Autogenous Laser Welding Research Articles

Welding Characteristics of Medium Titanium Plates with Autogenous Laser Welding and Narrow-Gap Laser Filling Welding Modes.

Titanium and titanium alloys with a medium thickness of 5 to 12 mm are widely used for ocean platforms, military equipment and in other fields because of their light weight, appropriate strength and corrosion resistance. In this study, autogenous laser welding and narrow-gap laser welding processes were researched and compared, and the welding characteristics, weld microstructure and joint strength were analyzed. The results showed that autogenous laser welding had higher efficiency, narrower weld width and higher microstructure uniformity. Autogenous laser welding can achieve the single pass weld penetration at laser keyhole mode. The weld width of narrow-gap laser welded joint was 12.5 mm, which was nearly three times than that of autogenous laser welding. The grain size of autogenous laser welding was obviously smaller and more uniform in depth than that of narrow-gap laser welding. In the weld zone, the coarse columnar α grains grew from the fusion line, while in the heat-affected zone, equiaxed α grains with needle and sawtooth α morphologies were presented. The microhardness of the heat-affected zone was higher than in the weld zone and the base metal due to the denser needle microstructure. The tensile samples all fractured at the base metal, indicating the welded joint strength efficiency was greater than 1.

Predictive tools for the cooling rate-dependent microstructure evolution of AISI 316L stainless steel in additive manufacturing

This study presents a thorough evaluation of advanced predictive tools for the solidification microstructure of AISI 316L stainless steel, taking into account both chemical composition and cooling rate. In order to achieve a broad range of cooling rates comparable to prominent additive manufacturing processes, autogenous laser welds were carried out on the steel plate by means of powderless directed energy deposition (DED) and selective laser melting (SLM) machines. Computational analysis of cooling rates and metallographic investigations revealed that DED welds solidify at moderate rates, exhibiting a primary ferrite (FA) solidification mode. Conversely, SLM welds solidify at significantly higher rates, showing dual solidification modes: initial austenite (A) at the fusion boundary and subsequent ferrite (F) at the interior. The WRC-1992 constitution diagram predicts the FA mode in accordance with the findings in the DED welds. An implicated Schaeffler diagram, proposed for a comparable cooling rate, also predicts the same mode. An artificial neural network model, referred to as ORFN, consistently predicts the variation of ferrite content within the DED welds based on the cooling rate variation. The dual mode observed in the SLM welds aligns with established knowledge regarding the alteration of stainless steel solidification under extremely high cooling rates. While the occurrence of the A mode at the fusion boundary is anticipated according to implicated Schaeffler diagrams for extremely high cooling rates, the transition to the F mode is not addressed explicitly.

MICROSTRUCTURE AND PROPERTIES OF LASER-WELDED BUTT JOINTS OF AlSi1MgMn ALUMINIUM ALLOY

The process of autogenous laser welding of butt joints of aluminium alloy AlSi1MgMn plates with thickness of 3.0 mm was investigated. The Yb:YAG disk laser was used in the study. The aim was to determine the influence of the basic parameters of laser welding on the joint quality, fusion zone geometry, microhardness distribution across the butt joint, structure and microstructure of fusion zone (FZ) and heat affected zone (HAZ) was studied and determined. The chemical composition of the base metal was determined by spark emission spectroscopy, while the phase constituents were determined by XRD analysis. Results of the study have shown that the geometry of welds is proper without excessive imperfections. No voids were found the FZ. However, weld face of the joints are slightly convex, while the roots are slightly concave. Microscopic observations showed no discontinuities in the fusion zone of the welds. A significant decrease in hardness in the FZ was observed. The hardness in the FZ of the test joints is approx. 67÷70 HV0.1. The fracture of the samples during tensile tests occurred in the FZ or at the boundary FZ/HAZ, and the tensile strength was ranged from 200MPa to 220MPa.

