US3391034A - Magnesium yttrium alloy - Google Patents

Description

United States Patent ABSTRACT OF THE DISCLOSURE An age hardened wrought magnesium base alloy containing about 8 to 11 Weight percent yttrium, the alloy exhibiting high strength properties, the yield strength of said alloy being substantially equal to its ultimate tensile strength.

The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment to us of any royalty there- This invention relates to high strength magnesium alloys and particularly, to magnesium base alloys containing yttrium exhibiting good age hardenability.

In general, the inherently coarse crystalline structure of pure magnesium and its attendant poor mechanical strength properties are well known and considerable investigation has been conducted with a view to finding alloying constituents which would effect a refining of such structure. One alloying constituent which has proven itself noteworthy in this regard and which is disclosed in US. Patent 2,219,056 is yttrium. This patent discloses that the addition to cast magnesium of between about 0.1

3,391,034 Patented July 2, 1968 ICC and about 10% by weight of yttrium results in substantial grain refinement and materially superior mechanical strength properties. A preferred yttrium range of 0.1 to 4% by weight is recited as is a preferred yttrium content of 2.5% by weight, the latter exhibiting a yield point of 6.8 kg./mrn. which converts to 9672 p.s.i. Unfortunately, the rigorous strength requirements of modern engineering applications, particularly in the aeronautical field, are such that the use of alloys having a yield strength less than 10,000 p.s.i. is severely limited. In addition, the applicability of the patented alloy becomes a matter of conjecture when specifications call for sheet, strip or other wrought form.

Accordingly, a principal object of the present invention is to provide an yttrium containing magnesium base alloy which is unattended by the foregoing disadvantages of the prior art.

Another object of the invention is to provide an yttrium containing magnesium base alloy exhibiting high strength properties in the age-hardened condition.

A further object of the invention is to provide an yttrium containing magnesium base alloy which is age hardenable to high yield strength without departing from suitable ductility.

Other objects of the invention will in part be obvious and in part appear hereinafter in the following detailed description.

The present invention is directed to magnesium base alloys containing about 8 to 11 percent by weight of yttrium. In general, these alloys may be produced in wrought form, as by rolling into sheet or strip, or may be cast into ingots or molds. The alloys are characterized by age hardenability and exhibit high strength proper- Table I.Tensile Tests on Wrought Magnesium-Yttrium Alloys Rolled and Aged Solution Treated and Aged Solution Treated and Prestramed 5% Alloy Aging Treatment U'IS YS Percent UIS YS Percent UTS YS Percen (K s.i.) (K s.i.) E (1") (K s.i.) (K s.i.) E (1) (K s.i.) (K s.i.) E (1) Mg-8.2Y No age 43. 2 39. 3 6 36. 4 24. 5 17 36. 0 32. 7 10 Aged at 200 0.:

50. 0 44. 0 3 36. O 26. 8 16 44. 0 40. 3 8 50. 6 44. 4 3 36. 3 26. 8 20 46. 9 40. 6 10 51. 0 44. 9 4 39. 7 30. 5 11 47. 7 41. 9 8 51. 0 46. 7 5 40. 8 31. 4 11 49. 1 43. 4 1O 45. 1 42. 4 5 36. 0 26. 6 12 43. 5 37. 5 13 49. 3 43. 2 7 36. 5 27. 4 14 42. 9 38. 0 13 49. 0 43. 7 7 34. 9 27. 3 13 41. 6 36. 6 8 46. 8 40. 8 6 36. 3 28. 1 12 44. 0 325. 3 7 Mg9.0Y No age 42. 8 38. 5 7 36. 7 28. 6 19 37. 4 35. 3 14 Aged at 200 C.:

2 days... 49. 8 43. 8 7 38. 0 31. 4 11 47. 5 44. 3 8 3% Clays 51. 2 45. 2 4 38. 6 31. 6 10 49. 7 45. 2 8 8 days 54. 2 46. 8 6 47. 5 39. 0 7 59. 0 46. 6 7 16 days 53. 0 46. 3 8 46. 6 38. 4 7 51. 8 47. 1 7 Aged at 225 C.

