Post-weld Annealing Research Articles

Microstructure and mechanical properties of continuous drive friction welded Ti2AlNb alloy under different rotational rates

Ti2AlNb-based alloy was joined in a continuous drive friction welding machine under different rotational rates (500, 1000 and 1500 r/min). The microstructure and mechanical properties of the joints were investigated. It is shown that the weld zone (WZ) is fully composed of recrystallized B2 phase, and the grain size decreases with increasing rotational rate. The thermo-mechanically affected zone (TMAZ) suffers severe deformation during welding, due to which most of original precipitation phase is dissolved and streamlines are present. In the heat affected zone (HAZ), only the fine O phase is dissolved. The as-welded joint produced using 1000 r/min has the best mechanical properties, whose strength and elongation are both close to those of the base metal, while the as-welded joint obtained using 500 r/min exhibits the worst mechanical properties. Post-weld annealing treatment annihilates the deformation microstructure and fine O phase precipitates in the joints, consequently improving the mechanical properties significantly. Decomposed α2 phase is a weakness for the mechanical performance of the joint since microcracks are apt to form in it in the tensile test.

Characterization and modeling of laser transmission welded polyetherketoneketone (PEKK) joints: Influence of process parameters and annealing on weld properties

Welding high-performance thermoplastics has gained popularity across various industries such as automotive, aerospace, and medical. Laser transmission welding (LTW) has emerged as an effective method for joining thermoplastic parts due to its precise control and high joint quality. PAEK (polyaryletherketone) are wide spreading over various industrial applications as a substitute to metals and thermosets when high durability and performance are required. Polyetherketoneketone (PEKK) is one of these PAEK and it has received less attention than PEEK until now. PEKK, being a semi-crystalline thermoplastic, requires additional care during processing due to its propensity to crystallize. This study presents both experimental and numerical investigations into LTW of PEKK molded parts, aiming to understand the influence of welding parameters and crystallinity on weld joint morphology and mechanical properties. PEKK plates, prepared in amorphous and semi-crystalline states, are subjected to LTW using a 975 nm diode laser. Material characterization confirms differences in crystallinity between the samples, which affect their thermal and optical properties, which are crucial for welding. Welding tests are conducted with varying laser power (between 75 and 95 W) and semi-transparent part thickness (2 and 4 mm). The morphology of joints is analysed. Assemblies undergo post-weld annealing treatment to examine its influence on weld crystallinity and consequent mechanical properties. Results reveal an anisotropic distribution of crystallinity within the heat-affected zone (HAZ). The depths of the molten layer (ML) and semi-crystalline layer (scL) vary with laser power and assembly type. A notable decrease in weld strength with laser power is highlighted, while annealing leads to enhanced crystallinity and improved weld strength. Despite variations, high weld strengths are achieved with annealing. Computational modelling elucidates the complex interplay between laser irradiation, temperature distribution, and crystallization kinetics observed experimentally. Overall, this comprehensive investigation provides valuable insights into optimizing LTW parameters for PEKK parts.

Effect of post-weld heat treatment on microstructure and mechanical properties of twinning-induced plasticity (TWIP) steel joints

The effect of post-weld heat treatment on microstructure and mechanical properties of twinning-induced plasticity (TWIP) steel joints obtained by melting electrode inert gas-shielded welding (MIG welding) was systematic studied. A total of two post-weld heat treatment processes are proposed, i.e., post-weld annealing treatment (PWAT) with temperature/time of 1100 ℃/1 h and subsequent furnace cooling and post-weld solution treatment (PWST) with temperature/time of 1100 ℃/1 h and subsequent water quenching, which were compared with the case of post-weld non-treatment (PWNT). Following annealing treatment at 1100°C, the joint tensile strength dropped by 6.6 % (from 845.46 MPa to 789.85 MPa), while its elongation at break increased by 40.87 % (from 29.80 % to 41.98 %). The significant increase in plasticity was due to the significant elimination of weld stresses in the joints after annealing. Moreover, the stresses in the weld metal of the PWST joints were instead significantly elevated and the carbides were solidified, which resulted in the lower strength. When post-weld heat treatment was applied, the impact toughness of the joints was lower than when untreated. This was primarily due to the greater percentage of the low-angle grain boundaries and the precipitation of MC-type carbides. Consequently, post-weld annealing treatment was an effective method to further enhance the strong plasticity of new twinning-induced plastic steel joints.

