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

摘要

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 mu m) in the Al-Li-Zr layers due to the precipitation of Al-3 (Zr,Li) and the nanoscale ultra-fine grains (320.0 rim) 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.