Research On The Diffusion Welding Process And Properties Of 6063 Aluminum Alloy Cooling Plate With Surface Nanocrystallization

The cooling plate with narrow passageway has the characteristics of compact structure,complex channel distribution and large welding area.Diffusion welding technology has its unique advantages in cooling plate,which can not only ensure the uniformity of welding,but also effectively control the deformation.Therefore,diffusion welding technology is the key technology of cooling plate connection.In consideration of 6063 aluminum alloy which can be strengthened by heat treatment has excellent advantages,such as strong corrosion resistance,low density,high specific strength and excellent processing formability.In this paper,6063 aluminum alloy with good comprehensive mechanical properties is used as the base metal,and transient liquid phase diffusion welding and solid phase diffusion welding are carried out respectively.The effects of process parameters on the microstructure and mechanical properties of diffusion welded joints was studied.In order to further improve the process of diffusion welding,6063 aluminum alloy was treated by ultrasonic surface rolling processing,and effects of USRP on the microstructure and tensile strength of diffusion welded joints and the connection mechanism of TLP joint were investigated.The results showed that when the heating temperature was 560 ? and the holding time was 60 min,the maximum tensile strength of the TLP joint with pure Cu as the interlayer reached 44.50 MPa;In the solid diffusion welded joint without interlayer,at 540 ? and 100 min,the tensile strength of the joint reached a maximum of 125.7 Mpa,about 91.6% of the tensile strength of the base metal under the same heat treatment condition.With the increase of heating temperature and holding time,the tensile strength of the two types of diffusion welded joints increased first and then decreased within a certain temperature range.After ultrasonic surface rolling treatment,the surface of aluminum alloy became bright and flat,and the surface roughness was reduced from 1.28 to 0.53;the microhardness from the top layer to the core reduced gradiently.Under the action ofalternating loads,the aluminum alloy surface structure undergoes violent plastic deformation due to dislocation movement,causing dislocation tangles and dislocation walls,which promoted the grain refinement to the nanocrystal level finally.Comparing the diffusion welded specimen treated by USRP with not treated by USRP,the surface tensile strength of the nano-TLP joints reached a maximum value of 51.8Mpa at a heating temperature of 560 ?.When the heating temperature of the phase diffusion welding joint was 520 ?,the maximum tensile strength of the joint reached127.36 Mpa,which was about 92.8% of the tensile strength of the base metal under the same heat treatment conditions.The results showed that the nano surface can improve the atomic diffusion coefficient,reduce the diffusion activation energy,and the nanometerization of the grain maked the grain boundary area increase significantly to increase the diffusion channel,so that the joint can be connected at a lower temperature,and the joint performance was better than that of the sample without USRP treatment.