# Accumulative Roll Bonding--A Review
## 4 Properties
### Strength and Ductility
#### 4.1.2 Sheets with Dissimilar Materials  
Based on the search made by the authors, although [PERSON] and [PERSON] [83] first produced ARBed dissimilar materials, the first seminal study on the mechanical properties of ARBed composite sheets seems to be reported by [PERSON] et al. [84], where the mechanical properties of multi-layered Al/Cu composite were investigated. The main goal was to fabricate an ARBed Al/Cu composite with better mechanical properties than those achieved from ARBed Al or ARBed Cu only. Demonstrated in Figure 12, the strengths of both ARBed Al/Al and Al/Cu composites have a striking increase compared to the commercial pure Cu and Al. In contrast, elongation of ARBed samples has considerably decreased compared to pure samples. It was noted that Al/Cu composites demonstrate higher strength than ARBed Al/Al while the elongations are almost the same.  
As seen, the strength varied considerably after each ARB cycle where the variations are controlled by two main strengthening mechanisms; i.e., strain hardening by dislocations and grain refinement. In the early cycles, work hardening was the proponent, while in higher cycles, UFG structure appeared to have a dominant strengthening role. Like other ARBed materials, elongation usually decreases intensively after the first cycle due to the reduced dislocation mobility as well as few shear bands [85]. With an increasing number of cycles after the first cycle, elongation increases due to increase in bond strength between matrix and reinforcement, since the Cu layers act as reinforcement due to their fracture during higher ARB cycles as can be seen in Figure 13. A similar trend in changing strength and elongation during ARB cycles is reported for Al/Ti [86], Al/Zn [87], Al/Ni [88], Cu/Ni [89] and AA1050/AA6061 [90] ARBed composites.  
[PERSON] et al. [91] studied the ARBed Cu/Zr multi-stacks and could achieve an enhanced tensile strength as ARB cycles increased due to microstructural refinement. As shown in Figure 14a, the elongation improved up to six cycles and then decreased with further increase in number of ARB cycles. For those samples processed for less than six cycles, fractography revealed formation of successive cracks along the interface between the Cu and Zr layers due to the inhomogeneous microstructure and strength differences between Cu and Zr. Zr is relatively hard and therefore only Zr layers sustain the  
Figure 12: (**a**) Yield strength and total elongation of Cu, Al, ARBed Al, and ARB Al/Cu composite, (**b**) engineering stress–strain curves for ARBed Al/Cu composite with cycles [84].  
Figure 13: Scanning electron microscope (SEM) micrograph of ARB processed Al/Cu composite cross sections (**a**) primary sandwich, (**b**) 1 st cycle, (**c**) 2 nd cycle and (**d**) 5 th cycle [84].  
external load and thus fracture quickly after the yield point. Different deformation behaviors lead to the separation of dissimilar layers; nonetheless, the mentioned mechanical difference gradually reduces and this considerably postpones final failure. As a result, the elongation moderately increases to reach a maximum value at six cycles. Similar trend has been reported for Al/Zn [92] and Al/Cu/Mn [93]. ARBed composites, however, still further research is required to investigate ARB of dissimilar materials since inconsistent trends are sometimes reported related to the strength and elongation variation [94; 95; 96].