Aluminum
A bluish-white metal of remarkable brightness, its specific gravity being only a quarter that of silver (2.56), or about the same as porcelain. Next to oxygen and silicon, it is perhaps the most abundant element upon the earth's surface, and is more abundant than any other metal, as it is supposed to constitute one twelfth of the solid crust of the earth. Most rocks and soils hold enormous quantities of this metal in combination with oxygen and silicon, and slate, marl, feldspar, clay, and many other common minerals contain it in large proportions.
Notwithstanding its abundance, it cannot be applied to the many uses for which it is so well suited, because as yet the methods for obtaining it are very costly, although considerable progress has been made of late in devising cheaper means to this end. The metal is malleable, ductile, and tenacious, and may be beaten into thin sheets, and drawn into fine wire, after the manner of silver. Hammering in the cold makes it hard, like soft iron; fusing softens it again. Hammering increases its specific gravity from 2.56 to 2.67. It melts at red heat, but does not oxidize at high temperatures; it is not acted upon by chemicals that would blacken silver, and because of this quality it preserves its lustre better than the latter metal, which is usually attacked by the sulphur contained in some foods, forming with the silver a dark composition. Nitric acid, even when concentrated, fails to touch it, and it is not soluble in dilute sulphuric acid. Concentrated hydrochloric acid dissolves it with evolution of hydrogen. The metal is also dissolved with solutions of caustic potash or soda, which forms aluminate of potash or soda, giving off hydrogen. Aluminum is employed extensively in the manufacture of delicate apparatus, ornamental articles, etc., but it is as yet only valuable as an alloy with other metals, such as steel, cast-iron, copper, nickel, and some others, the quality of which is very perceptibly improved by certain additions of aluminum. The property of this metal, when combined with steel, iron, and copper, is to increase their tensile strength and resistance to oxidation. The fluidity of cast-iron is much improved by this metal, and it is claimed that the castings are much more sound and cleaner when alloyed with a surprisingly small amount of aluminum.
Alloyed with brass or copper, it improves equally tensile strength, color, and durability, and gives a dense solid casting free from porosity. To effect the above result it is only necessary to flux with from 1/2 to 1 per cent of aluminum.
The true bronze--aluminum 10, copper 90--is a somewhat brittle, gold-colored alloy at the first melting, but it increases in tenacity and strength with successive meltings, until at a dull red heat it may be forged and hammered until it has become cold, without presenting any cracks at the edges. One of the qualities possessed by aluminum bronze is that it may be made softer and more ductile by plunging into cold water while hot. The tensile strength of good bronze is about 90,000 pounds per square inch. In making this bronze in crucibles, use a layer of charcoal over the copper, but no flux. When the copper has melted, push the aluminum down into the molten copper before lifting out the crucible, after which it may be skimmed clean and poured. No time should be lost in handling this alloy after it has been well stirred and freed from slag.
Small proportions of gold, silver, tin, or zinc increases the hardness, but does not materially affect the ductility of aluminum. Three per cent of zinc improves it; 7 per cent of tin impairs its lustre, and with lead, mercury, and antimony it will not combine. Articles made in this metal may be freed from the bluish tint, and made to appear like frosted silver by immersing in a hot solution of potash. Soldering aluminum has so far proven a difficult task; most solders will not stick to the surface of aluminum and owing to its high heat conductivity, the heat is very rapidly drawn away from any of the molten solders, causing them to freeze before flowing sufficiently. These difficulties have been largely overcome by having the aluminum to be soldered hot, the surfaces especially cleaned, and with very hot soldering bits or careful work with the blow pipe, and with special alloys for solders and special fluxes. Several such methods are successfully used. Soldering bits of nickel are better than copper ones, and especially good work has been done with those kept hot by a gasolene torch or electric appliance. Due to the peculiar nature of aluminum and its commercial impurities, ordinary hard solder (composed of silver and tin), soft solder (composed of lead and zinc), or any of the ordinary forms of solder, do not "stick" to the metal. The Pittsburgh Reduction Company have a process protected by letters-patent for treating aluminum so that certain forms of solder will work satisfactorily with it.
Due to the high heat conductivity of aluminum, the heat from the molten solder is conducted away from it so rapidly that it will not "flow under" as satisfactorily as could be desired. The above-mentioned company have arrangements for overcoming this difficulty and soldering satisfactorily. The quality of ordinary bronze, or gun-metal (copper 90, tin 10), is much improved by an addition of about 2 per cent aluminum. All anti-friction metals, especially babbitt-metal, are improved by the addition of from 1/4 to 1/2 of 1 per cent aluminum.
