Effect of preferred orientation on the damping capacity of magnesium alloys
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i¥IAGNESIUM, whether cast o r wrought, exhibits r e l a tively high d a m p i n g p r o p e r t i e s at engineering s t r e s s l e v e l s . H o w e v e r , s o f t n e s s o r l a c k of s t r e n g t h l i m i t s i t s a p p l i c a t i o n in m e c h a n i c a l s t r u c t u r e s . E a r l i e r w o r k o n d a m p i n g of m a g n e s i u m a n d i t s a l l o y s d e m o n s t r a t e d t h a t a l l o y i n g e l e m e n t s w h i c h a r e p r e s e n t in a s e p a r a t e p h a s e o r i n s o l i d s o l u t i o n r e d u c e the d a m p i n g of m a g n e s i u m - b a s e a l l o y s . 1 T h e r e d u c t i o n in d a m p i n g c a p a c i t y i s u s u a l l y c o r r e l a t e d w i t h the s t r e n g t h e n i n g e f f e c t of the a d d i t i o n . 1'2 T h e a n i s o t r o p y of the h e x a g o n a l s t r u c t u r e of m o s t m a g n e s i u m - b a s e a l l o y s i n t r o d u c e s a n o t h e r f a c t o r of i m p o r t a n c e t o the d a m p i n g . I n m a n y a l l o y s of m a g n e s i u m , i n c r e a s e d h a r d n e s s a n d s t r e n g t h a r e o b t a i n e d by d i f f e r e n t m e t h o d s of f a b r i c a t i o n , but a t the e x p e n s e of d a m p i n g p r o p e r t i e s . T h e d a t a h e r e s h o w t h a t the d a m p i n g p r o p e r t i e s m a y be a f f e c t e d m o r e by the f a b r i c a t i o n m e t h o d , h e n c e the p r e f e r r e d o r i e n t a t i o n , t h a n by the a l l o y i n g a d d i t i o n s . I n a d d i t i o n , i t i s s h o w n t h a t the d a m p i n g c a n be a t t r i b u t e d t o s t r e s s - i n d u c e d a n e l a s t i c s h e a r p r e s u m a b l y due t o d i s l o c a t i o n m o t i o n on the b a s a l planes. It i s p o s s i b l e that a c o m p r o m i s e b e t w e e n h i g h s t r e n g t h a n d h i g h d a m p i n g ( o p p o s i n g f a c t o r s ) m a y be o b t a i n e d by t a i l o r i n g the f a b r i c a t i o n m e t h o d . T h u s , w i t h p r o p e r o r i e n t a t i o n of the a n i s o t r o p i c s t r u c t u r e o f m a g n e s i u m a l l o y s , v i b r a t i o n o c c u r r i n g i n one p l a n e o r d i r e c t i o n m a y be r e d u c e d w h i l e r e t a i n i n g n e c e s s a r y m e c h a n i c a l p r o p e r t i e s in a d i f f e r e n t d i r e c t i o n . F o r e x a m p l e , a s t r u c t u r a l m e m b e r u n d e r t e n s i o n m a y be p r o n e to v i b r a t e in a f l e x u r a l o r b e n d i n g m o d e . EXPERIMENTAL A s e r i e s of M g - 4 . 5 C e a l l o y s w e r e p r e p a r e d w i t h c e l l m a g n e s i u m (99.76 p c t M g ) a n d c e r i u m (99.8 pct C e ) . A t o t a l of s i x 2 . 2 - 1 b . ( 1 - k g ) h e a t s w e r e m e l t e d i n MgO c r u c i b l e s a n d p o u r e d i n t o i r o n m o l d s . The s t o c k f r o m t h r e e h e a t s was f o r g e d at 9 0 0 ° F ( 4 8 2 ° C ) i n t o b a r s . T h e f i r s t forging produced a l ~ - i n , sq cross-section. ALFRED E, SCHWANEKE and ROBERT W. NASH are Supervisory Resear
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