Heat-resistant magnesium alloy

Abstract

A heat-resistant magnesium alloy according to the present invention includes Mg, a major component; a first alloying element “M 1 ” being any one or more members that are selected from the group consisting of Al and Ni; a second alloying element “M 2 ” being any one or more members that are selected from the group consisting of Mn, Ba, Cr and Fe; and Ca; and it has a metallic structure including: Mg crystalline grains; plate-shaped precipitated substances being precipitated within grains of the Mg crystalline grains; and grain-boundary crystallized substances being crystallized at grain boundaries between the Mg crystalline grains to form networks that are continuous microscopically. Since the plate-shaped precipitated substances exist within the Mg crystalline grains, the movements of dislocation within the Mg crystalline grains are prevented, and accordingly it becomes less likely to deform. Moreover, since the grain-boundary crystallized substances, which form the networks, are present continuously microscopically at the grain boundaries between the Mg crystalline grains, the strength at the grain boundaries improves. The heat-resistant magnesium alloy according to the present invention in which both of the Mg crystalline grains' granular interior and the grain boundaries between the Mg crystalline grains are strengthened exhibits high mechanical characteristics even in high-temperature regions.

1 . A heat-resistant magnesium alloy being characterized in that it includes:
 magnesium (Mg), a major component;   a first alloying element “M 1 ” being any one or more members that are selected from the group consisting of aluminum (Al) and nickel (Ni);   a second alloying element “M 2 ” being any one or more members that are selected from the group consisting of manganese (Mn), barium (Ba), chromium (Cr) and iron (Fe); and   calcium (Ca); and   
     it has a metallic structure including:
 Mg crystalline grains; 
 plate-shaped precipitated substances being precipitated within grains of the Mg crystalline grains; and 
 grain-boundary crystallized substances being crystallized at grain boundaries between the Mg crystalline grains to form networks that are continuous microscopically. 
 
   
   
       2 . The heat-resistant magnesium alloy as set forth in  claim 1 , wherein said precipitated substances comprise a Laves-phase compound with type-“C15” crystalline structure. 
   
   
       3 . The heat-resistant magnesium alloy as set forth in  claim 1 , wherein said precipitated substances are precipitated parallel to the {001} plane of Mg crystal. 
   
   
       4 . The heat-resistant magnesium alloy as set forth in  claim 1 , wherein said grain-boundary crystallized substances comprise an Mg-“M 1 ”-Ca-system compound. 
   
   
       5 . The heat-resistant magnesium alloy as set forth in  claim 1 , wherein said grain-boundary crystallized substances comprise a mixed-crystal phase of a Laves-phase compound with type-“C14” crystalline structure and a Laves-phase compound with type-“C36” crystalline structure. 
   
   
       6 . A heat-resistant magnesium alloy as set forth in  claim 5 , wherein said mixed-crystal structure includes the type-“C14” crystalline structure more than the type-“C36” crystalline structure. 
   
   
       7 . The heat-resistant magnesium alloy as set forth in  claim 1  having fine particles that include “M 2 ” within said Mg crystalline grains. 
   
   
       8 . The heat-resistant magnesium alloy as set forth in  claim 1  including:
 Ca in an amount of from 2% by mass or more to 4% by mass or less;   said first alloying element “M 1 ” in an amount of from 0.9 or more to 1.1 or less by mass ratio with respect to Ca (“M 1 ”/Ca);   said second alloying element “M 2 ” in an amount of from 0.3% by mass or more to 0.6% by mass or less; and   the balance comprising Mg and inevitable impurities;   when the entirety is taken as 100% by mass.   
   
   
       9 . The heat-resistant magnesium alloy as set forth in  claim 8  including said second alloying element “M 2 ” in an amount of from 0.3% by mass or more to 0.5% by mass or less. 
   
   
       10 . The heat-resistant magnesium alloy as set forth in  claim 1  including:
 Ca in an amount of from 1.235 atomic % or more to 2.470 atomic % or less;   said first alloying element “M 1 ” in an amount of from 1.34 or more to 1.63 or less by atomic ratio with respect to Ca (“M 1 ”/Ca);   said second alloying element “M 2 ” in an amount of from 0.13 atomic % or more to 0.27 atomic % or less; and   the balance comprising Mg and inevitable impurities;   when the entirety is taken as 100 atomic %.   
   
   
       11 . The heat-resistant magnesium alloy as set forth in  claim 10  including said second alloying element “M 2 ” in an amount of from 0.15 atomic % or more to 0.25 atomic % or less. 
   
   
       12 . The heat-resistant magnesium alloy as set forth in  claim 1 , wherein:
 said first alloying element is Al; and   said second alloying element is Mn.