Enhanced Toughness and Ductility of Friction Stir Welded SA516 Gr.70 Steel Joint via Post-Welding Annealing.

The SA516 Gr.70 steel possessing excellent toughness and plasticity has been widely used in the cryogenic field. However, the appearance of coarse bainite in the heat affected zone (HAZ) of the fusion welded joint deteriorates the toughness and ductility. In this work, 4.5 mm thick SA516 Gr.70 steel was joined using shielded metal arc welding (SMAW) and friction stir welding (FSW), respectively, and the microstructure and mechanical properties of joints were investigated in detail. The Charpy energy in the HAZ in the FSW joint was 80 J/cm2, which was higher than that of the HAZ in the SMAW joint (60 J/cm2) and due to microstructure refinement. In addition, the total elongation (TE) of the SMAW joint was 17.5%, which was higher than that of the FSW joint (12.1%) and caused by a wider nugget zone with high hardness. The post-welding annealing was used to improve the toughness and ductility of the SMAW and FSW joints, and the microstructure and mechanical properties of the joints after annealing were analyzed. The toughness in the HAZ of the SMAW and FSW joints were 80 and 103 J/cm2, and the TE of the SMAW and FSW joints were 18.6% and 25.2%, respectively. Finally, the as-annealed FSW joints exhibited excellent toughness and ductility. The abovementioned excellent mechanical properties were primarily attributed to the appearance of tempering martensite, decrease in dislocation density, and fine grain.

Improved resistance to hydrogen embrittlement in the nugget zone of friction stir welded medium Mn steel via post-welding annealing

In this work, medium-Mn steel was friction stir welded and then intercritically annealed. Hydrogen diffusion and hydrogen embrittlement (HE) behavior in the nugget zone (NZ) were investigated. The as-welded NZ exhibited the highest HE index (HEI) of 79.2%, and hydrogen‑induced cracks propagated along the grain boundary, probably depending on grain boundary decohesion caused by H segregation. However, this condition was improved by post-welding annealing since fine lath reversed austenite, acting as a strong hydrogen trap, was introduced into the ferritic matrix, inhibiting the segregation of H to grain boundaries. Ultimately, the lowest HEI of 10.7% was obtained in the as-annealed NZ.

Post-weld annealing of friction stir welded carbon fiber reinforced low-melt polyaryletherketone

This study explores the influence of post-weld annealing on friction stir welded (FSW) carbon fiber reinforced thermoplastic (CFRTP) in woven laminate form. Field advancement occurs in three key areas including furthering the understanding low-melt polyaryletherketone (LMPAEK) welding/processing, effects of post-weld annealing on CFRTP joints, and determining feasibility for friction stir welding (FSW) of thermoplastics reinforced with continuous carbon fibers. High temperature annealing just below LMPAEK’s melting point improved ultimate tensile strength by up to 30% and weld toughness by up to 91%. Improvements to mechanical performance result from increases in joint crystalline content from 14.09% in non-annealed joints to 27.91% in joints subject to 280 ◦C annealing. Annealing does not reduce porosity in the weld zones, rendering necessary further improvements to the FSW process for CFRTP joints. Further analysis also indicates that despite its slight molecular modifications, LMPAEK has highly similar crystalline structure and response to thermal treatment compared to PEEK.

Weldability of ductile cast iron using AISI-316L stainless steel ER rod

This paper analyzes the corrosion resistance and the mechanical and microstructural properties of a welded joint of ductile cast iron using AISI316L stainless steel as filler material and three different heat treatments: preheating at 250 and 450 ºC and a post-weld annealing treatment. The results show the presence of ledeburite at the interface between the weld bead and the heat affected zone and at the root pass, along with a loss of strength and ductility when the welding coupons are preheated. An annealing does not eliminate the presence of ledeburite and leads to a massive precipitation of chromium carbides at the areas of the weld bead where dilution is higher. Corrosion rate was lower for the annealed coupon, but in that case, the corrosion of the weld bead increases due to the precipitation of chromium carbides.

