This chapter contains the engineering properties and characteristics of wrought and cast magnesium alloys used in aircraft and missile applications. Magnesium is a lightweight structural metal that can be strengthened greatly by alloying, and in some cases by heat treatment or cold work or by both.
4.1.1
ALLOY INDEX — The magnesium alloys in this chapter are listed in alphanumeric sequence in each of two parts, the first one being wrought forms of magnesium and the second cast forms. These sections and the alloys covered under each are shown in Table 4.1.
| Section | Designation |
|---|---|
| 4.2 | Magnesium-Wrought Alloys |
| 4.2.1 | AZ31B |
| 4.2.2 | AZ61A |
| 4.2.3 | ZK60A |
| 4.3 | Magnesium-Cast Alloys |
| 4.3.1 | AM100A |
| 4.3.2 | AZ91C/AZ91E |
| 4.3.3 | AZ92A |
| 4.3.4 | EZ33A |
| 4.3.5 | QE22A |
| 4.3.6 | ZE41A |
4.1.2 MATERIAL PROPERTIES
4.1.2.1
Mechanical Properties — The mechanical properties are given either as design values or for information purposes. The tensile strength ( ), tensile yield strength ( ), elongation (e), and sometimes the compressive yield strength ( ) are guaranteed by procurement specifications. The properties obtained reflect the location of sample, type of test specimen and method of testing required by the product specification. The remaining design values are “derived” values; that is, sufficient tests have been made to ascertain that if a given material meets the requirements of the product specification, the material will have the compression ( ), shear ( ) and bearing ( and ) strengths listed.
4.1.2.1.1
Tension Testing — Room-temperature tension tests are made according to ASTM E 8. The yield strength ( ) is obtained by the "offset method" using an offset of 0.2 percent. The speed of testing for room-temperature tests has a small effect on the strength and elongation values obtained on most magnesium alloys. The rate of stressing generally specified to the yield strength is less than 100,000 psi per minute and the rate of straining from the yield strength to fracture is less than 0.5 in./in./min. It can be
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4.1.2.1.2
Compression Testing — Compression test methods used for magnesium are specified in ASTM E 9. The values given for the compressive yield strength ( ), are taken at an offset of 0.2 percent. References 4.1.2.1.2(a) and (b) provide information on test techniques.
4.1.2.1.3
Bearing Testing — Bearing tests of magnesium alloys are made according to ASTM E 238. The size of pin used has a significant effect on the values obtained, especially the bearing ultimate strength ( ). On tests made to obtain the data on magnesium alloys shown in this document, pin diameters of 0.187 and 0.250 inch were used. For pin diameters significantly larger than 0.250 inch lower values may be obtained. Additional information on bearing testing is given in References 4.1.2.1.3(a) and (b). Bearing values in the property tables are considered to be “dry pin” values in accordance with the discussion in Section 1.4.7.1.
4.1.2.1.4
Shear Testing — The shear strength values used in this document were obtained by the “double shear” method using a pin-type specimen, the “punch shear” method and the “tension shear” method as applicable. Just as tensile ultimate strength ( ) values vary with location and direction of sample in relation to the method of fabrication, the shear strength ( ) may be expected to reflect the effect of orientation, either as a function of the sampling or the maximum stresses imposed by the method of test. Information on shear testing is given in Reference 4.1.2.1.4.
4.1.2.1.4
Fenn, R. W., Jr., and Clapper, R. B., "Evaluation of Test Variables in the Determination of Shear Strength", American Society for Testing and Materials, Proceedings 56, pp 842-858 (1956).
- 4.1.2.1.5(a) Dorn, J. E., and Meriam, J. L., "Properties and Heat Treatment of Magnesium Alloys, Part II, Notch Sensitivity of Magnesium Alloys", OSRD No. 1819, Report M-104, pp 68 (September 1943).
