Chill zone formation in Al–Li alloy welds

Abstract

The presence of a fine equiaxed zone (also known as the ‘chill zone') along the fusion boundaries in Al–Li alloy welds has recently been reported. Preferential failure along the chill zone during tensile testing has also been observed. Such zones have not been reported in other aluminium alloy welds. The chill zone was considered to form as a result of high undercooling during solidification of Al–Li alloys. In another study, Al₃(Li,Zr) aided nucleation was proposed to be the mechanism of nucleation of the chill grains. The present work demonstrates that the chill zone forms only under conditions when the base alloy contains Al₃Zr particles before welding. The presence of Al₃Zr particles within the chill grains has been shown for the first time. The grain structure of the base metal does not have any role in the formation of the chill zone. A chill zone is also observed in a non-Li bearing Al alloy which contains Zr. It is further shown that in pulsed current and oscillating arc welds, the chill zone is not restricted to the fusion line (as in continuous current welds), but also occurs in the weld interior.