低频电磁场频率对半连铸高强Al合金组织结构的影响

利用光学显微镜和透射电镜研究了在低频电磁场作用下,电磁场频率对半连铸直径100mm铝合金铸锭显微组织结构的影响·结果表明:与常规铸锭相比,当电流为100A,频率为15Hz时,晶粒尺寸有所减小,并且等轴晶数目增多·当频率增到25Hz时,晶粒细化最明显·随频率继续增大,晶粒尺寸又有所增大;在电流为100A,电磁场频率为25Hz时,晶内位错密度较高,沉淀相尺寸较小,析出相主要为颗粒状的η′,η相和小片状的T相,此时晶界两侧无析出带宽度为100nm左右;当电磁场频率为15Hz时,晶内沉淀相尺寸有所增大,析出相主要为片状和长板条状的η相、片状的T相和颗粒状的η′相,晶界两侧无析出带宽度增到300nm左右...

Effect of Frequency of LF Electromagnetic Field on Microstructures of Semi-Continuously Cast High-Strength Al Alloy

The effect of frequency of LF electromagnetic field on microstructure of Φ100 mm semi-continuously cast Al alloy ingot was investigated by metalloscope and TEM. The results show the grain size decreases somewhat, but number of equiaxial grains increases with a current 100 A at 15 Hz as compared with conventional ingot, grain refinement is found to be most obvious at 25 Hz. But grain size turns to increase then with increasing frequency. With a current 100 A at 25 Hz, the intergranular dislocation density becomes higher with smaller size of precipitates which are mainly granular η', η and lamellar T phases and the precipitate-free zones on both sides of grain boundary are about 100 nm wide. However, the size of intergranular precipitates increases somewhat at 15 Hz, which are mainly lamellar or lath η, lamellar T and granular η' phases with precipitate-free zones about 300 nm wide.