电磁搅拌对Al-Si合金流动性及凝固组织的影响

采用同心三螺旋线流动性测试装置,通过对比试验的方法,获得了不同浇注温度条件下未经电磁搅拌处理、经电磁搅拌处理及电磁搅拌后再保温处理的铝合金流动指数和凝固组织,进而探讨了电磁搅拌对合金熔体结构的影响。结果表明:与未经电磁搅拌处理相比,经电磁搅拌处理后合金熔体的流动指数明显提高,浇注温度722℃时,流动指数提高约2%,浇注温度670℃时,流动指数提高约13%,其本质原因在于电磁搅拌作用使熔体中微观不均匀的Si—Si原子集团尺寸和形状发生改变,进而使熔体温度场与浓度场更加均匀、形核率得到进一步提高,且电磁搅拌温度愈低,这种作用愈强烈;电磁搅拌后再保温处理的流动指数降低7%,且凝固组织比较粗大,说明合金熔体经保温处理后电磁搅拌作用会发生衰退乃至最终消失。

Influence of Electromagnetic Stirring on Fluidity and Solidification Structure of Al-Si Alloy

Using concentric three-helix spiral fluidity test, flow properties and solidification structures of AI-Si alloy melts with/without electromagnetic stirring (EMS) , and isothermal treated after EMS at different pouring temperatures are investigated. The compared experiment results indicate that: compared with the alloy melt without treatment by EMS, the flow property of melt treated by EMS improves notably at different pouring temperature. When the pouring temperature is 722 ℃, the flow index improves by 2%, and by 13% when the pouring temperature is 670 ℃. This phenomenon is attributed to the further homogenization of atomic groups in alloy melt under condition of EMS, which makes temperature field and concentration filed of alloy melt more homogeneous and improves the state and structure of alloy melt essentially. At this time, solidification process and structure also change, and the lower of the pouring temperature, the stronger of this phenomenon. However, flow index of alloy melt by isothermal treatment after EMS reduces by 7%, and its solidification structures become coarse, which illustrates that the role of EMS is weaken by the isothermal treatment after EMS, even disappears finally.