The role of lithium atoms in the structural changes in Al−Li alloy

Abstract

The dependence of structural changes in preeipitating Al-10 at% Li alloy on the annealing temperatures as traeed by X-rays, eleetrie resistivity and mierohardness measurements revealed the formation and subsequent dissolution of Al-Li preeipitates in the temperature range of 25--500 ~ The observed variations were attributed to the effect of the annealing temperature on the behaviour of Li atoms within the Al matrix. The inerease of the Li concentration in the matrix due to the dissolution of Al-Li precipitates, being 3.75 at ~/o Li as obtained from X-ray measurements agreed well with the value 4.0 at % Li obtained from resistivity measurements. I n t r o d u c t i o n I t has been reported [1] t h a t in supersaturatedAl-Li alloys, the fl-phase (Al-Li) preeipitated b y annealing in the t e m p e r a t u r e range of 150--300 oC and dissolved at higher t e m p e r a t u r e s leads to the dispersion of the exeess Li atoms b y diffusion t h r o u g h the matrix. Sueh struetural ehanges affeeted largely b o t h the eleetrieal [2] and meehanieal [1] properties of the alloy.The present work airas at traeing the role of Li a t o m s in the Al m a t r i x in the struetural ehanges of different t e m p e r a t u r e s in the alloy from X -r a y diffraetion tests. Also, it is aimed at relating the variations in eleetrie resist i v i t y and mierohardness to these struetural ehanges. ExperimentalSamples of Al-10 at Yo Li were produced b y a m e t h o d previously deseribed [3]. Quenehing from 560 ~ to room t e m p e r a t u r e with a rate of 3 • 103 ~ was earried out to bring the samples in a m e t a s t a b l e s t a n d a r d eondition of solid solution. Isoehronal annealings were done b y heat pulses of 10 min at t e m p e r a t u r e s sueeessively increasing in steps of 20 ~ After eaeh heat pulse the resistanee of the samples was measured at room t e m p e r a t u r e using a standard potentiometrie m e t h o d [4]. A d u m m y sample helped to aeeount for the effeet of t e m p e r a t u r e variation. Microhardness m e a s u r e m e n t s I~ Acta Physica -,4cademiae Scientiarum Hungaricae 46, 1979