Experimental analysis of overlap fiber laser welding for aluminum alloys: Porosity recognition and quality inspection

In recent years, laser welding has become increasingly popular in the manufacturing industry due to its advantages, including a narrow heat affected zone, low levels of distortion, the possibility of remote processing, and high welding speeds compared to conventional electric arc welding techniques. In the automotive industry, the need for overlapped joint welding, particularly for chassis assembly, has become increasingly relevant. The internal porosity detection and control in laser welding of aluminum alloys has gained significant attention. To support laser users in optimizing the welding process, this paper presents an experimental methodology followed by a phenomenological analysis of the quality of overlapped welded joints. The study focuses on the laser welding of two different aluminum alloy configurations (1.6-mm-thick AA 6061-T6 and 2-mm-thick AA 6061-T6) using three welding strategies (ScanLab remote laser welding system, Trumpf D70 laser head, and Precitec YW52 wobbling head) to evaluate single and multiple laser variants for process parameter tuning. Additionally, the paper discusses the use of X-ray technology as an offline monitoring method for porosity recognition, and analyzes laser beam characterization and beam profile shape to calculate beam distribution. Then, statistical analysis of all methods is conducted and regression analysis is performed. These findings provide valuable insights into the integration of laser welding technology in the automotive and surface transportation industries. The analysis of results indicates that as the spot size decreases, the real spot size changes more abruptly with increasing Z position, whereas with a larger spot size, the beam size remains stable up to +/- 20–30 mm in Z position due to the large lens. Porosity is mainly caused by either a too small spot size (in the absence of wobbling; ≤0.4 mm) or low travel speed (≤4.0–4.5 m/min). On the other hand, if the spot size is too large, hot cracking can occur in autogenous laser welding.

Analysis of the springback effect of laser welded DP600 high-strength steel thin sheets

Steel sheets are produced with increasingly smaller thicknesses, without compromising the properties of the steel, maintaining ductility, strength, and energy absorption after impact can total depth enhance vehicle energy efficiency, lower manufacturing costs, and address the springback effect. The springback effect of laser-welded DP600 two-phase steel sheets was studied in this research. Parameters such as punching speed, initial bending angle, and time were varied. Tests including tensile tests, Vickers hardness, and optical microscopy analysis were conducted to correlate results with material properties. Autogenous laser welding joined DP600 steel plates at the bending position. Controlling springback ensures better quality in vehicle manufacturing and assembly. The results revealed that increasing the punch descent speed from 4 to 12 mm/min, for an internal angle of 90°, on the first day of observation, led to higher springback values (0.58°–3.3°, respectively), while increasing the initial curvature angle (30°–90°), maintaining a constant speed of 4 mm/min on the first day of observation, and impacting the elastic return (6.74°–0.58°, respectively). Furthermore, the observation time demonstrated a continuous increase in the springback variation during 6 days after the flexural test before stabilization (6.89°– 8.7°), maintaining a constant value of 8 mm/min and the internal angle of doubles of 30°.

MICROSTRUCTURE AND PROPERTIES OF LASER-WELDED BUTT JOINTS OF X2CRTINB18 STEEL

The process of autogenous laser welding of stainless steel X2CrTiNb18 was investigated. The Yb:YAG disk laser was used in the study for welding of 1.5mm thick butt joins. The influence of basic laser welding parameters on the joint quality, fusion zone geometry, microhardness distribution across the butt joint, structure and microstructure of fusion zone (FZ) and heat affected zone (HAZ) was studied and determined. The quality level of the test joints was determined according to the PN-EN ISO 13919-1 standard. The chemical composition of the base metal was determined by spark emission spectroscopy. Results of the study have shown that laser welding parameters have a significant influence on the quality of butt joints. However, it is possible to produce joints that meet the high requirements and criteria of quality. The width of HAZ of the butt joints welded in the investigated range of parameters was narrow and did not exceed 0.2 mm. It was found that the most common imperfections of the analysed joints are concavity of the weld face and insufficient penetration. The HAZ region of joints is characterized by mainly ferritic microstructure with complex carbides precipitates. In turn, the fusion zone is dominated by a ferritic microstructure but also precipitates were observed, which were identified as fine dispersion carbides. Hardness of the base metal is round 160÷170HV0.3. A tendency to increase in hardness in the HAZ and FZ was observed. The maximum hardness measured in HAZ was approx. 220HV0.3, while in the FZ 190HV0.3.

