Mechanical property and microstructure of resistance spot welded twinning induced plasticity-dual phase steels joint

Abstract

The present paper deals with the joining of twinning induced plasticity and dual phase steels, carried out by spot welding process with two different pulse durations (200 and 380 ms), by keeping other parameters constant. The microstructural and elemental analysis of the joints was characterised by optical microscopy and electron probe microanalyser. The mechanical properties of the joint were understood from microhardness measurements across the fusion zone as well as through shear and cross-tensile tests. The pulse duration of 380 ms has resulted in good macrostructure with negligible shrinkage void. It also shows smooth transition in hardness across the twinning induced plasticity steel/nugget/dual phase steel interfaces and good mechanical properties as compared to the joint prepared by pulse duration of 200 ms. Larger pulse duration results in sufficient time for the diffusion of alloying elements and yields negligible void formation due to Kirkendall effect.

Welding metallurgy of stainless steels during resistance spot welding Part II –heat affected zone and mechanical performance

“…1,[9][10][11][12][13][14][15] Fusion zone size is controlled by heat generation and heat dissipation, which in turn are governed by the welding parameters and physical properties of the BM.…”

“…martensite formation in FZ and HAZ and martensite tempering in HAZ) have been studied in reasonable details. [5][6][7][8][9][10][11][12][13] However, the welding metallurgy of stainless steels during RSW is yet to be addressed. There are limited works on the resistance spot weldability of stainless steels.…”

“…Generally, spot welds fail at four different modes ( Fig. 1): 1,[10][11][12][13][14][15][16][17] (i) interfacial failure mode in which fracture propagates through the FZ (ii) pullout failure (PF) mode in which failure occurs via withdrawal of the weld nugget from one sheet; in this mode, fracture may initiate in the BM, HAZ or HAZ/FZ depending on the metallurgical and geometrical characteristics of the weld zone and the loading conditions (iii) partial interfacial failure mode in which the fracture first propagates in the FZ and is then redirected towards the thickness direction (iv) partial thickness-partial pullout (PT-PP) mode in which fracture initiates in a manner similar to PF mode; however, some part of mating sheet thickness is removed by a slant crack through the FZ during final crack propagation around the circumference of the weld nugget. Generally, the pullout mode is the preferred failure mode due to its higher associated plastic deformation and energy absorption.…”

Welding metallurgy of stainless steels during resistance spot welding Part I: fusion zone

“…[7][8][9] Therefore, study of welding metallurgy of stainless steel sheets is a prerequisite for their use in automotive structural parts. Mechanical performance of resistance spot welds is significantly affected by: 7,[10][11][12][13][14][15] (i) weld physical attributes, particularly the fusion zone (FZ) size: the weld nugget size is controlled by heat generation and heat dissipation, which in turn are governed by electrical resistivity and thermal conductivity of the metal sheets being welded respectively. 7 Table 1 16 shows a summary of physical properties of the ASS, FSS, martensitic stainless steel (MSS) and DSS compared with low carbon steel.…”

Problems in the Welding of Automotive Alloys

“…It therefore becomes essential to develop joining techniques for dissimilar metals, 18,19 and even between different classes of alloy systems. [20][21][22][23] Magnesium in many automotive applications requires to be joined to aluminium, and there are important problems with the formation of brittle intermetallic compounds at the junctions. 24 There clearly are joining related issues that need to be the focus of research before claiming success in the development of materials for automotive applications.…”