Alloys with Small Percenlayes of alloys of aluminum with copper in pro portions of from 2 to 15 per cent have been advantageously used to harden aluminum in cases where a more rigid metal is required than pure aluminum. Copper is the most mon metal used at present to harden aluminum. A few per cent of copper decreases the shrinkage of the metal, and gives alloys that are especially adapted for art castings. The remainder of the range, from 20 per cent copper up to over 85 per cent, give crystalline and brittle alloys of no use in the arts, which are of a grayish-white color up to 80 per cent copper, where the distinctly yellow color of the copper begins to show itself.
Aluminum will Iroa awl Sleet nininuin combines with iron in all proportions. None of the alloys, however, have proved of value, except those of small percentages of aluminum with steel, cast-iron, and wrought-iron. So far as experiments have yet gone, other elements can better be employed to harden aluminum than iron, the presence of which in metallic aluminum is regarded as entirely a deleterious impurity, to be avoided if possible. It has been experimentally proved that the addition of aluminum to the steel just before" teeming" causes the metal to lie quiet and give off no appreciable quantity of gases, producing ingots with much sounder tops. There are two theories to account for this: one, that the aluminum decom poses these gases and absorbs the oxygen contained in them ; the other is, that aluminum greatly increases the solubility in the steel of the gases which are usually given off at the moment of setting, thus forming blow-holes and bubbles. This latter theory is the one which at present has the greatest weight of authority. In all cases the aluminum should be thrown into the ladle after a small quantity of the steel has already entered it. There is danger of adding too large a qnantitv of aluminum, in that the metal will set very solid and will lie liable to form deep "pipe:" in the ingots. To add just the right proportion of aluminum requires some little experience on the part of the steel manufacturer, but successful results have been secured with from It to lbs. of aluminum to a ton of steel. If the metal be " wild " in the ladle, full of occluded gases, too hot, or oxidized, a larger proportion of aluminum can be advantageously added. R. A. Hadfield says that the influence of aluminum appears to be like that of silicon, though acting more powerfully. The same writer, together with M. Howe and Osmond, claims that an addition of aluminum does not lower the melting
point of the steel. Steel with an addition of one tenth of one per cent of aluminum seems to solidify in the molds folly as quickly as steel without the addition of the aluminum. Aluminum seems to take the oxygen out of steel very much in the same way that mang,anese does, The addition of aluminum in quantities of from 2 to 3 lbs. per toe where the steel is to be cast in heavy ingots which will receive only scant work. Here it seems to increase the ductility as measured by the elong.ation and reduction of area of tensile test specimens, without materially altering the ultimate strength. In steel castings the bene fit from the use of a small percentage of aluminum, ordinarily in the proportion of from 2 to 3. lbs per ton, has become widely recognized, and it is being generally used. The ad ditions of aluminum are most always made by throwing the metal in pieces weighing a few ounces each into the ladle as the steel is pouring into it. in east-iron, from 2 to 5 lbs, of aluminum per ton is put into the metal as it is being pound from the cupola or melting furnace. To soft gray No. 1 foundry iron it is doubtful if the metal does much good, except. perhaps, in the way of keeping the iron melted for a longer time: but where difficult cast ings arc to be made, where much loss is occasioned by defective castings. or where the iron will not flow well or give sound and strong castings, the aluminum certainly in many cases allows of better work being done and stronger and sounder castings being made, having it closer grain, and hence much cosier tooled. The tendency of the aluminum is to change combined carbon to graphitic., and it lessens the tendency of the metal to chill. Aluminum in proportions of two per cent and over materially decreases the shrinkae-e of cast-imn. The effect of aluminum in wrought-iron is not very !narked in the ordinary puddling process. It seems to :tad somewhat to the strength of the iron, lint the amount is not of suf ficient value to induce the general use of aluminum for this purpose. The peculiar !property of almninnm in reducing the long range of temperat tire between that at which wrought-iron first softens and that at which it bOCOInce fluid, i; taken Avant:we of in the well-known Mit is process for making wrought-iron castings." It is for this that aluminum is utmost used in wrought-iron at present.