Improvement in toughness and ductility of friction stir welded medium-Mn steel joint via post-welding annealing

The medium-Mn steels have a great application potential in the engineering fields due to its excellent strength and toughness. However, the presence of coarse martensite and segregation of Mn in the fusion-welded medium-Mn steel joint severely deteriorated toughness and ductility. In this work, 6 mm thick medium-Mn steel plates were joined by friction stir welding, and then were intercritically annealed to enhance the toughness and ductility of the joint. The as-welded nugget zone (NZ) contained lath martensite with low proportion of high angle boundaries (HABs), leading to the joint with lower elongation of 22.5% and the impact energy of 73.6 J/cm 2 . However, the as-annealed NZ consisted of ferrite and austenite because partial martensite changed to reversed austenite, while other martensite became ferrite during annealing. In addition, the proportion of HABs in the as-annealed NZ increased obviously. In comparison with as-welded joint, the impact energy and elongation of the as-annealed joint was increased by 70.7% and 44.4%, respectively. The abovementioned excellent mechanical properties were attributed to the high proportion of HABs and a large amount of ultra-fine reversed austenite with high thermal and mechanical stability, which provided a significant transformation induced plasticity effect, obviously inhibiting crack initiation and propagation. This systematic work provided a reference for welding similar materials containing retained austenite.

Effect of Post-Weld Annealing on Microstructure and Growth Behavior of Copper/Aluminum Friction Stir Welded Joint.

Friction stir welding of 1016 pure aluminum and T2 pure copper with 2 mm thickness was carried out in the form of lap welding of copper on the upper side and aluminum on the lower side. The growth of interface microstructure between 1016 pure aluminum and T2 pure copper welded by friction stir welding was studied. The growth mechanism of the intermetallic compound (IMC) layer in the Cu-Al lap joint was revealed by annealing at 300, 350, 400 °C. The intermetallic compound (IMC) layer in the lap joint grows again during annealing, and only the original structure of the intermetallic compound (IMC) layer grows at lower annealing temperature and holding time. At higher annealing temperature and holding time, the original structure of intermetallic compound (IMC) layer no longer grows, and a new layered structure appears in the middle of the original structure. There is a gradient change of microhardness in the nugget zone. With different holding times, different softening phenomena appear in the metals on both sides of copper and aluminum. When the hardness decreases to a certain extent, it will not continue to decrease with the increase of holding time. When the annealing temperature is 350 °C and 400 °C, the strength of the tensile sample increases first and then decreases with the increase of holding time. At the interface of Cu-Al, the fracture runs through the whole intermetallic compound (IMC) layer.

The effect of annealing temperature on microstructure and mechanical properties of dissimilar laser welded superelastic NiTi to austenitic stainless steels orthodontic archwires

Annealing after welding is a common operational process to improve the mechanical properties of metallic joints through releasing residual stresses in the weld zone. In this study, the effect of post weld annealing on the microstructure and mechanical properties of dissimilar laser-welds for orthodontic archwires of NiTi alloy to austenitic stainless steel has been investigated. In order to do this, the laser-welded wires were annealed at temperatures of 100, 200, and 300 °C for 1 h and then they were quenched in water. Results show that annealing at 100 °C does not affect the microstructure and mechanical properties of joints but post weld heat treatment at 200 °C ends in an increase in the tensile strength to an order of 1.91 times of the strength of as welded (non-heat-treated) joints. Also, precipitation and increase of intermetallic compounds, such as Cr2Ti, and Fe2Ti, at the weld zone during heat treatment at 300 °C, results in a reduction in the mechanical properties of joints. Therefore, post-weld annealing is an effective process on improving mechanical properties of dissimilar joints of these two alloys. However, a suitable heat-treatment temperature is needed in order to achieve desired results.

