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 large and small sized Cu（solid）/Al（liquid） couples were prepared to investigate the directional growth behavior of primary a（Al） phase during a concentration-gradient-controlled solidification process under various static magnetic fields（SMFs）.The results show that in the large couples,the α（Al） dendrites reveal a directional growth character whether without or with the SMF.However,the 12 T magnetic field induces regular growth,consistent deflection and the decrease of secondary arm spacing of the dendrites.In the small couples,the α（Al） dendrites still reveal a directional growth character to some extent with a SMF of ≤5 T.However,an 8.8 T SMF destroys the directional growth and induces severe random deflections of the dendrites.When the SMF increases to 12 T,the a（Al） dendrites become quite regular despite of the consistent deflection.The directional growth arises from the continuous long-range concentration gradient field built in the melt.The morphological modification is mainly related to the suppression of natural convections and the induction of thermoelectric magnetic convection by the SMF.
The effect of trace element vanadium on the superplasticity of 5083 aluminium alloy sheets was studied by high temperature tensile optical microscopy. The results showed that trace element vanadium added into 5083 alloy could refine the fibrous structure of the rolling sheet, restrain the grain growth during recrystallizafion, and improve the superplasficity of 5083 alu-minium alloy. The size of recrystallized grains of the sheets was reduced from 100 to 20 um, and the elongation percentage of 5083 aluminium alloy sheets in 510℃ was improved from 208% to 254% after the trace element vanadium was added into the conventional 5083 aluminium alloy.
A new method was introduced to achieve directional growth of Sn crystals. Microstructures in liquid （Pb）/ liquid （Sn） diffusion couples were investigated under various static magnetic fields. Results show that the β-Sn crystals mainly reveal an irregular dendritic morphology without or with a relatively low static magnetic field （〈0.3 T）. When the magnetic field is increased to 0.5 T, the β-Sn dendrites close to the final stage of growth begin to show some directional character. With a further increase in the magnetic field to a higher level （0.8-5 T）, the β-Sn dendrites have an enhanced directional growth character, but the dendrites show a certain deflection. As the magnetic field is increased to 12 T, the directional growth of the β-Sn dendrites in the center of the couple is severely destroyed. The mechanism of the directional growth of the β-Sn crystals and the deflection of the β-Sn crystals with the application of static magnetic field was tentatively discussed.
Lei LiBo XuWei-Ping TongHui ZhangChun-Yan BanLi-Zi HeZhi-Hao ZhaoYu-Bo ZuoQing-Feng ZhuJian-Zhong Cui
