollow tube and the vacuum chamber, and filling the cylindrical part with the molten metal to manufacture the cast bar and tube made of the magnesium alloy;
• cooling the hollow tube with the cooling device while introducing the molten metal into the cylindrical part to solidify the molten metal in the cylindrical part;
• and
• continuously vibrating the hollow tube after the molten metal is introduced into the cylindrical part until completing solidification of the molten metal in the cylindrical part;
• wherein the negative pressure generating the suction force is stably formed in the vacuum chamber, and the negative pressure in the vacuum chamber is varied depending on a size of the hollow tube,
• the vibrating device includes an enforced vibration device externally applying physical vibration, an ultrasound vibration device applying ultrasound waves or an electromagnetic induction vibration device applying electromagnetic induction,
• after the vicinity of the opening of the hollow tube is heated with the heating device, the opening of the hollow tube is inserted into the molten metal furnace to prevent breakage of the hollow tube caused by a temperature difference between the hollow tube and the molten metal and to prevent plugging of the hollow tube caused by a rapid solidification of the molten metal,
• an internal structure of the cast bar and tube made of the magnesium alloy is a spheroidized structure, and cracks or seams are not formed in the cast bar and tube made of the magnesium alloy, and
• when an upset process is performed on the cast bar and tube made of the magnesium alloy, the cast bar and tube made of the magnesium alloy has deformation ability equal to or more than 70 percent, the deformation ability being evaluated by comparing a height of the cast bar and tube made of the magnesium alloy before the upset process with a height after the upset process, and a value of the deformation ability being calculated as dividing a difference height between the height before the upset process and the height after the upset process by the height before the upset process, and multiplying a hundred for percent indication.