Next generation of free machining aluminium alloys

Free Machining alloys (FMA) use low melting point additions of elements such as Pb, Bi and Sn to provide chip breaking mechanisms, which impart excellent free machining properties to aluminium alloys. Environmental legislation is, however, driving the removal of Pb, together with a reduction in heavy-element additions such as Bi and Sn. This requires the development of a new range of Pb-free FMA with equivalent machinability to that of the Pb-containing alloys but with lower levels of Bi and/or a fraction of hard second phase particles based on Fe and Si to act as chip breakers. Moreover, the application of alternative liquid metal treatments based on melt conditioning techniques offers the ability to have a dramatic impact on the chip breaking mechanisms.