Effect of post-weld heat treatment on microstructure and mechanical properties of welded joints of 6061-T6 aluminum alloy

6061 aluminum alloy T-joints were welded by double-pulsed MIG welding process. Then, the post-weld heat treatment was performed on the welded T-joints. The weld microstructure under different aging temperature and time was investigated by transmission electron microscopy and scanning electron microscopy. The mechanical properties were examined by hardness test and tensile test. The results showed that the micro-hardness was sensitive to heat treatment temperature and time. Increasing temperature was beneficial to the shortening of peak aging time. There were a large number of dislocations and few precipitates in the welded joints. With the increase of post-weld heat treatment temperature and time, the density of dislocation decreased. Meanwhile, the strengthening phase precipitated and grew up gradually. When the post-weld heat treatment temperature increased up to 200℃, large Q' phases were observed. And they were responsible for the peak value of the micro-hardness in the welded joints.

Effect of post-weld heat treatment on microstructure and properties of Ti-23Al-17Nb alloy laser beam welding joints

The mechanical properties of Ti-23Al-17Nb (mole fraction,%) laser beam welding alloy joint at room temperature are comparable to that of the base materials.However,the strength and ductility of the as-welded joint deteriorate seriously after high temperature circulation.The effect of post-welded heat treatment on the microstructure and mechanical properties of the joint was investigated.The heat treatment was taken at 980 ℃ for 1.5 h,then furnace cooling and air cooling were performed separately.The results indicate that proper post-welded heat treatment improves the ductility of the joint at high temperature.

Effect of post-weld heat treatment on joint properties of dissimilar friction stir welded 2024-T4 and 7075-T6 aluminum alloys

The effect of post-weld heat treatment on dissimilar friction stir welded AA7075 and AA2024 joints was studied. After welding in constant parameters, solution heat treatment and various aging treatments were given to the welded joints. Microstructural and phase characterizations were done using optical microscope, SEM, FE-SEM, XRD and EDS techniques. Finally, mechanical properties of post-weld heat treated joints were evaluated and compared with as-welded joints. Results show that both 2024-T6 and 7075-T6 post-weld heat treatment procedures considerably improve the mechanical strength of the welded joint, with higher strength obtained for the 7075-T6 procedure, in comparison with the as-welded joint. This is explained by the formation of fine precipitates during the aging process, despite the abnormal grain growth. Fracture occurs at the interface between thermo-mechanical affected zone（TMAZ） and heat affected zone（HAZ） on the retreating side（AA7075） of as-welded joint, while by applying post-weld heat treatment fracture location shifts towards the stir zone（SZ） of the welded joint. Also, for post-weld heat treated samples, fracture surface is predominantly inter-granular, while in as-weld joint, fracture surface is mostly trans-granular. This is explained by dissolution and coarsening of precipitates within grains in post-weld heat treated joints.

Effect of Post-weld Heat Treatment on Microstructure and Mechanical Properties of Friction Stir Welded SSM7075 Aluminium Alloy

7XXX series aluminium alloys generally present low weldability by fusion welding methods because of the sensitivity to weld solidification cracking, vaporization of strengthening alloys and other defects in the fusion zone. Friction stir welding（FSW） can be deployed successfully with aluminium alloys. We presented the effect of post-weld heat treatment（PWHT） on the microstructure and mechanical properties of SSM7075 joints. Semi solid plates were butt-welded by FSW at a rotation speed of 1110 r/min, welding speeds of 70 and 110 mm/min. Solution treatment, artificial aging, and T6（solution treatment and artificial aging combined） were applied to the welded joints, each with three samples. It was found that the T6 joints at the speed of 70 mm/min yielded the highest tensile strength of 459.23 MPa. This condition best enhanced the mechanical properties of FSW SSM7075 aluminium alloy joints.

