Aluminum alloys may exhibit a variety of microstructures within the fusion
zone adjacent to the fusion boundary. Under conventional weld solidificatio
n conditions, epitaxial nucleation occurs off grains in the heat-affected z
one (HAZ) and solidification proceeds along preferred growth directions, in
some aluminum alloys, such as those containing Li and Zr, a nondendritic e
quiaxed grain zone (EQZ) has been observed along the fusion boundary that d
oes not nucleate epitaxially from the HAZ substrate. The EQZ has been the s
ubject of considerable study because of its susceptibility to cracking duri
ng initial fabrication and repair. The motivation of this investigation was
to develop a technique that would allow the nature and evolution of the fu
sion boundary to be studied under controlled thermal conditions.
A melting technique was developed to simulate the fusion boundary of alumin
um alloys using the Gleeble(R) thermal simulator. Using a steel sleeve to c
ontain the aluminum, samples were heated to incremental temperatures above
the solidus temperature of a number of alloys. In Alloy 2195, a 4Cu-1Li all
oy, an EQZ could be formed by heating in the temperature range approximatel
y from 630-640 degrees C. At temperatures above 640 degrees C, solidificati
on occurred by the normal epitaxial nucleation and growth mechanism. Fusion
boundary behavior was also studied in Alloys 5454-H34, 6061-T6 and 2219-T8
. Nucleation in these alloys was observed to be epitaxial. Details of the t
echnique and its effectiveness for performing controlled melting experiment
s at incremental temperatures above the solidus are described.