Evolution of microstructure and mechanical properties for multi-layered Al-1100 strips and Al-Gr composites fabricated by accumulative roll bonding

Aluminium-graphite (Al-Gr) composites fabricated via the accumulative roll bonding (ARB) process are the new functional composites with excellent microstructural and mechanical properties. In this work, an aluminiumgraphite composite is fabricated by the accumulative roll bonding process. 1.25 wt% of graphite was introduced in steps during each roll bonding pass, and the effect of reinforcement on increasing the number of ARB passes was studied. The microstructural characterization revealed that, with increasing rolling passes, the bonding of interfaces is significantly improved, and the graphite is preferentially extended by breaking into fragments resulting in a uniformly distributed composite structure. An electron backscatter diffraction (EBSD) analysis assisted detailed understanding of the microstructure in terms of morphology, orientation, and grain refinement. The results showed typical lamellar grains parallel the rolling direction during initial rolling passes. However, the lamellar structure breaks with repeated rolling reductions, yielding a more homogeneous microstructure with considerable grain refinement. A significant accumulation of dislocations resulted in larger misorientations; thus, a composite with a good combination of LAGB and HAGBs was developed after six ARB passes. The microstructural evolution and significant grain refinement were reflected in the mechanical properties of the processed composite. The tensile test results showed that the ultimate tensile strength of multi-layered Al-1100 improved four times, whereas the aluminium-graphite composite showed three times improvement compared with the initial Al-1100 strip. On the other hand, the microhardness of Al-1100 and Al-Gr composite also increased to 52 % and 36 %, respectively.