Microstructure characterization of electron beam welded joints of Ti_3Al after post-weld heat treatment

The effect of post-weld heat treatment on the microstructure characterization of electron beam welded(EBW) joints of Ti3Al-Nb was investigated.The results show that the microstructure of the weld is predominantly metastable,the columnar crystal metastructure of B2 phase.The microstructure morphology of the weld is significantly influenced by the method of the heat treatment.The microstructure of the weld is laminar structure(Widmanstaten structure) consisted of interphase α2 and B2 after post-weld heat treatment of 1000 ℃/2 h.The mechanism of the post-weld heat treatment makes the hardness distribution of joints homogeneous,but makes the whole joint somehow softened.

Development of an automatic post-weld inspection system based on laser vision

In order to overcome the limitations of manual post-weld visual inspection approach, an automated inspection system is developed which uses three-dimensioual laser vision system based on the principle of optical triangulation. The system hardware consists of a modular development kit （MDK）, a computer, an actuating mechanism and so on. In image processing algorithms, extraction accuracy of centric line of laser stripe is the critical factor that determines the system performance. So according to the features of laser stripe image, a novel algorithm is developed to detect the central line of laser stripe fast and accurately. Experiments have demonstrated that this system can be used in various weld features inspection of both butt and fillet types of weld. Compared with traditional manual inspection method, this method has obvious dominance. The three-dimensional reconstruction result shows that this system has high accuracy and reliability.

Effect of Post-weld Heat Treatment on Microstructure and Fracture Toughness of 30CrMnSiNi2A Steel Welded Joints

The electron beam local post-weld heat treatment (EBLPWHT) is a rather new method that provides the advantages of high precision, flexibility and efficiency, energy saving and higher productivity. This paper studies the effect of two post-weld heat treatment processes on the microstructure, mechanical properties and fracture toughness of an electron beam welded joints in 30CrMnSiNi2A steel. EBLPWHT, in a vacuum chamber, immediately after welding and a traditional furnace whole post-weld heat treatment (FWPWHT) were compared. The experimental results show that, after EBLPWHT treatment, the main microstructure of weld was changed from coarse acicular martensite into lath martensite, HAZ was changed from lath martensite, bainite into lower bainite, and base metal was changed from ferrite and pearlite into upper bainite and residual austenite. The microstructures of different zones of joints in FWPWHT condition were tempered sorbite. The properties of welded joints can be improved by the EBLPWHT in some extent, and especially largely for the fracture toughness of welded joints. However the value of fracture toughness of base metal is comparatively low, so appropriate heat treatment parameters should be explored in the future.

Influence of post-weld heat treatment on microstructure and properties in heat-affected zone of KMN steel joint

The influence of temperature during post-weld heat treatment on the microstructure and properties of KMN steel joints was investigated. The results reveal that after heat treatment, the martensite transformed to tempered sorbite, causing the softening of the resultant joints. XRD test shows that the residual austenite content decreased obviously when the joint was heattreated at 550 ℃ and 580 ℃, which degraded the impact toughness of heat-affected zone （ HAZ）. When the heat treatment temperature increased further, the dispersion strengthening from the precipitation of alloying elements improved the impact toughness of HAZ. The aggregation and coarsening of carbide also contributed to the improvement of impact toughness of HAZ.

NUMERICAL ANALYSIS OF RESIDUAL STRESSES IN TITANIUM ALLOY DURING ELECTRON BEAM LOCAL POST-WELD HEAT TREATMENT

The distributions of temperature and residual stresses in thin plates of BT20titanium alloy are numerically analyzed by three-dimensional finite element software duringelectron beam welding and electron beam local post-weld heat treatment (EBLPWHT). Combined withnumerical calculating results, the effects of different EBLPWHT mode and parameters, including heattreating position, heating width and heating time, on the distribution of welding residual stressesare analyzed. The results show that, the residual tensile stresses in weld center can be largelydecreased when the weld is heat treated at back preface of the plate. The numerical results alsoindicated that the magnitude of the residual longitudinal stresses of the weld and the zone vicinityof the weld is decreased, and the range of the residual longitudinal stresses is increased alongwith the increase of heating width and heating time.

