| 4A60 aluminum alloy/08AL steel laminated composite strip which combine relatively high strength and plastic of low carbon steel, and good brazing, heat dissipation of 4A60 aluminum alloy, had a broad application in industrial, household appliances and other fields. In this paper,4A60 aluminum alloy/08AL steel as the research material, the laminated composite strip was produced by "surface treatment-roll bonding-diffusion annealing" three-step cold roll bonding. The influence of surface treatment, the deformation distribution of the aluminum/steel laminated composite diffusion annealing on the bonding strength, the degree of strain hardening and the mechanism of cold rolling bonding was investigated by means of peeling test, tensile strength test, optical microscope (OM), scanning electron microscopy (SEM), energy spectrum analysis (EDS) and X-ray diffraction (XRD). The main conclusions are as follows:1) Research on metal surface pre-treatment process and surface morphology combined with the relationship between strength, microstructure and properties of composite group element layer, optimizing the metal surface pre-treatment process and obtaining an optimal micro-topography of surface to bonding. This paper researched different parameters of surface pre-treatment on composite metal layer (surface roughness, surface micro-topography, grinding times and speed), which had an influence on bonding strength and surface characteristics. Study found that:uneven microstructure on surface in metal composite layer was conducive to metal group element layer forming mechanical occlusion and contributed to subsequent of cold roll bonding; meanwhile, the bonding strength of composite strip increased with increasing of roughness when surface roughness Sa in a range of 1.65um-3.35um; Grinding times were 2～3, speeding was 6～9mm/s and the morphology of steel surface was parallel to the rolling direction which could get a good combination of interface.2) Research on deformation law of laminated composite strip in cold roll bonding, including relationship of reduction and bonding strength of laminated composite strip, each element layer distribution of deformation in cold rolling process. It came to a conclusion that the initial reduction of bonding and the minimum stable reduction of bonding of 4A60 Al/08Al St laminated composite strip was 15% and 50% by method of numerical simulation, and the numerical simulation results was correct through experimental verification. Through research of deformation distribution found that the deformation distribution of steel and aluminum existed inconsistencies in process of cold roll bonding (CRB). and with increasing of reduction, the deformation of Al/St also increased, but the deformation of deviation value between aluminum layer and the steel layer was decreased and remained stable ultimately, the deformation of aluminum and steel conformed to be consistent finally.3) Study the changes in microstructure and properties of laminated composite strip by cold rolling process, and characterized by metal hardness, grain size and mechanical properties of changes. Experimental results showed that with increasing of reduction, composite bonding strength and steel surface roughness increased when composite rolling reduction in a range of 25%～60%, steel surface roughness Sa attained to 4um, interfacial shear strength achieved 56Mpa when reduction reached to 60%. At the same time, the micro-hardness of mental increased significantly because of severe work hardening of internal metal, and hardness changes accorded with Boltzmann equation.4) Study on the aluminum/steel composite heat treatment process, explored influence of rolling reduction, annealing temperature and annealing time on composite bonding strength, organization and performance. The results showed that heat treatment produced metal elements diffusion between composite layer, so that the interface could form firmly metallurgical bonding; annealing time had a little effect on elements diffusion region, and the diffusion region formed a "platform" area of about 3.5um width, the area of intermetallic compound was Fe2A15 phase and a small amount of metal phase was Fe4A113; composite optimal annealing process system was 520℃ 24h for reduction of 50%.5) Metallography and SEM images were observed through experiment in the rolling process, a preliminary study of main mechanism for 4A60 Al/08AL St in cold roll bonding was the theory of three stages, including mechanical occlusion, energy theory, film mechanism, diffusion theory and a variety of binding mechanism of interaction. |
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