Wrinkling and Strengthening Behaviors in the Two-Layer-Sheet Hot-Forming-Quenching Integrated Process for an Al-Cu-Mg-Alloy Thin-Walled Curved-Surface Shell.

The thin-walled curved-surface component is an important structural element in aerospace. Wrinkling, springback and thermal distortion occur easily when forming these components. To form thin-walled components with high precision and strength, a two-layer-sheet hot-forming-quenching integrated process was proposed, in which wrinkling is prevented by thickening the upper sheet and springback is reduced by solution and die quenching. Selecting an appropriate upper sheet is crucial to suppress wrinkling and accomplish effective die quenching. The effect of the upper sheet on the wrinkling and strengthening behaviors of an Al-Cu-Mg-alloy melon-petal shell was thus studied in detail. The anti-wrinkle mechanism was analyzed through numerical simulation. The forming quality, including forming precision, deformation uniformity and strength, were further evaluated. The wrinkle gradually decreased with the increasing thickness of the upper sheet, resulting from the depressed compressive stress at the edge of the target sheet. A defect-free specimen with a smooth surface was finally formed when the thickness of the upper sheet reached three times that of the target sheet. The profile deviation was ±0.5 mm. Excellent thickness uniformity in a specimen can be obtained with a maximum thinning rate of 6%. The full strength, ranging from 455 to 466 MPa, can be obtained in all regions of the specimen, indicating that effective strengthening can be accomplished with the two-layer-sheet die quenching. The results indicated that high forming quality and full strength can be obtained in a two-layer-sheet hot-forming-quenching integrated process. This research has great potential for engineering applications using aluminum-alloy curved-surface thin-walled components.