Dual-phase (DP, ferrite+martensite) steels are crucial for automotive components, predominantly spot-welded using thin Zn-coated cold-rolled sheets. However, the effect of martensite morphologies, ...namely fine-lamellar (LD) or coarse-globular (GD) shapes, on Zn-assisted liquid metal embrittlement (LME) remains underexplored. This study investigates LME mechanisms during resistance spot welding of Zn-coated DP steel sheets with LD or GD microstructures. Analysis focuses on cracks within the weld shoulder zone, categorized into sub-critical HAZ (SCHAZ), inter-critical HAZ (ICHAZ), and upper-critical HAZ (UCHAZ). The LME susceptibility index, calculated as total crack length divided by total contact length, increased in the order of LD-SCHAZ, LD-ICHAZ, GD-ICHAZ, and GD-SCHAZ. These results indicated that the microstructure of the GD sheet itself was very vulnerable to the cracking because the initial microstructure was almost retained in the SCHAZ. Cracking analysis in the LD-SCHAZ and GD-SCHAZ suggested that martensite grains near ferrite/ferrite boundaries impeded crack growth by deflecting propagation, and that the LD sheet showed higher crack resistance due to unfavorably oriented ferrite/martensite boundaries.
•DP steels with different morphologies were prepared.•LME susceptibility was evaluated after RSW.•Fine-lamellar morphology shows greater LME resistance than coarse-globular.
In this experimental study, the effects of major laser process control parameters, such as the laser power, beam scanning speed and assisting gas flow rate, on cut surface integrity defined by the ...kerf width, taper percentage, and the extent of heat affected zone (HAZ) were investigated. Response surface methodology (RSM) along with central composite design (CCD) of the experiment was used to optimize the process parameters to get better-cut surface quality. The optimum values of process parameters corresponding to cut surface with minimum defects are laser power 260 W, cutting speed 4500 mm per min, and assistance gas flow rate 14.23 l/min and the corresponding kerf width, taper percentage, and the width of HAZ are found to be 163.7 µm, 5.75%, and 573.28 µm. The confirmation experiments have been conducted that provide favorable results with an error of 2.70%, 1.87%, and 0.36%, for kerf width, taper percentage, and width of HAZ, respectively.
•Peak temperature and aspect ratio of weld bead width to depth for aluminum alloy was first time investigated.•Regression models were developed to determine significant parameters.•Positive ...correlation between laser power and temperature and negative correlation between welding speed and temperature.•Weld bead width was profoundly affected by laser power while peak temperature was influenced by welding speed.
This work focuses on the study of parametric effect of laser power and welding speed on peak temperatures, aspect ratio of weld bead width to depth and heat affected zone width for specimens having various thicknesses through transient thermal analysis for AA5083 aluminium alloy. Taguchi array was used to design the experiments to be carried out through Finite Element (FE) simulations which have been carried out with a general purpose commercial FE code, ABAQUS. Results show positive correlation between laser power and temperatures and negative correlation between welding speed and temperature. It is found that the aspect ratio of weld bead width to depth is affected by welding speed while laser power influence the width of heat affected zone. It is concluded that laser power has a significant effect on weld bead width and welding speed has a pronounced effect on peak temperatures.
This study aimed to investigate the effect of the welding heat input on the heat affected zone (HAZ) of AW 6005-T6 aluminium alloy for a butt-welded joint using gas metal arc welding. The ...determination of the thermal cycles, metallography, and the resulting mechanical properties in the zone makes its possible. The study involved using a welding experiment, numerical simulation, physical simulation, and mechanical tests. The welding was carried out using the pulsed gas metal arc welding (GMAW) transfer and type J thermocouples were used to develop the thermal cycles in the HAZ. Simufact® Welding was utilized for the numerical simulation. Optical microscope was used to evaluate the microstructures and Vickers microhardness test was done along the weld cross-section. The HAZ was located on the weld cross-section with a mean hardness of 63.7 HV0.1, which is considerably lower when compared with the base metal (BM) which has a hardness of 100 HV0.1. This indicates thermal softening occurred due to the heat input to the material. There is a match in the hardness values of the Gleeble samples and the locations on the weld cross section suggested by the model showing validity of the simulation. It is important to note the fact that there is an influence of heat input into aluminum AW 6005-T6 weld joints and its mechanical properties in the design of welding process parameters for automotive parts. The welding parameters can be optimized to decrease the heat input into the weld, as this can directly affects the mechanical properties in the HAZ.