A new post-weld heat treatment to improve toughness of 9Cr-1Mo steel weld metals

9Cr-1Mo ferritic steels have been used in the conventional power generation plants due to their excellent creep resistance. However, one of the main obstacles in welding 9Cr-1Mo steels is the formation of undesirable coarse columnar grains in weld metal whieh ean severely compromise the toughness. A new post-weld heat treatment （PWHT） is developed in the present work. Unlike the conventional processes in which the post-weld heat treatment is carried out below Ac1 , the use of temperatures above the Ac1 of 9Cr-1Mo alloy is considered. The new PWHT at a temperature above Ac1 improves the toughness of 9Cr-1Mo weld metals effectively. The improvement in toughness is mainly due to refinement and homogenization of mierostruetures. Key words

Analysis on mechanical properties of nickel-iron steel after post-weld heat treatment

X-ray diffraction was utilized to measure the residual stress of 45 mm UNS N08810 plates after post-weld heat treatment at temperatures of 680℃ and 900℃, which showed reductions of 86.9% and 71.6% in the residual stress, respectively. This indicates that post-weld heat treatment can play a significant role in reducing residual stress, while no significant effects on tensile stress and micro-hardness of the welding joint were observed after treatment.

Microstructure and mechanical properties of friction welds between TiA l alloy and 40Cr steel rods

Direct friction welding of Ti Al alloy to 40 Cr steel rods was conducted, and the microstructure and mechanical properties of the resultant joints in as-welded and post-weld heat treatment（PWHT） states were investigated. The martensitic transformation occurred and brittle Ti C phase formed near the interface due to C agglomeration, which degraded the joint strength and increased the microhardness at the interface in as-welded state. Feathery and Widmanstatten structure generated near the interface on Ti Al alloy side. After PWHT at 580 °C and 630 °C for 2 h, the sorbite formed and C dispersed at the interface, leading to the increase of the joint strength from 86 MPa in as-welded state to 395 MPa and 330 MPa, respectively. The heat-treated specimen fractured with quasi-cleavage features through the zone 1 mm away from the interface on TiA l alloy side, but the as-welded specimen failed through the interface.

Correlation between Process Variables in Shielded Metal-Arc Welding (SMAW) Process and Post Weld Heat Treatment (PWHT) on Some Mechanical Properties of Low Carbon Steel Welds

This investigation was conducted to correlate process variables in shielded metal-arc welding (SMAW) and post weld heat treatment on some mechanical properties of low carbon steel weld. Three hundred and sixty pieces of weld samples were prepared. The samples were welded together using AWS E6013 electrodes with DC arc welding process. Varying welding currents of 100 A, 120 A, 140 A were used with a terminal voltage of 80 V. The weld samples were prepared for hardness, tensile and impact test. The prepared samples were then subjected to normalising heat treatment operation at temperatures of 590°C, 600°C, 620°C, 640°C, 660°C, 680°C, and 700°C. It was observed that increase in welding current led to an increase in hardness and ultimate tensile strength values of as-weld samples while impact strength de-creases. After post heat treatment operation the hardness and ultimate tensile strengths decreases while impact strength increases. From this outcome we conclude that there is correlation between the welding current and mechanical proper-ties of weld metal on one hand and normalising temperatures and mechanical properties on the other hand. As the cur-rent increases the hardness and strength increases but impact strength reduces, while hardness and strength continuously reduces but impact strength increases as normalising temperatures increases.

