| The aluminum/steel composite structure takes full advantage of the lightweight features of aluminum and aluminum alloys and the strength and cost advantages of high-strength steel,so it has been applied in many fields such as automobiles,marine,aerospace,and chemical industries.Compared with any fusion welding method,continuous drive friction welding has its unique advantages as a solid-phase joining technology for welding dissimilar metals with rotating interfaces.However,so far,the inhomogeneity of the friction interface structure and the difference in the mechanical properties of the joint are the key issues that restrict the continuous drive of aluminum/steel friction welding composite connection.In this paper,the performance and structure of the continuous drive friction welded joint of pure aluminum 1060/Q235 low carbon steel were studied,and the degree of influence of the process parameters on the mechanical properties of the joint was determined through orthogonal experiments.The effects of different process parameters on the mechanical properties and microstructure of the joint were analyzed by single factor variable experiments.The results show that the joint has the best comprehensive mechanical properties under the mechanism of"top first and then brake",which is 1500 r/min speed,30 MPa friction pressure,1 s friction time,80 MPa pressing pressure,1 s pressing time,and the pressing pressure has the greatest effect on the tensile strength of the joint.The fracture mode of the joint is a mixed fracture mode of quasi-cleavage fracture+plastic fracture.There is an"arc"tearing weak morphology in the tensile fracture of the slice,which is the boundary line of the fracture morphology of two regions with different mechanical properties.In order to further improve the unevenness of the friction interface structure,five types of conical Q235 low carbon steel rods at 5°,10°,15°,20°,and 25°were paired with 1060 aluminum rods performed with continuous drive friction welding butt joint experiments.These collected the temperature of the interface center as well as 1/3R and 2/3R during the welding process.After welding,the joints were subjected to tensile testing,fracture analysis,and microstructure analysis of the joint interface.The results show that presetting the taper on the joint will change the thermodynamic cycle of the interface in the direction of the rotating friction radius and affect the structure and joint mechanical properties.As the cone tilt angle increases,the overall temperature of the joint decreases,and the highest peak temperature area shifts from 2/3R to 1/3R.The results show that under the same process parameters,the increase in the tilt angle of the conical end face makes the corona bonds of the friction interface of the joint move from the outside to the inside due to a decrease in friction heat and increase in tangential stress;the corona bonds become narrower.Under certain technological conditions,a reasonable cone can improve the homogenization of the radial intermetallic compounds at the joint interface.Here,the thickness of intermetallic compound layer of the 15°tilt angle joints has the smallest gradient along the radius.The average thickness was about 0.85?m and the average tensile strength reached a maximum of 77.5 MPa.This is 96%of the base material of 1060 pure aluminum.At the same time,the IMCs layer at the same position is composed of several different compounds arranged in sequence including Fe Al close to the steel side,Fe2Al5 close to the aluminum side,and Fe Al2 between them.In order to further expand the application of aluminum/steel continuous drive friction welding,and provide ideas and methods for strengthening and toughening joints,carried out two cycles(30 d/60 d)thermoelectric coupling test(static load 40kg+high temperature 300?+DC 60 A),the evolution behavior of the structure and structure of the welding interface at different times was obtained,and the influence of thermoelectric coupling on the structure change and bonding strength was studied.The failure behaviors at different positions of the interface are analyzed through fracture observation.The thickness of the radial IMCs layer of the original joint interface is not uniform,and there is no obvious IMCs formation in the central area.After 30 days of thermoelectric coupling,an IMCs layer with a width of 0.3-0.5?m at the center of the interface is formed,which is dispersed from the steel side to the aluminum side in a granular form,the overall tensile fracture is in the thermal influence zone of the aluminum base metal.After 60 days of thermoelectric coupling,a corrosion groove appeared between the IMCs layer and the steel side,IMCs are broken,and no cracks are generated on the steel side,a large number of cracks and cavities from the IMCs layer to the inside of the aluminum base metal are formed on the aluminum side,segregation of components at the weld and crack tip,and the overall tensile fracture at the weld.The speed of interfacial corrosion and crack growth is proportional to the thickness of the interface IMCs layer,namely?(center)<?(1/2R)<?(2/3R).Due to the uneven structure of the original joint interface and the difference in organization growth efficiency at different positions of the interface during the thermoelectric coupling test,the inner side of 2/3R is dominated by quasi-cleavage fracture,and the outer side of 2/3R is the combined result of dimple fracture and quasi-cleavage fracture. |
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