Page 178 - Manufacturing Engineering and Technology - Kalpakjian, Serope : Schmid, Steven R.

Section 6.3 Magnesium and Magnesium Alloys l57

6.3 Magnesium and Magnesium Alloys

Magnesium (Mg) is the lightest engineering metal available, and it has good vibration-
damping characteristics. Its alloys are used in structural and nonstructural applica-
tions wherever weight is of primary importance. Magnesium is also an alloying
element in various nonferrous metals.
Typical uses of magnesium alloys are in aircraft and missile components,
material-handling equipment, portable power tools, ladders, luggage, bicycles, sport-
ing goods, and general lightweight components. Like aluminum, magnesium is find-
ing increased use in the automotive sector, mainly in order to achieve weight savings.
Magnesium alloys are available either as castings (such as die-cast camera frames) or
as wrought products (such as extruded bars and shapes, forgings, and rolled plates
and sheets). Magnesium alloys are also used in printing and textile machinery to
minimize inertial forces in high-speed components (Section 3.2).
Because it is not sufficiently strong in its pure form, magnesium is alloyed with
various elements (Table 6.5) in order to gain certain specific properties, particularly
a high strength-to-weight ratio. A variety of magnesium alloys have good casting,
forming, and machining characteristics. Because they oxidize rapidly (i.e., they are
pyrop/ooric), a fire hazard exists, and precautions must be taken when machining,
grinding, or sand-casting magnesium alloys. Products made of magnesium and its
alloys are, nonetheless, not a fire hazard during normal use.

Designation of Magnesium Alloys. Magnesium alloys are designated with the
following:

a. One or two prefix letters, indicating the principal alloying elements.
b. Two or three numerals, indicating the percentage of the principal alloying ele-
ments and rounded off to the nearest decimal.
c. A letter of the alphabet (except the letters I and O) indicating the standardized
alloy with minor variations in composition.
d. A symbol for the temper of the material, following the system used for alu-
minum alloys.
For example, consider the alloy AZ91C-T6:

° The principal alloying elements are aluminum (A, at 9%, rounded off) and
zinc (Z, at 1%).
° The letter C, the third letter of the alphabet, indicates that this alloy was the
third one standardized (later than A and B, which were the first and second

TABLE 6.5
Properties and Typical Forms of Selected Wrought Magnesium Alloys
Ultimate
0 tensile Yield Elongation
COIHPOSIIIOH ( M strength strength in 50 mm
Alloy Zn Mn Zr Th Condition (MPa) (MPa) ( %) Typical forms
AZ31B 3.0 1.0 0.2 _ - F 200 Extrusions
0.2 - - H24 220 Sheet and plates
- -
AZSOA 8.5 0.5 T5 275 Extrusions and forgings
HK31A 0.7 3 H24 200 Sheet and plates
ZK60A 5.7 - 0.55 T5 300 Extrusions and forgings