Study On Magnetic Pulse Form-fit Of 6061 Aluminum Alloy-45 Steel Tubes Based On Flat Coil

The lightweight high-strength material is used to realize the light weight of the automobile instead of the traditional steel material.Magnetic pulse form-fit technology is a reliable technique for realizing connection by plastic deformation,especially for dissimilar material tubes connection.Conventional magnetic pulse crimping requires the use of coils and field shapers that mate with tube diameters,or multiple field shapers of different diameters,which increases manufacturing costs,complicates the connection process and reduces the production efficiency.A new method of magnetic pulse form-fit based on flat coil is proposed in this paper.By means of numerical simulation,process test,mechanical property test and micro-analysis,the torsion joint of 6061 aluminum alloy-45 steel is systematically studied.The main research contents are as follows:Firstly,the magnetic pulse form-fit joint numerical model is established by combining the BEM and FEM,and the characteristics of the electromagnetic field and the structure field are analyzed.The influence of different groove depths,groove edge radii,discharge energies for outer tube deformation degree and the fittability of inner and outer tube are investigated using single variable method.The results show that the induced eddy current and the electromagnetic force of the outer tube are distributed symmetrically about the axial symmetry plane of the coil.The current density on the outer tube gradually becomes smaller in the thickness direction of the wall,wherein the current density on the cell near the coil is large.In the connecting region,the electromagnetic force exerted by the outer tube at the center of the groove is the largest,and the deformation is also the largest;In the non-connecting region,the outer tube does not deform,and the electromagnetic force of the outer tube free end is maximized at a position close to the groove,gradually decreasing in the direction away from the groove.The maximum value of the electromagnetic force in the non-connected region is greater than the maximum value of the electromagnetic force in the connecting region.The deformation of the outer tube is symmetrical about the center line of the groove on the radial cross section.The embedding rate and the connecting rate of the outer tube are positively correlated with the discharge energy and the edge radius of the groove,and there is a negative correlation with the depth of the groove.When the embedding rate of the outer tube reaches about 80%,the innerwall of the outer tube begins to contact the bottom of the groove,and then increases with the embedding rate of the outer tube,and the connecting rate of the inner and outer tube is increased rapidly,so that the fittability of the inner and outer tubes is better.Secondly,according to the result of numerical simulation,the process tests of the torsion joint of different groove depths,groove edge radii,discharge energies and groove numbers are carried out,then the torsion performance tests of joints are carried out under quasi-static state.The results show that two failure modes occur: the outer tube is twisted out and the parent metal of the outer tube fails.The single groove strength of the joint is positively correlated with the discharge energy and the depth of the groove,and there is a negative correlation with the edge radius of the groove.When the discharge energy is 16 kJ,the depth of the groove is 3mm,and the radius of the groove edge is 0 mm,the strength of the single groove of the joint is the largest,which reaches 27.53% of the strength of the base material of the outer tube;And when the discharge energy is 14 kJ,the depth of the groove is 1mm,and the radius of the groove edge is 0mm,the torsional strength of the single groove of the joint is minimized,reaching 11.41% of the strength of the outer tube mother material.The increase in the number of grooves hardly changes the single groove strength of the joint but increases the overall strength of the joint.At last,the macro-microscopic analysis of the deformation,shearing and local necking at different positions of the outer tube is carried out.The failure mechanism of joint is revealed by combining the results of the simulation and mechanical test.The results show that the actual deformation of the outer tube is in good agreement with the numerical simulation results.The shearing rate of the outer tube is always greater than the local necking rate.And the greater the deformation of the outer tube,the more the outer tube shears and necks,the greater the difference between the shearing rate and the local necking rate.This is due to the severe plastic deformation of the outer tube material on the shearing and local necking zones,and the extent to which the grain is elongated in the shearing zone is much higher than the local necking zone.When the discharge energy is too large,cracks appear on the local necking region.The failure mechanism of the joint is found to be positively correlated with the shearing rate and the deformation angle of the outer tube in the case of the failure mode being twisted out of the outer tube,and there is a negative correlation between the relative rotation angles of the inner and outer tubes before and after the torsional failure.