表面脉冲电磁场处理下7A04铝合金凝固组织演变

Solidified Microstructure Evolution of 7A04 Alloy Under Surface Electromagnetic Pulse Treatment

采用一种新型熔体表面脉冲电磁技术对7A04超硬铝合金凝固组织进行细化处理。通过分析脉冲电磁场对组织形貌、晶体择优取向及凝固温度过程的影响,探讨脉冲电磁场下凝固组织演变机理。结果表明,随着脉冲电磁场强度增加,凝固组织发生球化细化→枝晶化再粗化的转变;在磁场强度为241mT时,晶粒尺寸可降低40%左右。由于晶体磁各向异性产生的磁能差导致凝固初期尺寸为225nm^100μm的晶粒发生转动,晶粒择优生长;此外,在脉冲电磁场孕育处理条件下,熔体凝固初期温度升高导致固相分数降低,有利于晶核运动,也可获得良好的组织细化效果。

A new technique termed surface electromagnetic pulse was developed for refining the solidification structure of the 7A04 super-hardness aluminum alloy.The effect of pulsed electromagnetic field on solidified microstructure,crystal orientation and cooling curves were investigated in order to explore the mechanism of microstructure evolution.The experimental results showed that the solidified structure was modified following rules of refining and spheroidization→coarsening and randomization with the increase of magnetic flux density,and a 40% reduction in grain size could be achieved when the increase of magnetic flux density was 241 mT.Magnetic rotation of crystals in size of 225 nm—100μm could be controlled due to crystal magnetic anisotropy which caused by magnetic energy difference,forming the pulse magnetic preferred orientation.Meanwhile,agood result for grain refinement could also be obtained by the pulse electromagnetic inoculation treatment.It can be explained that the fraction of solid in the melt which was decreased by solidification initial temperature rise was benefit for particle motion.