| This subject is a part work of "Foundational research on the high quality aluminum alloy products and effectively use of aluminum resource", which is supported by the Key Foundational Research Program of China (973). The main content of this work is to study the effects of application of out-phase electromagnetic field on the casting process and the cast microstructures of aluminum alloys in the horizontal direct chill casting (HDC) process and develop a high effective and economical technology-horizontal direct chill casting under an out-phase electromagnetic field (OPEHDC) to obtain aluminum alloy ingots with high metallurgical quality.The content of this study include the effects of different electromagnetic fields on the surface quality and microstructures of HDC 7075 aluminum alloy ingots, the effects of out-phase electromagnetic field on the HDC casting processes of 7075 aluminum alloy, the effects of out-phase electromagnetic field on the microstructures of different aluminum alloys in HDC process, and the effects of combined application of out-phase electromagnetic fields and addition of grain refiner on the as-casting structure of 7075 aluminum alloy and commercial aluminum. The main results are presented as followings:4 kinds of electromagnetic fields were applied in the HDC casting process to cast 7075 aluminum alloy. The result shows that different electromagnetic fields have different functions in the HDC casting process. Current of 50Hz 200A was applied in the coil 1 around runner which can increase the flow speed of liquid and effectively avoid the formation of floating grains in the HDC casting process, while can't improve the as-casting microstructures and surface quality effectively. Current of 20Hz 100A was applied in the coil 2 around the mold which can refine the as-cast microstructures effectively, reduce the thickness of segregation layer of the ingots, lead to defects of porosity under the sub-surface of the ingots and can't avoid the formation of floating grains. As current of 50Hz 200A was applied in the coil 2, the as-cast microstructures become finer and the thickness of segregation layer decreased at a certain extent, no obvious porosity and rarefaction were found in the ingots, while the floating grains still exit in the ingots. As the current with 90 degrees difference was applied in coil 1 and coil 2 simultaneously, an out-phase electromagnetic field formed in the liquid. The as-cast microstructures and surface quality were effectively improved and the floating grains disappeared.The effect of application of the out-phase electromagnetic field in HDC on the process and the metallurgical quality of ingots of 7075 alloy was investigated in detail. The results show that when out-phase electromagnetic field was applied, the effect of gravity on the HDC casting process was eliminated effectively, the temperature distribution in the pool become more uniform, cooling difference between upper surface and bottom surface and depth of sump was reduced, the sump shape was changed to be more symmetric about geometrical center of the mold, the thickness of segregation layer decreased and the surface quantity and the microstructures of the ingots were improved, the area of feathery grains decreased and the area of equiaxed grains increased, the equiaxed grains were refined and the floating grains eliminated so that the quality of the ingots was improved.Thickness of solidification shell in the primary cooling region decreased and the depth of the sump increased with increasing of casting speed. And then, the cold shuts were reduced and the segregation knots increased, thickness of segregation layer decreased, the region of the feathery grain in the cross-section was increased. The function of out-phase electromagnetic field in improving as-cast microstructures was reduced.The out-phase electromagnetic field was applied in HDC process to cast different aluminum alloys (commercial aluminum 1070,2024,3004,5182,6063,7050) ingots and the effect of out-phase electromagnetic field on the as-cast microstructure was investigated. As-cast microstructures of different aluminum alloys were different in the HDC ingots. Coarse columnar grains are formed easily in the alloys with low alloying elements, such as commercial aluminum1070,6063 and 3004. While for the alloys with high alloying elements such as 2024,5182,7075 and 7050, feathery grains are formed easily in the common HDC process. Coarse floating grains are founded in all aluminum alloys used in this experiment in the common HDC ingots. The out-phase electromagnetic field can change the as-cast structure of all aluminum alloys. Grain refine effect caused by out-phase electromagnetic field is different for the different aluminum alloys. Out-phase electromagnetic field can avoid the formation of floating grains in HDC process for all aluminum alloys.The combined effects of addition of grain refiner and application of the out-phase electromagnetic field in HDC process on the as-cast microstructures of 7075 alloy and commercial aluminum1070 were investigated first time. The result shows the efficiency in grain refinement by application of out-phase electromagnetic field decreased with increasing in addition of grain refiner. For 7075 aluminum alloy,72.3% grain size reduction was observed by application of out-phase electromagnetic field in no grain refiner, and 24% grain size reduction was observed by application of out-phase electromagnetic field in addition 2 wt.% of grain refiner. For commercial aluminum1070,84.3% grain size reduction were observed by application of out-phase electromagnetic field in no grain refiner, and 12.3% grain size reduction is observed by application of out-phase electromagnetic field in addition 1 wt.% of grain refiner. Change of grain nucleus number caused by increasing in Al-5Ti-B by per 0.01 wt.% (PI) is difference. For 7075 aluminum alloy the nucleation number caused by each increase in Al-5Ti-B by P1 increased firstly and then decreased for all casting conditions (with or without out-phase electromagnetic field). As addition of Al-5Ti-B is 0.1 wt.%, the nucleation number caused by each increasing in Al-5Ti-B by P1 is maximum,579 nuclei were formed in 1 cm2 area for the traditional HDC ingots,1238 nuclei were formed in 1 cm2 area in the OPEHDC ingots. For commercial aluminum1070 the nucleus number caused by increasing in Al-5Ti-B by P1 decreases for all casting conditions with the addition of grain refiner increasing, (with or without out-phase electromagnetic field). As addition of Al-5Ti-B is 0.02 wt.%, the nucleus number caused by each increase in Al-5Ti-B by P1 is maximum,1882 nuclei were formed in 1 cm2 area for the traditional HDC ingot,3031 nuclei were formed in 1 cm2 area for the OPEHDC ingots. In the same grain refiner addition condition, the nucleus number in OPEHDC casting is more than that of traditional HDC casting. The combined effect of grain refiner and out-phase electromagnetic field on grain refinement is not a single addition of the independent effects by grain refiner addition and application of out-phase electromagnetic field. The grain refinement effective of application of out-phase electromagnetic field decreases with increasing in addition of grain refiner.
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