ALUMINUM AND ITS ALLOYS.
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 + Cu6) = | 0.9180 | + 0.0616 | + 0.0203 |
| Ag + 24 (Al + Cu7) = | 0.9241 | + 0.0570 | + 0.0188 |
| Ag + 24 (Al + Cu8) = | 0.9330 | + 0.0504 | + 0.0166 |
| Ag + 24 (Al + Cu9) = | 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 + Cu6) = | 0.8643 | + 0.0622 | + 0.0734 |
| Zn + 2(Al + Cu9) = | 0.9053 | + 0.0435 | + 0.0512 |
| Zn + 2(Al +Cu12) = | 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 + Cu15) = | 0.9203 | + 0.0267 | + 0.0530 |
| Fe + (Al + Cu9) = | 0.9399 | + 0.0446 | + 0.0149 |
Also a four-element alloy of
| Cu | Al | Zn | Fe | ||
|---|---|---|---|---|---|
| 1. | Fe + Zn + (Al + Cu12) = | 0.8386. | + 0.0305. | + 0.0712. | + 0.0600 |
| 2.. | Fe + Zn + (Al + Cu15) = | 0.8666. | + 0.0249. | + 0.0588. | + 0.0496 |
The tensile strength of the above alloys as drawn wire is 82,000 pounds for the first, and 107,000 pounds for the second.
All of the alloys in which zinc or zinc and iron enter in place of silver, the color is affected and the luster diminished.
With nickel and platinum for the third element, we have:
| Cu | Al | Ni | |
|---|---|---|---|
| Ni + 6 (Al + Cu6) = | 0.9129 | + 0.0634 | + 0.0237 |
| Pl + 21 (Al + Cu6) = | 0.9117 | + 0.0656 | + 0.0225 |
Those alloys into which platinum is introduced are less affected by acids than those in which silver takes the place of platinum; platinum producing a higher luster than silver.
In the alloys of aluminum bronze with the more difficultly fusible metals, it is preferable to fuse the bronze first, then add the other metal in small shavings or wire; by this means the less fusible metal absorbs the other without raising the heat of the furnace excessively. Add the least fusible metal last, a little at a time, allowing the heat of the melted metal to fall by degrees, which prevents boiling and evaporation. The crucibles for mixing the alloys should be of plumbago lined with a paste of lime.
Avoid sand crucibles, as silicium may be reduced and absorbed by the aluminum, inducing brittleness. If found brittle, remelt with cryolite as a flux, or stir the melted metal or alloy with a hard wood stick that has been slightly charred.
In adding aluminum to the copper, cut it in small pieces and push it to the bottom of the crucible with a dry, hard wood stick split so as to hold the pieces.
Sodium chloride (common salt) calcined to evaporate the water, and caustic soda with pulverized charcoal, may be used as a flux for pure aluminum. Avoid borax as a flux, as its metal may suffer reduction, making the aluminum brittle. Aluminum will alloy with tin alone, but is liable to separate on refusion. Does not alloy with lead.
Bismuth, even in minute quantity, makes these alloys brittle.
The East Indian steel called wootz is, according to analysis, alloyed with aluminum. No reliable solder has yet been found for pure aluminum that will flow freely under the blow pipe or from a soldering iron.
A process recently adopted in France is to plate the parts to be united with alloys of tin 5, aluminum 1, upon which tin solder will flow. These proportions may be slightly varied to suit requirements for hardness.
Harder solders to be used with a blowpipe may be made with alloys of zinc, tin, and aluminum.
Aluminum is now made at the works of M. Deville, at Javelle, near Paris, and at Salindres, France; also at Birmingham, England. The product of late has reached the value of $20,000 annually in Europe. It has been claimed to be made in Philadelphia at a reduced cost. The present price in New York is $1.25 per oz. As its bulk is over four times as great as silver, its comparative cost is but one-third that of silver—a point not often considered when the price is quoted.
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