Effect of post weld heat treatment on properties of variable polarity TIG welded AA2219 aluminium alloy joints

AA2219 aluminium alloy joints were fabricated by variable polarity tungsten inert gas （VPTIG） welding process and the effects of post weld heat treatment （PWHT） on the tensile properties, microstructure and fatigue behaviour of the welded joints were investigated. The VPTIG welding process was adopted because it could meet the need of cathode cleaning and meanwhile it could reduce the deterioration of tungsten electrode furthest. The welded samples were divided into as-welded （AW） sample and PWHT sample. The PWHT method used on the samples was solution treatment （535 ℃, 30 rain）, water quenching and artificial aging （175 ℃, 12 h）. The experimental results show that, compared with the AW samples, the microstructure characteristics and mechanical properties of the AA2219 joints after PWHT were significantly improved. The improvement of yield strength, ultimate tensile strength, and fatigue strength are 42.6%, 43.1% and 18.4%, respectively.

Effect of post weld heat treatment on microstructure and mechanical properties of gas tungsten arc welded AA6061-T6 alloy

Double-V butt TIG welding process was performed on two plates of AA6061-T6 using ER5356 filler. The microstructure,mechanical and nanomechanical properties of the joint were evaluated in as-welded and after post weld heat treatment (PWHT) usingXRD, FESEM, EBSD, nanoindentation and tensile tests. The results show that PWHT led to microstructural recovery of the heataffected zone (HAZ) in addition to the appearance of β-phase (Al3Mg2) at the grain boundaries of weld zone. The hardness (Hnano) inall zones increased after PWHT while the elastic modulus (Enano) was improved from 69.93 GPa to 81 GPa in weld area. All resultsindicate that PWHT has created a homogenous microstructure in the weld zone in addition to outstanding improvement inmechanical properties for the weld zone which surpass the base metal.

Temperature field analysis of main steam pipe under local post weld heat treatment

In local post weld heat treatment, the temperature difference is the criterion of the process. The temperature field in the main stream pipe under local post weld heat treatment is simulated by finite element method. A close-loop control program is designed to simulate the temperature field of two different pipes. Both the skin effect of induction heating and electro-thermal coupled effect are considered in the heating model. The local heat treatment temperature difference at the inner and outer side of the pipe is analyzed and the different convection conditions are also considered. The simulation results show that in appropriate induction heating process, the temperature difference in the pipe can be controlled within 30 ℃.

Effect of Post Weld Heat Treatment on Microstructure and Fracture Toughness of Friction Welded Joint

The effect of post weld heat treatment on the microstructure and fracture toughness of friction welded joints of Ti-6.5Al-1Mo-1V-2Zr alloy was studied. The experimental results show that equiaxial grains were formed at the center of the weld metal while highly deformed grains were observed in the thermomechanically affected zone. The fracture toughness of the weld metal was lower than that of the thermomechanically affected zone under as-weld and post weld heat treatment conditions. With increasing temperature of post weld heat treatment, the fracture toughness of weld center and thermomechanically affected zone increased. The fractographic observation revealed that the friction welded joints fractured in a ductile mode.

Effect of Post-weld Heat Treatment on Mechanical Characteristics of AZ31 Magnesium Alloy Welded Joints

Tungsten inert gas（TIG） welding was performed on 2.7 mm thick commercial extruded AZ31 B magnesium alloy plates. We investigated the effect of post-weld heat treatment（PWHT） on the microstructure, mechanical properties and precipitated phase of the weld joints. The results showed that during the annealing treatment（200 ℃-1 h, 250 ℃-1 h, 300 ℃-1 h, 350 ℃-1 h, 400 ℃-1 h, and 450 ℃-1 h）, the average grain size in the weld seam was the minimum after annealing at 400 ℃ for 1 hour, and then abnormally grew up after annealing at 450 ℃ for 1 hour. The mechanical properties enhanced when the joints were processed from 200 ℃-1 h to 400 ℃-1 h but sharply decreased with increasing annealing temperature. In contrast to the annealing treatment, solution treatment（250 ℃-10 h, 300 ℃-10 h, 350 ℃-10 h, 400 ℃-10 h, and 450 ℃-10 h） exhibited a better ductility but a slight deterioration in tensile strength. Especially speaking, no eutectic compounds（such as Mg17 Al12） were observed in the weld seam. The supersaturated Al atoms were precipitated in a coarse spherical shape dispersed in the weld seam. The precipitated Al atoms dissolved in the matrix substances at the condition（400 ℃-1 h） or（250 ℃-10 h）. The solution treatment caused grain coarsening and precipitated Al atoms dissolved in the weld seam substantially, which resulted in a drop in micro-hardness at the weld seam compared to the area of the annealed joints.

Prediction of welding residual stress in multipass narrow gap welded pipes with large thickness

The objective of this study is to investigate the influence of post weld heat treatment （PWHT） on the distribution of residual stress in welded pipes with large thickness. The detailed pass-by-pass finite element simulation was developed to study the residual stress in narrow gap multipass welding of pipes with a wall thickness of 150 mm and 89 weld beads. The effect of PWHT on welding residual stress was also investigated by means of numerical analysis. The simulated results show that the hoop stress is tensile stress in the weld region and compressive stress in the parent metal areas adjacent to weld seam. After heat treatment, the residual stresses decrease substantially, and the simulated residual stress is validated by the experimental one. The distribution of the through-wall axial residual stress along the weld center line is a self-equilibrating type.

