Microstructural refinement through inoculation of type 7020 Al–Zn–Mg alloy welds and its effect on hot cracking and tensile properties

Weld solidification cracking in age-hardenable aluminium alloys is usually minimised by adjusting weld metal composition. One way of reducing cracking susceptibility is to refine the weld metal microstructure, which offers the additional benefit of improving mechanical properties. In the current work, grain refinement was achieved in weld fusion zones of a medium-strength Al–Zn–Mg alloy through inoculation with Ti, Ti+B and Zr. It was found that the grain structure in the refined welds was equiaxed in all three dimensions and that this led to a reduction in hot cracking tendency and to an improvement in hardness and tensile properties, especially ductility.