CORROSION RESISTANCE OF LASER WELDED SHEETS OF STAINLESS STEEL 316L

The autogenous laser welding with a disk laser was used for producing butt joins of 2.0 mm thick sheets of AISI 316L stainless steel. The influence of basic laser welding parameters on the shape, microhardness distribution, microstructure and corrosion resistance of the joints was determined. The tests of corrosion resistance were conducted in a salt chamber under artificial NaCl environment conditions. The corrosion tests were conducted in accordance with the PN EN ISO 9227 standard. The produced test joints of 2.0 mm thick stainless steel were characterized by high quality, homogeneous and low-grained microstructure, and very narrow heat affected zone. The results of microhardness measurements indicated that the fusion zone was slightly hardened comparing to the 2.0 mm thick stainless steel sheet AISI 316L. The obtained results of corrosion test under artificial NaCl environment conditions showed that the tested butt joints are resistant for corrosion under the test conditions.

Influence of heat input on intermetallic formation in dissimilar autogenous laser welding between Inconel 718 and AISI 316L steel

Intermetallic formation during dissimilar welding of Inconel and stainless steel significantly hinders producing sound-quality weld. In the present work, a high-power CO2 laser welding system is employed to join Inconel 718 and AISI 316L stainless steel without using any filler materials. The finite element based thermal model provides the temperature distribution in the weld zone and consequently the solidification parameters (G/R and G.R). The micro-segregation and intermetallic formation in laser welding are correlated with these solidification parameters. The segregation of principal alloying elements triggers the formation of intermetallic phases during solidification. The presence of various phases like Laves, NbC, and TiC in the fusion zone reduces with increase in heat input. The amount of these intermetallic phases present in the weld zone is estimated by XRD analysis. With an increase in heat input, the mode of solidification changes from columnar to equiaxed dendrites that is characterized at reduced value of solidification parameter (G/R). The intermetallic Laves particle diminishes significantly (more than 90%) with a reduction of G/R parameter. In equiaxed dendrites, the segregation and formation of these secondary particles reduces to more than 40% compared to the columnar dendritic structure. Overall, the reduction in the intermetallic particles improves the joint efficiency up to 100% with an elongation of 14.2% for the equiaxed structure of the laser welding system.

High cycle fatigue strength of additively manufactured AISI 316L Stainless Steel parts joined by laser welding

The present paper deals with the high cycle fatigue behavior of 316L stainless steel parts, obtained either by rolling or by LPBF additive manufacturing process, and their assemblies by autogenous laser welding. The aim is to study the effects of this assembly process on the fatigue strength, assessed at a 106 cycles, of additively produced parts, compared to that of raw rolled products. An original campaign of high cycle fatigue tests based on seven batches of specimens, manufactured additively or cold rolled, one-pieced or assembled, raw or polished, is carried out with a positive load ratio (R= 0.1). A stress relieving heat treatment is applied to all specimens to reduce residual stress levels. Particular attention is paid to identifying the damage mechanisms associated with each batch. Preliminary results allowed an original conclusion that laser welding does not degrade the fatigue strength of additively produced parts. In addition, the fatigue behavior of the studied system depends essentially on the stress concentration generated on the surface or a few micrometers in the underlayer, mainly by the roughness of the LPBF produced parts combined with the lack of fusion (LoF) defects, and in a second order by the geometry of the laser welding channel. Furthermore, additively produced parts showed higher sensitivity to the presence of defects than rolled parts.

Influence of heat input on bead profile and microstructure characteristics in laser and laser-hybrid welding of Inconel 617 alloy

Bead profile and microstructure analysis are greatly influenced by heat input in any welding process. The present work provides a comprehensive comparative investigation on these aspects during Autogenous Laser welding (ALW) and Laser-MIG Hybrid welding (LHW) processes in Inconel 617 superalloy. In case of LHW, weld bead profile formed was a typical wine-cup shaped one, whereas, in case of ALW, bead profile observed was Y-type shape on account of differences in number of heat sources and intensity profiles. Weld bead width and penetration depth were found to increase with heat input in both ALW and LHW processes. The fusion zone (FZ) area of LHW was found to increase by 3 times as compared to ALW as a result of high heat input in LHW than ALW. Indeed, the addition of MIG source to laser in LHW produced wide upper bead width (trebled) as compared to ALW. Radius of curvature (ROC) at neck zone, an important bead profile characteristic for assessing liquation cracking susceptibility, was found to increase with heat input and was significantly higher in LHW than ALW due to heat stagnation at neck zone. In comparison with ALW, LHW showed a coarser columnar/cellular dendritic microstructure in FZ with segregation of inter-dendritic carbides relatively richer in Mo and Cr. Secondary dendritic arm spacing (SDAS), cooling rates and microhardness will also be discussed.

