Properties Of Resistance Spot Welds Research Articles

A novel method to evaluate the mechanical properties of resistance spot welds under dynamic loading

The mechanical properties of resistance spot welds are integral in dictating joint performance in service. However, previous studies have evaluated the joint response to loading under the quasi-static condition which is not a true indication of the loading condition in service. This work has developed a novel method to evaluate spot welds under dynamic loading using two test geometries (opening and shear mode). The testing technique was used to compare the mechanical properties of a conventional and in-situ post-weld heat treatment (PWHT) schedule. Our developed method can expand the testing capability of single-spot welds under dynamic loading.

Fatigue properties of resistance spot‐welded maraging steel produced by selective laser melting

AbstractThis research study investigates the fatigue properties of resistance spot welds (RSWs) made from selective laser‐melted (SLMed) maraging steel (MS1) and compares them with dual‐phase (DP) steel RSWs. The findings reveal that MS1 spot welds exhibit superior fatigue properties compared with DP steel RSWs, regardless of the printing orientation of the MS1 substrate. Furthermore, fatigue fracture occurs at the MS1 substrate, with a transition of fracture location observed from MS1 to itself and MS1‐to‐DP600 dissimilar welds. The results of structural stress analysis indicate that the weld nugget diameter is not the only factor affecting the fatigue life. The study also highlights the importance of considering materials inhomogeneity and fracture modes in fatigue life assessment. Based on the findings, the study recommends the development of a new fatigue life prediction curve for spot welds of additive manufacturing (AM) materials. Such a curve would be beneficial in promoting the further application of AM technology for functional parts of design verification vehicles (DCV) and production cars. Overall, the research contributes to the understanding of the fatigue properties of RSWs made from SLMed MS1 and DP steel, which has implications for the design and manufacturing of parts in the automotive industry.

Effect of post-weld tempering pulse on microstructure and mechanical properties of resistance spot welding of Q&P1180 steel

Resistance spot welds (RSWs) of quench and partitioning (Q&P) steels exhibit poor mechanical properties due to the brittleness of the nugget microstructure. To solve this problem, the nugget microstructure in RSWs of Q&P1180 steel was modified by applying a post-weld tempering pulse with different protocols. Effects of the post-weld tempering pulse on microstructural evolution and mechanical properties of RSWs were investigated. The results indicate that a proper post-weld tempering pulse (cooling time of 1000 ms and post welding current of 4 kA) achieved a 70% improvement in the cross-tension peak load and a 6% improvement in the tensile-shear peak load. The nugget, consisting of tempered martensite and retained austenite with low hardness and high toughness, hindered the crack propagation towards the nugget during the cross-tension test and improved cross-tension property. In the tensile-shear testing, a new failure mechanism was discovered. Despite the decrease in nugget hardness, the improvement of toughness helped enlarge the effective area subjected to the shear load during the tensile-shear test, resulting in the improvement of the tensile-shear property.

The effect of silicon content on liquid-metal-embrittlement susceptibility in resistance spot welding of galvanized dual-phase steel

Abstract Liquid metal embrittlement (LME) can have a significant effect on the mechanical properties of resistance spot welding (RSW) advanced high strength steels (AHSS). An understanding of the role of alloying elements such as silicon (Si) on microstructure details and RSW parameters, both of which influence LME cracking is essential for design of LME-resistant AHSS. The present study has shown that increasing Si-content from 0.7 wt.% to 1.8 wt.% increased LME susceptibility in dual phase (DP) steels. It has been demonstrated that increasing Si led to higher heat inputs and early expulsion due to the higher resistivity of the higher Si-content grade during RSW that was related to more severe LME-cracking. Furthermore, increasing Si-content had a significant effect on microstructural evolution during processing prior to RSW, including increased ferrite grain size, decarburization layer depth, and internal oxides density, all of which were related to an increased LME crack susceptibility.

