| The melting points of copper and aluminum are different greatly,and the defects such as oxidation,a large number of brittle phases,voids and so on are easy to appear in the traditional joining technology.In this paper,the friction stir bonding technology is used to realize the connection between industrial pure aluminum/T2 copper and industrial pure aluminum/Zn foil/T2 copper.The effects of process parameters on weld shape,microstructure and mechanical properties of joint interface are analyzed.The interface microstructure growth behavior of copper/aluminum joint bonded with Zn foil was studied.Friction stir welding is used to realize the connection of copper/aluminum by lap welding,other parameters are fixed,only the welding speed or the rotation speed or lower pressure of the stirring head is changed,the weld surface is formed,the tunnel defect in the cross section of the weld,the microstructure of the interface transition layer and the thickness of the Al2Cu intermetallic compound layer formed by the copper interface change obviously.When the welding speed is 65mm/min,the rotation speed of the stirring head is 775rpm,the inclination angle of the stirring head is 1.5°and the stirring head drop 0.1mm,the maximum shear strength of the sample is 2.13k N.Copper/aluminum friction stir connection was carried out by adding Zn foil between copper plate and aluminum plate,and the effects of main process parameters on the microstructure and properties of the joint were studied.On the basis of the parameters without Zn foil,the rotation speed of the stirring head needs to be increased by nearly 300rpm in order to obtain a weld with better macroscopic shape.The tunnel defect in the cross section of the joint changes with the welding speed,the rotation speed of the stirring head,the thickness of Zn foil and the pressure under the stirring head,but it is not significant enough.The combination of parameters is as follows:the welding speed is 65mm/min,the rotation speed of the stirring head is 1475rpm/min,the thickness of Zn foil is 0.1mm,the stirring head drop 0.1mm,and the maximum shear strength of the sample is 2.04k N when the inclination angle of the stirring head is 1.5°.The horizontal hardness curve of the copper side on the cross section of the joint shows a"W"shape,but the microhardness of the joint is higher than that of the copper/aluminum friction stir welded joint without Zn foil.After heating and heat preservation treatment of the copper/aluminum joint with Zn foil,it is found that the microstructure of the transition layer at the interface grows or evolves,which is typically represented by the increase of the thickness of Al2Cu intermetallics,and the increase of temperature is easier to transform to Al4.2Cu3.2Zn0.7intermetallics.When the annealing temperature is 300?,350?and 400?respectively,the maximum load of the specimen against shear fracture decreases with the extension of holding time,especially at 400?.The results show that the interfacial structure is sensitive to temperature,and the higher temperature is more likely to lead to the significant decrease of mechanical properties.In the fracture morphology,the tear edge is narrow and the area is small,which fully proves that the strengthening phase on the fracture interface grows up due to heating and heat preservation,weakens the strengthening effect,reduces the ability to resist fracture in the shear test,and breaks under the action of low shear force. |
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