Accumulative Roll Bonding And Interface Behavior Of Steel-Al Ultra-Thin Strips

Steel-Aluminum multilayer composite fabricated by solid phase operation is a typical metallic composite that combines the fine performances of the two elementary materials.Applying Accumulative Roll Bonding(ARB)on Steel and Aluminum ultra-thin strips can not only induce the metallically connection and solid phase diffusion between steel and aluminum with repeatedly strong rolling force,but also refine the interface structure with superimposed severe plastic deformation.It is a new method for fabricating low-density ultra-thin steel-based strips.In this paper,the chief of original work and results are as follows:(1)Cold Roll Bonding(CRB)experiment is carried out on the independently designed micro-forming mill,where combined forming conditions can be achieved.Six layers of Q195 ultra-thin strips with the thickness of 24 μm and five layers of 1060 ultra-thin strips with the thickness of 16 μm are alternatively stacked together as the raw material.Following on,the composite strip is ARBed under room temperature for seven passes without intermediate annealing.By comparing the strip shapes and compound strength,it is found that in the initial CRB pass,with the prepressed load of 50 kN of negative roll gap,Fe-Al interfaces gained good connection.In the followed ARB passes,increasing 5kN between the passes can make the composite strip to achieve fine bonding,meanwhile the composite remained good shape.Edge cracks continually extend to the center of the composite strip,thus the ARB process lasted for eight passes in total;(2)Interface structures and component distribution of Fe-Al composite under different passes are observed.Steel and Aluminum ultra-thin strips achieved interface connection via thin film mechanism.Multilayer interface structure showed an evolution of "stacked layers—continuous fibers—chaos fragments”.Every bonding passes lead the steel layers to neck down and tear apart,inlaying steel layers into Aluminum layers.Fe-Al interface moves into Steel layers,and increases with the increase of the rolling passes.Diffusion layer remains a thickness of 2～3μm,thus more and more elementary metal is mixed on the interfaces,making the equalization of the composite strip to grow.Aluminum atoms on the interfaces achieved deformation induced solid diffusion,the diffusion coefficient is D7passes=1.49×10-9 cm2/s;(3)Composite interface structure’s effect on tensile strength and breaking mechanism is analyzed.For specimens under the first and second passes,their axial tension is mainly loaded by the continuous steel layers.For specimens after the third pass,with the steel layers cracked down,their axial tension is mainly loaded by Aluminum layers.Multilayer composite after second pass has the largest tensile strength,which is 352 MPa.Multilayer composites under different passes show different crack ways under axial tensile tests,because their different interface structures.For composite under the first pass,tensile crack is dominated by the defects on the interfaces.For composite under the second pass,tensile crack is dominated by the ductile fracture of steel layers.For composite under the fourth pass,tensile crack is dominated by the ductile fracture of Aluminum layers.