It forms a metal with high tensile strength
while being ductile and malleable.
Aluminum zinc is suitable for castings which must be stiff and hard.
Nickel aluminum has a tensile strength of 40,000 pounds per square inch.
Magnalium is a silver-white alloy of aluminum with from 5 to 20 per cent of
magnesium, forming a metal even lighter than aluminum and strong enough to
be used in making high-speed gasoline engines.
HEAT TREATMENT OF STEEL
The processes of heat treatment are designed to suit the steel for various
purposes by changing the size of the grain in the metal, therefore the
strength; and by altering the chemical composition of the alloys in the
metal to give it different physical properties. Heat treatment, as applied
in ordinary shop work, includes the three processes of annealing, hardening
and tempering, each designed to accomplish a certain definite result.
All of these processes require that the metal treated be gradually brought
to a certain predetermined degree of heat which shall be uniform throughout
the piece being handled and, from this point, cooled according to certain
rules, the selection of which forms the difference in the three methods.
_Annealing._--This is the process which relieves all internal strains
and distortion in the metal and softens it so that it may more easily be
cut, machined or bent to the required form. In some cases annealing is used
only to relieve the strains, this being the case after forging or welding
operations have been performed.
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