The thematic issue of Materials Science and Technology contains a selection of papers hand-picked from the 2016 Brass Alloys conference held in Stockholm 25–27 May 2016.
Brass is one of the oldest alloys in widespread use today and for this reason it is often considered that there is little new to say about it. Conferences on copper alloys are few and far between; the last was in France in 2006 and we are not able to recall any previous meeting that was specifically devoted to brasses. This situation is seriously neglectful of an industry that turns over some $18 billion per annum and which is currently transforming itself in the face of various challenges.
Brass has several attributes that make it almost indispensable in industrial production. It is relatively inexpensive and can be readily formed by casting, forging and machining processes. Correctly alloyed, it presents excellent resistance to corrosion, finding innumerable uses in hydraulics of most kinds. It also possesses good mechanical properties, in particular remarkable ductility in sheet forming. This latter feature is a result of very fine scale mechanical twinning whereby brass preceded the now so fashionable TWIP steels by many centuries.
What, then, are the questions which are so pressing that they attracted more than seventy international attendees for three days of discussions in Stockholm? The most evident and urgent is the concern regarding lead as an alloying element in brass. Lead, in additions up to about 3%, remarkably improves the hot-workability and, in particular, the machinability of brass, with significant benefit to its economic competitiveness. However, environmental concerns are raising a large question mark over the use of lead in any circumstances so alternative solutions are very actively being sought with many different approaches. Authorities in the EU and elsewhere have not yet banned lead in these applications but they award approvals over limited periods of time with no guarantee of their renewal. Lead in brass is, accordingly, living on borrowed time.
Brass is one of the world’s most recycled materials and this ironically creates an even greater environmental difficulty since the lead in existing products is also re-cycled. Although it is easy to add lead to brass it is not possible at present to remove it by any cost-effective process. Since the monetary value of leaded brass products in the World can be roughly estimated as $150 billion, the economic investment is huge and there is an urgent need for technical solutions to purification of existing alloys.
An old but still vibrant research area concerns ways of improving corrosion resistance in water applications. Dezincification and intergranular corrosion are both long-known problems where it is necessary to find solutions that avoid the occurrence of both since resistance to the one may risk exposure to the other. Fresh studies and new experimental methods are showing how micro-alloying of brass with the elements arsenic, antimony and phosphorus can be optimised for this purpose. The situation is complex since these may also react with tramp elements like iron and aluminium in the multiply re-cycled metal. For the first time computational thermodynamics are now being applied which can predict and rationalise the interactions between all these elements so that improved alloys can now be developed on the basis of scientific understanding rather than by trial and error as in former times. The following papers are a selection from the total of 26 presentations given at Brass Alloys 2016.