Effect of enhanced convection on the microstructure of Al-Cu-Li welds
The effects of enhanced convection induced by a high-gravity environment on the resulting weld microstructure of a 2195-T8 (Al-Cu-Li) alloy have been investigated. Stationary (spot) bead-on-plate gas tungsten arc welds were performed at 1, 5, and 10 g (1 g = 9.8 m/s{sup 2}) using the multigravity research welding system (MGRWS). Of particular interest was the gradual disappearance of a narrow band of fine equiaxed grains (EQ) located along the fusion boundary of the weld as g level increased. The presence of this equiaxed zone (EQZ) may affect weld mechanical properties and therefore compromise structures incorporating welds of Al-Cu-Li alloys. The qualitative verification of a proposed mechanism for equiaxed grain formation along the fusion boundary of Al-Cu-Li alloy welds by Gutierrez and Lippold is also presented. The high-g environment causing enhanced convection is believed to alter the thermal and fluid flow conditions within the weld pool, thereby creating an environment in which there is neither a stagnant boundary layer nor an unmixed zone. Furthermore, the precipitates aiding in the precipitation of the fine, equiaxed grains are believed to be swept into the weld pool at high-g and completely dissolved. As a result, the environment for equiaxed grain formation has been eliminated. The analysis of the microstructural evolution from 1 to 5 to 10 g qualitatively verifies this proposed mechanism. At 1 g, a prominent EQZ formed; at 5 g, the EQZ was scattered in location along the fusion boundary and of reduced width; at 10 g, the EQZ had completely disappeared leaving a near perfect line separating the large grains of the heat-affected zone from the fine dendrites of the fusion zone.
- Research Organization:
- Clarkson Univ., Potsdam, NY (US)
- OSTI ID:
- 20000599
- Journal Information:
- Welding Journal (Miami), Vol. 78, Issue 10; Other Information: PBD: Oct 1999; ISSN 0043-2296
- Country of Publication:
- United States
- Language:
- English
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