Steel is rendered more fluid for casting with by a small percentage of aluminum added to each ladleful of metal before pouring. From 3/8 to 1 pound to a ton of steel is usually sufficient for this purpose; it diffuses through the mass without stirring, makes sounder castings and freer from honeycomb. Its effect upon gray cast iron is not very pronounced, but white iron containing combined carbon 4.80, and no graphite, is changed to a gray iron containing graphitic carbon 3.45, combined carbon 0.93, by the addition of about 3.20 per cent of aluminum, thus causing an entire change from white iron to gray.
Most type-metal mixtures are appreciably improved by a further alloy of from 5 to 10 per cent aluminum, the edges of the type being made harder and metal more durable.
With nearly all brass mixtures it imparts a higher degree of homogeneity, and lessens the tendency to corrosion.
Zinc galvanizing is made more easy of accomplishment, and with improved results, by adding a slight proportion of aluminum to the zinc, a thinner and more tenacious coating being made possible by this means. Besides the numerous aluminum alloys given elsewhere, there are many new compositions which are claiming considerable attention, in which aluminum enters as a principal ingredient, some of which are as follows: Bourbounz-metal contains aluminum 85.74, tin 12.94, silicon 1.32. Nickel-aluminum contains aluminum 8, nickel 20.
Metalline contains aluminum 25, copper 30, cobalt 35, iron 10. Rosine, for jewelry, contains aluminum 30, nickel 40, tin 20, silver 10. Cobalt-bronze contains aluminum 10, copper 40, cobalt 50. See ALUMINUM ALLOYS; ALUMINUM-BRONZE ALLOYS.
The impurities most commonly found in aluminum are silicon and iron, and it may be said of the metal made by the Pittsburgh Reduction Company that these two impurities are the only ones found. Silicon in aluminum exists in two forms, one seemingly combined with aluminum as combined carbon exists in pig-iron, and the other as an allotropic graphitoidal modification. For many purposes the pure aluminum cannot be so advantageously used as that containing 3% or 4% of impurities, as the pure aluminum is soft and not so strong as the less pure. It is only where extreme malleability, ductility, sonorousness, and non-corrodibility are required, that the purest metal should be used.
The purity of commercial aluminum varies from 94% to 99.75%. The Pittsburg Reduction Company sells its commercial aluminum in three grades. The No. 1 grade of aluminum has an analysis approximately as follows: Silicon . . . . . 0.50%, Iron . . . . . 0.25%. Aluminum . . . . . 99.25%. They always have, however, in stock metal still purer than this; some running as high as 99.90% pure, which is sold at an added price for special uses. The No. 2 grade ordinarily runs quite uniform in composition, and has an analysis approximately as follows:
Silicon . . . . . 3%. Iron . . . . . 1%. Aluminum . . . . . 96%. This metal, however, is not guaranteed to be over 94% pure. Sound ingots of the No. 1 grade metal, suitable for rolling, are kept in stock of the following sizes: 12 inches x 18 inches x 1 3/8 inch. 12 inches x 18 1/4 inches x 1 1/8 inch. 11 1/2 inches x 16 1/4 inches x 1 inch. 12 1/2 inches x 6 inches x 3/4 inch. 5 1/2 inches x 2 inches x 1/2 inch.
Aluminum for remelting is kept in stock of the various grades of metal, in what are called "waffle" ingots. They are square placques, three inches on a side and of about 3/4 inch thickness, and weigh about one half pound each. They are connected together with thin webs.
A sheet of aluminum twelve inches square and one inch thick weights 14.12 pounds; a bar of aluminum one inch square and 12 inches long weighs 1.176 pounds; a bar of aluminum one inch in diameter and 12 inches long weighs 0.918 pounds.
Weight.--The weight per cubic inch of cast aluminum is .092 lb.; of rolled aluminum, .098 lb.