Evolution behavior of phase and performance in Ni-based coating layer based on high temperature thermal field

Effect of post-welding heat treatment on the microstructure and properties of BNi-2 brazing coating was analyzed. The phase transformation in the heat treatment process was analyzed by high temperature metallographic microscope, scanning electron microscope and X-ray diffraction, and the microhardness after the post heat treatment was tested by microhardness tester. The results show that the microstructure of brazing BNi-2 brazing coating is mainly CrB phase, Ni solid solution phase and eutectic phase of Ni_(3)B and Ni_(3)Si. After brazing,the overall hardness value is higher, generally higher than 510 HV, and the microhardness in some areas is higher than 700 HV. After quenching, the solid solution phase of Ni increased, and the eutectic phase of Ni and Ni_(3)Si decreased, leading to the softening of the brazing coating, the area whose microhardness in the range of 342 HV–454 HV increased. After tempering the brazed coating samples, the eutectic phases of Ni and Ni_(3)Si grew and the hardness recovered, but the overall hardness distribution was still lower than the brazing one. The results of the brazing post-heat treatment test show that the post-welding heat treatment will bring adverse effects on the hardness distribution of the coating, which may affect the wear resistance of the coating.

Microstructure and fracture toughness of electron beam welded joints of 30CrMnSiNi2A steel

Two post weld heat treatments (PWHT), 900 ℃ oil quenched and low temperature tempered (PWHTA) and high temperature tempered and then 900 ℃ oil quenched and low temperature tempered (PWHTB), are employed to treat the weldment. Then the effect of two post weld heat treatment processes on the microstructure,mechanical properties and fracture toughness of electron beam welded joints of 30CrMnSiNi2A steel have been discussed. The results show that, after two kinds of PWHT the microstructure and hardness at every zones of EBW joints are nearly same. Although the welds have good mechanical properties, fracture toughness of both weld and heat affected zone (HAZ) is low, the CTOD values of welds are comparatively higher than that of HAZ. Microstructure and fracture toughness of two EBW joints have no evident differences.

Secondary Austenite Morphologies in Fusion Zone of Welded Joint after Postweld Heat Treatment with a Continuous Wave Laser

In order to improve the weldability of duplex stainless steels,obtaining more secondary austenite in the weld metal is an effective way.Therefore,optimizing the secondary austenite by changing its morphology,volume fraction and stability may be expected to enhance the ductility of the weld.The secondary austenite morphologies in the fusion zone of the laser continuously heat treated welds of 2205 duplex stainless steel were investigated.The secondary austenite morphologies were found to be influenced by different laser power level.The secondary austenite with penniform,freely grown and dendritic shape appeared in the course of 4,6 and 8 kW continuous heat treatment,respectively.It was found that there were three kinds of morphologies of secondary austenite in the fusion zone treated by different power,i.e.,widmannst¨atten austenite,grain boundary austenite and intragranular austenite.The results demonstrated that the mechanism of the secondary austenite formation was a displacement mechanism during the initial austenite lath formation and a diffusion mechanism during cooling.The nitrides provided the nitrogen for the transformation and at the same time acted as nucleation sites for the secondary austenite.

Effects of Welding Procedure on Corrosion Resistance and Hydrogen Embrittlement of Supermartensitic Stainless Steel Deposits

The effects of shielding gas and post weld heat treatment on the pitting resistance, stress corrosion crack- ing and hydrogen embrittlement of supermartensitic stainless steel deposits were studied. Two all-weld-metal test coupons were prepared using a metal-cored wire under Ar＋ 5% He and Ar＋18%CO2 gas shielding mixtures. Solubi- lizing and solubilizing plus double tempering heat treatments were done with the objective of achieving different mi crostructural results, The samples welded under Ar＋5% He showed higher pitting corrosion resistance, for all post weld heat treatments, than those welded under Ar＋18% CO2. The different post weld heat treatments generated higher susceptibility to this corrosion mechanism. None of the samples presented signs of stress corrosion cracking, but in those subjected to the heat treatment, grain boundary selective attack was observed, on the surfaces of all the samples studied. The samples with highest hardness were more susceptible to hydrogen damage, thereby leading to reduced tensile strength on this condition.

Formation and evolution of layered structure in dissimilar welded joints between ferritic-martensitic steel and 316L stainless steel with fillers

Dissimilar high-energy beam(HEB)welding is necessary in many industrial applications.Different composition of heat-affected zone(HAZ)and weld metal(WM)lead to variation in mechanical properties within the dissimilar joint,which determines the performance of the welded structure.In the present study,appropriate filler material was used during electron beam welding(EBW)to obtain a reliable dissimilar joint between reduced-activation ferritic-martensitic(RAFM)steel and 316L austenitic stainless steel.It was observed that the layered structure occurred in the weld metal with 310S filler(310S-WM),which had the inferior resistance to thermal disturbance,leading to severe hardening of 310S-WM after one-step tempering treatment.To further ameliorate the joint inhomogeneity,two-step heat treatment processes were imposed to the joints and optimized.δ-ferrite in the layered structure transformed intoγ-phase in the first-step normalizing and remained stable during cooling.In the second-step of tempering,tempered martensite was obtained in the HAZ of the RAFM steel,while the microstructure of 310S-WM was not affected.Thus,the optimized properties for HAZ and 310S-WM in dissimilar welded joint was both obtained by a two-step heat treatment.The creep failure position of two dissimilar joints both occurred in CLAM-BM.