VPPA welds of Al-2024 alloys: analysis and modelling of local microstructure and strength

The microstructural features of variable polarity plasma arc welded Al-Cu-Mg 2024-T351 with 2319 filler have been studied by TEM, SEM and DSC. Fusion zone, partial melting zone, resolutionising zone, overageing (for S phase), peak ageing (for S phase) and under ageing zones (for S phase) have been identified. The Ω phase has been observed between re-solutionising zone and peak ageing zone. The hardness profile contains two peaks. The microstructure development, and resulting hardness and yield strength profiles are modelled using a model which combines primary precipitation, resolution, partial/full melting and resolidification (Scheil type) and reprecipitation, in a two precipitate – two mechanism approach. Hardness profiles and microstructures are accurately predicted. The hardness peak in the re-solutionising zone is due to re-solutionising and subsequent Cu-Mg co-cluster formation; and the second hardness peak is caused by S phase strengthening.