Effect of depressurizing speed on mold filling behavior and entrainment of oxide film in vacuum suction casting of A356 alloy

The effect of depressurizing speed on mold filling behavior and entrainment of oxide film of A356 alloy was studied. The mold filling behavior and velocity fields were recorded by water simulation with particle image velocimetry. The results show that the gate velocity first increased dramatically, then changed with the depressurizing speed: the gate velocity increased slowly at relatively high depressurizing speed; at reasonable depressurizing speed, the gate velocity kept unchanged; while at lower depressurizing speed, the gate velocity decreased firstly and then kept unchanged. High gate velocity results in melt falling back under gravity at higher speed. The falling velocity is the main factor of oxide film entrainment in vacuum suction casting. The design criterion of depressurizing rate was deduced, and the A356 alloy castings were poured to test the formula. The four-point bend test and Weibull probability plots were applied to assessing the fracture mechanisms of the as-cast A356 alloy. The results illuminate a method on designing suitable depressurizing speed for mold filling in vacuum suction casting.