Study on microstructure and properties of resistance spot welding of Mg/Ti dissimilar materials

ABSTRACT The dissimilar material of AZ31 Mg alloy and TA15 Ti alloy were welded by resistance spot welding. The influence of welding current on the interface of nuggets is studied. The microstructure, hardness, tensile strength and fracture surface of joints are analysed. The results indicate that when the electrode pressure and welding time are determined, the failure load of the joint can be improved by the increase in the welding current; however, excessively high welding current will cause cracks near the interface. Under the welding current of 14.5 kA, the electrode pressure of 0.22 MPa and the welding time of 200 ms, the maximum failure load of the joint can reach 4.79 kN, which is almost the same as the shear strength of AZ31B magnesium alloy base metal.

A study on the effect of chemical composition on the microstructural characteristics and mechanical performance of DP1000 resistance spot welds

This paper reports on the factors governing the mechanical properties of resistance spot welded hot dip galvanized DP1000 under tensile-shear and cross-tension loading. In particular the effects of chemical composition on the microstructural evolution and mechanical properties of DP1000 resistance spot welds are studied thoroughly, by comparison of a higher and lower carbon alloying approach. It is shown that DP1000 steel with higher carbon content attains a martensitic microstructure in the weld nugget with smaller prior austenite grains and finer block sizes. The intervariant boundary fraction analysis also reveals that DP1000 steel containing lower carbon content shows stronger variant selection as the fraction of variants belonging to the same Bain group is higher for this steel. Intervariant plane distribution also reveals that the most of intervariant boundaries for both steels terminated at or near {011} slip planes. Mechanical testing of the welds reveals that the steel with higher carbon content shows a better mechanical performance in tensile-shear test, whereas the DP steel with a lower carbon content exhibits higher maximum load of cross-tension test. The key factors controlling the mechanical response of resistance spot welds during two different mechanical tests are explored via nanoindentation, slit-milling method combined with digital image correlation and micro-cantilever bending. It is demonstrated that the strength and/or hardness of the weld nugget is the key parameter governing the tensile-shear strength of the spot welds, while the fracture toughness of the weld is the dominant parameter that determines the cross-tension strength.

Effect of Microstructure and Texture on Mechanical Properties of Resistance Spot Welded High Strength Steel 22MnB5 and 5A06 Aluminium Alloy

The present study aims to investigate the effect of microstructure and texture on mechanical properties of resistance spot welding of high strength steel 22MnB5 and 5A06 aluminium alloy as a function of welding parameters. The pseudo-nugget zones (NZs) at the steel side have undergone full recrystallisation with a fine-grained ferrite structure containing a small amount of retained austenite and a high hardness of approximately 500 HV, which is a 35% increase in hardness compared to the base material (BM) with fine lath martensitic structure. The NZs at the Al side contain both a recrystallisation texture and shear texture. Higher tensile shear strength with increasing weld time could be linked to the random texture at the Al side. The highest tensile shear strength was achieved at an intermetallic layer thickness of 4 mm.

Microstructure and Mechanical Properties of Resistance Spot Welds for Fe-based Metallic Glass

The lap joints of Fe-based metallic glass ribbons were carried by resistance spot welding, and the microstructures of spot welds were investigated by X-ray diffraction and transmission electron microscopy. The results indicated that the perfect formations of joints without typical defects such as spatter were achieved with optimized parameters. Except for little nano-particle Fe2B, no other crystalline particle was detected by TEM, revealing that the most microstructure in spot weld remains amorphous. The maximum tensile-shearing force was 45.0 N with the optimized parameters of 1 kA weld current, 30 N electrode force and 0.02 ms weld time. The spot weld failed as pullout failure mode propagating along the interface of nugget zone. The study demonstrates that resistance spot welding is an effective and practical welding process for Fe-based metallic glass.

Effect of specimen configuration on fatigue properties of dissimilar aluminum to steel resistance spot welds

