THE SOLIDIFICATION BEHAVIOR OF 8090 AL-LI ALLOY

In this work, the solidification and segregation behaviors of 8090 Al-Li alloy have been investigated with differential thermal analysis (DTA) and the metallographic-electron microprobe method. The results show that 8090 Al-Li alloy has a much more complex solidification path than Al-Li binary alloy due to the addition of many alloying elements and the presence of impure elements. Solidification begins at about 635-degrees-C with the reaction of L --> alpha-Al + L', and this reaction goes on to termination. The alloying element Cu and impure elements Fe and Si have a strong segregation tendency. During solidification, Cu segregates to the interdendrite and finally forms alpha-Al + T2 eutectic. As a result, the solidification temperature range is greatly extended. Iron and Si form the insoluble constituents Al7Cu2Fe, AlLiSi, etc., although their concentrations in the alloy are quite low. With the increase of Fe content, there is a eutectic reaction of alpha-Al/Al3Fe at about 595-degrees-C. The formation of insoluble constituents is influenced by both concentrations of impure elements in the alloy and the cooling rate.