Towards a better understanding of the phase transformations in explosively welded copper to titanium sheets

The influence of post-process annealing on the growth kinetics of the intermetallic phases and mechanical properties of titanium/copper bimetallic sheets were analysed using scanning and transmission electron microscopies, X-ray synchrotron radiation, and mechanical testing. In order to weld two metal sheets, an explosive welding technique was utilised. Subsequently, the clads were subjected to post-weld annealing at 973 K from 0.25 to 1000 h. In the bonded state, the interface exhibited a wavy structure with only a small amount of solidified melt zones, composed of non-equilibrium phases of variable chemical compositions. After short annealing times (<1 h) these non-equilibrium phases transformed into equilibrium phases of TiCu4 and Ti3Cu4via spinodal decomposition. For longer annealing times (>1 h), the growth of four intermetallic layers: Ti2Cu, TiCu, Ti3Cu4, and TiCu4 situated along the entire interface is predominant. It was observed that the phases enriched with Cu and Ti were situated near the Cu and Ti parent sheets, respectively. The nano-hardness of the intermetallic phases decreased as the Ti content increased, whereas the Young's modulus reached its highest values for phases with equiatomic or close-to-equiatomic composition.

Effect of post heat treatment on the phase composition and strength of laser welded joints of an Al–Mg–Li alloy

In the present work, the effects of laser beam welding and post-weld heat treatment on the phase composition and mechanical properties of the 1424 alloy (Al–Mg–Li) joints were investigated. Holding the joints at a certain temperature was followed by quenching and artificial aging. The structural studies were carried out using electron microscopy, conventional X-ray diffractometry, and synchrotron radiation diffractometry. The heat treatment conditions were optimized to favor the formation of strengthening phases in the welds, the presence of which imparted mechanical strength to the joints. For the first time, 1424 Al alloy joints with a weld strength of σuts = 500 MPa have been obtained; this value of strength was achieved by applying post-weld annealing followed by quenching and artificial aging.

Pathways to improve the austenite–ferrite phase balance during resistance spot welding of duplex stainless steels

ABSTRACTTwo different transformation pathways were employed to improve the phase balance in the fusion zone (FZ) of 2304 duplex stainless steel during resistance spot welding: (i) downsloping current modification aiming at controlling the weld cooling rate and (ii) in situ post-weld short annealing of the weld aiming at formation of secondary austenite in the FZ. Both pathways enabled enhancing the austenite volume fraction in the FZ. However, the in situ post-weld annealing was more effective than the downsloping current modification. It was proved that generating a homogenous microstructure with an improved phase balance via proper in situ post-weld annealing treatment can enhance the corrosion resistance of the weld nugget compared to the unbalanced FZ produced in the as-welded condition.

Effect of Annealing on the Microstructure and Properties of Electron Beam Welded 4J34 Kovar Alloy

Electron beam welding of 4J34 Kovar alloy was conducted, and the microstructure and mechanical properties of the joints in as-welded and postweld annealing treatment (PWAT) states were investigated. The martensitic transformation occurred and led to the generation of α lath martensite due to the rapid cooling in the as-welded condition. After annealing treatment, part of the α martensite transformed to γ austenite and subsequently developed the bulk γ phase and α/γ lamellar microstructures in the fusion zone (FZ) of the postwelded joint. Grains in the heat-affected zone (HAZ) clearly developed and penetrated into the FZ, causing the disappearance of the fusion line between the FZ and the HAZ. All the joints in both the as-welded and PWAT conditions exhibited ductile fracture. The maximum tensile strength of 505 MPa was obtained in the as-welded joint with the welding speed of 150 mm/min. The linear expansion coefficients of the joint and base metal decreased with the increase in temperature. However, the decreasing rate of PWAT joints was lower than that of the as-welded joints.

Effect of the Heat-Treatment Conditions on the Structure and Mechanical Properties of the Base and Weld Materials of the VT41 Alloy Blisks in the HPC of an Advanced Engine

The influence of the conditions of complete and incomplete postwelding annealing on the strength properties of the welded joints of a VT41 alloy is studied. These annealing conditions are developed for the ring welded joints of a VT41 alloy. The optimum conditions are determined for the production of large welded joints of a VT41 alloy for a high-pressure compressor in an advanced engine. The mechanical properties of the base and weld metals are compared after complete and incomplete postwelding annealing. The microstructure of the welded joints after heat treatment is investigated.

