Symbol, Al. Equivalent, old, 13.7; new. 27.49. Specific gravity, cast,
2.46. Hammered, 2.67. Specific heat, 0.2143, Heat conductivity, 0.66 on
silver scale = 100.
Melting point, 1,250° or 1,560° Fah., according to different
authorities.
A shining, white, sonorous metal, having a shade between silver and
platinum. It is malleable and ductile, does not oxidize when exposed to
dry or moist air, and is not chemically affected by hot or cold water.
Sulphureted hydrogen gas, which so readily tarnishes silver, has no
action upon this metal.
Having but one defect in its uses as a pure metal (difficulty in
soldering), it enters largely as an alloy of other metals, making
the baser metals more valuable in resisting oxidation, and as a good
as well as cheap imitation of the precious metals.
Its power to ameliorate the condition of the alloys of copper, zinc,
tin, iron, nickel, silver, gold, and platinum by portions sometimes
less than a thousandth part is beautifully illustrated in the elegant
articles of tableware, bric a brac, and ornamental hardware now
coming upon the commercial market. Its uses in the mechanic arts in
the various forms of bronzes in filling a long wanted requirement of
combined ductility, strength, sonorousness, and freedom from oxidation,
thus giving to its alloys a high value for articles of house hardware,
carriage and harness trimmings, quick running machinery, journal
bearings, propeller blades, and artillery. Piano wires made from its
alloys will vibrate ten seconds longer than the best now in use.
For the kitchen and for articles for the toilet, there is no more
beautiful and cleanly ware. An alloy of silver 20 and aluminum 80 parts
by weight, for nautical and other instruments, is without a rival in
beauty and lightness; the sea air does not tarnish it.
The aluminum-silver alloys are more valuable than pure silver for table
service; its wares will not be destroyed by the constant polishing that
wears out our plate, and holds an immunity from the destructive effects
of the fatty and acetic acids.
For watch cases it wears cleaner than pure silver, and for watch
movements it is far superior to the brass and nickel or German silver
heretofore used. An alloy is now made in France that has elastic
qualities equal to steel for watch springs, and with the valuable
property of being free from magnetic effect.
The aluminum bronzes, when combined with five per cent. of gold, have
all the beauty, finish, and durability of color of eighteen carat gold;
they are entering largely into the manufacture of watch cases and
jewelry.
The composition most approved is made of copper 85, aluminum 10, gold
5, parts by weight. This can be soldered with any of the jeweler's
solders of gold, silver, and zinc in the usual way.
The most important alloy, _aluminum bronze_, is composed of aluminum
10 parts, copper 90 parts by weight; specific gravity, 7.7. It has a
pale gold color, harder than ordinary bronze, takes a fine polish, is
malleable and ductile, but when rolled into sheets requires annealing
at every third passage through the rolls, and when drawn into wire must
be frequently annealed. It may be forged cold or hot, and can be drawn
in tubes. In wire it has a tensile strength of 100,000 lb.
This alloy is often found to be brittle at the first mixing, but
becomes ductile after remelting. It is softened while being worked by
plunging in water at a low red heat.
The Parisian gold colored alloy is made of aluminum 10.7, copper, 89.3,
by weight; used much for cheap French jewelry.
A non-oxidizable alloy in a moist atmosphere: Aluminum, 25, iron 75
= 25 per cent. aluminum. A hard bright alloy, with the properties of
silver: Silver 5 (by weight); aluminum 95 = 5 per cent. aluminum.
The silver alloys with aluminum bronze, as represented in the four
following atomic formulas, are of a rich gold color, and well adapted
for jewelry, watch cases, etc.:
Cu Al Ag
Ag + 24 (Al + Cu_{6}) = 0.9180 + 0.0616 + 0.0203
Ag + 24 (Al + Cu_{7}) = 0.9241 + 0.0570 + 0.0188
Ag + 24 (Al + Cu_{8}) = 0.9330 + 0.0504 + 0.0166
Ag + 24 (Al + Cu_{9}) = 0.9400 + 0.0450 + 0.0150
The figures being proportional weights.
A cheap alloy for journal boxes and machinery may be made by
substituting zinc for silver in the following atomic proportions:
Cu Al Zn
Zn + 2(Al + Cu_{6}) = 0.8643 + 0.0622 + 0.0734
Zn + 2(Al + Cu_{9}) = 0.9053 + 0.0435 + 0.0512
Zn + 2(Al + Cu_{12}) = 0.9273 + 0.0333 + 0.0394
This is subject to considerable shrinkage in casting, but is tenacious,
and when drawn into wire has a tensile strength of ninety to one
hundred thousand pounds.
The following alloys, in which iron enters as a third element, are well
adapted for gun metal, being hard, tenacious, laminable, and ductile:
Cu Al Fe
Fe + (Al + Cu_{15}) = 0.9203 + 0.0267 + 0.0530
Fe + (Al + Cu_{9}) = 0.9399 + 0.0446 + 0.0149