The Influence Of High Magnetic Field On The Grain Growth Behavior Of Ultrafine1050Alloy By CryoECAP Technology

The microstructures and mechanical properties of as-cast and as-rolled1050alloy fabricated by cryogenic equal channel angular pressing (cryoECAP) after annealing at different temperatures without or with high magnetic field were investigated by optical microscopy, scanning electron microscopy, transmission electron microscopy and hardness test. The following results are obtained:The microstructure of as-cast sample is coarse columnar grains, and microstructure of as-rolled sample is deformed fibrous tissue paralleled to the rolling direction, the grains are refined by the repeated ECAP pressings. With the increase of pressing pass, the extrusion flow lines become finer, the equaxed grains are obtained after eight passes with size of0.9μm for as-cast sample and0.7μm for as-rolled sample. The Vicker hardness is increased by130after the first ECAP pass, and the increment of hardness becomes less in subsquent passes. The hardness of as-rolled sample is higher than that of as-cast sample.When the as-cast sample after8ECAP passes annealed below250℃, many sub-grains locate inside the elongated grains along the extrusion direction; with increasing annealing temperature, the subgrains gradually transform into the low angle boundaries (LABs) and then the high angle boundaries (HABs) by grain rotation, the recrystallization completes at250℃, and the grain size and the ratio of HABs and LABs increase slightly; When the annealing temperature is above250℃， the grain growth rate accelerates remarkedly, and the ratio of HABs and LABs gradually increases. Compared with sample annealed without high magnetic field, the number of LABs is much more, the grain growth rate is slightly higher at low temperature, the grain growth rate is slower at high temperature, the grain size distribution is more homogeneous, no abnormal grain growth occurs, and TEM microstructure observations show that sub-grain and LABs form fasterly at low temperature. The softening in hardness occurs at250℃～300℃, The hardness of specimen annealed with high magnetic field is lower, and the time for softening is ealier. When the sample annealed at low temperature without high magnetic field, the strong Goss texture appears and weakens with the increase of temperature; while, with the application of high magnetic field, the weak Goss texture and cube texture exist, and the cube texture enhances with increasing temperature; all the textures weaken due to the occurence of recrystallization.When the as-rolled sample after8ECAP passes annealed at150℃～400℃, change of microstructure is the same to that in as-cast sample after8ECAP passes, with the increase of annealing temperature, the elongated grains grow to the coarse equiaxed grains, and the grain size gradually increases. The as-rolled sample after8ECAP passes after annealing has finer grain, more HABs, higher dislocation density and hardness. With the application of high magnetic field, the grain size distribution is homogeneous, and the percentage of LABs is greater than that in sample annealed without high magnetic field, while but HABs is still dominated, the dislocation density is lower. When annealing without high magnetic field, softening happens at200℃, the rotating Goss texture weakens with rising temperature; When annealing with high magnetic field, softening occurs at150℃, the strong cube texture exist at low temperature, all the textures weaken at high temperature.