Interface phenomena and bonding mechanism in the new method of cross wedge rolling bimetallic shaft

Abstract

Since the drive shaft mainly relies on the outer metals to transmit torque, its inner materials are the dead weight. Therefore, a new method of cross wedge rolling (CWR) bimetallic shaft by using bimetallic billet to directly roll-bond laminated shaft was proposed. In this work, we conducted experimental studies including rolling trial, element diffusion, microhardness, fracture morphology and microstructural evolution to investigate the new method. In the rolling trial, the assembled billet with a tolerance of H7/p6 have significantly reduced the ellipse of outer sleeves. The defects such as spiral grooves, knifing grooves, necking, and cracking appeared on the rolled shafts, which are the typical defects of CWR process and can be avoided by optimizing parameters. The TEM observations demonstrate that the 42CrMo/Q235 interfaces can be metallurgically bonded without large cracks and obvious oxides, which agree with the detection results of element diffusion, fracture morphology and microhardness. As the elements diffuse with each other, the interface microhardness was gradually transited, and small dimples appeared on the tensile fracture. Based on experimental results, the bonding mechanism was discussed. The rolling interface is compressed in the radial direction and stretched in tangential direction because of Mannesmann effect. Due to the radial compressive stress is greater than tangential tensile stress, the bimetallic shaft can be roll-bonded eventually. Under the hot CWR deformation, the microstructure of the bimetallic shaft experiences dislocation pile-up, interface bending, grain nucleation and growth, thus realizing metallurgical bonding at micro scale. This new CWR process is efficient and high-performance, which can be extended to have industrial applications in high-end equipments with an economical way.