Tube Hydroforming of Magnesium Alloys at Elevated Temperatures

In this paper, a hydraulic forming machine with the functions of axial feeding, counter punch, and internal pressurization is designed and developed. This self-designed forming machine has a capacity of 50 tons for axial feeding and counter punch, 70 MPa for internal pressurization, and $300°C$ for forming temperature. Using this testing machine, experiments of T-shape protrusion of magnesium alloy AZ61 tubes at elevated temperatures are carried out. A commercial finite element code DEFORM 3D is used to simulate the plastic deformation of the tube within the die during the T-shape protrusion process. Different kinds of loading paths for the pressurization profile and the strokes of the axial feeding and the counterpunch are scheduled for analyses and experiments of protrusion processes at $150°C$ and $250°C$⁠. The numerical thickness distributions and the flow line configurations of the formed product are compared with the experimental results to validate this finite element modeling. The thickness distribution of the formed product or the flowability of AZ61 tubes at $150°C$ and $250°C$ is discussed. The effects of the forming rate on tube flowability at $250°C$ are also investigated. Through the observation of the flow line configurations of the tube material, adequate backward speeds of the counter punch relative to the axial feeding for preventing the material from accumulating at the die entrance region are verified. Finally, a sound product with a protrusion height of 49 mm is obtained.