Aluminum alloying

Aluminum alloying

Aluminum alloying

Because pure aluminum has a relatively low tensile strength and hardness as well as poor casting qualities, it is often desirable to alloy with it other elements. Copper, manganese, and nickel, owing to their high melting points, are added in the form of rich alloys or hardeners. For copper, the hardener most generally used contains 50% aluminum and 50% copper. The eutectic alloy containing 33 per cent copper is used to some extent, since it has the advantage of a somewhat lower melting point. The melting point of the 50-50 alloy is sufficiently low, however, so that no difficulty is experienced in alloying it with pure aluminum and it is often more convenient to use the higher percentage of copper. In the case of manganese, the hardener rarely contains more than 12 per cent of this metal because of the difficulty due to high melting point and excessive segregation if a greater percentage is used. The usual composition varies from 8 to 12 per cent. With nickel, concentrations up to 25 per cent are used satisfactorily.

These hardeners may be made with comparative ease by first melting the aluminum and then slowly adding the alloying element, generally in the solid form, to the molten mass, with constant mixing. For this operation it is necessary to raise the temperature of the metal considerably higher than is desirable in the ordinary remelting operation. Sometimes hardeners containing two or more elements in addition to the aluminum are used. In such cases, it is necessary to have the elements in the correct ratio for the alloy in which the hardener is to be finally used. Silicon is generally added in the form of a hardener, but may be introduced quite satisfactorily without the use of an intermediate alloy. If a hardener is used, the silicon content generally does not exceed 20 per cent. Magnesium and zinc, because of their low melting points, are added directly to the charge shortly before the metal is ready to be poured. In the case of magnesium, it is especially desirable that the metal be held well under the surface of the molten bath until it is completely dissolved, so as to prevent excessive oxidation. For this purpose, an inverted, perforated cup similar to a phosphorizer is generally used.

In alloying aluminum it is preferable to use an open-hearth furnace of large capacity so as to produce a large quantity of metal of uniform composition. The aluminum pig and rich alloy are charged together and the molten mass thoroughly stirred at frequent intervals. One very satisfactory way of promoting thorough mixing in a large open-hearth furnace is to tap metal from the front of the furnace and return this metal to the back of the furnace, thus establishing a thorough circulation. If the mixing is not properly done, considerable segregation may result; for example, a difference of 1 per cent copper in an alloy containing about 4.5 per cent has been found between the top and bottom of the melt. The metal after being thoroughly mixed may be cast into ingot form for remelting in the same plant, or for shipment; or if castings are being made, may be transferred to small iron-pot furnaces where a variety of temperatures may be obtained to suit the casting conditions. If the metal is intended for further fabrication, it is generally cast into the desired form; as for example, sheet ingots or billets, which are stored until the cast analysis is received.

Some metal is lost during the melting and skimming operation, but the actual melting loss in satisfactory open-hearth operation is generally less than 1 per cent of the total metal melted. A greater percentage than this is removed from the melt in skimming both the furnace and the pouring pots, but these skimmings are collected and puddled with a suitable flux, as described later in discussing secondary metal remelting, so that the major part of the metallic aluminum which has been trapped in the dross is recovered.

Clickaluminum alloying for more info.

POST COMMENT

Why Finding The Right Electricians Is Important Tesla Magic Formula Generator - Effective Implies To Generate Free Electrical Ability Choosing the Appropriate Digital Scales For the Application Tesla Solution Generator - Get Electrical Power Through The Air Which is the Best Electric Toothbrush? Central Air Conditioner Prices - Deciding What To Buy How To Buy Digital Camera Shops Online Aluminum extrusion How to Secure Your School or Church Family Directory in the Digital Age High Risk Merchant Processor Digital MP3 player DVR USB - Problem Trigger Points Window Blinds – Excellent way to keep your Electricity Expenses down