Magnesium gadolinium alloys

Abstract

This invention relates to gadolinium-containing magnesium containing alloys, particularly those which possess high strength combined with corrosion resistance, and an optimized balance of strength and ductility. The described alloys consist of 2.0 to 5.0, preferably 2.3 to 4.6, at % in total of gadolinium and at least one of soluble heavy lanthanides and yttrium, wherein the ratio of the aggregate amount of soluble heavy lanthanides and yttrium to the amount of gadolinium is between 1.25:1 and 1.75:1, from 0 up to 0.3 at % of zirconium, preferably at least 0.03 at %, optionally with zinc, wherein when zinc is present the amount of zinc is such that the ratio of the weight of zinc to the weight of zirconium is preferably less than 2:1, all other lanthanides in an aggregate amount of less than at 0.2 at %, the balance being magnesium, with any other element being present in an amount of no more than 0.2 at %.

1 . A magnesium alloy consisting of:
 2.0 to 5.0 at % in total of gadolinium and at least one element selected from the group consisting of soluble heavy lanthanides and yttrium, wherein the ratio of the aggregate amount of soluble heavy lanthanides and yttrium to the amount of gadolinium is between 1.25:1 and 1.75:1,   all other lanthanides in an aggregate amount of less than 0.02 at % and   the balance being magnesium, with any other element being present in an amount of less than 0.2 at %.   
   
   
       2 . An alloy as claimed in  claim 1  wherein the total amount of gadolinium, at least one soluble heavy lanthanide and yttrium is 2.3 to 4.6 at %. 
   
   
       3 . An alloy as claimed in  claim 1  wherein said ratio is approximately 1.5:1. 
   
   
       4 . An alloy as claimed in  claim 1  wherein at least one soluble heavy lanthanide is present in an amount of at least 0.1 at %. 
   
   
       5 . An alloy as claimed in  claim 4  wherein the at least one soluble heavy lanthanide is erbium. 
   
   
       6 . An alloy as claimed in  claim 1  wherein all other lanthanides are present in an aggregate amount of less than 0.1 at %. 
   
   
       7 . An alloy as claimed in  claim 1  wherein any other element is present in the amount of less than 0.1 at %. 
   
   
       8 . An alloy as claimed in  claim 7  wherein any other element is present only as an incidental impurity. 
   
   
       9 . An alloy as claimed in  claim 1  additionally containing zinc in an amount of from 0.06 to 0.6 at %. 
   
   
       10 . An alloy as claimed in  claim 9  wherein zinc is present in an amount of from 0.07 to less than 0.5 at %. 
   
   
       11 . An alloy as claimed in  claim 1  additionally containing a grain refining element in an amount up to its solid solubility limit in the alloy. 
   
   
       12 . An alloy as claimed in  claim 11  wherein the grain refining element is zirconium in an amount of from 0.03 to 0.3 at %. 
   
   
       13 . An alloy as claimed in  claim 12  wherein zirconium is present in an amount of from 0.06 to 0.1 at %. 
   
   
       14 . An alloy as claimed in  claim 12  additionally containing zinc wherein the amount of zinc is such that the ratio of the weight of zinc to the weight of zirconium is less than 2:1. 
   
   
       15 . An alloy as claimed in  claim 14  wherein the zinc/zirconium ratio is less than 0.75:1. 
   
   
       16 . An alloy as claimed in  claim 1  having a corrosion rate less than 50 mils per year in a standard salt-fog test. 
   
   
       17 . A magnesium alloy consisting of 5.5-6.5 wt % Y, 6.5-7.5 wt % Gd and 0.2-0.4 wt % Zr with the remainder being magnesium and incidental impurities. 
   
   
       18 . An alloy as claimed in  claim 17  containing 0.3 to 0.35 wt % Zr. 
   
   
       19 . An alloy as claimed in  claim 1  when wrought and in the form of an extrusion, sheet, plate forging or mechanical part.