Study on the Fine Grain Size and Microhardness at the Interface of AZ31/Mg‐Y Composites

AZ31/Mg‐Y/AZ31 composites are fabricated by hot rolling bonding. To identify the formation mechanism of the microstructure in the interface adjacent region, additional hot rolling or/and diffusion annealing are also conducted on the base of the initial AZ31/Mg‐Y/AZ31 composite. Scanning electron microscopy, energy dispersive spectroscopy, and electron backscatter diffraction are used to characterize the microstructures and chemical compositional distributions. Vicker's microhardness tests are conducted to determine the local mechanical property. It is found that in the Mg–Y layer of the AZ31/Mg‐Y/AZ31 composite, the grain size in the interface‐adjacent region is much finer than that in the central part. Much finer Al₂Y particles compared with those in the traditional Mg–Al–Y alloys are formed in the interface‐adjacent region. The formation of the fine grain in the interface‐adjacent region may be mainly related to the Al₂Y particles rather than the accommodation deformation between layers. Both the grain refinement and the formation of Al₂Y particles contribute to strengthening of the Mg–Y layer. The results in this work may provide a novel method to prepare fine and dispersed high‐melting‐point particles in Mg alloys, thus leading to strong and high‐thermal‐stability Mg alloys.