Centrifugal Casting of Al-Cr-Cu Alloy Slurry, Structure-Controlled by Two-Step-Stir-Mix-Quenching Process

We developed a two-step stir, mix, and quenching (SMQ) process to produce an Al-Cr-Cu alloy slurry with a high volume fraction of fine primary intermetallic crystals. In this process, we used a hypoeutectic Al-Cu alloy melt for the first melt and a hyperperitectic Al-Cr alloy melt with a higher liquidus temperature for the second and third melts. In the first step of the process, we stir-cast the first melt in a vessel to produce a semi-solid slurry containing aluminum solid solution (α-phase), and then mixed the second melt into the slurry. The hypoeutectic Al-Cu alloy slurry acted as a coolant, whose apparent heat capacity is enhanced by the latent heat of fusion of α-phase. The second melt was thus rapidly quenched, precipitating numerous primary intermetallic crystals when it contacted the slurry. In the second step of the process, we cooled the mixed alloy slurry while agitating it until it crystallized a certain quantity of α-phase, and then quenched the third melt into the slurry. An Al-6.7 mass%Cr-1.8 mass%Cu alloy slurry produced by this process was centrifugally cast to produce a tubular casting with thin, flange-like part. In the major portion of the tubular casting, fine primary intermetallic crystals were uniformly distributed. The average size of the primary crystals was 15±2 (μm), and their volume fraction was 0.22±0.05.