Grain Refinement Behavior of Accumulative Roll Bonding-Processed Mg-14Li-3Al-2Gd Alloy

Mg-14Li-3Al-2Gd sheets were prepared by four-layer accumulative roll bonding (FARB). The grain size of Mg-14Li-3Al-2Gd alloy is refined from 252.8 to 5.3 μm after 4 cycles FARB. The refinement can be mainly attributed to the continuous dynamic recrystallization (CDRX). During FARB process, a large number of interlayer interfaces are introduced in the sheets, which have a significant impact on the CDRX. With the increase of FARB cycles, the interface spacing decreases rapidly. In the high cycles, some of layers are fully metallurgically bonded, which makes the corresponding interface disappear and the interface spacing becomes relatively increased. When the interface spacing is small, the dislocation first forms the lath-shaped substructure, then forms lath-shaped sub-grains with straight boundary. With the further deformation, necking and fracture occur in the lath-shaped sub-grain or other lath-shaped substructure, forming the equiaxed substructure with a small size. When the interface spacing is large, the substructure directly becomes equiaxed and randomly divides the deformed grains, forming the equiaxed sub-grains and grains.