低频电磁场对半连铸高强Al合金组织结构的影响

Influence of low frequency electromagnetic field on microstructures of semi-continuously cast high-strength Al alloy

利用光学显微镜、X射线衍射仪和透射电镜, 研究了在不同电流和频率作用下, 半连铸 d100 mm高强高韧Al合金铸锭组织结构的变化。结果表明: 在电磁场频率为25 Hz时, 当电流从60 A增大到100 A时, 电流越大, 晶粒细化越明显; 在电流为100 A时, 晶粒细化的最佳频率为25 Hz; 与常规铸锭相比, 随电流增大, 铸锭内沿[311]方向产生的织构逐渐消失, 并且铸锭边缘和中心部位的点阵常数逐渐趋于一致, 这表明溶质元素的分布更加均匀; 在电流和频率分别为100 A和25 Hz时, 晶界附近无析出带宽度变窄, 约为100 nm。此时, 无论是在晶内还是沿晶界, 析出相的尺寸明显减小, 并且有亚稳相, 形态近似为颗粒状。

Microstructures of semi-continuously cast d100mm Al alloy ingot at different current intensities and frequencies were studied in details by optical microscope, X-ray diffraction and TEM to investigate the effect of electromagnetic field on microstructures of ingot. When current increases from 60 to 100A at 25Hz, the grains are gradually refined; When current is 100A, the optimum frequency of grain refinement is 25Hz. In contrast to the as-cast ingot, with the increase of current, texture produced along [311] direction gradually eliminates, and lattice constants at the center and edge of the ingot are more and more close, which shows that the distribution of solute atoms is more uniform. At current of 100A and frequency of 25Hz, width of precipitate-free zones on both sides of grain boundary becomes narrower and is about 100nm, the size of precipitates deposited both inside grains and along grain boundaries becomes smaller, and there exists metastable phase, with basically granular shapes.