Porosity, microstructure and mechanical property of welded joints produced by different laser welding processes in selective laser melting AlSi10Mg alloys

The welding process has been recently introduced to join of the materials fabricated by powder bed fusion (PBF) additive manufacturing (AM) to meet the requirement for the large parts and their repair in service. However, one of the main issues is the high susceptibility to the hydrogen pores occurred during fusion welding of the PBF aluminum (Al) alloys. Autogenous laser welding of a selective laser melting (SLM) AlSi10Mg alloy was firstly carried out in comparison with the casting AlSi10Mg alloy to examine the hydrogen pore characteristics. Single-pass welding with filler powders and laser melting deposition (LMD) welding were then performed on SLM AlSi10Mg alloys to reduce the hydrogen pores. The porosity, microstructure, microhardness and tensile property of the welded joints were investigated. As a result, a high susceptibility to hydrogen pores of SLM AlSi10Mg alloys is occurred in the weld metal (WM) of the welded joint produced by autogenous laser welding and single-pass laser welding due to the high hydrogen content pre-existing in the base metal (BM). However, LMD welding has been shown to effectively reduce the pore size and the porosity generated in the WM of SLM AlSi10Mg alloys. The laser welding of SLM AlSi10Mg alloys produces lower hardness and ultimate tensile strength (UTS) than that of the BM. However, the LMD welding of SLM AlSi10Mg alloys achieves higher hardness and UTS than those of the autogenous laser welding and single-pass laser welding, which is attributed to the refined microstructures and the reduced hydrogen pores in the WM.

Analysis of Autogenous Laser Welding in Low Carbon and Large Thickness Steel

With the use of laser welding, it is possible to join different steel, with different thicknesses, with or without the action of protective layers. The quality of laser radiation makes it possible to get certain characteristics that are impossible to get by other processes, such as high welding speeds, less metallurgical effects suffered by the heat-affected zone (ZAC), and this process also does not require filler metal, therefore it is free from possible contamination. Combined with traditional welding methods, laser welding produces narrower weld beads, allowing for better prevention of corrosion and thermal distortions. Although the process already has high industrial knowledge, some random defects, such as porosities and inconsistencies, are still found. This work presents a systematic study to determine the influence of laser welding parameters and how these parameters influence welding defects. For this, the experimental part was carried out in the welding laboratory - LABSOLDA, of the Federal University of Santa Catarina - UFSC, during the laser welding processes, a welding speed of 2.4 m/min was reached. For this experiment, argon was used as a shielding gas and 1020 steel was used as the base material.

Metallurgical and Mechanical Characterization of Low Carbon Steel—Stainless Steel Dissimilar Joints Made by Laser Autogenous Welding

This paper addresses the metallurgical and mechanical characterization of dissimilar joints made by laser autogenous welding between thin sheets of low-carbon steel (CS) and austenitic stainless steel (SS). The welding technology applied, previously optimized to produce sound dissimilar joints, is based on the heat source displacement from the weld gap centerline towards CS, in order to reduce the SS overheating. The research includes optical microscopy observations, energy dispersive X-ray analysis (EDX) to assess the wt% of Cr, Ni, and Fe in all regions of the dissimilar welded joint, hardness measurements, and tensile tests of transverse-welded flat specimens. In comparison with classical determination of the joint overall mechanical characteristics, the novelty of this research consists of experimental assessment of the local mechanical behavior of the fusion and heat affected zones by using a digital image correlation technique (VIC-2D). This is an efficient tool for determining the constitutive properties of the joint, useful for modelling the mechanical behavior of materials and for verifying the engineering predictions. The results show that the positive difference in yielding between the weld metal and the base materials protects the joint from being plastically deformed. As a consequence, the tensile loading of flat transverse specimens generates the strain localization and failure in CS, far away from the weld.

