T.O. 1-1A-9
SECTION IV
MAGNESIUM ALLOYS
4-1. CLASSIFICATION.
4-2. Magnesium alloys are produced and used in many shapes and forms, i.e., castings, extruded bars, rods, tubing,
sheets and plate and forgings. They are suitable for varied stress and non-stress aerospace applications. Their inherent
strength, lightweight, shock and vibration resistance are factors which make their use advantageous. The weight for an
equal volume of magnesium is approximately two-thirds of that for aluminum and one-fifth of that for steel.
4-3. The current system used to identify magnesium alloys, is a two letter, two or three digit number designation in that
order. The letters designate the major alloying elements, (arranged in decreasing percentage order, or in alphabetical
order if the elements are of equal amounts), followed by the respective digital percentages of these elements. The
percentage is rounded off to the nearest whole number or if a tolerance range of the alloy is specified, the mean of the
range (rounded off to nearest whole number is used. A suffix letter following the percentage digits, denotes the latest
qualified revision of the alloy. For example: Alloy Designation AZ92A would consist of 9% (mean value) aluminum and
2% (mean value) zinc as the major alloying elements. The suffix 'A' indicates this is the first qualified alloy of this type.
One exception to the use of the suffix letter is that an 'X' denotes that impurity content is controlled to a low limit. Some
of the letters used to designate various alloying elements are:
A
Aluminum,
E
Rare Earth,
H
Thorium,
K
Zirconium,
M
Manganese,
Z
Zinc.
4-4. DEFINITIONS.
4-5. HARDNESS. Hardness is the resistance of a metal to plastic deformation from penetration, indentation, or
scratching. The degree of hardness is usually a good indication of the metals strength. The hardness of a metal can be
accurately measured using the Brinell on Rockwell process of testing. Tables 4-4, 4-5 and 4-6 list the nominal hardness
of various magnesium alloys. Brinell hardness testing is explained in Section VIII of this manual.
4-6. TENSILE STRENGTH. The useful tensile strength of a metal is the maximum stress it can sustain in tension or
compression without permanent deformation. The yield strength is that point of stress, measured in pounds per square
inch, at which permanent deformation results from material failure. The data in Tables 4-4, 4-5 and 4-6 lists the nominal
yield strengths of various alloys. The yield point in magnesium is not reached abruptly, but rather a gradual yielding
when the metal is stressed above the proportional limit. Tensile and yield strengths decrease at elevated temperatures.
4-7. TEMPER is the condition produced in the alloy by mechanically or thermally treating it to alter its mechanical
properties. Mechanical includes cold rolling, cold working, etc.; thermal includes annealing, solution and precipitation
heat treat and stabilization treating. See paragraph 4-12 for temper designations.
4-8. SHEAR STRENGTH is the maximum amount (in pounds per square inch) in cross sectional stress that a material
will sustain before permanent deformation or rupture occurs.
4-9. ELONGATION is the linear stretch of a material during tensile loading measured before and after rupture. In
magnesium it is the increase in distance which occurs when stretch is applied between two gage marks placed 2 inches
apart on the test specimen. After rupture the two pieces are fitted together and remeasured. The elongation is the
percentile difference of the amount of stretch in ratio to the original 2 inches.
4-10. PHYSICAL PROPERTIES. Magnesium, in its pure state, has a specific gravity of 1.74, weighing .063 pounds per
cubic inch. Similar data for magnesium alloys are included in Table 4-6 as well as other physical property information.
4-11. CHEMICAL PROPERTIES. Chemically bare magnesium is resistant to attack by alkalis, chromic and hydrofluoric
acids and many organic chemicals including hydrocarbons, aldehydes, alcohols, phenols, amines, esters and most oils.
It is susceptible to attack by salts and by galvanic corrosion from contact with dissimilar metals and other materials.
Adequate protection of the metal against unfavorable conditions can be maintained generally, by using proper surface
finish (See paragraph 4-93) and assembly protection. The chemical property constituents of the various alloys are listed
in Table 4-3.
4-12. TEMPER DESIGNATION SYSTEM . The hyphenated suffix symbol which follows an alloy designation denotes the
condition of temper, (heat treat or strain hardening), to which the alloy has been processed. These symbols and their
meanings are listed below: (Heat treating itself is discussed in subsequent paragraphs of this section of the manual).
-AC
As-Cast
-F
As-fabricated
-O
Annealed
-W
Solution heat treated - unstable temper
-T
Treated to produce stable tempers other than for -O
-T2
Annealed (cast products only)
-T3
Solution heat treated and then cold worked
-T4
Solution heat treated
-T5
Artificially aged only
-T6
Solution heat treated and then artificially aged
4-1
