Stability of interfaces in explosively-welded aluminum-titanium laminates

Abstract

Aluminum (6061)/titanium (6-4) laminates were produced by single-shot explosive-welding for applications requiring light-weight structures [1]. Strengthening obtained with these laminates is a combination of shock-induced hardening and the presence of well-adhered interfaces in the composite. The interfaces are stronger than, at least, the weaker component of the laminate [2]. The thicknesses of the aluminum and titanium sheets were in the range 0.508 to 1.600 millimeters. Strengths as high as 825 MPa were achieved, depending on the relative amounts of aluminum and titanium [1]. Planar (straight) interfaces were assured in the laminates, since a wavy configuration would possibly be accompanied by excessive heat generation and an attendant intermetallic formation resulting in weaker interfaces [3]. Response surface methodology [4], a combination of statistical and mathematical techniques, was used to investigate the relationship among the mechanical properties (yield strength) and two design variables, volume percentage of the more ductile component (Al) and abundance of interfaces (or interfacial density). A second-order model was fitted from a central composite design, which comprised nine different combinations of three levels of design variable [1]. At these relatively large thicknesses, the dominant strengthening mechanism was expected to be hardening produced by shock-wave passage. The fitted secondorder model, which employs aluminum content and interfacial density as indicators of strengthening by shock-waves and by the Koehler mechanism [5], respectively, is also in good agreement with this expectation. The fitted second-order model in terms of coded variable was determined as: