半固态AZ91D镁合金的触变性

利用Couette型同轴双桶流变仪，对等温搅拌和重熔加热的半固态AZ91D镁合金浆料的触变性能进行了研究．实验结果表明：经过连续降温和等温搅拌，半固态浆料的表观粘度逐渐降低，并达到一个稳态值；此时，若停止搅拌剪切，并经过某一时段的等温静置，再次在某一剪切速率下搅拌时，半固态浆料的表观粘度会突然升高，然后再迅速降低，最后到达一个稳态值，呈现出典型的剪切变稀特性；延长静置时间、或增加固相分数、或降低剪切速率，再次剪切搅拌时，半固态浆料到达稳态表观粘度的时间随之增长，同时稳态表观粘度值也相应增大；重熔加热后的半固态浆料的稳态表观粘度比相同固相分数的等温搅拌的半固态浆料的稳态表观粘度低；随重熔加热保温时间的延长，半固态浆料的稳态表观粘度逐渐降低，当稳态表观粘度达到最低值后，随重熔加热保温时间的延长，稳态表观粘度又逐渐增大．

THIXOTROPIC PROPERTIES OF SEMI-SOLID AZ91D MAGNESIUM ALLOY

Through a Couette type viscometer, the thixotropic behaviors of semi-solid AZ91D magnesium alloy slurries stirred isothermally and remelted were studied. After continuously cooled and stirred isothermally, the apparent viscosity of the semi-solid slurry descreases gradually and reaches the steady state, at this time if the slurry is rested isothermally for some time and stirred again at some shearing rate, the apparent viscosity of the slurry increases rapidly and then quickly falls down to a steady state value, which is a typical shear-thinning behavior. With increasing the resting time and the fraction of solid and decreasing the shearing rate, the steady apparent viscosity will increase at the same shearing rate and the time required for the semi-solid slurry to reach the steady state also becomes longer. The experimental result also shows that the steady apparent viscosity of the remelted slurry is lower than that of the semi-solid slurry stirred isothermally if their solid fractions are the same; with increasing the holding time, the steady apparent viscosity of the remelted slurry decreases and gradually reaches a lowest value, and then increases again.