Failure Behavior of Three-Steel Sheets Resistance Spot Welds: Effect of Joint Design

There is a lack of comprehensive understanding concerning failure characteristics of three-steel sheet resistance spot welds. In this article, macro/microstructural characteristics and failure behavior of 1.25/1.25/1.25?mm three-sheet low carbon steel resistance spot welds are investigated. To evaluate the mechanical properties of the joint, the tensile-shear test was performed in three different joint designs. Mechanical performance of the joint was described in terms of peak load, energy absorption, and failure mode. The critical weld nugget size required to insure pullout failure mode was obtained for each joint design. It was found that the joint design significantly affects the mechanical properties and the tendency to fail in the interfacial failure mode. It was also observed that stiffer joint types exhibit higher critical weld size. Fusion zone size along sheet/sheet interface proved to be the most important controlling factor of spot weld peak load and energy absorption.     

Mechanical properties of martensitic stainless steel weld/adhesive hybrid bonds

Hybrid weld-adhesive bonding (AB) was used as an approach to improve the mechanical properties of martensitic stainless steel resistance spot welds. The weld fusion zone in both techniques was composed of predominantly martensite and δ-ferrite. It was found that the presence of adhesive does not induce excess hardening effect in the fusion zone. It was shown that hybrid AB/resistance spot welding) i.e. weld-bonding) technique can double the peak load and energy absorption of the joints compared to those of the resistance spot welds. To obtain high performance weld-bonded joints, heat generation during welding should be controlled to produce weld bonds with large fusion zone size, but without detrimental effect on the adhesive strength.     

Dependence of overload performance on weld attributes for resistance spot welded galvanized low carbon steel

Microstructure and failure behavior of galvanized low carbon steel resistance spot welds were investigated. Failure mode, peak load and energy absorption obtained in tensile-shear test were used to describe spot welds performance. It was found that weld fusion zone size, electrode indentation and expulsion can significantly affect the mechanical performance of spot welds. Failure mechanism of spot weld which fail via pullout mode during tensile-shear test was “through thickness” localized necking in the base metal. However, those spot welds which have experienced severe expulsion during welding, failed at the fusion zone/HAZ interface. This can contribute to the reduction in energy absorption capability of spot welds due to the harder microstructure of the fusion zone/HAZ compared to the soft ferritic base metal.     

Ferritic–austenitic stainless steels dissimilar resistance spot welds: metallurgical and failure characteristics

The paper addresses the microstructure and failure characteristics of dissimilar resistance spot welds between austenitic stainless steel and ferritic stainless steel. The fusion zone (FZ) of dissimilar welds exhibited complex microstructure consisting of ferrite, austenite and martensite. The development of this triplex structure in the FZ was explained by analysing the phase transformation path and austenite stability. Results showed that all dissimilar welds failed in partial thickness–partial pull-out failure mode. It was shown that the fraction of the nugget fracture of the weld is reduced by increasing the FZ size improving the mechanical performance of the weld. Peak load and energy absorption of the similar and dissimilar welds were compared and analysed.     

Prediction of the failure mode of automotive steels resistance spot welds

ABSTRACT

In this study, the critical nugget size, at which the failure state in tensile shear test changed from the interfacial failure mode to the pull-out failure one, was estimated as a function of nugget and base metal hardness. The proposed approach could address the effect of various parameters involved in resistance spot welding process, such as sheet thickness, base metal chemical composition and physical properties of electrodes and sheets. The reliability of the present model was evaluated using independent experimental results. Based on the obtained results, the effect of steel composition on critical nugget diameter was found to be more important, especially for the sheets thicker than about 1?mm, whereas predicted nugget sizes by previous models could not guarantee the pull-out failure mode.     

Microstructure–properties relationship of TLP-bonded GTD-111 nickel-base superalloy

Relationship between microstructure and mechanical properties of transient liquid phase-bonded joints of GTD-111 nickel-base superalloy using a Ni–Si–B interlayer was investigated. Shear strength and hardness profile of the joints were discussed with respect to the bond microstructure. In the bonding condition, in which isothermal solidification has not been accomplished completely, eutectic constituent which has the highest hardness in the bond region is the preferential failure source. Additionally, it was found that when isothermal solidification is completed, the extent of γ′ formation in the bond region is the controlling factor for joint strength. Shear strength of bonds after post-bond heat treatment was close to that of the base metal.     

Microstructure and failure behavior of dissimilar resistance spot welds between low carbon galvanized and austenitic stainless steels

Resistance spot welding was used to join austenitic stainless steel and galvanized low carbon steel. The relationship between failure mode and weld fusion zone characteristics (size and microstructure) was studied. It was found that spot weld strength in the pullout failure mode is controlled by the strength and fusion zone size of the galvanized steel side. The hardness of the fusion zone which is governed by the dilution between two base metals, and fusion zone size of galvanized carbon steel side are dominant factors in determining the failure mode.     

Metallurgical and Mechanical Characterization of Laser Spot Welded Low Carbon Steel Sheets

This paper aims at investigating metallurgical and mechanical characterization of low carbon steel laser spot welds. Microstructural examinations, microhardness tests and quasi‐static tensile‐shear tests were preformed. Mechanical properties of the welds were described in terms of peak load and failure mode. The effects of laser spot welding parameters including pulse frequency, laser energy, welding speed, pulse width and welded circle diameter, on low carbon steel laser spot weld performance were studied using the Taguchi design of experiment method. It was found that the effective laser pulse energy is the controlling factor in the determination of mechanical strength of laser spot welds.     

Solid solution strengthening of transient liquid phase bonded nickel based superalloy

This paper aims at probing and quantifying the effect of filler alloy chemistry on solid solution strengthening mechanism of transient liquid phase bonded of a cast Ni–Fe–Nb based superalloy. Bonding was performed using three different nickel based filler alloys including Ni–4·5Si–3·2B, Ni–7Cr–4·5Si–3·2B–3Fe and Ni–15·2Cr–4B. The hardness of isothermal solidification zone was proved to be the controlling factor for the shear strength of the joints. It is concluded that the initial chromium content of the filler alloy and the extent of base metal dissolution, which in turn is controlled by the initial boron content of the filler alloy, play important roles in strengthening of the isothermal solidification zone. Bonding using Ni–15·2Cr–4B resulted in eutectic free joint with the highest shear strength.     

Aging response of transient liquid phase bonded wrought IN718 superalloy: influence of post-bond heat treatment

Aging response of transient liquid phase Nb bearing wrought IN718 nickel base superalloy is studied. The aging behaviour of the joint is influenced by low Nb+Al+Ti content of isothermal solidification zone (ISZ) and formation of Nb–Cr–Mo based boride precipitates in diffusion affected zone (DAZ). It was shown that applying a post-bond heat treatment which was able to eliminate the diffusion induced boride precipitates in DAZ and increase the Nb+Al+Ti content of the ISZ improved the aging response and shear strength of the joint.