General Motors (GM) has developed a proprietary resistance spot welding process using a Multi-Ring, Domed (MRD) electrode geometry that is capable of producing welds between aluminum alloys and steel materials with acceptable joint strength. This work presents fatigue properties of resistance spot welds (RSWs) produced between dissimilar 1.2-mm thick wrought aluminum AA6022-T4 and 2.0-mm thick IF steel RSWs in tensile-shear and coach-peel configurations. The results were compared to those of spot welds made of 1.2-mm thick and 2.00-mm thick AA6022-T4. The tensile-shear and coach-peel spot welds exhibited limited scatter in fatigue life for both stack-ups. The overall fatigue life of the tensile-shear AA6022-T4 to IF stack-ups was much greater than that of the AA6022-T4 to AA6022-T4 stack-ups. However, in coach-peel, there was no significant difference in fatigue life between the two stack-ups. In both tensile-shear and coach-peel fatigue tests the fracture mode for both stack-ups was primarily crack growth through the 1.2-mm thick AA6022-T4 sheet. The superior performance of the tensile-shear AA6022-T4 to IF steel RSWs was most likely a result of larger weld nugget size along with microstructural features that improved performance. These included more favourable notch root openings as well as columnar grain growth and alloying of the aluminum nugget with iron that could retard fatigue crack propagation.

Točkasto varjenje jekel DQSK/DP600: rast jedra zvara

The weld-nugget size is the key issue in determining the mechanical properties of resistance spot welds. This paper aims at investigating the weld-nugget growth of dissimilar-resistance spot welding of ferrite-martensite DP600 and drawing-quality special-killed (DQSK) low-carbon steel. It was revealed how the weld-nugget size is influenced by the main welding parameters: welding current, welding time and electrode force. The weldability lobe was established and proper welding conditions for the welds with a sufficient size and without an expulsion were determined. Using the experimental data, an empirical relationship between the weld-nugget size and the welding parameters was developed.

Effect of holding time on microstructure and mechanical properties of resistance spot welds between low carbon steel and advanced high strength steel

The effect of holding time on microstructure, hardness and mechanical properties of unequal thickness weld joints between low carbon steel and advanced high strength steel is investigated in the present work. The microstructures in the regions of weld nugget, heat affect zone and base metal are obviously different. The hardness of fusion zone both at low carbon steel and advanced high strength steel sides shows a slight variation and it is much higher than that of base metal. The peak load and failure mode of the weld joints are carried out via tensile shear test and finite element analysis. The test result demonstrates that the peak load and failure mode depend on the resistance force generated via the failure zone. For a given fusion size, the increase of holding time raises the hardness of fusion zone, and affects the peak load and failure mode of weld joints via enhancing the interfacial resistance capability. The increase of holding time reduces the welding efficiency, thus, a suggestion based on the test result is proposed that the holding time should be less than 15 cycles to ensure the manufacturing efficiency. A nonlinear finite element analysis is applied to simulate the tensile test procedure. The simulation demonstrates the necking phenomenon and failure process at interfacial or base metal around the weld nugget.

Nucleus geometry and mechanical properties of resistance spot welded coated–uncoated DP automotive steels

In this study, mechanical properties of resistance spot welding of DP450 and DP600, galvanized and ungalvanized automotive sheets have been investigated. The specimens have been joined by resistance spot welding at different weld currents and times. Welded specimens have been examined for their mechanical, macrostructure and microstructure properties. Depending on the weld current and time, effects of zinc coating on tensile properties, microhardness values as well as microstructure nugget geometry and nucleus size ratio have been investigated. X-ray diffraction analysis has been used to investigate the phase that formed at the joint interface. Result of the experiment show that nugget diameter, indentation depth and tensile load-bearing capacity are affected by weld parameters. Coating prevents full joining at low parameters. Microhardness increased in heat-affected zone and weld metal.

Resistance Spot Welding of dissimilar Steels

This paper presents an analysis of the properties of resistance spot welds between low carbon steel and austenitic CrNi stainless steel. The thickness of the welded dissimilar materials was 2 mm. A DeltaSpot welding gun with a process tape was used for welding the dissimilar steels. Resistance spot welds were produced with various welding parameters (welding currents ranging from 7 to 8 kA). Light microscopy, microhardness measurements across the welded joints, and EDX analysis were used to evaluate the quality of the resistance spot welds. The results confirm the applicability of DeltaSpot welding for this combination of materials.