The weight per cu. ft. of cast aluminum is . 158.989 lbs. The weight per cu. ft. of rolled aluminum is . 169.510 lbs. The weight per cu. ft. of wrought iron is . . . 480.000 lbs. The weight per cubic foot of soft steel is . . . . 490.450 lbs. The weight per cubic foot of brass is . . . . . 524.160 lbs. The weight per cubic foot of copper is . . . . . 558.125 lbs. The weight of a given bulk of cast aluminum being 1, soft steel or iron is 3.0 times as heavy; copper is 3.6 times as heavy; nickel, 3.5 times as heavy; silver, 4 times as heavy; lead, 4.8 times as heavy; gold, 7.7 times as heavy, and platinum 8.6 times as heavy.
Strength.--The tensile, crushing and transverse tests of aluminum vary very considerably with different conditions of hardness, due to cold working; also by the amount of work that has been put upon the metal, the character of the section, etc. Cast aluminum has about an equal strength to cast iron in tension, but under compression is comparatively weak. The following is a table giving the average results of many tests of aluminum of 98.5% purity: POUNDS Elastic limit per sq. in. in tension (castings) . . . . . 8,500 Elastic limit per sq. in. in tension (sheet) 12,500 to 25,000 Elastic limit per sq. in. in tension (wire) 16,000 to 30,000 Elastic limit per sq. in. in tension (bars) 14,000 to 25,000 Ultimate strength per sq. in. tension (castings) . . . . . 18,000 Ultimate strength per sq. in. tension (sheet) 24,000 to 50,000 Ultimate strength per sq. in. tension (wire) 30,000 to 65,000 Ultimate strength per sq. in. tension (bars) 28,000 to 45,000 Per cent of reduction of area in tension (castings) . . . . 15 Per cent of reduction of area in tension (sheet) . . 20 to 30 Per cent of reduction of area in tension (wire) . . 40 to 60 Per cent of reduction of area in tension (bars) . . . 30 to 40 Elastic limit per square inch under compression in cylinders, with length twice the diameter . . . . . 3,500 Ultimate strength per square inch under compression in cylinders, with length twice the diameter . 12,000 The modulus of elasticity of cast aluminum is about 11,000,000.
Aluminum in castings can readily be strained to the unit stress of 1500 lbs. per sq. inch in compression, and to 5000 lbs. per sq. inch in tension. It is rather an open metal in its texture; and for cylinders, to stand pressure, an increase in thickness over the ordinary formulae should be given to allow for its porosity.
Under transverse tests, pure aluminum is not very rigid, although the metal will bend nearly double before breaking, while cast iron will crack before the deflection has become at all large.
The texture and strength of aluminum are greatly improved by subjecting the ingots to forging or pressing at a temperature of about 600 deg. Fahrenheit. Taking the tensile strength of aluminum in relation to its weight, it is as strong as steel of 80,000 pounds per square inch. Comparative results in this way are tabulated below as taken from Richards' work on "aluminum." Weight of 1 Cubic Foot in Pounds. Tensile Strength per Square Inch. Length of a Bar able to Support its own Weight in Feet. Cast iron . . . . . 444 16,500 5,351 Ordinary bronze . . . . . 525 36,000 9,893 Wrought iron . . . . . 480 50,000 15,000 Hard structural steel . . . . . 490 78,000 23,040 Aluminum . . . . . 168 26,800 23,040 ROLLED COPPER has a specific gravity of 8.93. One cubic foot weighs 558 125/1000 lbs. One square foot of one inch thick weighs 46 51/100 lbs. ROLLED ALUMINUM has a specific gravity of 2.72. One cubic foot weighs 169 510/1000 lbs. One square foot of one inch thick weighs 14 126/1000 lbs. Rolled copper is 3.283 times heavier than similar sections of rolled aluminum. COMPARATIVE WEIGHT OF METALS. Approximate Percentage. Metals. Weights per Square Foot 1 Inch Thick. Heavier than Iron. Lighter than Iron. Iron, rolled . . . . . 40.000 . . . . . . . . Steel, rolled . . . . . 40.833 2 per ct. . . . . Aluminum, rolled . . . . . 14 126 . . . . 62.91 per ct. Brass. rolled . . . . . 43 68 7 per ct. . . . . Copper, rolled . . . . . 46 51 13 per ct. . . . . Gold. rolled . . . . . 100.8 150 per ct. . . . . Lead, rolled . . . . . 59.80 50 per ct. . . . . Nickel, rolled. . . . . 43.2 7 per ct. . . . . Silver, rolled . . . . . 54.75 36 7/8 per ct. . . . . Tin, rolled . . . . . 38. . . . . 5 per ct. Zinc, rolled . . . . . 37.6 . . . . 6 per ct. TENSILE STRENGTH OF SOME ALUMINUM BRASS ALLOYS.
