Study On Electromagnetic Twin-roll Casting 2099 Al-Li Alloy

2099 Al-Li alloy belongs to Al-Cu series which can be strengthened by heat treatment.The alloy has low density,high modulus of elasticity,high specific strength,high specific stiffness,excellent low temperature performance,good corrosion resistance,low anisotropy and well weld ability,which make it become one of the most important aerospace materials.The 2099 Al-Li alloy strip is generally produced by hot rolling process with the disadvantages of high cost,complex process and time consuming.Twin-roll casting process has the characteristics of short process,low cost and high efficiency.Using twin roll casting to the produce 2099 Al-Li alloy strip can effectively reduce cost and energy consumption,significantly improve economic benefits.In this paper,the 2099 Al-Li alloy was fabricated by twin roll casting.The pulse current,static magnetic field and electromagnetic oscillation field(composite field)were applied to produce 6 mm cast-rolled strip.The influence of different external field parameters on the microstructures and properties of the strip was studied and several conclusions were attained as follows:(1)The 2099 Al-Li strip with the thickness of 6mm was successfully manufactured when the roll-casting speed was 1.05 m/min and the pouring temperature was 705?.(2)The strip without any outfields has coarse grain and severe central segregation in the middle of the strip.The main elements of central segregation are Cu and Zn.(3)The microstructure of the strip was obviously refined when the duty ratio is 15%,the frequency is 20 Hz and the current intensity is 400 A.At this condition,the secondary dendrite spacing is 6.6?m and the macrosegregation is also alleviated.(4)The grain refining effect of the 2099 Al-Li strip is remarkable when the static magnetic field strength is 35 mT.During that time,the secondary dendrite spacing is 7.4?m and the macrosegregation is also improved.(5)When the current duty ratio,current frequency,current intensity and magnetic field strength are 15%,20 Hz,400 A and 35 mT,the secondary dendrite spacing of the strip is 6.4 ?m and the central segregation is well suppressed.(6)Comparing the microstructures and properties of the strips with different external fields,it can be found that the microstructure and properties of the strip are improved obviously by applying composite fields.After applying the composite fields,the secondary dendrite spacing of the strip decreased from 9.7?m to 6.4 ?m and the conductivity of the alloy decreased from 16.9%IACS to 15.24%IACS;the precipitation of the second phase is significantly suppressed and the central segregation zone of the cast strip is basically eliminated.Moreover,the mechanical properties are also improved.