Effect of heat treatment conditions on ballistic behaviour of various zones of friction stir welded magnesium alloy joints

Ballistic behaviour of different zones of post-weld heat-treated(PWHT)magnesium alloy(AZ31B)target against 7.62 mm×39 mm armour-piercing(AP)projectile with a striking velocity of(430±20)m/s was determined.Magnesium alloy(AZ31B)welded joints were prepared by using friction stir welding(FSW)process and subjected to different heat treatment conditions.The microhardness values of non-heat-treated and heat-treated FSW joints were investigated.The results indicated that PWHT process(250°C,1 h)has improved the microhardness of heat-treated FSW joints.Scanning electron microscope(SEM)microstructure showed that heat treatment has caused the formation of fineα-Mg grains and tiny precipitates and made the dissolution ofβ-Mg17Al12 phase into the Mg matrix.The ballistic behaviour of PWHT zones was estimated by measuring the depth of penetration(DOP)of the projectile.Lower DOP value was observed for the base metal zone(BMZ)of a heat-treated welded joint.Post ballistic SEM examinations on the cross-section of all three zones of crater region showed the formation of adiabatic shear band(ASB).

In-situ evaluation for corrosion process at fusion boundary of stainless steel strip overlay joints in H2S containing solution

The present work studied the corrosion properties around the fusion boundaries of 2.25Cr-1Mo steel with stainless steel strip overlay joints under as welded condition and after post-weld heat treatment (PWHT) in H2 S containing solution (NACE TM-01-77 standard) with different time. An in-situ observation method was introduced for evaluating corrosive progress in the fusion boundary in H2 S containing solution, that is, the samples were marked firstly at the boundary and then treated in the solution for variant time. Each time after the corrosion treatment, the observations were kept to focus at the same marked area by using scanning electron microscopy (SEM) to observe the corrosion progress. The results reveal that the fusion boundary is the worst region for corrosion resistance when comparing with other boundaries, and a broad fusion boundary has a stronger resistance for "hydrogen induced disbonding" than a narrow one.

Effect of bonding temperature and heat treatment on microstructure and mechanical property of Mg−6Gd−3Y alloy vacuum diffusion bonded joints

Diffusion bonding of as-cast Mg−6Gd−3Y magnesium alloy was carried out at temperatures of 400−480℃ with bonding pressure of 6 MPa for 90 min.Diffusion bonded joints were solution treated at 495℃ for 14 h and then aged at 200℃ for 30 h.Microstructures and mechanical properties of joints were analyzed.The results showed that rare earth elements and their compounds gathering at bonding interface hindered the grain boundary migration crossing bonding interface.Tensile strength of as-bonded and as-solution treated joints increased firstly and then decreased with the bonding temperature increasing due to the combined effects of grain coarsening and solid-solution strengthening.As-bonded and solution-treated joints fractured at matrix except the joint bonded at 400℃,while aged joints fractured at bonding interface.The highest ultimate tensile strength of 279 MPa with elongation of 2.8%was found in joint bonded at 440℃ with solution treatment followed by aging treatment.

Development of SA-533 Type B CL. 1+SA-240 Type 304L roll-bonded clad steel plate for safety injection tank of CAP1400 nuclear power plant

Aiming to meet the demand of the country＇ s nuclear demonstration project on the CAP1400 nuclear power plant, Baosteel uses the roll-bonding technology and develops the SA-533 Type B CL. 1 ＋ SA-240 Type 304L high-strength and high-toughness clad steel plate with a shear strength of over 310 MPa for the nuclear power plant＇ s safety injection tank. The properties of the quenched and tempered and the simulated post-weld heat treatment states are systematically studied herein through a comprehensive inspection and evaluation of the composition,microstructure,and properties of the clad steel plate. The results show that the bonding interface has high shear strength and that the base metal has high strength and good toughness at low temperatures. Hence, the performance fully meets the technical requirements of the CAP1400 nuclear power plant＇ s safety injection tank in the country＇ s nuclear demonstration project. The roll-bonded clad steel plate can be used to manufacture the safety injection tank of the CAP1400 nuclear power plant.

Residual Stress Consideration in Fatigue Damage of Offshore Wind Turbine Monopiles: To Be or Not to Be?

