The Influence of Precooling on Liquid Metal Embrittlement and Microstructure Properties of Galvanized 22MnB5 Tubes

To address the issue of liquid metal embrittlement (LME) susceptibility in galvanized 22MnB5 steel during the hot stamping process, the material's performance is affected. This study proposes a method combining precooling and tube hydroforging to produce galvanized tubular hot stamping parts. The primary workflow comprises four distinct stages: the heating phase, thermal retention phase, precooling phase, and the tube hydroforging phase. Notably, the precooling stage employs two distinct approaches: air precooling and boiling water precooling. The composition and morphology of the zinc coating and the microstructure and mechanical properties of the 22MnB5 steel are investigated using two precooling methods at different hydroforging temperatures. The results show that when the initial hydroforging temperature is below 800 °C, the precooling combined with the tube hydroforging process eliminates LME. With increasing precooling time, the oxidation reaction forms ZnO and Fe₂O₃ on the coating. By comparing the composition, morphology, and mechanical properties of the coatings at hydroforging temperatures of 800 °C and 500 °C, it is concluded that the boiling water precooling aligns more effectively with the requirements of industrial production, with the optimal forming temperature being within the range of 750–800 °C.