| With the higher fuel standards and the environmental protection consciousness enhancement,the lightweight materials of aluminum alloy and high strength steel will be used widely in automotive manufacturing.A5052 aluminum alloy that is high strength,strong corrosion resistance,easy machining and good weldability,is suitable for application in lightweight cars.DP 600 high strength steel can be used in the automotive lightweight parts,which require high strength and high impact absorption.Aluminum alloy and steel in physical and chemical properties,chemical composition and mechanical properties of significant difference,and two kinds of dissimilar metals of welding is poorer;hence the welding of A5052 and DP 600 is of great significance.This paper studies A5052/DP 600 resistance spot welding,A5052/DP 600 resistance spot welding with Zn slice interlayer,and A5052/DP 600 resistance spot welding with the auxiliary plate,focuses on macrostructure,microstructure,intermetallic compounds(IMC),optimum technological parameters,mechanical properties,effect of process parameters on mechanical properties,fracture form and the nugget process of joint.The overall appearance of the nugget of A5052/DP 600 joint presents a similar shape of the flat-bottomed frying pan.For the nugget formation on the aluminum alloy side,the nugget begins to grow from the interface and then grow outward.The steel side nugget is formed from the center of the steel side and is expanded outward.The structure of aluminum alloy in base material(BM)exhibits columnar crystal.The grain size of the columnar grains in the heat affected zone(HAZ)is smaller when close the fused zone(FZ).The boundaries of HAZ and FZ show a columnar crystal structure which is different in FZ with a columnar crystal structure.The structure of the steel side of FZ is mainly composed of martensite.The structure of HAZ is ferrite and martensite.The intermetallic compounds(IMC)formed in the joints are Fe4Al13,Fe2Al5.The maximum tensile-shear of A5052/DP 600 resistance spot welding joint is 5.5 KN,and the corresponding nugget diameter,welding current,welding time and welding pressure are 6.3 mm,12.5 KA,14 Cycle and 3 KN,respectively.The fracture form of joint is the interfacial failure pattern.The addition of 50 μm Zn slice interlayer will change the resistance mode of the Al/Fe resistance spot welding joint,and the different resistance mode results in difference macroscopic characteristics of the joint after welding.There is a region where there is no melting due to insufficient heat in the region of aluminum side near the electrode,which is called HAZ of the joint.Comparing to A5052/DP 600 resistance spot welding without Zn interlayer,IMC of welded joints have Fe4Al13 phase,Fe11Zn40 phase and Fe2Al5 phase,and the needle-like Fe4Al13 was shorter in length,and the Fe2Al5 morphology changes from flat to tongue.The fracture mode of the joint was plug failure.When the welding current,welding time and welding pressure are 13.5 KA,14 Cycles,and 3 KN,respectively,the tensile-shear force of the joint was 7.06 KN and the reduction rate of the joint is 22%.There are more shrinkage and shrink loose in the aluminum side nugget for A5052/DP 600 resistance spot welding with the auxiliary plate.IMC attached to the aluminum alloy side is the needle-like Fe4Al13,and IMC attached to the steel side is Fe2Al5.When the welding current,welding time and welding pressure are 16 KA,14 Cycle and 3.3 KN,respectively,the fracture absorption energy of joint is 13.24 J,and the tensile-shear force of joint reaches 10.796 KN,and the reduction rate of joint is 23%.The tensile-shear force of A5052/DP 600 resistance spot welding with the auxiliary plate increased 96% and 55% compared to the resistance spot welding of A5052/DP 600 and A5052/DP 600 with Zn interlayer,respectively. |
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