Aluminium, cold worked

Photographs 3, 4, and 5 refer to aluminium cold worked to 50,100, and 300 % respectively. The flow lines in the direction of rolling are evident. 

Aluminium and magnesium melt at just over 900 K. Room temperature is 0.3 T and 100°C is 0.4 T, . Substantial diffusion can take place in these alloys if they are used for long periods at temperatures approaching 80-100°C. Several processes can occur to reduce the yield strength loss of solutes from supersaturated solid solution, overageing of precipitates and recrystallisation of cold-worked microstructures. 

Stress-corrosion cracking occurs in certain aluminium alloys which have been developed for medium and high strength by employing variations in composition, cold work and heat treatment The main alloys are based upon Al-Mg, Al-Mg and Al-Cu, but stress corrosion also occurs in Al-Ag, Al-Cu-Mg, Al-Mg-Si, Al-Zn and Al-Cu-Mg-Zn alloys. It has... 

The melting point of aluminium (660°C). The operating temperature usually reaches 750-850°C in pretreatment and 700°C in the bath, causing a loss in tensile properties of cold-drawn wire. On the other hand, if cold-worked material which is to be subsequently annealed is used in this process the annealing and coating operations may be combined, with obvious economic advantage. 

It seems, therefore, that 200-300 % cold work is the maximum for the working of aluminium, giving what might be called the Maximum Effective Cold Work. ... 

Cold work 50 % — Aluminium Iron. Silicon Carbon Alumina... 

This shows that, in the treatment of aluminium, it is advisable to employ extensive cold work, up to a maximum amount varying between 200 % and 300 %, always provided that the work is followed by an anneal adequate in duration and at a suitable temperature. 

Annealed aluminium possesses a Brinell Hardness of 23 under 500 or 1000 kg, corresponding with a Tensile Strength of approximately 10 kg. per sq. mm. (6-35 tons per sq. in.). In the case of the thick series, the maximum hardness, as also the maximum Tensile Strength, occurs at 200 % cold work. 

The absolute minimum cold work should be specified for sheet aluminium required for pressing or other work of a similar nature. The amount of cupping, which annealed sheet will stand, is clearly superior to that which sheet, worked even very little, can support. 

We are therefore of the opinion that aluminium should be used in the annealed condition, certainly as regards aeronautical work the increased strength, which results from cold work, as described in this chapter, should be attained by other means, such as increase of thickness, or the employment of alloys. 

As regards the variation in mechanical properties with cold work and annealing, aluminium has been subjected to very detailed investigation by Robert Anderson, who has published the following articles —... 

Then, if the phenomena be investigated more closely, it is evident that the unfortunate incidents mentioned have occurred in the case of excessively cold-worked aluminium—wires, sheets, or pressed utensils. 

We have, ourselves, verified these disintegrations due to cold work. We have not carried out experiments on aluminium, but the investigations we have made on the cold working of brass lead us to infer that the working of aluminium cannot be irrelevant to these disintegrations. 

The practical durability of cold-worked aluminium will be a predominant factor to be considered in solving the problem of the practical and economical uses of which it is capable (for wires and cables for electrical conductors). 

Object. Tensile and Shock tests at a temperature of 15° on test pieces of sheet aluminium possessing various degrees of cold work. 

Among aluminium alloys, particularly those with high strength within the AlZnMg and AlCu series have been liable to SCC. In heavily cold-worked AlMg alloys with Mg content > 5% and in cast AlCuSi alloys, SCC may also occur. Finally, it may be developed in AIMgSi alloys after poor heat treatment [7.27]. 

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