비파괴 계장화 압입시험을 이용한 저항 점용접부 물성 평가

Nondestructive instrumented indentation test is the method to evaluate the mechanical properties by analyzing load - displacement curve when forming indentation on the surface of the specimen within hundreds of micro-indentation depth. Resistance spot welded samples are known to difficult to measure the local mechanical properties due to the combination of microstructural changes with heat input. Particularly, more difficulties arise to evaluate local mechanical properties of resistance spot welds because of having narrow HAZ, as well as dramatic changed in microstructure and hardness properties across the welds. In this study, evaluation of the local mechanical properties of resistance spot welds was carried out using the characterization of Instrumented Indentation testing. Resistance spot welding were performed for 590MPa DP (Dual Phase) steels and 780MPa TRIP (Transformation Induced Plasticity) steels following ISO 18278-2 condition. Mechanical properties of base metal using tensile test and Instrumented Indentation test showed similar results. Also it is possible to measure local mechanical properties of the center of fusion zone, edge of fusion zone, HAZ and base metal regions by using instrumented indentation test. Therefore, measurement of local mechanical properties using instrumented indentation test is efficient, reliable and relatively simple technique to evaluate the tensile strength, yield strength and hardening exponent.

Factors affecting mechanical properties of resistance spot welds

The present paper addresses the factors governing the mechanical performance of low carbon resistance spot welds. Correlations among the process parameters (welding current, welding time, electrode force and holding time), physical spot weld attributes and mechanical performance are analysed. Peak load and energy absorption of spot welds during the tensile shear test are used to describe spot welds performance. It is shown that weld nugget size, electrode indentation, failure mode and strength/ductility of the failure location are the main factors affecting peak load and energy absorption of spot welds.

Key factors influencing mechanical performance of dual phase steel resistance spot welds

Quasi-static tensile shear mechanical properties of resistance spot welds of three dual phase (DP) grades including DP600, DP780 and DP980 are investigated. Results showed that weld fusion zone size, failure mode and the strength/ductility of failure location are the main factors governing the peak load and the energy absorption of spot welds. Heat affected zone (HAZ) softening plays an important role in mechanical properties of DP steels with higher volume fraction of martensite (i.e. DP780 and DP980). It was shown that the peak load of the spot welds is not proportionally correlated to the tensile strength of the base metal. Pronounced HAZ softening in DP980 resulted in reducing its tendency to fail in interfacial failure mode in comparison to DP780. In addition, despite its lower base metal ductility, DP980 weld exhibits enhanced ductility and energy absorption than DP780 due to its pronounced HAZ softening.

Influence of Reduced Cooling Time on the Properties of Resistance Spot Welds

Reducing the cooling time in a resistance spot welding schedule offers two possible advantages. The first is decreased weld cycle time, which is of great importance in particular to car body assembly lines performing hundreds of millions of spot welds each year. Decreasing each resistance spot weld cycle time by a mere 0.1 s leads to substantial cost savings. The second advantage is the possibility to reduce the hardness in the weld metal and thereby improve fracture behaviour. Reducing the cooling time leads to reduced cooling rate of the weld metal and potentially a softer material. Two and three-sheet joint combinations of martensitic, dual phase, transformation induced plasticity (TRIP), complex phase and hardened boron steels were investigated in this study. The joints were evaluated by shear-, peel-and cross-tension testing as well as metallographical examinations and hardness measurements. With knowledge of the materials weldability, and evaluation of the behaviour when welding with reduced cooling time, it was possible to develop optimised weld schedules and thereby increased productivity. It is recommended that the programming of the hold time in the power sources is modified in order to enable full flexibility in setting of the hold time / cooling time. This study showed that the cooling time could be reduced significantly without endangering the joint integrity.

Embrittlement of copper by liquid bismuth

Liquid metal embrittlement (LME) can have a significant effect on the mechanical properties of resistance spot welding (RSW) advanced high strength steels (AHSS). An understanding of the role of alloying elements such as silicon (Si) on microstructure details and RSW parameters, both of which influence LME cracking is essential for design of LME-resistant AHSS. The present study has shown that increasing Si-content from 0.7 wt.% to 1.8 wt.% increased LME susceptibility in dual phase (DP) steels. It has been demonstrated that increasing Si led to higher heat inputs and early expulsion due to the higher resistivity of the higher Si-content grade during RSW that was related to more severe LME-cracking. Furthermore, increasing Si-content had a significant effect on microstructural evolution during processing prior to RSW, including increased ferrite grain size, decarburization layer depth, and internal oxides density, all of which were related to an increased LME crack susceptibility.