Aluminum. Copper. Zinc. Tensile Strength per Square Inch. Lbs. 1.00 57.00 42.00 68,600 1.15 55.80 43.00 70,200 1.25 70.00 28.00 36,900 1.50 78.00 27.50 42,300 1.50 77.50 21.00 33,417 2.00 70.00 28.00 52,800 2.00 70.00 28.00 52,000 2.50 68.00 30.00 65,400 3.00 67.00 30.00 68,600 3.30 63 00 33.30 86,700 3.30 63.30 33.30 77,400 3.30 63.30 33.30 92,500 3.30 63.30 33.30 90,000 5.80 67.40 26.80 96,900 TABLE SHOWING WEIGHT IN POUNDS OF SHEET AND BAR ALUMINUM AND BRASS. Rolled brass is 3.021 times heavier than rolled aluminum. Rolled steel is 2.890 times heavier than rolled aluminum.
Thickness or Diameter in Inches. Sheets per Square Foot. Square Bars One Foot Long. Round Bars One Foot Long. Alum'um. Brass. Steel. Alum'um. Brass. Steel. Alum'um. Brass. Steel. 1-16 .884 2.7 2.556 .00450 .015 .013 .00346 .011 .010 1-8 1.769 5.41 5 112 .01834 .055 .053 .01453 .045 .042 3-16 2.647 8.12 7.65 .04118 .125 .119 .03253 .1 .094 1-4 3.530 10.76 10.20 .073364 .255 .212 .05780 .175 .167 5-16 4.412 13.48 12.75 .1152 .350 .333 .09032 .275 .261 3-8 5.294 16.25 15.30 .1654 .51 .478 .12970 .395 .375 7-16 6.177 19. 17.85 .2253 .69 .651 .1768 .54 .511 1-2 7.060 21.65 20.40 .2941 .905 .850 .2308 .71 .667 9-16 7.942 24.3 22.95 .3723 1.15 1.076 .2924 .9 .845 5-8 8.824 27.12 25.50 .4595 1.4 1.328 .3609 1.1 1 043 11-16 9.706 29.77 28.05 .5564 1.72 1.608 .4367 1.35 1.262 3-4 10.590 32.46 30.60 .6620 2.05 1.913 .5198 1.55 1.502 13-16 11.470 35.18 33.15 .7768 2.4 2.245 .6104 1.85 1.763 7-8 12.35 37.85 35.70 .9008 2.75 2.603 .7074 2.15 2.044 15-16 13.23 40.55 38.25 1.034 3.15 2.989 .8122 2.48 2.347 1 14.12 43.29 40.80 1.176 3.65 3.400 .924 2.85 2.670 1.1-16 15.00 45.95 43.35 1.328 4.08 3.838 1.043 3.20 3.014 1.1-8 15.88 48.69 45.90 1.488 4.55 4.303 1.169 3.57 3.379 1.3-16 16.76 51.4 48.45 1.659 5.08 4.795 1.303 3.97 3.766 1.1-4 17.64 54.18 51.00 1.838 5.65 5.312 1.444 4.41 4.173 1.5-16 18.52 56.85 53.55 2.027 6.22 7.857 1.592 4.86 4.600 1.3-8 19.41 59.55 56.10 2.224 6.81 6.428 1.747 5.35 5.0<??>9 1.7-16 20.30 62.25 58.65 2.431 7.45 7.026 1.909 5.85 5.518 1.1-2 21.18 65. 61.20 2.647 8.13 7.650 2.079 6.37 6.008 1.9-16 22.06 67.75 63.75 2.872 8.83 8.301 2.256 6.92 6.520 1.5-8 22.94 70.35 66.30 3.107 9.55 8.978 2.440 7.48 7.051 1.11-16 23.82 73. 68.85 3.350 10.27 9.682 2.631 8.05 7.604 1.3-4 24.70 75.86 71.40 3.602 11. 10.41 2.830 8.65 8.178 1.13-16 25.58 78.55 73.95 3.865 11.82 11.17 3.036 9.29 8.773 1.7-8 26.46 81.25 76.50 4.135 12.68 11.95 3.249 9.95 9.388 1.15-16 27.43 84. 79.05 4.415 13.5 12.76 3.467 10.58 10.02 2 28.22 86.76 81.60 4.706 14.35 13.60 3.696 11.25 10.68