Study on Microstructure Evolution and Fracture Behavior of Al/Al/Cu Multilayer Composites

The microstructure evolution, mechanical properties, and the fracture mode of Al/Al/Cu multilayer structural composites produced by accumulative roll bonding (ARB) were investigated by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersion spectrometry (EDS), electron backscattered diffraction (EBSD), tensile test at room temperature and microhardness tests. The results show that during the ARB process, the Cu layer undergoes the process from straightening, necking to fracture due to the difference in the strain hardening index and strength coefficient between Al and Cu. The shear stress caused by the severe plastic deformation makes the Cu grains elongated and flattened along the rolling direction, forming a fibrous shape. After the ARB5 cycles, the Cu grains undergo dynamic recrystallization, and a large number of equiaxed grains appear, with average grain size of 750 nm. After ARB3 cycles, the ultimate tensile strength (UTS) of the composite reaches the maximum value of 625 MPa, and the elongation is 6.67%. During the tensile process, the transverse microcracks are first initiated at the Al3003/Cu interface, and then the microcracks propagate longitudinally along the Al layer. Finally, the microcracks in the Al layer merge into the main cracks, which develops in the direction of the shear bands with the rolling direction. With the increase of ARB cycles, the bonding strength of the Al3003/Cu interface increases, and the Al/Al/Cu multilayer structural composite changes from delamination-necking fracture to delamination-shear fracture and finally to shear fracture.