Interface transition zone and the interface influence zone are critical factors in determining the interfacial bonding strength and ductility of heterogeneous metallic laminates. In this study, an innovative process—“cold spraying + pulsed current rolling”—is proposed for fabricating Mg/Al laminates, significantly enhancing both interface strength and ductility. Notably, the average interface shear strength achieved is three times that of conventional hot rolling, reaching 70.7 MPa, while the interface shear strain increases from 3.4 % to 28 %. The high-velocity impact of cold-sprayed aluminum particles on Mg and Al substrates forms a three-dimensional interface, effectively expanding the interfacial bonding area and refining the interfacial microstructure. The fine-grained coating structure produced by cold spraying acts as a primer, facilitating the formation of a nanocrystalline interface during pulsed current assisted rolling. The interface comprises an ultrafine nanocrystalline Al coating with grain sizes around 30 nm and β-phase nanotwins approximately 300 nm in scale, significantly enhancing the interfacial bonding strength. Together with the Mg and Al substrates, the nanocrystalline transition layer forms a layered gradient transitional structure that evolves into a 50-µm-wide interface-affected zone during deformation. This unique feature promotes strain delocalization, effectively mitigates strain concentration at the interface, and improves its fracture toughness. Additionally, the nanocrystalline interface increases the grain boundary area, promoting atomic diffusion and strengthening metallurgical bonding both between the coating and the substrate and within the coating itself. The “cold spraying + pulsed current rolling” process offers a straightforward approach to fabricating laminated nanostructured transition layers, demonstrating great potential in the interfacial design of heterogeneous materials.

In this study, the cold-spraying process was utilized to deposit Al particles onto an Al slab, an Mg slab, and both Al and Mg slabs to form an ultra-thin interlayer, and then the clad slabs were rolled at 400 ℃, developing three roll-bonding processes: the roll-bonding process with cold-sprayed Al powder on the Al slab (CS-Al), the roll-bonding process with cold-sprayed Al powder on the Mg slab (CS-Mg), and the roll-bonding process with cold-sprayed Al powder on both the Al slab and the Mg slab (CS-Both). The effects of three different cold-sprayed Al particle interlayer processes on the mechanical properties of rolled Mg/Al clad plates were investigated to improve the mechanical properties. The microstructure, texture evolution, intermetallic compound formation, mechanical properties, and mechanisms involved in the Mg/Al clad plate rolling were systematically investigated. The results showed that the pre-bonding between the particles and the substrates through cold-spraying had a significant impact on the bonding strength of the Mg/Al clad plates, and the CS-Both process can increase the average shear strength of the Mg/Al clad plates to 49.24 MPa at a medium reduction rate of 37.5 %, 2.5 times that of the conventional rolling process. The CS-Both process constructed more evident dual microscopic three-dimensional interfaces and promoted more thorough atomic diffusion at the interface through the double-sided cold-spraying process. Meanwhile, the dual cold-sprayed Al coatings on both the Mg slab and Al slab underwent dynamic recrystallization during rolling to form a homogeneous unit with no additional coating interfaces. Fine grain strengthening and dislocation strengthening were judged to be important mechanisms for improving the mechanical performance of the interfacial layer.

Innovative pulsed current-assisted multi-pass rolling tests were conducted on a 12-roll mill during the rolling deformation processing of SUS304 ultra-thin strips. The results show that in the first rolling pass, the rolling reduction rate of a conventionally rolled sample (at room temperature) is 33.8%, which can be increased to 41.5% by pulsed current-assisted rolling, enabling the formation of an ultra-thin strip with a size of 67.3 μm in only one rolling pass. After three passes of pulsed current-assisted rolling, the thickness of the ultra-thin strip can be further reduced to 51.7 μm. To clearly compare the effects of a pulsed current on the microstructure and mechanical response of the ultra-thin strip, ultra-thin strips with nearly the same thickness reduction were analyzed. It was found that pulsed current can reduce the degree of work-hardening of the rolled samples by promoting dislocation detachment, reducing the density of stacking faults, inhibiting martensitic phase transformation, and shortening the total length of grain boundaries. As a result, the ductility of ultra-thin strips can be effectively restored to approximately 16.3% while maintaining a high tensile strength of 1118 MPa.Therefore, pulsed current-assisted rolling deformation shows great potential for the formation of ultra-thin strips with a combination of high strength and ductility.

This review presents a thorough survey of the roll bonding process with a focus on the bimetallic bars/tubes as well as the bonding models and criteria. The review aims to provide insight into cold, hot and cryogenic bonding mechanisms at the micro and atomic scale and act as a guide for researchers working on roll bonding, other joining processes and bonding simulation. Meanwhile, the shortcomings of roll bonding processes are presented from the aspect of formable shapes, while bonding models are shown from the aspect of calculation time, convergence, interface behavior of dissimilar materials as well as hot bonding status prediction. Two well-accepted numerical methodologies of bonding models, namely the contact algorithm and cohesive zone model (CZM) of bonding models and in simulations of the bonding process are highlighted. Particularly, recent advances and trends in the application of the combination of mechanical interlocking and metallurgical bonding, special energy fields, gradient structure, novel materials, green technology and soft computing method in the roll bonding process are also discussed. The challenges for advancing and prospects of the roll bonding process and bonding model are presented in an attempt to shed some light on the future research direction.