Correlation between softening mechanisms and deformation non-uniformity of laser-welded titanium alloy tube during gas bulging process

In this paper, post-weld annealing was carried out to adjust the flow stress difference between weld seam and base material (BM). Deformation non-uniformity of laser-welded titanium alloy tubes before and after annealing was evaluated by gas bulging at 800°C. Results show that after double annealing (950°C/2h, air cooling+600°C/2h, air cooling), weld seam and BM had similar peak stress at first during tensile test at 800°C, 0.001s−1, then the flow stress difference between them changed dynamically due to different softening rates. The maximum flow stress difference ratio was reduced from 36% to 17% after annealing. Deformation uniformity of the bulged tube was improved by 24.6% after annealing, but the higher softening rate of BM during gas bulging confined its further improvement. At early stage of gas bulging of the annealed tube, the main softening mechanism for weld seam was dynamic recovery and that for BM was globularization of secondary α and phase transformation of α to β. At middle-late stage of gas bulging, the main softening mechanism for weld seam was partial globularization of lamella α and that for BM was wide dynamic recrystallization.

Impact Property of Low-Activation Vanadium Alloy NIFS-HEAT-2 After Electron Beam Welding and Neutron Irradiation

In order to investigate the effect of post-weld heat treatment (PWHT) and post-irradiation annealing (PIA), electron-beam-weld specimens of the reference low activation vanadium alloy, NIFS-HEAT-2, were neutron-irradiated to a fluence of 7.62 × 1023 neutron m−2 (E > 1 MeV) at 563 K in Belgian Reactor-2. In the present experiments, unexpected oxidation of the surface of the samples occurred during the neutron irradiation, and significantly degraded impact properties of the weld metal, while the degradation was not significant for the base metal. The removal of the oxidized layer by electro-polishing improved the impact properties of the weld metal. Although complete removal of the oxidized layer could not be confirmed, it is revealed that impact absorbed energy of the weld metal with post-weld heat treatment at 1073 K was comparable to that of the base metal after the post-irradiation polishing. In other words, irradiation embrittlement of the weld metal was successfully suppressed by the PWHT. PIA at 773 K and above was effective to recover the irradiation hardening and irradiation embrittlement. Mechanisms of the irradiation hardening, irradiation embrittlement and its recovery were discussed.

Improvements in W-Eurofer first wall brazed joint using alloyed powders fillers

This paper studies the improvements of 80Cu-20Ti alloyed powders as filler material for W-Eurofer joints of the next generation of fusion power plants. The advantages derived from their alloyed composition allow shortening the heating stage up to 3 times with respect to pure powders. Besides, the better flowing capabilities and lower melting range make possible to work with lower brazing temperature. Operational brazeability of W-Eurofer joints using a mixture of 80Cu-20Ti alloyed powders has been achieved for brazing temperatures of 960°C and 940°C, holding the temperature during 1–5 and 10min, respectively. Hardening and softening processes of the Eurofer occurs during the brazing cycle, but the as received hardness conditions could be recovered by the application of a post-weld annealing treatment. The highest shear strength was obtained for the sample fabricated at 960°C for 5min.

Growth kinetics of Al–Mg intermetallics during post-weld annealing treatment

We explored the growth kinetics of intermetallic compound (IMC) layers at the joint interface of the friction stir lap welded Mg alloy to Al alloy joint during post-weld annealing treatment. The intermetallic layer formed between the Al alloy and Mg alloy was composed of continuous β phase and γ phase; the β phase layer grows faster than the γ phase layer. A quantitative analysis of the IMC layer thickness as a function of aging time and temperature was performed. The diffusion coefficients were calculated from the parabolic relationship between the migration of the interface and the annealing time. The activation energies for IMC growth were determined as 113.5 and 69.3 kJ mol−1 for the γ and β phases, respectively.

Effect of Nano-Particle Addition on Grain Structure Evolution of Friction Stir-Processed Al 6061 During Postweld Annealing

The fabrication of nano-composites is quite challenging because uniform dispersion of nano-sized reinforcements in metallic substrate is difficult to achieve using powder metallurgy or liquid processing methods. In the present study, Al-based nano-composites reinforced with Al2O3 particles have been successfully fabricated using friction stir processing. The effects of nano-Al2O3 particle addition on grain structure evolution of friction stir processed Al matrix during post-weld annealing were investigated. It was revealed that the pinning effect of Al2O3 particles retarded grain growth and completely prevented abnormal grain growth during post weld annealing at 470 °C. However, abnormal grain growth can still occur when the composite material was annealed at 530 °C. The mechanism involved in the grain structure evolution was discussed therein.