Comparison of mechanical properties and microstructure of weld nugget between weld-bonded and spot-welded dual-phase steel

Abstract

Weld bonding, which is a combination of resistance spot welding and adhesive bonding, is finding application in vehicle structures that involve advanced high-strength steels. The strength of weld-bonded specimens is attributed to the strength of the weld nugget and adhesive strength. The existence of an insulating epoxy adhesive layer causes a rise in contact resistance and current density during the welding stage, and thus enhances the heat input. The aim of the present study is to explore the mechanical properties and microstructure of the weld nugget in weld-bonded dual-phase steel by means of comparison with a spot-welded nugget. Tensile-shear tests, weld lobe determination, microstructural characterization, and microhardness tests of weld-bonded and spot-welded specimens were conducted. The results of tensile-shear tests show that the weld nuggets of weld-bonded specimens have a higher tensileshear force and energy absorption, and exhibit button-pullout fracture more easily at lower welding current. The weld lobe of weld-bonded dual-phase steel is too narrow. The results of microstructural characterization and microhardness tests indicate that, compared with resistance spot welding specimens, weld-bonded specimens have a larger nugget size at lower current; finer martensite and lower hardness in the heat-affected zone; and slightly more ferrite and lower hardness in the fusion zone. The comparative results are useful for optimizing the processing parameters and improving the weld quality of weld bonding.

Small-scale resistance seam welding of 304 stainless steel with capacitor discharge welding machine

“…In the resistance welding, mechanical tests such as, tensile-shear, coach peel, U-tensile and cross-tension have been used to determine the strengths and mechanical properties of spot welds under different loading conditions. 30–34 In this work, the most widely used mechanical tests such as, tensile-shear and peel tests were used to investigate the maximum strength and also the failure mode of the weld seams. Mechanical tests were performed on two groups of specimens.…”

Microstructure and Mechanical Properties of Welded Advanced Materials for Automotive Applications

“…It also improves the corrosion, noise resistance and joint stiffness [67]. Some studies related to microstructures and mechanical properties of WB joints have been reported [31,32,68,69]. Chang et al [31] studied a computational model and the stress field characteristics of WB joints for a car body steel sheet and observed a serious stress concentration existing at the edge of the weld spot in the spotwelded joints, and it could be removed or reduced by the application of adhesives.…”

Resistance spot weld bonding of steel sheets

“…• increase in strength [1,5,6,7] and absorption of total destruction energy [1,6,7,8,9] also measured in crash tests [10,11]; • obtaining increased structural rigidity [1,9]; • improvement of tightness (elimination of seals) and corrosion resistance [5,11];…”