- 4.1.2.1.5(b) Dorn, J. E., and others, "Properties and Heat Treatment of Magnesium Alloys, Part V, Section I, The Sensitivity of Magnesium Alloy Sheet to Drilled, Reamed, and Punched Holes. Part V, Section II, The Notch Sensitivity of Magnesium Alloy Extrusions and the Influence of Various Factors", OSRD No. 3043 (NRC Research Project NRC-21), Final Report M-177, pp 202 (December 1943).
- 4.1.2.1.5(c) Doan, J. P., and McDonald, J. C., "The Notch Sensitivity in Static and Impact Loading of Some Magnesium-Base and Aluminum-Base Alloys", American Society for Testing and Materials, Proceedings 46, pp 1097-1118 (1946).
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4.1.2.1.5
Stress Raisers — The effect of notches, holes, and stress raisers on the static properties of magnesium alloys is described in References 4.1.2.1.5(a) through (c). Additional data on the strength properties of magnesium alloys are presented in References 4.1.2.1.5(d) through (h).
4.1.2.1.6
Creep — Some creep data on magnesium alloys are summarized in Reference 4.1.2.1.6.
4.1.2.1.7
Fatigue — Room-temperature axial load fatigue data for several magnesium alloys are presented in appropriate alloy sections. References 4.1.2.1.7(a) and (b) provide additional data on fatigue of magnesium alloys.
4.1.3
PHYSICAL PROPERTIES — Selected experimental data from the literature were used in determining values for physical properties. In other cases, enough information was available to calculate the constants. Estimated values of some of the remaining constants were also included. Estimated values are noted.
4.1.4
ENVIRONMENTAL CONSIDERATIONS — Corrosion protection must be considered for all magnesium applications. Protection can be provided by anodic films, chemical conversion coatings, paint systems, platings, or a combination of these methods. Proper drainage must be provided to prevent entrapment of water or other fluids. Dissimilar metal joints must be properly and completely insulated, including barrier strips and sealants.
Strain-hardened or age-hardened alloys may be annealed or overaged by prolonged exposure to elevated temperatures, with a resulting decrease in strength. Maximum recommended temperatures for prolonged service are reported, where available, for specific alloys.
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4.1.5
ALLOY AND TEMPER DESIGNATIONS — Standard ASTM nomenclature is used for the alloys listed. Temper designations are given in ASTM B 296. A summary of the temper designations is given in Table 4.1.5.
Table 4.1.5. Temper Designation System for Magnesium Alloysᵃ Basis of Codification
The designations for temper are used for all forms of magnesium and magnesium alloy products except ingots and are based on the sequence of basic treatments used to produce the various tempers. The temper designation follows the alloy designation, the two being separated by a dash. Basic temper designations consist of letters. Subdivisions of the basic tempers, where required, are indicated by a digit or digits following the letter. These designate specific sequences of basic treatments, but only operations recognized as significantly influencing the characteristics of the product are indicated. Should some other variation of the same sequence of basic operations be applied to the same alloy, resulting in different characteristics, then additional digits are added to the designation.
NOTE-In material specifications containing reference to two or more tempers of the same alloy which result in identical mechanical properties, the distinction between the tempers should be covered in suitable explanatory notes.
Basic Temper Designations
- F As Fabricated. Applies to the products that acquire some temper from shaping processes not having special control over the amount of strain-hardening or thermal treatment.
- Annealed Recrystallized (wrought products only). Applies to the softest temper of wrought products.
- H Strain-Hardened (wrought products only). Applies to products that have their strength increased by strain-hardening with or without supplementary thermal treatments to produce partial softening. The H is always followed by two or more digits.
- H1 Strain-Hardened Only. Applies to products that are strain-hardened to obtain the desired mechanical properties without supplementary thermal treatment. The number following this designation indicates the degree of strain-hardening.
- H2 Strain-Hardened and Then Partially Annealed. Applies to products which are strain-hardened more than the desired final amount and then reduced in strength to the desired final amount by partial annealing. The number following this designation indicates the degree of strain-hardening remaining after the product has been partially annealed.
- H3 Strain-Hardened and Stabilized. Applies to products that are strain-hardened and then stabilized by a low temperature heating to slightly lower their strength and increase ductility. This designation applies only to alloys which, unless stabilized, gradually age soften at room temperature. The number following this designation indicates the degree of strain-hardening remaining after the product has been strain-hardened a specific amount and then stabilized.
