Use an acidic dip such as a mixture of citric and phosphoric acids. This is quite gentle and with care easy to use.
Photo micrographs of commercially important and/or metallurgically interesting copper and copper alloys and processings (on the CDA Inc site).
These are the engineering standards prepared for material for use by the Ministry of Defence. They have replaced NES (Naval Engineering Standards), which in their turn replaced DGS (Directorate General Ships) standards.
Copper chromium (CC101) – conductivity is 80% IACS – strength good up to 400°C.
Copper sheet is available in pre-patinated form. As well as green, other attractive colours such as brown, gold and silver are available. See www.kme.com and www.aurubis.co.uk.
It reduces by about 3%.
Suggest DEF STAN 02-834, which is a naval grade of aluminium bronze with a low magnetic permeability. This meets MOD requirements.
Various copper alloys have particular strengths under specific sea water conditions but on balance 90-10 copper-nickel has excellent corrosion resistance in many applications and is perhaps the most versatile. There is a detailed description of the properties and applications of this and other popular copper nickel alloys on the www.coppernickel.org website. Of course, aluminium bronze alloys, particularly nickel aluminium bronze, are also recognised for their corrosion resistance in severe seawater conditions and for that reason also have established applications as propellers and pumps and valves.
CW505L is the most ductile brass, but for simple forming the more economical 63/37 Common Brass (CW508L) should be used.
70/30 brasses CZ106 (CW505L).
(a) Remove surface oxide with dilute (10%) hydrochloric acid
(b) Neutralise with bicarbonate solution (lye)
(c) Seal by chromate conversion
(f) Clean with detergent annually.
After exposure to seawater, copper alloys develop a surface oxide film which provides protection from corrosion.