Die cast magnesium components

Abstract

Die casting of some magnesium alloys may yield castings that are susceptible to corrosion when exposed to salt water or other aggressive oxidizing environments. Such corrosion may result from the existence of different microstructures in a cross-section of the die casting (e.g. between the surface of the part and the center) that produce galvanic couples that are susceptible to such corrosive attack. However, a die temperature may be determined for casting of the part such that a more uniform cross-sectional microstructure is produced in which minimal or negligible galvanic potentials are produced.

1 . A method of making a cast article of a magnesium alloy composition that may yield metallurgical phases of different compositions in different sections of the article when a charge of molten alloy composition is received in a set of closed metal dies and cooled in the dies to solidify the charge and shape the article, the method comprising;
 predetermining a temperature or temperature range at which the set of dies may be maintained to receive the charge of molten magnesium alloy and cool and solidify the alloy at a cooling rate such that the cast microstructure does not produce a galvanic coupling for a liquid environment to which the part may be exposed; and, thereafter   maintaining the temperature of the dies at the predetermined temperature for casting of such parts.   
     
     
         2 . A method as recited in  claim 1  in which the temperature for the set of dies is predetermined by producing castings at different test temperatures until a useful predetermined temperature is discovered. 
     
     
         3 . A method as recited in  claim 1  in which the magnesium alloy to be cast is AXJ 530. 
     
     
         4 . A method as recited in  claim 1  in which the magnesium alloy to be cast is AXJ530 and the liquid environment to which the part may be exposed comprises salt water. 
     
     
         5 . A method as recited in  claim 1  in which the magnesium alloy to be cast comprises more aluminum than any other alloying element. 
     
     
         6 . A method as recited in  claim 1  in which the magnesium alloy to be cast comprises more aluminum than any other alloying element and the liquid environment to which the part may be exposed comprises salt water. 
     
     
         7 . A method as recited in  claim 1  in which the different sections of the part are in a cross-section of the part and include a surface and a central region of the part. 
     
     
         8 . A method as recited in  claim 1  in which the different sections of the part are in a cross-section of the part and include a surface and a central region of the part, and the liquid environment to which the part may be exposed comprises salt water.