【摘要】 研究减压速度对真空吸铸A356合金充填行为和氧化膜卷入过程的影响。利用粒子图像测速仪通过水模拟方法观察充填行为,并获得速度场的变化规律。结果表明,介质流入型腔后,充型速度首先快速增加,随后随着减压速度的不同,充型速度的变化表现出3种不同情况:减压速度较大时,充型速度继续增加;减压速度合理时,充型速度保持不变;减压速度较低时,充型速度先降低后保持不变。充型速度越大,射流越严重,介质在重力作用下回落至液面时的速度越大,这是导致真空吸铸过程中氧化膜卷入的主要原因。推导了减压速度的设计原则,据此浇注了A356合金铸件。测试了其四点弯曲强度,并利用韦伯统计评价了铸件的可靠性,证明了减压速度设计原则的准确性。更多还原

【Abstract】 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.更多还原