METAL PROPERTIES, CHAR, USES, AND CODES - OD1643 - LESSON 1/TASK 1
repair hardware, repair parts, jigs, and devices.
But determining
the type of welding or machining process needed to repair or
fabricate these metal component parts, jigs, and devices requires
knowledge of the properties, characteristics, uses and identification
codes of metals.
The responsibility of ensuring that the personnel are trained, and of
providing them with the capability to identify the various metals
belongs to the shop technician in charge of the service section. For
this purpose, the following paragraphs describe the processes for
identifying the physical and mechanical properties of various metals.
2.
Identification of Physical and Mechanical Properties of Various
Metals
a.
General.
The distinguishing characteristics or qualities that
are used to describe a substance such as metal are known as its
Those physical properties which describe the
behavior of a metal when it is subjected to particular types of
mechanical usage are called mechanical properties.
Subsequent paragraphs describe the physical and mechanical properties
of metals.
The mechanical properties are of chief concern and will
therefore receive greater coverage.
b.
Definition of Metal and Alloy.
(1) Before going into a discussion of the properties of metals,
first let us define the terms "metal" and "alloy".
The basic
chemical elements are divided into metals and nonmetals; however,
there is no sharp dividing line between the two.
A metal may be
defined as a chemical element that possesses metallic luster and
which, in electrolysis, carries a positive charge that is liberated
at the cathode.
Most nonmetallic elements do not possess metallic
luster, and in electrolysis the nonmetals carry negative charges that
are liberated at the anode.
Of all the natural chemical elements,
about 70 are metals and, of these, about 39 are used commercially.
(2) An alloy is a metallic substance, but it is not a single chemical
element. An alloy is formed by the union or mixture of two or more metals; in
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