Quantitative Phase Analysis of the FSW Joints of Al–Cu–Li and Al–Cu–Mg Alloys

Quantitative phase analysis methods are analyzed in relation to the friction stir welding (FSW) joints of a V-1469 alloy (Al–Cu–Li system) and an AA2519 alloy (Al–Cu–Mg system). For Al–Cu–Mg alloys, a method is proposed to estimate the amount of metastable (θ', θ") phases as the difference between the total fraction of all copper-containing phases and the amount of the equilibrium θ phase, which are determined by measuring the lattice parameter of the solid solution and a stereological procedure, respectively. Quantitative ratios of intermetallic phases in FSW joint zones are found for both alloys. The lower strength in the weld zone is shown to be caused by a relative decrease in the concentration of intermetallics with the highest strengthening effect in this zone compared to the base metal. These intermetallic compounds are found to be the θ' (Al₂Cu) phase in the A2519 alloy and the T₁ (Al₂CuLi) phase in the V-1469 alloy.