| Continuous drive friction welding(CDFW)has been applied in the electrolytic aluminum industry to connect the aluminum guide rod and steel claw of anode guide rod by virtue of its remarkable advantages in the connection of dissimilar metals.However,in practical applications,the guide rod needs to withstand complex working conditions such as thermal cycling and alternating current.Due to the significant differences in thermal physical properties of aluminum and steel,the welding interface needs to withstand alternating loads caused by thermal stress caused by thermal mismatch.Moreover,the distribution of intermetallic compounds(IMCs)at the interface of CDFW joints is uneven along the radial direction,resulting in defects such as voids,cracks,and necking.The structural design of joint is an important technological measure of continuous drive friction welding.By changing the end face structure,the thermal stress distribution of the joint in complex working conditions can be changed,the phenomenon of stress concentration at the joint interface can be improved,and the negative impact of thermal stress on the joint can be reduced,so as to improve the service reliability of the joint.Based on this,this article takes 1060 pure aluminum and Q235 low-carbon steel as the research objects,and combines the weak positions of the joint found in the previous thermal mechanical coupling experiments.Different sizes of concentric rings are designed on the end face of the steel bar to be welded.ABAQUS is used to establish thermal mechanical coupling experimental simulation models for each joint,and the influence of ring size on the stress strain distribution and temperature field of the joint is analyzed,and the optimal ring size is obtained.The influence of structural design on the thermal mechanical coupling of aluminum/steel continuous drive friction welded joints was studied by comparing and analyzing the actual thermal mechanical coupling experimental results.The main research content and achievements are as follows:Six types of concentric ring sizes with different diameters and heights were designed.ABAQUS finite element simulation software was used to establish a numerical simulation model for thermal mechanical coupling experiments of planar and concentric ring joints.The distribution patterns of stress,strain,and temperature fields of each model were studied.The results indicate that the cooling process is the main period for the generation of thermal stress in the joint,and the presence of concentric rings inhibits the lateral transfer of heat at the interface,resulting in a lower rate of temperature change at the interface within the rings than at the planar joint;And the ring constrains the deformation of Al,changing the distribution of thermal stress on the Al side,so the deformation of the concentric circular ring joint is smaller and there is no necking phenomenon;The cumulative plastic strain of planar joints is concentrated on the outer periphery of the interface,while concentric ring joints are mainly concentrated on both sides of the chamfer at the top of the ring.Comparing the simulation results of six concentric rings,it was found that the higher the ring height,the larger the stress distribution area;The larger the diameter,the greater the deformation on the outer side of the aluminum rod,and the smaller the cumulative plastic strain;At the same time,all six models generated stress concentration in the area about 8mm away from the interface center on the Al side,and the smaller the diameter and height of the circular ring,the higher the stress;The equivalent plastic strain distribution cloud maps of each concentric ring joint are almost the same.Comparing the strain of the two key nodes,the strain on the outer circumference of the interface decreases as the diameter increases.After comprehensive consideration,the ring size of Model 3 with a diameter of 17-21 mm and a height of 2mm was selected for subsequent experiments.Welding experiments were conducted on concentric ring joints and planar joints.The dynamic torque during the welding process was calculated using the main motor stator voltage current method.Post weld analysis shows that the concentric ring structure hinders the flow of some plastic metals during the welding process,affecting the formation of flash edges.The curl of flash edges is less than that of planar joints,and the maximum tensile strength of the overall tensile test is similar to that of planar joints,but fracture occurs at the interface;The IMCs distribution thickness at the plane joint interface shows a gradually increasing trend from the center to the circumference,while the IMCs at the concentric ring joint interface are mainly concentrated at the top of the ring,and are rarely present in other areas.The interface behavior of the planar joint and the concentric ring joint under the action of thermal-mechanical coupling(temperature 60 ℃ ～ 500 ℃ & static load600N)was studied.The planar joint has been tested for 720 h,that is,240 cycles,and the concentric ring joint has been tested for 240 h,480h,720 h and 900h(macro cracks appear).The comprehensive analysis of the interface microstructure and fracture shows that the inhomogeneity of the interface microstructure of the planar joint leads to the uneven distribution of IMCs along the radial direction,which leads to irregular changes in the fracture morphology.A crack vertical to the interface appeared in the center of the interface,and the fracture form was mainly a mixed fracture of ductile fracture and cleavage fracture;discontinuous IMCs were formed from the center of the interface to the inner side of the "ring",and ductile fracture and cleavage fracture of Al metal mainly occurred;The IMCs at the "circle" position are evenly distributed in a "strip shape",and cleavage fracture mainly occurs.It shows that under the thermal-mechanical coupling,the center of the interface and the "ring" position where hard and brittle IMCs exist are weak areas,which are easy to affect the reliability of the joint.However,no obvious defects were found in the concentric ring joint at 240 h.At 480 h,small holes appeared on the Al side of the joint center.At 720 h,the small holes had increased,and obvious cracks appeared at the chamfers on both sides of the top of the ring.At 900 h,the hole at the joint 0R has expanded and grown to form a crack,and the crack at the chamfer of the ring has also expanded further.It shows that these holes and cracks all nucleate and grow on the Al side with the experimental accumulation,and the growth direction is parallel to the interface.During this process,the interface between 1/2R and the top of the ring is still well connected.The0.68R-0.84 R "replaces" the position of the weak zone of the planar joint,the fracture form is ductile-brittle mixed,and the interface strength is higher.The difference in the crack growth direction indicates that the concentric ring structure changes the main driving force of the crack growth.The main driving force of the crack in the planar joint is the thermal stress parallel to the interface generated by the temperature cycle,while the main driving force of the crack in the concentric ring joint is the axial static load force. |
