High-strength and ductility bimodal-grained Al–Li/Al–Li–Zr composite produced by accumulative roll bonding

Microstructure evolution and mechanical behavior of bimodal-grained Al–Li/Al–Li–Zr laminated composite by accumulative roll bonding (ARB) were investigated. As-rolled Al–Li and as-annealed Al–Li–Zr sheets were bonded up to 5 cycles at room temperature. In the 5-cycle ARB processed Al–Li/Al–Li–Zr layered composite, straight and continuous bonding interfaces were formed between the soft Al–Li layers and hard Al–Li–Zr layers. No macro shear bands were observed, indicating that a uniform deformation occurred between different materials in the ARB process. A bimodal grain distribution of the micro-size elongated grains (1.3 μm) in the Al–Li–Zr layers due to the precipitation of Al₃(Zr,Li) and the nanoscale ultra-fine grains (320.0 nm) in the Al–Li layers due to the recrystallization process was found. Microhardness in the Al–Li and Al–Li–Zr layers and tensile strength of the composite increased with the number of ARB cycles. However, the ductility first decreased at the 1-cycle ARB process then increased at 2–5 cycles ARB process. The best mechanical properties (UTS = 388 MPa and EL = 12.7%) were obtained in the 5-cycle ARB process. The high strength and ductility could be explained for the contributions from strain hardening, grain refinement, no macro shear bands and the formation of a bimodal grain size distribution.