Research On Ultrasonic-assisted Casting Technology And Mechanism Of 2195 Aluminum-lithium Alloy Ingot

2195 aluminum-lithium alloy is an advanced lightweight structural material,its comprehensive performance can rival that of composite materials.Once applied to aerospace equipment,it is very competitive to reduce the weight of components,and improve the safety and carrying capacity.Due to the abnormal activity of lithium elements,Al-Li alloy is easy to absorb hydrogen,oxygen,and various chemical reactions during the melting and casting process.Furtherly,the Al-Li ingots obtained by conventional manufacturing technology have more defects such as internal looseness,porosity,and inclusions,which weaken the quality of the products.Because of the above manufacturing and quality problems,ultrasonic field assisted casting technology is introduced based on the in-depth analysis of the conventional manufacturing process of AlLi alloy,a new casting technology was proposed in this paper on the manufacturing process of Al-Li alloy which was composed of ultrasonic treatment and atmosphere protection.In this paper,the effects of the key parameter factors involved in this technology,such as the atmospheric environment pressure,the amount of Li element ratio,and the ultrasonic power,on the quality of Al-Li alloy ingots were investigated.The mechanism of an ultrasonic field on the quality improvement of ingots from different levels was explored.Finally,the ultrasonic-assisted casting technology for 2195 Al-Li alloy ingots was developed and successfully applied in the manufacture of ingots of various specifications.The main research contents and conclusions of this paper are as follows:(1)The conventional casting experiments of 2195 Al-Li alloy were carried out.The effect of atmospheric pressure on the quality of 2195 AlLi alloy ingots was emphatically explored.The research shows that the content of lithium and hydrogen elements in 2195 Al-Li alloy ingots was very sensitive to the change in ambient pressure.Additionally,the content of hydrogen in ingots was proportional to the ambient pressure.While the content of lithium was inversely related to it.When the ambient pressure of the atmosphere was lower than 5 KPa,the lithium loss increased sharply.In addition,under the conventional process conditions of single atmosphere protection,serious problems such as segregation and coarse microstructure would generate in Al-Li alloy ingots.(2)The mechanism of the ultrasonic field on the solidification of 2195Al-Li alloy was revealed utilizing basic experiments,finite element simulations,and theoretical calculations.The results show that the application of ultrasound was conducive to promoting heat transfer and reducing the content of lithium elements in the surface layer,resulting in a lower saturation vapor pressure and reducing the loss of Li elements.Meanwhile,the cavitation and acoustic effects generated by the ultrasonic system promoted the nucleation,growth,and discharge of gas nuclei in the melt pool.The hydrogen content of the ingot was further reduced by the above physical effect.Additionally,the homogeneity of the Al-Li alloy ingots was evidently increased by the fracture and depolymerization of agglomerated particles under high circumferential cyclic loading generated by ultrasonic.On the other hand,a large number of heterogeneous cores in the melt were activated by ultrasound,promoting nucleation and reducing the density difference of the interface flow.Thus,the refinement of the ingot microstructure was realized in this way.(3)A novel set of melting and casting equipment with compound atmosphere protection and ultrasonic technology applied for the manufacture of Al-Li alloy was designed in this paper.Ultrasonic-assisted casting experiments of 2195 Al-Li alloy ingots were carried out based on the above equipment.Subsequently,the quality change pattern of Al-Li alloy ingots under different lithium element ratios and ultrasonic power was obtained.The experiments show that the hydrogen content in Al-Li alloy can be significantly reduced by up to 63% with the application of ultrasound.What’s more,the segregation of ultrasonic ingot was obviously ameliorated by 25-60%,and the uniform refinement effect for both α-Al matrix and eutectic phases was optimized,with a refinement rate of 36%-45%.At the same time,the loss of lithium elements could be effectively controlled.The higher the ratio of lithium elements,the less loss of elements would obtain,and the loss rate can be reduced by 55-75%.When the atmosphere condition is 0.12 MPa and the ultrasonic vibration power is1500W-1600 W,the hydrogen content and Li element loss rate of 2195aluminum-lithium alloy ingots are effectively reduced,and the microstructure refinement effect reaches the peak.(4)According to the basic ultrasonic assisted casting experiment,a combination of process parameters was developed and the casting experiments of 2195 Al-Li alloy with different specifications were carried out.Three specifications of ingots were successfully manufactured and the ingot quality was quantitatively analyzed.The results show that compared with conventional ingots,the average hydrogen content of the ultrasonic ingot was controlled within 0.098ml/100g-Al.The degassing efficiency was about 45%-52%.And the Li loss was controlled within 5.5%.The macro-segregation rate of ingot microstructure was significantly improved with a segregation rate less than ± 0.05.Besides,the grain size and other technical indicators have been greatly ameliorated,e.g.,the grain refining rate exceeded 38% with an average grain size less than 225 μm,and the refining rate of eutectic phases reached 45%.The products were all in sufficient with the requirements of product technical indicators.