Alloys Without Added Copper

Alloy 7020 is the most widely used alloy for rolled or extruded semi-products in different fields such as transport, the mechanics industry, and armaments. 

In the quenched and artificially aged condition (T5 or T6), i.e. its normal use condition, its mechanical strength is in the order of 360-400 MPa. Its corrosion resistance is satisfactory, unless it is welded. 

Its heat resistance is rather poor as soon as the temperature exceeds 120-130 °C. Exposure to temperatures above 200 °C can sensitise the alloy to exfoliation corrosion. 

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Modifications to Precipitates. Silicon is sometimes added to Al—Cu—Mg alloys to help nucleate S precipitates without the need for cold work prior to the elevated temperature aging treatments. Additions of elements such as tin [7440-31-5] Sn, cadmium [7440-43-9] Cd, and indium [7440-74-6] In, to Al—Cu alloys serve a similar purpose for 9 precipitates. Copper is often added to Al—Mg—Si alloys in the range of about 0.25% to 1.0% Cu to modify the metastable precursor to Mg2Si. The copper additions provide a substantial strength increase. When the copper addition is high, the quaternary Al CuMg Si Q-phase must be considered and dissolved during solution heat treatment. 

Lithium will form alloys with some of these metals at temperatures only slightly above its melting point. In rough qualitative tests with the lithium at 200° to 250 °C. alloys containing 56% zinc, 63% copper, 28% aluminum, and 20% tin were made by adding 60-mesh powders of these metals to the liquid lithium. Solution was rapid all melts were fluid in the ranges examined. The tin alloys were pyrophoric. The melts were made in heavy oil without a protective atmosphere. tinder these same conditions, alloys were not formed with nickel, manganese, titanium, or zirconium. 

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