ALUMINUM AND ITS ALLOYS Aluminum.—A large part of the crust of the earth consists of this met al. It is most abundant in different varieties of clay, but occurs in the rock known as feldspar, and also in corundum, emery, and in the precious stones sapphire and ruby.
Improved methods of manufacture have in recent years greatly reduced the cost of aluminum, which should be one of the cheapest of metals, and it is likely to be further reduced in time to come.
Aluminum nearly chemically pure is now made commercially at a price which admits of its use for various wares and utensils. The leading qual ity of aluminum is its lightness, it be ing hardly more than 2.5 times as heavy as water. Steel is nearly 3 times as heavy as aluminum, copper 3.6 times, lead 4.8 times, gold 7.7 times.
Aluminum is not, however, a very strong metal, being under tensile strain about equal to cast iron, and less than half as strong as wrought iron. Pure aluminum is white with a bluish tint. Upon exposure to the air it acquires a thin film of white oxide like zinc, which prevents further tarnishing but increases the bluish tint. It conducts heat about one half as well as silver. It can be dissolved in hydrochloric acid, and is corroded rapidly by caus tic alkalies, as potash and soda, chlo rine, iodine, and similar substances.
To Solder Aluminum.—Moisten the surface with Venetian turpentine, and solder with pure zinc, using a solder ing iron.
Aluminum Alloys. — Aluminum 95
and silver 5 gives a beautiful alloy susceptible of a high polish, which is likely to have many important uses in the arts.
Aluminum bronze, an alloy of cop per with 2 to 12 per cent of aluminum, has great strength and ductility and resists corrosion. More than 10 per cent of aluminum is usually not ad visable, and down to 5 per cent is usually preferred. Additional alu minum increases the hardness and lightens the color, 10 per cent alloy having a yellowish-gold and the 21 per cent alloy having a deep red-gold shade. These bronzes can be forged, rolled, hammered, or cast in almost every way that steel can, and with greater strength, ductility, and power to withstand corrosion.
Silver bronze, a substitute for Ger man contains 67.5 copper, 18 manganese, 13 zinc, 5 silicon, 1.2 aluminum. It is used in electrical engineering for resistance coils.
Aluminum is added to cast iron at the rate of 2 to 5 pounds a ton to re duce the range of temperature be tween which the iron first softens and that at which it becomes fluid. Five to 10 ounces of aluminum added to each ton of steel or open-hearth met al, or 7 to 16 ounces for Bessemer metal, helps to quiet the steel in pour ing. Four ounces of aluminum added to 10 tons of smelter in galvanizing improves the finish of galvanized iron or steel sheets.