Sheet aluminium 2024-T3 alloy was treated in a range of acid solutions. These acid solutions included HNO 3 , H 2 SO 4 , and H 3 PO 4 alone, with HF, and with a combination of the oxidant sodium persulphate (Na 2 S 2 O 8 ) and HF. Changes in the surface chemistry and morphology of the matrix and intermetallics were characterised by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDXS), Rutherford backscattering spectroscopy (RBS), and X-ray photoelectron spectroscopy (XPS). Etch rates for each acid solution were determined by weight loss after repeated immersion. In addition, the acid solutions were analysed by inductively coupled plasma atomic emission spectroscopy (ICP-AES) to determine the amount of aluminium and alloy component dissolution.MST/4948

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Four boron/aluminum aft pylon "boat tail" skins are designed and fabricated and three of them are installed on three DC-10 aircraft for a 5-year flight service demonstration test. The fourth skin is retained as a spare and all skins will be replaced at the end of the service period by their titanium counterparts. Inspection and tests of the exposed skins will establish the ability of the boron/aluminum composite to withstand long time flight service conditions, which include exposures to high temperatures, sonic fatigue, and flutter. The results of a preliminary testing program yield room temperature and elevated temperature data on the tension, compression, in-plane shear, interlaminar shear, bolt bearing, and tension fatigue properties of the oriented 11 ply boron/ aluminum laminates and this information together with a stress analysis are used to obtain FAA approval. Present state-of-the-art technology (emphasizing low cost) was used in the fabrication of the skins and these are installed on the existing titanium substructure with the same number of the same sized mechanical fasteners as are used for the present titanium (8 x 67 inches) and are 2.032mm (0.080 inch) thick. Although maximum weight saving was not sought, the 1.56Kg (3.45 lb) weight of the constant thickness boron/aluminum skin is 26% less than the chemically milled titanium skin.