Effect of heat treatment conditions on the incremental hole flanging of AA6061 aluminum alloy sheets

Abstract

In this study, the effect of heat treatment on the incremental hole flanging of 1.5 mm-thick AA6061 aluminum alloy sheets was experimentally investigated. Specimens were subjected to three conditions: annealed, solution treated, and artificially aged (T6). Flanging was performed using a five-stage forming strategy with wall angles increasing from 50° to 90° and a 10mm hemispherical-head tool at 1000 mm/min. Flange wall thickness distributions, Vickers microhardness, and optical/scanning electron microscopic microstructural analyses were performed to correlate mechanical and microstructural responses with formability. The annealed condition exhibited the highest formability (hole expansion ratio, HER: 1.30–1.35; wall thickness: 1.45–1.48 mm), while solution-treated and aged specimens showed a progressively lower HER (1.27–1.29 and 1.23–1.25) and thinner walls (1.35–1.40 and 1.25–1.30 mm). Larger initial hole diameters reduced HER and wall thickness, with severe edge fracture in aged specimens. Microstructural analysis revealed that annealed specimens had equiaxed grains and coarse Mg 2 Si precipitates enabling homogeneous strain, whereas aged specimens displayed fine precipitates, high hardness, and premature edge fracture. These results provide practical guidance for selecting pre-forming heat treatments to enhance flange quality and suggest that flanging in the annealed or solution-treated state followed by postforming aging can optimize both formability and the final strength.