| A hybrid of RSW and adhesive bonding,weld-bonding is an innovative and promising hybrid joining technology,as it has excellent dynamic and static bearing capacity,especially sealing properties.In this paper,1.5 mm thick DP590 dual-phase steel was used as the research material,and its weld-bonding process was studied.The statics and microstructure characteristics of spot welded and weld-bonded joint were compared.The influence of spot welding process parameters on the process of weld-bonding was analyzed through simulation analysis.The orthogonal test of spot welded and weld-bonded joint was designed respectively,and the mechanical properties of two kinds of joints were studied.Double pulse current mechanism was used in weld-bonded joint.The results showed that the optimal welding parameters of double pulse weld-bonded joint are as follows: the primary welding time is 80 ms,the primary welding current is 12 kA,the cooling time is 40 ms,the secondary welding time is 60 ms,the secondary welding current is 12 kA,and the electrode pressure is 0.3 MPa.The maximum average shear strength of spot welded and double pulse weld-bonded joints was 9521.7 N and 9921.4 N,respectively.And their energy absorption values were 78.91 J and 126.20 J respectively.The metallographic analysis showed that the double pulse weld-bonded joint had larger nugget diameter compared with the spot welded and the single pulse weld-bonded joint.The nugget area of weld-bonded joint was composed of lath martensite.The maximum hardness of the weld nugget zone of double pulse weld-bonded joint was 249.4 HV.The experiment proved that the introduction of double pulse current weld-bonding technology can effectively improve the mechanical properties of joints.The failure modes and fracture analysis of the weld-bonded joints were carried out by means of SEM scanning electron microscope.The results showed that the fracture surface of weld-bonded joint showed a lot of dimple characteristics,indicating that thejoint had ductile fracture.During the failure process of weld-bonded joint,the adhesive layer occurred brittle fracture firstly due to the weak deformation resistance of the adhesive,and then the weld nugget was loaded individually until the joint was completely invalid.Therefore,the load-displacement curves of the weld-bonded specimens show two peaks.The first peak corresponds to the brittle fracture of the adhesive layer,and the second peak corresponds to the failure of the welding zone.A simulation model of spot welded and weld-bonded joint was established,and the evolution characteristics of temperature field of spot welded and double pulse weld-bonded joint in forming process of joint nugget were analyzed.The results showed that the nugget was initially formed on the contact surface of the two plates,and then extended to two directions,transverse and radial.Compared with the single pulse joint that had only one growth period,the nugget of double pulse weld-bonded joint experienced two growth periods.Compared with single pulse joint,the double pulse weld-bonded joint had more heat supply,making it had a larger nugget diameter.A scanning acoustic microscopy was used to detect the spot welded joint and the ultrasonic A scan signal and C scan image of joints were studied.The relationship between the spectral amplitude of ultrasonic A scan signal of joints under different welding process and its mechanical properties was analyzed.The results showed that when the maximum value of the amplitude of the spectrum increases slowly,the shear strength of the corresponding joint will also increase.When the maximum value of the amplitude of the spectrum increases dramatically,the welding spatter which leads to a drop in the welding quality of the joint is generated for the corresponding joints. |
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