The retained-substrate aluminium wire direct energy deposition process produces a thin mechanically active interlayer where the substrate heat affected zone, partly molten metal, fusion zone, first deposited layer, and top AA2319 deposit take load through distinct mechanisms. The aim of this paper is to investigate AA2319 deposits deposited on 2219-T8, 2024-T3, conventional rolling 6061-T6, and rapid solidification 6061-T6 substrates in as-deposited, inter-pass rolling, heat treatment, and rolling and heat treatment states. The issue to be addressed was whether retained interface performance was dominated by chemical compatibility, local hardening, sensitivity of first layer defects, or substrate side heat affected zone softening. Factors taken into consideration were tensile behavior, microhardness distribution, optical microscopy, SEM fractography, EDS composition analysis, and digital image correlation. 2219+2319 couple demonstrated the best compatibility of the alloys. In the as-deposited state, the proof stress was 118 $\pm$ 8 MPa, ultimate tensile strength was 257 $\pm$ 13 MPa, and elongation was 8.5 $\pm$ 1.5\% elongation, indicating that the softer AA2319 deposit controlled the tensile response. Inter-pass rolling increased the proof stress to 224 $\pm$ 21 MPa, whereas elongation was lowered to 2.2 $\pm$ 0.7\%. It indicated that deformational strengthening alone failed to confer the damage tolerance of the lower wall. The highest strength coupled with inter-face-tolerance was observed in the case of the rolled-then-heat-treated 2219+2319 combination with 272 $\pm$ 22 MPa of proof stress and 362 $\pm$ 26 MPa of ultimate tensile strength, and without failure at the fusion line. In the 2024+2319 interface, however, magnesium alloy dilution of the lower portion increased the fusion zone hardness to about 99 HV. Yet due to low elongation and sensitivity to grain-boundary cracking, the lower deposited portion remained less desirable. Softened heat-affected zones on the substrate side of 6061 interface dictated performance, rather than cracking within the lower deposit, as was seen for other substrates. Quickly-solidified 6061 provided better results in terms of strength and uniformity of strain following heat treatment compared to normally-rolled 6061. Direct corrosion data could not be obtained; thus, any corrosion analysis was limited to mechanical- and chemical-vulnerable regions.

aluminium alloys; AA2319; wire direct energy deposition,WAAM,retained substrate,fusion boundary,heat-affected zone,inter-pass rolling,microhardness,digital image correlation,localized degradation