The purpose of this paper was to investigate the impact of residual stresses on fatigue damage of offshore wind turbine monopiles by numerical analysis approach using ABAQUS software, a finite element analysis (FEA) tool. Three monopile models with the same dimension (within standard range) have been developed in ABAQUS and partitioned circumferentially into equal rings. Longitudinal partitions have been rotated through 180°as obtainable in practice. Characteristic loads typical of a real life offshore wind turbine environment have been applied to all three models, with tensile and compressive residual stresses applied as additional loads at the critical weld region to the first and second models while the third model had no additional load. With zero boundary conditions applied in all six degrees of freedom, the simulation has been run for 107 cycles of wind and wave loads as recommended in standards in each case. Stress results obtained from the critical weld region in the three models showed that the presence of tensile residual stresses equal to the material yield stress contributed a maximum 0.05% to fatigue damage of the monopile when compared with results from the model with no residual stress while the presence of compressive residual stresses with the magnitude of the yield stress of the material caused a gain of 0.06% in fatigue life by similar comparison, indicating negligible contribution of residual stresses to the stress build up in the critical weld region, thus suggesting that the magnitude of the residual stress as high as the yield stress of the material of the monopile is not large enough to cause the monopile to open up in the axial direction.

Effects of Microstructural Modification Using Friction Stir Processing on Fatigue Strength of Butt-Welded Joints for High-Strength Steels

Friction stir processing (FSP) is an effective surface-microstructure modification technique using a rotational tool to refine and homogenize microstructure of metallic materials. In this study, FSP was conducted on the surface of the heat-affected zone (HAZ), which is a region exhibiting degraded mechanical properties and shown to have microstructural changes, of butt-welded joints for two high-strength steels with tensile strength grades of 490 MPa and 780 MPa (hereafter HT490 and HT780, respectively). Inhomogeneous mixing of materials derived from weld metals and base metals (BMs) in a stir zone (SZ) produced inhomogeneous distribution of elements and microstructure depending on the set of the advancing side and retreating side in the SZs. The welded joints with FSP for HT490 exhibited higher hardness than that of the BM through whole of the SZ surface (fine polygonal ferrite grains and bainite structure with laths at the Mn-rich and Mn-poor regions, respectively). On the other hand, those for HT780 exhibited the minimum hardness value similar to that of the BM at the SZ surface (a few polygonal ferrite grains in the matrix of martensite laths). Fatigue strength increased by about 35 MPa and 15 MPa in stress amplitude at 107 cycles as fatigue limit due to FSP. Fatigue failure occurred at the BM and the SZ, respectively, in the welded joints modified by FSP for HT490 and HT780, in comparison with the HAZs in the as-welded joints for both grade steels. The difference in fatigue strength increase due to FSP and failure location between the welded joints for HT490 and HT780 can be attributed to the topmost SZ microstructures and their distribution.

Microstructure,mechanical properties and post-weld heat treatments of dissimilar laser-welded Ti_(2)AlNb/Ti60 sheet

Dissimilar joining of Ti_(2)AlNb and Ti60 rolled sheet was performed by laser beam welding.The microstructures and mechanical properties of as-welded and post-weld heat-treated Ti_(2)AlNb/Ti60 joints were investigated by microstructure observation and mechanical properties testing.The fusion zone(FZ)of the as-welded joint consisted of B_(2)/βmatrix and small S2 balls.The heataffected zones HAZ-Ti_(2)AINb and HAZ-Ti60 for the aswelded joint were characterized asα_(2)+B_(2)/β+O andα'+α+β+S_(2),respectively.The tensile strength and elongation of as-welded sheet were 597.5 MPa and 6.2%at650℃,respectively.Most of the plastic deformation was taken place at the side of Ti60 alloy.With the increase in the heat treatment temperature,the anchoring strength between each other of B_(2)/βgrains was enhanced by the precipitated lamellarα'and O grains at the FZ.The depth of the fracture dimples increased with the heat treat temperature increasing.The heat-treated welding joint at970℃presented a good balance of the tensile strength and plasticity,where the tensile strength and the elongation were enhanced to 669.7 MPa and 7.1%at 650℃,respectively.