Castable magnesium alloys
This invention relates to magnesium-based alloys particularly suitable for casting applications where good mechanical properties at room and at elevated temperatures are required. The alloys contain: 2 to 4.5% by weight of neodymium; 0.2 to 7.0% of at least one rare earth metal of atomic No. 62 to 71; up to 1.3% by weight of zinc; and 0.2 to 0.7% by weight of zirconium; optionally with one or more other minor component. They are resistant to corrosion, show good age-hardening behaviour, and are also suitable for extrusion and wrought alloy applications.
1. A castable magnesium based alloy comprising (in % by weight):
at least 85% of magnesium;
2.0 to 3.5% of neodymium;
1.0 to 1.7% of gadolinium;
0.2 to 1.3% of zinc;
0.2 to 0.7% of zirconium;
up to 1% of calcium;
up to 0.4% of hafnium and/or titanium;
up to 0.5% of manganese;
no more than 0.001% of strontium;
no more than 0.05% of silver;
no more than 0.1% of aluminum;
no more than 0.01% of iron; and
excluding yttrium added to the alloy;
with any remainder being incidental impurities.
2. An alloy as claimed in claim 1 wherein the alloy contains 2.5 to 3.5% by weight of neodymium.
3. An alloy as claimed in claim 1 wherein the alloy contains about 2.8% by weight of neodymium.
4. An alloy as claimed in claim 1 wherein the alloy contains about 1.5% by weight of gadolinium.
5. An alloy as claimed in claim 1 wherein the alloy contains zinc in an amount of 0.2 to 0.6% by weight.
6. An alloy as claimed in claim 1 wherein the alloy contains zinc in an amount of about 0.4% by weight.
7. An alloy as claimed in claim 1 wherein the alloy contains zirconium in an amount of 0.4 to 0.6% by weight.
8. An alloy as claimed in claim 1 wherein the alloy contains zirconium in an amount of about 0.55% by weight.
9. An alloy as claimed in claim 1 wherein the alloy contains less than 0.005% by weight of iron.
10. An alloy as claimed in claim 1 wherein the amount of said incidental impurities of said alloy is not greater than 0.3% by weight.
11. A cast or wrought product when formed from an alloy as claimed in claim 1 .
12. A product formed from the alloy of claim 1 wherein said product has an elongation of greater than 5%.
13. A product formed from the alloy of claim 1 wherein said product has a corrosion resistance at a rate less than 100 mpy according to ASTM B117.
14. A method of producing a product formed from the magnesium based alloy of claim 1 including the steps of sand casting, permanent mold casting or high pressure die casting said magnesium based alloy.
15. A method as claimed in claim 14 including the step of age hardening the cast alloy at a temperature of 150° C. for at least 10 hours.
16. A method as claimed in claim 14 including the step of age hardening the cast alloy at a temperature of 200° C. for at least 1 hour.
17. A method as claimed in claim 14 including the step of age hardening the cast alloy at a temperature of 300° C.
18. A method as claimed in claim 14 including the steps of solution heat treating and then quenching the cast alloy.
19. A method as claimed in claim 18 wherein the quenching step is effected by hot water quenchant.
20. A method as claimed in claim 14 wherein said product is in its T6 temper.
21. A cast product produced by a method as claimed in claim 14 .