A proposed mechanism for equiaxed grain formation along the fusion boundary in aluminum-copper-lithium alloys
- United Airlines Repair Facility, San Francisco, CA (United States)
- Ohio State Univ., Columbus, OH (United States)
The effects of welding conditions, composition and solidification substrate have been systematically studied in an effort to determine the nature of nondendritic equiaxed grain formation in Al-Cu-Li welds. The equiaxed zone (EQZ) in these alloys forms preferentially at the fusion boundary of arc welds and may have important implications with respect to both weld cracking susceptibility and structural integrity. Over a wide range of weld heat input, achieved by varying weld travel speed and current during autogenous gas tungsten arc welding, it was not possible to eliminate this zone, although its width and the grain size varied considerably. The solidification substrate had a profound effect on EQZ formation. The EQZ did not form when solidification occurred from an as-cast weld metal substrate. Under other substrate conditions, including the as-cast/solution heat treated condition, an EQZ was always present. Both lithium and zirconium influence EQZ formation, with zirconium exhibiting a more dominant effect. At low levels of lithium and zirconium (0.5 Li, 0.03 Zr), an EQZ was not observed. A unified heterogeneous nucleation mechanism is proposed to describe EQZ formation in Al-Cu-Li welds.
- OSTI ID:
- 616407
- Journal Information:
- Welding Journal, Vol. 77, Issue 3; Other Information: PBD: Mar 1998
- Country of Publication:
- United States
- Language:
- English
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