Influence of the alumina thickness at the interfaces on the fracture mechanisms of aluminium multilayer composites

Three aluminium multilayer composites based in fifteen alternate layers of Al 6082 and pure Al 1050 have been produced by hot roll-bonding. Alumina layers of three different thicknesses were grown at the interfaces by an anodizing process. The influence of alumina thickness on the toughness of the multilayer laminates has been studied. These laminate composites have been tested at room temperature under Charpy impact test, three point bending test at low strain rate and shear tests on the interfaces. All three laminates exhibited higher impact toughness than the as-received Al 6082 alloy being highest for the one with the thicker alumina layer. The fracture mechanism of the laminate materials was shown to depend on the alumina thickness and on the imposed strain rate during the mechanical tests. At low strain rate, intrinsic toughening mechanisms were dominant, while at high strain rate extrinsic mechanisms like delamination were also activated increasing the impact toughness.