Magnesium alloys containing heavy rare earths
Magnesium alloys which possess good processability and/or ductility while retaining good resistance to corrosion and/or degradation comprising Y: 0-10% by weight, Nd: 0-5% by weight, wherein the total of Y+Nd is at least 0.05% by weight, one or more heavy rare earths selected from Ho, Lu, Tm and Tb in a total amount of above 0.5% and no more than 5.5% by weight, Gd: 0-3.0% by weight, and Sm: 0-0.2% by weight. The alloy optionally includes one or more of: Dy: 0-8% by weight; Zr: 0-1.2% by weight; Al: 0-7.5% by weight; Zn and/or Mn: 0-2% by weight in total; Sc: 0-15% by weight; In: 0-15% by weight; Ca: 0-3% by weight; Er up to 5.5% by weight, provided that the total of Er, Ho, Lu, Tm and Tb is no more than 5.5% by weight; and one or more rare earths and heavy rare earths other than Y, Nd, Ho, Lu, Tm, Tb, Dy, Gd and Er in a total amount of up to 0.5% by weight; the balance being magnesium and incidental impurities up to a total of 0.3% by weight.
1. A medical implant comprising a magnesium alloy composition, the composition consisting of:
Y in an amount of ≤0.3% by weight,
Nd in an amount of 0.05-5% by weight,
one or more heavy rare earths selected from Ho, Lu, Tm and Tb of above 0.5% by weight each and no more than 5.5% by weight in total,
Zr in an amount of 0.1-0.8% by weight,
Gd in an amount of 0-7% by weight,
one or more of Zn, Mn, Yb, Sm, Al, Fe, Dy, Er, La, Si and
Magnesium.
2. The alloy as claimed in claim 1 wherein Zn and/or Mn are present in an amount of up to 2% by weight in total.
3. The alloy as claimed in claim 1 wherein Yb is present in an amount of up to 0.02% by weight.
4. The alloy as claimed in claim 3 wherein the Yb content is less than 0.01% by weight.
5. The alloy as claimed in claim 1 wherein Sm is present in an amount of up to 0.04% by weight.
6. The alloy as claimed in claim 5 wherein the Sm content is less than or equal to 0.02% by weight.
7. The alloy as claimed in claim 1 having a magnesium content of at least 85% by weight.
8. The alloy as claimed in claim 1 wherein the alloy exhibits a corrosion rate as measured according to ASTM B117 of less than 40 Mpy.
9. The alloy as claimed in claim 1 wherein the area percentage of any precipitated particles formed during processing of the alloy having an average particle size of between 1 and 20 μm is less than 5%.
10. The alloy as claimed in claim 1 wherein when the alloy is in the T4 or T6 condition the area percentage of any precipitated particles having an average particle size of between 1 and 15 μm is less than 3%.
11. The alloy as claimed in claim 9 wherein said particles are rich in Nd, such that the particles have a percentage composition of Nd greater than the percentage composition of any other element in the particle.
12. The alloy as claimed in claim 1 when wrought.
13. The alloy as claimed in claim 2 wherein the content of Zn+Mn is up to 0.40% by weight.
14. The alloy as claimed in claim 1 wherein the content of Nd is 0.05-3.35% by weight.
15. A wrought magnesium alloy composition consisting of:
Y in an amount of ≤0.3% by weight,
Nd in an amount of 0.05-5% by weight,
one or more heaving rare earths selected from Ho, Lu, Tm and Tb of above 0.5% by weight each and no more than 5.5% by weight in total,
Zr in an amount of ≤0.1% by weight,
Al in an amount of 1-7.5% by weight,
one or more of Ca, Gd, Zn, Mn and
magnesium.
16. The alloy composition of claim 15 wherein Ca is present in an amount of up to 3% by weight.
17. The alloy as claimed in claim 15 wherein Zn and/or Mn is present in an amount of up to 2% by weight in total.
18. The alloy as claimed in claim 1 wherein Al is present in an amount of up to 7.5% by weight.
19. The alloy as claimed in claim 1 wherein Dy is present in an amount of up to 8% by weight.
20. The alloy as claimed in claim 1 wherein Er is present in an amount of up to 5.5% by weight.
21. The alloy as claimed in claim 1 wherein Fe is present in an amount of up to 0.004% by weight.
22. The alloy as claimed in claim 1 wherein Si is present in an amount of up to 0.1% by weight.
23. The alloy composition of claim 15 wherein Gd is present in an amount of up to 7% by weight.