Grain refinement of Al-Cu foundry alloys with B additions

Cu provides a grain refining effect for aluminium alloys that starts to deteriorate at similar to 6 wt-% Cu. There is no improvement in grain size over that already obtained with 4-5 wt-% Cu when AlCu4 and AlCu5 alloys are inoculated with 0.02 wt-% B. Al-Cu alloys with >6 wt-% Cu, on the other hand, enjoy a remarkable grain refinement upon the addition of 0.02 wt-% B. AlB3 is an excellent grain refiner also for those foundry alloys that contain less Cu but additionally Si, such as A208 and A319. A common feature of these alloys is a liquidus temperature below 640 degrees C, estimated to be the temperature at which AlB2 particles start to precipitate out of the melt. Heterogeneous nucleation of alpha(Al) on freshly formed AlB2 particles follows and produces very small equiaxed grains.