Bulging limit of AZ31B magnesium alloy tubes in hydroforming with internal and external pressure

The bulging process of AZ31B magnesium alloy tubes in hydroforming with internal and external pressure (THFIEP) was simulated using the commercial finite element software Dynaform and considering plasticity theory and the yield criterion. The investigations focused on the influence of the processing parameters (the corner radius of the tool ( r ), the taper angle of the conical core ( φ ), the length of the bulging zone ( l ), the axial supplement of the tubes ( s ), the internal pressure ( P i ), and the external pressure ( P o )) on the maximum bulging diameter ( d max ). The results showed that the d max increased significantly with increasing r when r was less than 3 mm, and d max remained stable with increasing r when r was larger than 3 mm. The influences of φ , l , s , P i , and P o on the d max were similar; the d max first increased then decreased with increasing values of these parameters. The optimum bulging processing parameters were determined, r was 5 mm, φ was 12°, s was 10 mm, l was 37.5 mm, P i was 34 MPa, P o was 17 MPa, and the obtained optimum d max was 40.43 mm.