Crystalline phases and granular structure of TIG-welded Zn–22Al–2Cu alloy plates

Rolled plates of the Zn–22Al–2Cu (weight %) alloy were welded by the Tungsten-Inert-Gas (TIG) welding process; this process had not been applied before to materials of this alloy. The welding conditions were experimentally determined. X-ray diffraction reveals that the crystalline phases η′S,η′T,α′S,α′Tη′S,η′T,α′S,α′T are present in the parent metal and in the fusion zone. The ɛ phase (CuZn4) is present in the fusion zone and the τ′ phase (Al4Cu3Zn) is present in the parent metal. Inside the fusion zone, a dendritic structure surrounded by a network was observed. From chemical analysis, it is found that the α′Sα′S, η′Tη′T and ɛ phases constitute the body of the dendrite and that the η′Sη′S and ɛ phases compose the surrounding network. Near the fusion line, in the grain growth zone, equiaxed grains surrounded by a network were observed. Beyond the grain growth zone the grain shape evolved from equiaxed to elongated. Finally, a penetration value of 2.8 mm was attained when an electrical current of 80 A was used and, with this penetration, the heat affected zone (HAZ) extended up to approximately 0.8 times the penetration value.