Factors affecting the grain-refinement of aluminum using titanium and boron additives
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AND
J. PEARSON
The d e v e l o p m e n t of g r a i n - r e f i n i n g t e c h n i q u e s for the c a s t i n g of a l u m i n u m , and the r e s u l t s a c h i e v e d u s i n g additions of t e r n a r y A 1 - T i - B m a s t e r - a l l o y s , a r e b r i e f l y d e s c r i b e d . A t e s t p r o c e d u r e is given for a s s e s s i n g the r e l a t i v e e f f e c t i v e n e s s of t h e s e m a s t e r - a l l o y s , and the r e s u l t s a r e r e l a t e d to the v a r i o u s kinds of alloy t r e a t e d , i n c l u d i n g those with c o n s t i t u ents which " p o i s o n " the g r a i n - r e f i n i n g agent. The e q u i l i b r i u m c o n d i t i o n s which affect the b e h a v i o r of the c o n s t i t u e n t s of the g r a i n - r e f i n e d alloys a r e e x a m i n e d q u a n t i t a t i v e l y f r o m a t h e r m o d y n a m i c viewpoint. One t h e o r y about the m e c h a n i s m of n u c l e a t i o n of a l u m i n u m on t i t a n i u m d i b o r i d e is e x a m i n e d and found i n a p p l i c a b l e . New data on the s o l u b i l i t y of TiB2, ZrB2, TiC, ZrC, CrsC2, CrB~ in liquid a l u m i n u m a r e p r e s e n t e d g r a p h i c a l l y . P r a c t i c a l a s p e c t s of alloy b e h a v i o r in g r a i n - r e f i n i n g p r a c t i c e a r e a n a l y z e d and d i s c u s s e d on the b a s i s of the q u a n t i t a t i v e data. A) THE P R A C T I C E OF G R A I N - R E F I N E M E N T IN ALUMINUM ALLOYS A1) R e a s o n s for G r a i n - R e f i n e m e n t It is well known that addition to a m o l t e n m e t a l of an agent which will p r o m o t e g r a i n - r e f i n e m e n t on c a s t i n g without i n t r o d u c i n g o t h e r n o t i c e a b l e a l l o y i n g effects will r e s u l t in i m p r o v e d m e c h a n i c a l p r o p e r t i e s and s u r face finish in the alloys cast. F u r t h e r , the u s e of s u i t able g r a i n - r e f i n i n g a g e n t s can p e r m i t a r a d i c a l i n c r e a s e in c a s t i n g s p e e d s . In the a l u m i n u m i n d u s t r y , this has led to the bulk of g r a i n - r e f i n i n g a g e n t s b e i n g used in the p r o d u c t i o n of ingots, e x t r u s i o n b i l l e t s and sheet for f a b r i c a t i o n , u s i n g e i t h e r s e m i c o n t i n u o u s or continuous m e t h o d s of c a s t i n g . Here, i n a d e q u a t e r a t e s of n u c l e a t i o n would give c o a r s e s t r u c t u r e s , which in e x t r e m e c a s e s r e s u l t in ingot c r a c k i n g , or, in other a l loys, s u r f a c e defects such as f e a t h e r c r y s t a l s , which a r e d e t r i m e n t a l in s h e e t and other p r o d u c t s r e q u i r i n g a superior finish. A2) D e v e l o p m e n t in Methods of G r a i n refining Aluminum A2.1) E a r l y Work. Cibula 1 showed that the p r e s e n c e of t i t a n i u m , p a r t i c u l a r l y in c o m b i n a t i o n with c a r b o n o r boron, p r o d u c e s a good g r a i n - r e f i n i n g effect in a l u m i num. Since his
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