Fluidity Evaluation of the AC4CH (A356) Aluminum Alloy Semi-Solid Slurry Made by Mechanical Vibration Method

The semi-solid process is promising as a near-net-shape method for producing high performance products. However, the method is hampered by poor formability because of low fluidity, and difficulty in making the semi-solid slurry. In previous work, we made semi-solid slurries containing small, spherical solid particles by applying mechanical vibration. In this study, we evaluated the fluidity of AC4CH aluminum alloy slurries made by applying mechanical vibration. In addition, we improved the slurry fluidity by applying shear stress to the slurry at the mold gate, and investigated the effect of the shear rate on the fluidity. The slurry was prepared by applying mechanical vibration at a frequency of 50 Hz and an acceleration amplitude of 166.6 m/s(2) (17 G). The fluidity was evaluated by injecting the slurry through a gate into a metallic mold with a spiral cavity, and measuring the fluidity length. The shear rate at the gate was controlled by changing the thickness of the gate (1.0, 2.2, and 4.0 mm). The fluidity of the slurry made by mechanical vibration was 25% to 40% that of liquid aluminum. Applying shear stress at the gate increased the fluidity by approximately 30%. The a-phase particles in the specimen became finer and rounder as the shear rate increased. Therfore, semi-solid slurry with high fluidity can be obtained by applying mechanical vibration and increasing the shear rate. Moreover, the slurry prepared by mechanical vibration had similar fluidity to the electromagnetically stirred slurry prepared at high shear rates and casting pressures. Our method could be used to to fabricate complex products by the semi-solid forming process.