半固态AlSi6Mg2铝合金的触变性

Thixotropic Behavior of Semi-solid AlSi6Mg2 Aluminum Alloy

利用Couette型同轴圆桶流变仪研究了等温搅拌的半固态AlSi6Mg2铝合金浆料的触变性能。试验结果表明:经过连续冷却和等温搅拌,半固态AlSi6Mg2铝合金浆料的表观粘度逐渐降低,并达到一个稳态值;此时,若停止搅拌并保温静置一段时间,又以某一剪切速率搅拌,半固态AlSi6Mg2铝合金浆料的表观粘度会突然增加,然后再迅速降低,最后达到一个稳态值,呈现出典型的剪切变稀特性;静置时间越长,合金浆料在开始剪切瞬间的表观粘度越大,同时达到稳态所需时间也越长,其稳态表观粘度值也略有提高;等温搅拌过程中突然增加剪切速率,半固态AlSi6Mg2铝合金浆料的表观粘度会突然降低,并逐步达到稳态;当剪切速率突然降低时,合金浆料的表观粘度会突然增加,然后逐步达到稳态。而且,剪切速率突然增加之后达到稳态所需要的时间要比剪切速率突然降低之后达到稳态所需要的时间短得多。

The thixotropic behavior of semi-solid AlSi6Mg2 aluminum alloy slurries was investigated through Couette type viscometer in the condition of isothermally stirring. The results show that apparent viscosity of the semi-solid AlSi6Mg2 aluminum alloy slurries is gradually declined to tend to a steady state with continuously cooling and isothermally stirring. However, the apparent viscosity of the slurries is rapidly increased and then quickly fallen down to a steady state value when stirring for the slurries is stopped at holding temperature for some time and then started again at some shearing rate, showing a typical shearing-thinning behavior. The longer the holding time is, the higher the apparent viscosity in initial shearing stage is and the longer the required steady state time is, meanwhile the steady apparent viscosity is slightly inclined. During isothermal shearing, the apparent viscosity will be declined or increased rapidly and then gradually declined to a steady state value with sharply raising or dropping shearing rate. The experimental results also show that the time required to reach a new steady state with sharply raising shearing rate is much shorter than that required with sharply dropping shearing rate.