Asymmetric rolling （ASR）, as one of severe plastic deformation （SPD） methods to make ultra-fine materials with enhanced performance is mainly used to prepare foil and thin strip. The asymmetrical rolling was achieved by adjusting the diameters of the upper roll and the bottom roll and was used to prepare hot-rolled thick plate of 5182 aluminium alloy. The shear deformation and plate shape control were experimentally studied. The experimental results show that asymmetrical rolling has a significant effect on metal deformation stream and can somehow refine microstructure and improve the uniformity of microstructure and properties. The asymmetrical rolling process can also reduce the rolling force. However, bending of rolling plate often happens during asymmetrical rolling process. The factors affecting the bending were discussed.
The combined electromagnetic fields were achieved by the application of an alternating magnetic field and a stationary magnetic field and were used during direct chill(DC) casting process to control the microstructure and macrosegregation of an Al-Zn-Mg-Cu alloy. Ingot microstructures were analyzed under an optical microscope(Leica DMR). The composition at different locations in the ingots was measured with inductively coupled plasma mass spectrometry(ICP) method. The results showed that the grain structure is transformed from dendrite to equiaxed structure and significantly refined with the application of combined electromagnetic fields. The uniformity of microstructure is also greatly improved. The combined electromagnetic fields show a significant effect on the distribution of elements. The negative macrosegregation in the centre area of the ingot is obviously reduced.
Yu-bo ZuoXu-dong LiuChao SunSen-sen YuanDan MouZhan-zhi LiJian-zhong Cui
Low frequency electromagnetic casting （LFEC） process with the application of an induction coil outside the conventional direct chill （DC） casting mould was used to prepare the flat ingot of 2524 alloy and the effect of electromagnetic field on the microstructure and macrosegregation of this alloy was systematically studied. The results show that the fiat ingot prepared by the LFEC process has a finer and more uniform as-cast microstructure and the grain morphology is transformed from dendrite and rosette-like to equiaxed structure. The LFEC process also shows a significant effect on macrosegregation, and with the application of electromagnetic field during casting process, the segregation in the centre of the ingot is obviously reduced. The mechanism of these effects was also discussed.
Aluminum has been the secondly main metallic material in the world, whose mechanical properties are very important for industrial applications. The sizes and shapes of grains are important in determining the performance in structural applications. How to control the microstructure during solidification process has been a research focus. This paper gives an overview on the recent progress in microstructure control for aluminium alloys solidification process, and introduces the different methods to control the microstructure in detail. The mechanisms of microstructure control for different methods are also discussed. Finally, a brief prospect on future work is presented.
WANG XiangJieLUO XiaoXiongCONG FuGuanCUI JianZhong
The effect of forging passes on the refinement of high purity aluminum during multi-forging was investigated. The attention was focused on the structure uniformity due to deformation uniformity and the grain refinement limitation with very high strains. The results show that the fine grain zone in the center of sample expands gradually with the increase of forging passes. When the forging passes reach 6, an X-shape fine grain zone is initially formed. With a further increase of the passes, this X-shape zone tends to spread the whole sample. Limitation in the structural refinement is observed with increasing strains during multi-forging process at the room temperature. The grains size in the center is refined to a certain size （110 μm as forging passes reach 12, and there is no further grain refinement in the center with increasing the forging passes to 24. However, the size of the coarse grains near the surface is continuously decreased with increasing the forging passes to 24.
