Numerical Simulation Of Semi Continuous Casting Of Large-Scale Magnesium Alloy Slab

Magnesium alloy is the lightest structural metal material with broad prospect.However,the fabrication of large scale and high quality magnesium slabs has become a bottleneck problem to restrict the domestic development of wrought magnesium alloys,due to the low thermal strength,small latent heat and heat capacity,poor castability,strong hot cracking tendency and significant problem of microporosity.As a part of 'National Basic Research Program(973 project)---The Key problem in the fabrication of high performance magnesium alloys',this work employed the numerical simulation software ANSYS/Fluent to study the effects of feeding condition and external fields(US and LFEC)during the semi continuous casting of 400×1450mm AZ80 magnesium alloy slabs.The effects of casting parameters,including casting speed,cooling water ratio,Ultrasonic power and current intensity,on the sump depth and mushy zone,temperature and flow field during US-LFEC semi-continuous casting of magnesium alloy slabs were also investigated.The conclusions could be drawn as following:(1)After decreasing the number of holes in the long direction of diversion channel(Channel B),the electromagnetic field could improve the feeding condition,decrease the sump depth the center of the wide direction as well as the corresponding sump depth difference along the wide direction.The sump depth under the ultrasonic horn became deeper in the ultrasonic field.(2)The velocity of the melt near the ultrasonic horn was significantly increased by 0.1 m/s(as large as 0.35m/s)under the ultrasonic streaming effect.It drew a vortex along the casting direction,which significantly modify the local temperature field.The effective range could be as large as 0.3m and 0.1m in the wide and thick direction,respectively.The intensity of the forced convection by electromagnetic field in the thick direction was stronger than that in wide direction.The forced convection in the center place of large face and the tip of diversion channel could reduce the thickness of the kish in the corresponding location.Meantime,the electromagnetic field could also eliminate the horizontal vortex in the tip area of the diversion channel.(3)The research on US-LFEC semi-continuous casting showed that the feeding condition did not change significantly compared to LFEC casting.What is more,the electromagnetic field could partly offset the sump depth increase by ultrasonic field near the ultrasonic horn during the US-LFEC casting.(4)In this work of US-LFEC casting process,increasing casting speed could decrease the cooling rate in the center of the large face,enlarge the cooling difference along the wide direction,increase the height difference of the kish,and significantly increase the sump depth of the location which was between the ultrasonic horn and the tip of diversion channel.When the ultrasonic power increased from 200W to 1300W,the two-phase zone got homogenized and its range also decreased;the difference of sump curvature decreased as well as the difference grain orientation at different locations.When the current intensity increased from 100A to 200A,the sump depth at the center of slab increased,and the thickness of the kish at face center also decreased,suggesting that properly decreasing current intensity is beneficial to the quality improvement of the slabs.