Liquation cracking in Inconel 617 alloy by Laser and Laser-Arc Hybrid welding

ABSTRACT The present study investigates susceptibility of Inconel 617 to liquation cracking in laser-based welding techniques such as autogenous laser welding (ALW) and laser-MIG hybrid welding (LHW) with variation in heat input. Advanced characterization techniques such as high-speed Nano-Indentation testing and micro X-ray diffraction techniques were utilized to analyze microstructural variations in correlating mechanical behavior of low-melting eutectics formed in partially melted zone (PMZ). Results indicated that the liquation cracking in PMZ was associated with the constitutional liquation reaction between intermetallic carbides and austenite matrix. With increase in heat input, its susceptibility reduced, although with enhancement in grain-boundary liquid film formation and was associated with the constitutional liquation of (Cr, Mo)-rich M23C6 carbides and γ matrix. Combined effect of induced thermal stress with presence of low-melting eutectics in partially melted zone was found to greatly influence liquation-cracking susceptibility in both the welding processes. Indeed, ternary eutectic comprising metallic carbides of Cr and Mo and austenite-matrix with low nano-hardness values compared to that of hard carbides present in base metal and weld fusion zone re-confirmed their influence on cracking susceptibility. Increase in heat input enhanced dissolution of Mo-rich M6C carbides that attributed to stress-relaxation and thereby reduce cracking propensity.

The effects of fusion ratio on microstructure and cryogenic toughness of dissimilar joint between SA553 and SUS304

The fusion ratio of base metal was adjusted by changing the welding conditions for dissimilar joint between SA553 and SUS304. Both the content and the size of retained austenite (RA) both at grain boundary and among martensite laths increased when the fusion ratio of SUS304 increased. The content, distribution and stability of RA were compared by SEM, TEM, XRD and EBSD before and after cryogenic treatment (−196 ℃, 100 h). After cryogenic treatment, the RA in weld metal of all specimens declined. The lower the austenite content, the more the decline ratio after low temperature immersion. The stress resulted from phase transformation played a vital role in the stability of RA according to EBSD analysis. With the decrease of RA content, the room temperature impact energy of weld metal increased, but the low temperature impact energy decreased. The difference between room temperature impact energy and low temperature impact energy is affected by the content of retained austenite. When the austenite content was higher than 30 %, the cryogenic impact toughness of weld metal met the application requirements. It is demonstrated that the dissimilar joint between SA553 and SUS304 made by autogenous laser welding is practical in the field of liquid natural gas (LNG).

Solidification cracking sensibility of narrow gap laser welding on ITER-grade austenitic stainless steel

This study aimed to investigate the solidification cracking in narrow gap laser welding (NGLW) of ITER grade austenitic stainless steel 316LN. The results show that NGLW of ITER grade 316LN presents high solidification cracking sensitivity. The cracking always occurred in the centerline of build-up weld with a certain depth, not in root and cosmetic layers. The crack mostly propagates on the surface of the weld and it could be be healed by the following layer welding. The healing efficiency depends on the overlapping zone between the two layers. Other various laser welding processes such as autogenous laser welding (ALW), double-sided NGLW, and narrow gap pulsed laser welding (NGPLW) were studied. These welding processes present better cracking resistance than that of NGLW because of the stress distribution, microstructural characteristic and constraint condition of welded joints.

Promoting austenite formation in laser welding of duplex stainless steel\u2014impact of shielding gas and laser reheating

Avoiding low austenite fractions and nitride formation are major challenges in laser welding of duplex stainless steels (DSS). The present research aims at investigating efficient means of promoting austenite formation during autogenous laser welding of DSS without sacrificing productivity. In this study, effects of shielding gas and laser reheating were investigated in welding of 1.5-mm-thick FDX 27 (UNS S82031) DSS. Four conditions were investigated: Ar-shielded welding, N2-shielded welding, Ar-shielded welding followed by Ar-shielded laser reheating, and N2-shielded welding followed by N2-shielded laser reheating. Optical microscopy, thermodynamic calculations, and Gleeble heat treatment were performed to study the evolution of microstructure and chemical composition. The austenite fraction was 22% for Ar-shielded and 39% for N2-shielded as-welded conditions. Interestingly, laser reheating did not significantly affect the austenite fraction for Ar shielding, while the austenite fraction increased to 57% for N2-shielding. The amount of nitrides was lower in N2-shielded samples compared to in Ar-shielded samples. The same trends were also observed in the heat-affected zone. The nitrogen content of weld metals, evaluated from calculated equilibrium phase diagrams and austenite fractions after Gleeble equilibrating heat treatments at 1100 °C, was 0.16% for N2-shielded and 0.11% for Ar-shielded welds, confirming the importance of nitrogen for promoting the austenite formation during welding and especially reheating. Finally, it is recommended that combining welding with pure nitrogen as shielding gas and a laser reheating pass can significantly improve austenite formation and reduce nitride formation in DSS laser welds.

