| Multilayered metal composite material is a new type of metal composite material that is made of two or more different sheet metal through the composite technology. Through rational design, it can be made full use of advantages of component materials to meet with industrial application.In this article, hot roll-bonding was used to produce composite sheet with the stacking order 6061/AZ31/Ti6Al4V/AZ31/6061. Analysis techniques like optical microscope(OM), micro-hardness test, tensile machine, scanning electron microscope(SEM), X-ray diffraction(XRD) and so on were used to analyze mechanical properties of composite sheet, strength of bonding interface and its bonding mechanics and fracture mechanics.The results show that due to the deformation go deep into the mid of composite sheet when the total deformation reaches 40% or more, Ti6Al4 V layer become to neck or fracture. When the roll-bonding temperature reaches to 450°C, the intermetallic compound, Al3Mg2, occurs. The place it is formed happens to fracture during tensile-shear test. So this is adverse to the strength of bonding interface. By analyzing the mechanical property of composite sheet and bonding strength of two kinds of interface, roll-bonding conducted under 400°C with reduction of 30% is the premium process to get a composite sheet with good comprehensive strength. The fracture place of these two kinds of interface is in the diffusion region of atoms and the fracture is brittle. Due to the additional shear strain is generated near the interface in the AZ31 layer, grains in this area is smaller than other place. However, the inhomogeneous is reduced with the increasing of roll-bonding temperature.The intermetallic compounds is going to appear with the increase of annealing temperature. Al3Mg2 is formed near 6061 layer when the annealing is conducted under 300°C for 1h. As the annealing temperature increase to 400°C and hold for 1h, two main kinds of intermetallic compounds is formed in the interface of 6061/AZ31, which Al3Mg2 is formed near 6061 layer and Mg17Al12 is formed near AZ31 layer. The place which these two kinds of intermetallic compounds are formed is going to fracture during tensile-shear test. This is harmful to the bonding strength of the interface. When the annealing is conducted at 200°C, there is no intermetallic compound formed in the interface of 6061/AZ31. The bonding strength of it is relative higher than the interface which intermetallic compound is formed. It fractures at the diffusion zone of atoms. In the AZ31/Ti6Al4 V interface, there is no other phase formed during annealing at different temperature. The strength of it increases with the increasing of temperature and the place fracture happens during tensile-shear test is moved from the interface diffusion area to AZ31 matrix. When the annealing temperature reaches to 400°C, the fracture occurs in the AZ31 matrix. However, fracture characteristic of the interface in sheet is still brittle. From the point of view on the integrity of composite sheet and the strength of two interfaces, the annealing of the sheet should be conducted at a relative low temperature.There is no new phase which is harm to the strength of bonding interface coming into being when the annealing was conducted at 200°C and the strength of two kinds of interface increase with the increasing of annealing time. The fracture place of 6061/AZ31 interface is moved from the diffusion area of atoms to AZ31 matrix. Also, the failure place of AZ31/Ti6Al4 V interface migration from diffusion zone of atoms to AZ31 matrix. The failure of the interface obtained through annealing for different times at 200°C is also caused by tearing which is a characteristic of brittle fracture. By analyzing the strength of the composite sheet comprehensively, annealing process of sheet should be set at a low temperature for a long time to obtain a good integrated strength. |
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