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I am at the design stage of an engineering project, part of which may include the use of a copper alloy casting. Since considerable machining is involved I am interested in machining data for cast copper alloys.

Machining data for copper casting alloys are similar to those of their wrought counterparts. The most easily machinable are classified as Group 1 and include CC491K (LG2) with a rating of 90% (this rating is based on a 100% value for free machining brass CZ121,CW609N). The more difficult alloys to machine are classified as Group 3 and include the aluminium bronzes such as CC333G (AB2) with a rating of 20%. For further details see CDA publication 44 Machining Brass, Copper and its Alloys.

I understand that welding may have an effect on the corrosion resistance of the nickel aluminium bronzes. If so what treatment may be carried out to reduce this effect?

Yes, the heating effect of welding has the effect of producing a phase change in the alloy which on cooling leads to the formation of the corrodable martensitic beta phase. Annealing at 675oC for 2 to 6 hours after welding restores the pre weld structure and relieves stress. It is very effective in resisting subsequent corrosion.

I have been asked to produce bolting for use inside a van used to carry explosives. The material must be non-sparking. What should I use?

Tiny particles can be detached from their parent object by the force of impact of a harder instrument or object in air. Elements like iron, when finely divided and hot, can ignite spontaneously as they oxidise, becoming even hotter. This results in dull red particles rapidly becoming bright white at a much higher temperature. At this temperature the particle is visible as a spark and can cause fire or explosion in a combustible environment. In common with most other copper base alloys, the particles detached from an aluminium bronze object due to impact against a ferrous or other harder objects, do not attain a dangerous temperature and are not visible as a spark. In view of their high strength, aluminium bronzes are the most favoured for applications where this is important. They may therefore be safely selected for non-sparking tools and equipment for handling combustible mixtures such as explosives.