Next generation of free machining aluminium alloys

自由加工合金(FMA)使用低熔点的添加元素，如铅、铋和锡来提供切屑断裂机制，从而赋予铝合金优异的自由加工性能。然而，环境立法正在推动铅的去除，以及铋和锡等重元素添加的减少。这就需要开发一种新的无铅FMA，其可加工性与含铅合金相当，但具有较低的铋含量和/或一小部分基于Fe和Si的硬质第二相粒子作为断屑材料。此外，基于熔体调节技术的替代液态金属处理技术的应用提供了对切屑断裂机制产生巨大影响的能力。

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.