Stress induced sensitization on heat affected zone (HAZ) of 304 LN austenitic stainless steel was studied using the thermo mechanical simulator (Gleeble 3800). The study was carried out using the ...weld thermal cycle and residual stresses, observed during pulse gas metal arc welding (P-GMAW) of 28 mm conventional groove weld. Layer wise study of weld seam deposition was done to understand the characteristic of stresses and thermal behavior on HAZ created by its adjacent weld seam during welding. The degree of sensitization, as a function of stress-type (tensile or compressive) and its magnitude under the thermal behavior of multi-pass heating and reheating in HAZ, has been studied through observations on changes in microstructure, electrochemical properties and variation in hardness of the matrix. It was observed that irrespective of its tensile or compressive nature, the increase in magnitude of residual stresses appreciably enhances the sensitization of the matrix by formation of Cr23C6 precipitate as confirmed by high-resolution transmission electron microscopy (HRTEM) analysis. Also the study includes widening of HAZ grain boundary as well as increase of degree of sensitization (electrochemical studies) and hardness.
Laser 3D printing is a promising technique to repair damaged Ni-based superalloy components. However, the occurrence of heat affected zone (HAZ) cracking severely limits its applicability. Here we ...unravel the cracking mechanism by studying the element, phase, defect, and strain distribution around an intergranular crack that initiated from the primary HAZ. Using synchrotron X-ray Laue microdiffraction, we measured high tensile strain/stress transverse to the building direction in both the primary HAZ and the cladding layers, as well as high-density dislocations, which resulted from the thermal contraction and rapid precipitation of γ′ phase. The crack initiated because the transverse tensile strain/stress tore up the liquid film formed by the low-melting point preexisting phases in the primary HAZ, such as γ/γ′ eutectics and coarse γ′ precipitates. The incoherent carbide particles were frequently observed near the crack root as local strain concentrators. In the cladding layers, micro-segregation could not be completely avoided, thus the hot crack continued to propagate over several layers with the assistance of the transverse tensile stress. Our investigations provide a useful guideline for the optimization of the 3D printing process to repair Ni-based superalloys with high susceptibility to hot cracking.
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•The heat affected zone cracking initiates due to the re-melting of preexisting intergranular γ/γ′ eutectics and coarse γ′.•The transverse tensile strain/stress causing the initiation and propagation of crack is quantitatively measured.•The micro-size MC carbides are considered to be a possible contributor to the hot cracking initiation.
The heat affected zone liquation cracking behavior was studied in laser additive manufactured Inconel 718. Liquation cracking was found initiating from the weak site near the fusion line in the ...pre-deposited layer, propagating along the interdendritic region with the further deposition proceeding layer by layer. Total cracking length calculation results showed that when controlling the heat input and height increment constant, liquation cracking susceptibility increased with the increase of laser scanning speed; and when controlling the laser scanning speed and height increment constant, liquation cracking susceptibility increased with the increase of heat input. The effect of grain boundary misorientation on susceptibility to liquation cracking was also investigated through electron backscatter diffraction (EBSD) measurement, and the results showed that liquation cracking tendency increased with the increase of grain boundary angle, which was considered to be attributed to the higher stability of liquation film at larger grain boundary during the last stage of solidification.
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•Liquation cracking propagates with the following deposition layer by layer.•The low interdendritic bridging reduces cracking resistance during solidification.•Liquation film stability is increased due to the improved heat accumulation.•Liquation cracking increases with increasing laser scanning speed and heat input.•Liquation cracking increases with the increase of grain boundary misorientation.
In the present study, in order to find out a valuable method to decrease the hardness of heat-affected zone (HAZ), elemental partitioning was introduced before welding simulation to realize elemental ...redistribution. The results demonstrate that about 10% reduction of HAZ hardness can be achieved by introduction of elemental partitioning. During elemental partitioning, the content of retained austenite increases with increasing of elemental partitioned time. Further research reveals that the value of geometrically necessary dislocation density decreases with elemental partitioning. It is found that the alloying elemental contents in the matrix after elemental partitioning are lower than that without elemental partitioning. In addition, the differences of grain size distribution and elemental distribution resulted in elemental partitioning are studied and compared to explain the reason for the reduction in hardness.
Fatigue crack growth tests have been conducted on S355 G10+M structural steel which is widely used in the fabrication of offshore structures. Fracture mechanics tests have been performed on compact ...tension specimens with the crack tip located in the heat affected zone. All tests were performed at room temperature in air and the obtained results are compared with the literature data available on a range of offshore structural steels and also the recommended BS7910 trends using the 2-stage law and simplified law. The specimen orientation, with respect to the location of the extraction within the welded plate, has also been examined and discussed in this work. Residual stress measurements have been performed prior to testing by using the neutron diffraction technique. Finally, a numerical model has been developed in order to calculate the effective stress intensity factor range in the presence of residual stresses. The results have shown that the residual stresses play a key role in the fatigue life of the welded structures, especially in the near threshold region.
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