Research On Roll Bonding Process Of Titanium-7A52Aluminum Alloy Clad Sheets

Due to its many advantages, such as low weight, high strength, high stiffness, wear resistance, titanium-7A52aluminum alloy clad sheets is widely used as aircraft skin and other components. Due to low cost, simple operation, high efficiency, environment friendly, etc, roll bonding technology is one of the most commonly methods to produce composite sheets in the present.In the experiment, producing composite sheets follows the "surface treatment-roll bonding-heat treatment" three steps method. Effect of roll bonding parameters and heat treatment processing on the bonding strength was measured by peeling test. By using scanning electron microscope (SEM) to observe the samples’bonding interfaces and peeled fractures, the roll bonding mechanism of the two different materials was analyzed and discussed. In purpose of analyzing the characteristics of roll bonded interface and its variation regulation during the heat treatment process, scanning electron microscope (SEM) and energy spectrum analysis (EDS) were used. The main results are followed:1.Because of the high critical deformation, it is hard to roll bonding when the temperature is below300℃. Rolled at450℃, the composite sheets are over-oxidation and the shape is not good. Titanium-7A52aluminum alloy can be roll-bonded from300℃to400℃with the reduction between40%to60%.2.At the fixed temperature level, the bonding strength is significantly increased with the increase of reduction. At the fixed reduction level, the bonding strength is higher at the lower temperature. So the temperature of300℃and the reduction of47%are the optimized rolling process parameters.3.Roll-bonding strength could be increased significantly by heat treatment. The bonding strength of samples that roll-bonded at the temperature of350℃with reduction of47.8%could be increased from56MPa to72MPa by annealing at470℃for24h. The bonding strength of samples that roll-bonded at the temperature of300℃with reduction of60%is73MPa.That is means that the strength of the samples bonded at300℃with the reduction of60%could meet the requirement. 4.Temperature range of380℃～580℃, titanium and aluminum are diffusing species in the Ti-Al system and TiAl3is the only compound observed in the experiment. With increasing temperature there is a change in the mechanism of TiAl3growth between500℃and550℃from diffusion-controlled to interface reaction limited kinetics. The parabolic growth of TiAl3is dominated by grain boundary diffusion at the temperature of500℃. The linear growth of TiAl3is dominated by interface reaction at the temperature of550℃. From the temperature of500℃to550℃, the growth of TiAl3is more complex. Kinetics calculation results of TiAl3indicate that the thickening of the layer is dominated by grain boundary diffusion and interface reaction.