Microstructures And Properties Of Al-Li Alloys Cast Under Low Frequency Electromagnetic Field

This project is a part of the National Natural Science Foundation's key project"Basic research on processing the ingots of Al-Li alloys with high cleanliness,fine grains and homogeneous distribution of alloying elements"(U1608252).The aim is to resolve the key problem of Al-Li alloy developments in our country-processing Al-Li alloy ingots with high quality by develop Low Frequency Electromagnetic Casting(LFEC)technology of Al-Li alloy.Weldalite-049,2A97 and 5A90 are selected as the research objects in this paper.The ingots were cast by LFEC.OM,SEM,EPMA,ICP chemical analysis,TEM and tensile testing were used in this experiment to study the effect of low frequency electromagnetic field on the microstructures and defects in ingots and the properties of Al-Li alloy after extrusion and T6 treatment.The main results are as follows:1)The ingots of Al-Li alloys were purified by means of decrease in slags and elimination of gas holes and loosen resulted from removing inclusions in liquid owing to fast flow of liquid alloy in mold during LFEC.2)The microstructures of the Al-Li alloys ingots cast by LFEC were refined obviously because the grain nucleation was promoted and grain growth was restrained.3)The alloying element macrosegregation in the ingots cast by LFEC were improved.The macrosegregation in the ingots became weakening with increase in intensity of electromagnetic field.4)The content of the alloying elements increased because of applying low frequency electromagnetic field during LFEC.5)Precipitates in the LFEC cast alloy extruded and T6 treated were finer and higher areal density comparing with those in DC cast alloys.6)Combining effects of above results resulted in increase in mechanical properties of LFEC cast Al-Li alloys in T6 condition.