Plastic deformation magnesium alloy having excellent thermal conductivity and flame retardancy, and preparation method therefor

Abstract

Disclosed is a magnesium alloy that has high thermal conductivity and flame retardancy and facilitates plastic working, wherein magnesium is added with 0.5 to 5 wt % of zinc and 0.6 to 3.5 wt % of tin (Sn) as a high-melting-point oxide-film-forming element, with, as necessary, 1.5 wt % or less of at least one selected from among calcium (Ca), silicon (Si), manganese (Mn) and mischmetal, the total amount of alloy elements being 2.5 to 6.3 wt %. A method of manufacturing the same is also provided, including melting high-melting-point alloy elements in the form of a master alloy in a magnesium—zinc alloy melt, followed by casting, removing a chill from the cast material, diffusion annealing, and then molding through a tempering process such as rolling, extrusion or forging. This magnesium alloy is improved in ductility by the action of alloy elements for inhibiting the formation of plate-like precipitates in a magnesium matrix structure, can be extruded even at a pressure of 1,000 kgf/cm 2 or less due to the increased plasticity thereof, and can exhibit thermal conductivity of 100 W/m·K or more and flame retardancy satisfying the requirements for aircraft materials and is thus suitable for use in fields requiring fire safety, thereby realizing wide application thereof as a heat sink or a structural material for portable appliances, vehicles and aircraft components and contributing to weight reduction.

What is claimed is: 
     
         1 . A magnesium alloy having high thermal conductivity and flame retardancy and facilitating plastic working, comprising: 0.5 to 5 wt % of zinc, 0.6 to 3.5 wt % of tin as a high-melting-point oxide-film-forming element, and a remainder of magnesium and inevitable impurities, wherein, among the inevitable impurities, an amount of aluminum or zirconium is controlled to 0.5 wt %. 
     
     
         2 . The magnesium alloy of  claim 1 , further comprising 1.5 wt % or less of at least one selected from among calcium, silicon, manganese and mischmetal, a total amount of alloy elements being 2.5 to 6.3 wt %. 
     
     
         3 . A method of manufacturing a magnesium alloy having high thermal conductivity and flame retardancy and facilitating plastic working, comprising:
 melting a magnesium ingot in a melting furnace with an air shut-off, thus obtaining a magnesium melt, which is then maintained at a temperature of 680 to 720° C.;   melting zinc in the magnesium melt, thus obtaining a magnesium—zinc alloy melt;   adding the magnesium—zinc alloy melt with at least one selected from among high-melting-point elements, including tin, yttrium, mischmetal, calcium, silicon and manganese, in a form of a master alloy and then performing mechanical stirring, thus obtaining a magnesium alloy melt; and   cooling a mold containing the magnesium alloy melt, thus producing a cast material.   
     
     
         4 . The method of  claim 3 , wherein the melt is cooled in a manner in which the mold is sank in a bath containing a coolant or a coolant is sprayed on an outer surface of the mold, and the melt is mechanically stirred during cooling, whereby solid nuclei of the mushy zone are dispersed. 
     
     
         5 . The method of  claim 4 , wherein the stirring during cooling of the melt is performed in a manner in which an impeller having a diameter of ⅕ to ⅔ of a billet diameter is inserted into the mold so as to perform mechanical stirring, whereby the solid nuclei of the mushy zone are dispersed. 
     
     
         6 . The method of  claim 3 , wherein the cooling is performed in a manner in which the mold is cooled in a bath at a cooling rate of 70 to 200° C./min, and the melt in the mold is mechanically stirred during the cooling, whereby solid nuclei of the mushy zone are dispersed. 
     
     
         7 . The method of  claim 3 , wherein the cooling is performed in a manner in which the magnesium alloy melt is placed in a mold of a continuous casting device and cooled at a cooling rate of 200 to 900° C./min by spraying a coolant onto an outer surface of the mold and a surface of a billet, and during the cooling, an impeller is inserted into the mold so as to perform mechanical stirring, whereby solid nuclei of the mushy zone are dispersed.