Achieving excellent bond strength and tensile strength synergy of ultrafine-grained Al/Cu bimetallic sheets developed by an innovative hybrid manufacturing process

In the present work, two new parameters that influence the bond strength and tensile strength of Al/Cu bimetallic sheets are explored using an innovative hybrid manufacturing process. The innovative hybrid manufacturing process includes engineering of four different microstructures, 1. Ultrafine grained (UFG); 2. Bimodal grained (BM); 3. Fine grained (FG) and 4. Coarse grained (CG) in parent Cu and Al via integration of cryogenic based thermo-mechanical treatment followed by an unique tailored criss-cross surface pattern generation and high deformation roll bonding to develop high performance Al/Cu engineered sheets with four microstructural combinations: UFG‐Al + UFG-Cu, UFG‐Al + BM-Cu, UFG‐Al + FG-Cu and CG‐Al + CG-Cu. The criss-cross pattern aids in initiation of crack at the junctions and fissure formations at cross paths during the roll bonding process. This kind of pattern develops mechanical bond in the form of nugget bunches, which result in enhancement of bond strength in all the microstructural combinations of Al/Cu bimetallic sheets. The ascending order of increase in bond strength-tensile strength synergy of all four engineered microstructural combinations is: CG‐Al + CG-Cu, UFG‐Al + FG-Cu, UFG‐Al + BM-Cu and UFG‐Al + UFG-Cu. The UFG‐Al + UFG-Cu combination has achieved an extraordinary bond strength of 18 N/mm, which is almost 1.6 times the bond strength of its conventional coarse grained counterpart CG‐Al + CG-Cu combination (10 N/mm). Similarly, the UFG‐Al + UFG-Cu combination showed excellent tensile strength of 323 MPa which is around 25 % higher than that of CG‐Al + CG-Cu combination (258 MPa). The engineered UFG microstructure in Al and Cu samples promote the dynamic recrystallization and partial diffusion kinetics at the interface region and established the mechanical and metallurgical bonding between Al/Cu bimetallic sheets during roll bonding process. The adopted surface pattern and the engineered microstructure have enhanced the bond strength and tensile strength of Al/Cu bimetallic sheets both at macro and micro levels. The underlying scientific knowhow for obtaining excellent bond strength-mechanical property synergy in the engineered Al/Cu bimetallic sheets are established.