THE FORMATION OF HIGH ANGLE GRAIN BOUNDARIES DURING THE PLASTIC DEFORMATION OF MAGNESIUM AND MAGNESIUM ALLOYS

A b s t r a c t T h i s paper d e a l s w i t h t h e f o r m a t i o n o f g r a i n b o u n d a r i e s d u r i n g p l a s t i c d e f o r m a t i o n o f p u r e magnesium, a m a t r i x t y p e magnesium a l l o y (Mg-6Zn-0.65Zr), and t h e two-phase Mg-8.1Li-4.2A1 a l l o y . It is shown t h a t t h e main p r o c e s s r e s p o n s i b l e f o r t h e g e n e r a t i o n o f r e c r y s t a l l i z e d g r a i n s is t h e f o r m a t i o n o f s u b g r a i n s under s m a l l deformat i o n s f o l l o w e d by t h e i r t r a n s f o r m a t i o n i n t o h i g h a n g l e b o u n d a r i e s . It is e s t a b l i s h e d t h a t an i m p o r t a n t r o l e i n t h e development of dynamic r e c r y s t a l l i z a t i o n i s p l a y e d by t w i n n i n g . The e f f e c t o f t h e c h a r a c t e r o f c r y s t a l l o g r a p h i c s l i p on t h e g e n e r a t i o n o f new g r a i n s is a l s o c o n s i d e r e d . The two-phase magnesium a l l o y was used t o show t h a t t h e o v e r l a p o f h e t e r o g e n e o u s t r a n s f o r m a t i o n w i t h dynamic r e c r y s t a l l i z a t i o n r e s u l t s i n t h e f o r m a t i o n o f i n t e r p h a s e b o u n d a r i e s .