The electro-hydraulic expansion bonding process: a new bonding-strength-enhancing composite method for bimetallic pipes

To expand the material compatibility window and improve the bonding strength of bimetallic pipes, this study proposes electro-hydraulic expansion forming, a novel high-strain-rate composite forming process. Unlike quasi-static methods, the proposed approach leverages the differential strain rate strengthening sensitivity between the base and liner materials to achieve superior bonding strength. Feasibility is demonstrated using a 3003-H18 aluminum alloy liner (outer diameter: 23–25 mm, wall thickness: 1 mm) and a 20# steel base pipe (outer diameter: 34 mm, wall thickness: 4 mm). Through integrated simulation and experimental validation, optimal processing conditions are identified: a 0.5 mm gap between the base and support pipe, combined with a discharge voltage of 7 kV, yields a shear strength of 3.469 MPa. More critically, the introduction of axial surface features via precision turning on the inner wall of the steel base pipe drastically enhances mechanical interlocking, increasing the shear strength to 7.753 MPa. Numerical simulations corroborate that for this material pair, the same parameter combination (a 0.5 mm gap and a discharge voltage of 7 kV) delivers a peak predicted surface-contact bonding strength of 6.96 MPa. Mechanistically, under high-strain-rate loading, the base pipe undergoes greater elastic deformation upon yielding than under quasi-static conditions, leading to increased elastic recovery upon unloading. This effect is more pronounced in the steel base pipe than in the aluminum liner, thereby generating substantially higher residual compressive stress at the interface—accounting for the marked improvement in shear strength.