Explosive Forming of Precipitation-Hardened Aluminum Alloy Tubes
R. A. Yildiz1,2
1TUBITAK, Informatics and Information Security Research Center, Gebze-Kocaeli 41470, Turkey
2Istanbul Technical University, Beyoglu, 34437 Istanbul, Turkey
Keywords: explosive metal forming, precipitation-hardened Al alloys, high strain forming, fracture energy, high explosive
Abstract
The explosive formability of common age-hardenable Al alloys (2024-T4, 2024-T6, 6061-T4, 6061-T6, 7075-T4, and 7075-T6) is investigated experimentally. Manufacturers utilize explosive forming to produce parts having large and complex geometries in a single operation. To investigate the explosive formability of the most common Al alloys used in the aerospace/aircraft industry, an experimental die design is constructed. Tensile tests are carried out to determine the mechanical behavior of the alloys at low strain rates. Charpy V-notch tests are used as input values to determine the fracture toughness and fracture energy. The strain rate considering the expansion angle is calculated through the analytical formula of the Gurney metal velocity. The strain rates obtained by explosive forming conducted in air are calculated roughly as 1.1·105 s-1, which is an extreme rate. The experimental results reveal that the 6061-T4 Al alloy could be explosively formed to the demanded geometry without any hollows, cracks, tearing, and fractured regions. It is clear that the T6 temper condition significantly improves the strength of the tested alloys, accompanied by reduction of ductility and crack initiation potential. Except for the 6061-T4 Al alloy, all of the tested alloys are fractured during explosive forming tests. Stereo microscopy and scanning electron microscopy investigations reveal transgranular fracture and cleavage facets resulting from brittle fracture initiated by high strain rates, which occurs in the peak-strength temper condition-T6 of the tested Al alloys.
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