1 day 48. 3 38. 5 7 38. 3 29. 0 19 44. 3 36. 6 10 2 days... 50. 7 44. 5 8 37. 8 30. 7 15 45. 2 40. 1 11 4 days 48. 9 43. 3 8 36. 4 30. 0 16 45. 0 30. 8 11 8 days... 48. 1 40. 6 0 39. 3 32. 4 12 48. 0 42. 8 8 Mg-l0.6Y N0 age 44. 6 40. 4 5 35. 1 27. 9 16 Aged at 200 C."

2 54. 7 4 days 58. 2 8 days 58. 3 Aged at 22 day 54.0

1 day 54 2 2 days 52. 6 4 days 54. 1 8 days. 54. 0 Mg-8.2Y No age [46. 3]

Aged at 200 C 34 d- [50. 7] day [51. 0] 1 day... [53. 7] 2 days [57. 0] 4 days. [58. 4] 8 days [57. 3] 16 days [57. 0]

1 K s.i. compressive YS. Z 52 K s.i. compressive YS.

ties together with acceptable ductility upon undergoing an aging reaction. While improved strength properties are obtained upon pure aging, as by aging after solution treatment, maximum strength properties develop upon strain accelerated aging, as by aging after rolling. Intermediate strength properties are obtained by aging after a combination of solution treatment and prestraining, yield strength being directly proportioned to the percentage of prestraining. Ductility of the age-hardened alloys is inversely proportional to yield strength and is acceptable in all cases, acceptable ductility being defined as a minimum of 3 to 5 percent elongation on a one-inch gage length. Additions of up to about 1 percent of silicon, manganese, and zirconium may be made to the inventive alloys with beneficial results.

In the course of the investigation leading to the present invention various magnesium-yttrium alloys were made and tested. Tests of strength and ductility were conducted after a variety of conditioning and aging treat ments and the results thereof are given in Table I, above.

Analysis of the test data set forth in Table I reveals conclusively that the inventive alloys are age hardenable, since in every case aging results in increased yield strength. Where an aging temperature of 225 C. is employed, ductility increases at the expense of yield strength. Table I also reveals that in almost all cases an acceptable ductility accompanies the improved strength properties.

It will be noted from Table I that while for the most part tests of tensile yield strength were conducted, some tests of compressive yield strength were also conducted. It was found that a fully hardened longitudinal specimen (Mg8.2%Y) having a tensile yield strength of 51.8 K s.i. had a compressive yield strength of 52 K s.i., and that a transverse specimen of the Mg10.6%Y alloy with a tensile yield strength of 55 K s.i. had a compressive yield strength of 45 K s.i. The compressive yield strength in commercial wrought magnesium alloys is usually on the order of /2 to /a. the tensile yield strength.

Investigative work with magnesium base alloys containing less than 8 percent by weight yttrium revealed significantly reduced strength properties while a content of more than 11 percent by weight yttrium was attended by undue brittleness.

While the invention has been described and disclosed in connection with specific embodiments thereof, it is understood that the invention is not limited thereto but may be otherwise embodied or practiced within the scope of the appended claims.

We claim:

1. A wrought alloy in the aged condition consisting essentially of 8 to 11 weight percent yttrium, the balance being substantially magnesium, said alloy having a minimum yield strength of about 44,000 p.s.i., an ultimate tensile strength in excess of about 50,000 p.s.i., and an elongation in 1 inch of at least 3%.

2. The alloy as described in claim 1 wherein said alloy contains 8.2 weight percent yttrium and is characterized by a yield strength of 44,000 p.s.i., an ultimate strength of 50,000 p.s.i. and an elongation in 1 inch of 3%.

3. The alloy as described in claim 1 wherein said alloy contains 9.0 weight percent yttrium and is characterized by a yield strength of 46,800 p.s.i., an ultimate tensile strength of 54,200 p.s.i. and an elongation in 1 inch of 6%.

4. The alloy as described in claim 1 wherein said alloy contains 10.6 weight percent yttrium and is characterized by a yield strength of 48,700 p.s.i., an ultimate tensile strength of 54,200 p.s.i., and an elongation in 1 inch of 5%.

References Cited UNITED STATES PATENTS 2,219,056 10/1940 Sauerwald -168 FOREIGN PATENTS 4/1965 Netherlands.

OTHER REFERENCES CHARLES N. LOVELL, Primary Examiner.