Subdivisions of the "H1", "H2" and "H3" Tempers: The digit following the designations "H1", "H2", and "H3" indicates the final degree of strain hardening. Tempers between 0 (annealed) and 8 (full hard) are designated by numerals 1 through 7. Material having a strength about midway between that of the 0 temper and that of the 8 temper is designated by the numeral 4 (half hard); between 0 and 4 by the numeral 2 (quarter hard); between 4 and 8 by the numeral 6 (three-quarter
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4.1.5 Temper Designation System for Magnesium Alloys (Continued)ᵃ
hard), etc. The third digit, when used, indicates a variation of a two-digit H temper. It is used when the degree of control of temper or the mechanical properties are different from but close to those for the two-digit H temper to which it is added. Numerals 1 through 9 may be arbitrarily assigned as the third digit for an alloy and product to indicate a specific degree of control of temper or special mechanical property limits.
- W Solution Heat-Treated. An unstable temper applicable only to alloys which spontaneously age at room temperature after solution heat-treatment. This designation is specific only when the period of natural aging is indicated: for example, W ½ hr.
- T Thermally Treated to Product Stable Tempers Other Than F, O, or H. Applies to products which are thermally treated, with or without supplementary strain-hardening, to product stable tempers. The T is always followed by one or more digits. Numerals 1 through 10 have been assigned to indicate specific sequences of basic treatments, as follows.
- T1 Cooled from an Elevated Temperature Shaping Process and Naturally Aged to a Substantially Stable Condition. Applies to products for which the rate of cooling from an elevated temperature shaping process, such as casting or extrusion, is such that their strength is increased by room temperature aging.
- T3 Solution Heat-treated and Then Cold Worked. Applies to products that are cold worked to improve strength, or in which the effect of cold work in flattening and straightening is recognized in applicable mechanical properties.
- T4 Solution Heat-treated and Naturally Aged to a Substantially Stable Condition. Applies to products that are not cold worked after solution heat-treatment, or in which the effect of cold work in flattening or straightening may not be recognized in applicable mechanical properties.
- T5 Cooled from an Elevated-Temperature Shaping Process and Then Artificially Aged. Applies to products which are cooled from an elevated-temperature shaping process, such as casting or extrusion, and then artificially aged to improve mechanical properties or dimensional stability or both.
- T6 Solution Heat-treated and Then Artificially Aged. Applies to products that are not cold worked after solution heat-treatment, or in which the effect of cold work is flattening or straightening may not be recognized in applicable mechanical properties.
- T7 Solution Heat-treated and Then Stabilized. Applies to products that are stabilized to carry them beyond the point of maximum strength to provide control of some special characteristics.
- T8 Solution Heat-treated, Cold Worked, and Then Artificially Aged. Applies to products which are cold worked to improve strength, or in which the effect of cold work in flattening or straightening is recognized in applicable mechanical properties.
- T9 Solution Heat-treated, Artificially Aged, and Then Cold Worked. Applies to products that are cold worked to improve strength.
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4.1.5 Temper Designation System for Magnesium Alloys (Continued)a
- T10 Cooled from an Elevated Temperature Shaping Process, Artificially Aged, and Then Cold Worked. Applies to products which are artificially aged after cooling from an elevated temperature shaping process, such as extrusion, and then cold worked to further improve strength.
A period of natural aging at room temperature may occur between or after the operations listed for tempers T3 through T10. Control of this period is exercised when it is metallurgically important.
Additional digits, may be added to designations T1 through T10 to indicate a variation in treatment that significantly alters the characteristics of the product.
4.1.6
JOINING METHODS — Most magnesium alloys may be welded; refer to “Comments and Properties” in individual alloy sections. Adhesive bonding and brazing may be used to join magnesium to itself or other alloys. All types of mechanical fasteners may be used to join magnesium. Refer to Section 4.1.4 when using mechanical fasteners or joining of dissimilar materials with magnesium alloys.