Formation mechanism of composite layer in hyperperitectic Al-Cr alloy ingot produced by injection quenching

In order to examine the formation mechanism of the double composite layer which occasionally forms in the Al-transition metal alloy pipes produced by Centrifugal Duplex Casting, a model experiment named “Injection Quenching” has been executed. In this experiment, a hyperperitectic Al-Cr alloy melt (the jet melt) was injected into a molten aluminum (the bulk melt) to be cooled rapidly. The primary intermetallic compound particles sedimented to the bottom of the mold. The mixed alloy was furnace-cooled, and was quenched at a given temperature to freeze the distribution of the primary particles. The obtained results are summarized as follows : (1) The primary particles crystallized with “copious nucleation” in the jet melt constitute the fine composite layer. (2) After the formation of the fine composite layer, floating particles dispersed in the bulk melt grow and pile up on the fine composite layer to constitute the coarse composite layer