Narrow gap laser welding (NGLW) of structural steels—a technological review and future research recommendations

Advanced welding processes for structural materials are gaining increasing importance for strategic applications in nuclear, aerospace, automobile, and defence sectors. These processes have been designed keeping in view the criterion of minimal stress generation, microstructure retentivity, and process reproducibility. Narrow gap laser welding (NGLW) is one such advanced welding technique that has been developed in the past decade owing to its fabricate-ability of thick-section steels at high welding speeds. Of the many advantages, several characteristics of the process outperform the traditional arc welding processes as well as single-pass autogenous laser welding, including process flexibility, increased welding productivity, excellent weld properties, and the potential for automation. This paper provides a state-of-the-art technological review on the NGLW process primarily for structural steels covering several topics including the effect of process parameters, structure-property relationship, and induced defects and residual stresses of NGLWed joints. A list of future research recommendations based on several research gaps is also reported in this article.

Fiber laser welding of AA 5754 in the double lap-joint configuration: process development, mechanical characterization, and monitoring

Aluminum alloys are widely spread in many industrial sectors due to their desirable characteristics as low density, good formability, high specific strength, and good resistance to corrosion. Autogenous laser welding is a technology that enables the use of these materials in the industrial process due to its high repeatability, reliability, and ease of automatization. In particular, in automotive applications, Al-alloys are welded in lap-joint configurations with more than 2 layers of material. The welding condition should be monitored in order to detect the complete penetration, hence guaranteeing the appropriate weld resistance. The use of non-invasive and coaxial monitoring solutions is highly desirable for the identification of weld defects during the process. This study investigates an autogenous laser welding process and monitoring in the double lap-joint configuration of sheets of AA 5754. First, the process parameters are investigated to identify the geometrical and mechanical characteristics of the resultant welding seams at different process conditions. The employed high-brilliance 3 kW fiber laser provided the possibility of reading the back-reflected light signal from an internal photodiode. The capability of this signal to be used as a non-invasive, coaxial, and remote monitoring system in order to predict the process outcome was tested. In the experiments the back-reflected light intensity could be correlated to the weld seam width at the second interface, as well as the strength of the joint to shear. Finally, the monitoring signal behavior was demonstrated under simulated weld defect conditions. The results show that weld anomalies such as lack of penetration, misalignment, and gap formation can be sensed through the monitoring approach.

Improvement in microstructure and high-temperature brittleness of laser-welded Ti-22Al-25Nb joints with the addition of TiB2 powder

Laser-additive welding using TiB 2 powder with different weight fractions and sizes was applied to join a Ti-22Al-25Nb (at.%) alloy. In the heat-affected zone (HAZ), the O→B2 phase transformation led to the formation of a single B2 phase region. In the case of the joints produced using the TiB 2 powder with a particle size of 4–10 μm, the fusion zone was composed of the B2 and intergranular TiB phases. In the case of the joints produced using the 40–100-μm TiB 2 powder, the B2 and intergranular TiB phases and unmelted TiB 2 particles were formed in the fusion zone as the TiB 2 weight fraction was higher than 6.0 wt.%. When the laser-additive welding was carried out using 3.1 wt.% of the 4–10-μm TiB 2 powder, the fusion zone grain size decreased to 63.1 μm, and the low-angle grain boundary (< 15°) fraction decreased to 10.4 % as compared to the case when autogenous laser welding was carried out. The intergranular TiB phase suppressed the formation of the O phase and improved the tensile properties of the joints at 650 °C. The high-temperature brittleness of the Ti 2 AlNb joints improved significantly with the addition of 3.1 wt.% of the 4–10-μm TiB 2 powder.