Aluminium – Copper Alloys

Copper has been the most common alloying element almost since the beginning of the aluminum industry, and a variety of alloys in which copper is the major addition were developed. Most of these alloys fall within one of the following groups:

    * Cast alloys with 5% Cu, often with small amounts of silicon and magnesium.
    * Cast alloys with 7-8% Cu, which often contain large amounts of iron and silicon and appreciable amounts of manganese, chromium, zinc, tin, etc.
    * Cast alloys with 10-14% Cu. These alloys may contain small amounts of magnesium (0.10-0.30% Mg), iron up to 1.5%, up to 5% Si and smaller amounts of nickel, manganese, chromium.
    * Wrought alloys with 5-6% Cu and often small amounts of manganese, silicon, cadmium, bismuth, tin, lithium, vanadium and zirconium. Alloys of this type containing lead, bismuth, and cadmium have superior machinability.
    * Durals, whose basic composition is 4-4.5% Cu, 0.5-1.5% Mg, 0.5-1.0% Mn, sometimes with silicon additions.
    * Copper alloys containing nickel, which can be subdivided in two groups: the Y alloy type, whose basic composition is 4% Cu, 2% Ni, 1.5% Mg; and the Hyduminiums, which usually have lower copper contents and in which iron replaces 30me of the nickel.

In most of the alloys in this group aluminum is the primary constituent and in the cast alloys the basic structure consists of cored dendrites of aluminum solid solution, with a variety of constituents at the grain boundaries or interdendritic spaces, forming a brittle, more or less continuous network of eutectics.

Wrought products consist of a matrix of aluminum solid solution with the other constituents dispersed within it. Constituents formed in the alloys can be divided in two groups: in the soluble ones are the constituents containing only one or more of copper, lithium, magnesium, silicon, zinc; in the insoluble ones are the constituents containing at least one of the more or less insoluble iron, manganese, nickel, etc.

The type of soluble constituents formed depends not only on the amount of soluble elements available but also on their ratio. Available copper depends on the iron, manganese and nickel contents; the copper combined with them is not available.

Copper forms (CuFe)Al6 and Cu2FeAl7, with iron, (CuFeMn)Al6 and Cu2Mn3Al20 with manganese, Cu4NiAl, and several not too well known compounds with nickel and iron. The amount of silicon available to some extent controls the copper compounds formed. Silicon above 1% favors the FeSiAl5, over the iron-copper compounds and (CuFeMn)3Si2Al15, over the (CuFeMn)Al6 and Cu2Mn3Al20 compounds.

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