Study On Low-temperature Diffusion Bonding Of TC4/1060Al And Properties Of Bonded Joints

Titanium and titanium alloy are widely used in industrial field due to its high strength, good corrosion resistance and high heat resistance properties. Aluminum and aluminum alloy also have board applications because of its good electrical conductivity, small density and good machining performance. Therefore, It is meaningful to realize the welding of titanium alloy and aluminum alloy.However, it has been reported that welding titanium alloy and aluminum alloy exists some technical difficulties. Firstly, the welding temperature must stay high to form effective bonded joint because of the surface oxide layers of base alloys. Secondly, the weldability of titanium alloy and aluminum alloy is poor. The mechanical properties of welded joints under high temperature will be extremely weakened because of the generation of large amount of brittle intermetallic compounds. In this paper, industrial commonly brand alloys- TC4 titanium alloy and aluminum alloy 1060 was chosen as base materials. In order to solve the welding problems above, this research focused on the influence of surface treatments before welding, diffusion welding parameters and the Al thin film interlayer introduced by magnetron sputtering on the microstructure, mechanical properties and diffusion mechanism of TC4/1060 Al bonded joints.Research results showed that TC4/1060 Al bonded joint with high shear strength could be prepared under low temperature of 400 °C after surface polishing treatments before welding. The fine polishing process could effectively reduce the thickness of oxide layer on the base materials and made the bonding of TC4 and 1060 Al at low temperature possible. What's more, no large amount of brittle intermetallic compounds could be detected by SEM, EDS and TEM in TC4/1060 Al bonded joints fabricated under low temperatures. TC4/1060 Al bonded joints prepared by different surface polishing treatment had different mechanical properties. The shear strength of TC4/1060 Al bonded joint increased with the increase of the mesh of polishing abrasive paper.Under the optimal condition of surface polishing treatments, welding parameters(welding temperature, welding pressure and holding time) had great influence on microstructure and mechanical properties of TC4/1060 Al diffusion bonded joint. Shear strength of TC4/1060 Al bonded joint increased initially and then tended to be constant with the increase of welding temperature and welding pressure. The shear strength of the joint increased initially and then decreased with holding time increased. The optimum welding parameter was 410 °C-10 MPa-120 min and the maximum shear strength is 74.7 MPa, which was as high as the shear strength of 1060 Al base material.The addition of Al film interlayer by magnetron sputtering further lowered the TC4/Al/1060 Al diffusion bonding temperature and improved the shear strength of the bonded joints. Compared with the TC4/1060 Al diffusion bonded joint, The shear strength of TC4/Al/1060 Al diffusion bonded joint increased from 53.2 MPa to 66.5 MPa, increased by 25%. What is more, the fracture mode was ductile fracture, and the micro-holes of the bonded joints disappear significantly. The fracture place occurred in 1060 Al base material. The microstructure of fracture surface showed that more plastic deforms was conducive to the mechanical properties of bonded joints. The formation of TC4/1060 Al and TC4/Al/1060 Al bonded joints under low temperature can be divided into 3 stages: large initial effective physical contact, formation of element diffusion layer at low temperature and slowly diffusion process.