Post-weld Heat Treatment Methods Research Articles

Effect of post-weld heat treatment methods on microstructure and fatigue behavior of Al-Mg-Si alloy oscillating laser welding

To address the softening issue in aluminum alloy weld joints, post-weld heat treatment(PWHT) techniques were employed to enhance the mechanical properties of Al-Mg-Si alloy weld joints joined by oscillating laser welding(OLW). A systematic investigation was conducted on the impact of two different PWHT methods, artificial aging(AA) and solution treatment followed by aging(STA), on the static mechanical properties, fatigue performance, and microstructure of the weld joints. The results indicated that both AA and STA could improve the tensile strength and fracture strain of the welded joints. Compared to AA, STA did not show a significant improvement in increasing tensile strength and elongation at break. Notably, AA significantly increases the fatigue life of the joints, while STA also contributes to enhanced fatigue life, albeit to a lesser degree. At the lowest stress level, the fatigue life of both STA and as-welded(AW) joints exceeded 106 cycles, with the STA joints exhibiting approximately 57.9% higher fatigue life than the AW joints. Microstructural analysis of the AW joints revealed the presence of dislocations and a few large-sized precipitate phases, primarily Mg2Si and AlFeSi phases. After AA, nano-scale second phases, mainly the AlFeSi phase, appeared in the weld joints, accompanied by a reduction in dislocation density. Following STA, there was a significant increase in the density and size of precipitate phases, with the coarse AlFeSi phase becoming more prominent and large-sized grain boundary precipitates appearing. The AA treatment, due to grain refinement and second phase precipitation, enhanced the hardness, tensile strength, and fatigue strength of the joints. As the STA joints exhibited more β-AlFeSi precipitates and grain boundary precipitates, the second phase strengthening effect was reduced. Although the mechanical properties of STA joints were better than those of AW joints, they were inferior to those of AA joints.

Review of recent trends in ultrasonic additive manufacturing: current challenges and future prospects

PurposeThis study aims to outline the current challenges in ultrasonic additive manufacturing (AM). AM has revolutionized manufacturing and offers possible solutions when conventional techniques reach technological boundaries. Ultrasonic additive manufacturing (UAM) uses mechanical vibrations to join similar or dissimilar metals in three-dimensional assemblies. This hybrid fabrication method got attention due to minimum scrap and near-net-shape products.Design/methodology/approachThis paper reviews significant UAM areas in process parameters such as pressure force, amplitude, weld speed and temperature. These process parameters used in different studies by researchers are compared and presented in tabular form. UAM process improvements and understanding of microstructures have been reported. This review paper also enlightens current challenges in the UAM process, process improvement methods such as heat treatment methods, foil-to-foil overlap and sonotrode surface roughness to increase the bond quality of welded parts.FindingsResults showed that UAM could solve various problems and produce net shape products. It is concluded that process parameters such as pressure, weld speed, amplitude and temperature greatly influence weld quality by UAM. Post-weld heat treatment methods have been recommended to optimize the mechanical strength of ultrasonically welded joints process parameters. It has been found that the tension force is vital for the deformation of the pre-machined structures and for the elongation of the foil during UAM bonding. It is recommended to critically investigate the mechanical properties of welded parts with standard test procedures.Originality/valueThis study compiles relevant research and findings in UAM. The recent progress in UAM is presented in terms of material type, process parameters and process improvement, along with key findings of the particular investigation. The original contribution of this paper is to identify the research gaps in the process parameters of ultrasonic consolidation.

A primary plus secondary local PWHT method for mitigating weld residual stresses in pressure vessels

Local post-weld heat treatment (PWHT) is often used for mitigating welding-induced residual stresses in pressure vessels and piping systems. As large and ultra-large pressure vessels are increasingly used in petrochemical and power generation industries, traditional local PWHT procedures stipulated in Codes and Standards become difficult to implement for some of the ultra-large vessels due to their very large diameter and overall length. In this paper, a new method referred to as primary-secondary heating based local PWHT technique (PS-PWHT) is proposed. Both finite element residual stress modeling and experimental residual stress measurements were performed for both validating the effectiveness of the proposed technique and elucidating the underling mechanisms. The results show that the PS-PWHT method can reduce welding-induced residual stresses in a significant manner, even leading to some level of compressive residual stresses at the vessel weld region.

Sources of variability and improvement in impact toughness of a low Cr–Mo steel weld metal

For the heat resistance steel weld metal, special post-weld heat treatments need to be performed to maintain the creep resistance, improve the impact toughness, and relieve the welding residual stress. In this paper, firstly, the three factors affecting variability and lower values of toughness were revealed. Secondly, two different post-weld heat treatment (PWHT) methods have been used to improve the impact toughness of a heat resistance steel weld metal. Two PWHT methods include post-weld direct tempering (PWDT) process at 690 °C/26 h/air cooling and post-weld normalized tempering (PWNT) process with re-austenitization at 960 °C/1.5 h/air cooling + tempering at 690 °C/26 h/air cooling. For three type specimens with as-welded (AW), PWDT, PWNT processes, the impact toughness and the hardness were measured, and the fracture surface, microstructures were observed and analyzed by scanning electron microscope (SEM). Results indicated that PWDT heat treatment can improve the impact toughness of the weld metals from the original 79 J - 169 J to 82 J–290 J because the microstructure is changed from granular bainite to block ferrite and granular bainite. PWNT heat treatment can remarkably improve the impact toughness of the weld metals from the original 79 J- 169 J to 148 J–325 J. It is attributed to that PWNT heat treatment process can remove the boundaries of the columnar grain zone and reheated zone, make the difference of the microstructure between the columnar grain zone and reheated zone decrease, and improve the homogeneity of the microstructure.

Experimental investigation on influence of electrode vibrations on hardness and microstructure of 1018 mild steel weldments

PurposeThe purpose of this study is to explore the importance of vibrations during welding process. In recent years, welding has gained its supremacy in the field of production. The main set back of the welding process is induced residual stresses, which is a major cause for many welding defects. These defects can be minimized by post-weld heat treatment methods, which is a time consuming and laborious process. In the recent past, a technique of exciting the weld-pool by vibrating the work-pieces was also adopted to minimize the above-mentioned stresses. A novel technique of electrode vibration is another effective way of transferring the vibrations to the weld-pool to influence the induced residual stress.Design/methodology/approachIn this research, the electrode is vibrated with the help of an electric motor. The specimens were prepared as per American Society for Testing and Materials standards and welded with varying frequencies and voltages. The weldments are tested for hardness along the weld bead and heat affected zone, also the microstructure of the fusion zone is analyzed.FindingsIt is observed that there is an improvement in the hardness because of the grain refinement, which is a result of proper excitation of the weld-pool. It is observed that there is an improvement in hardness test up to 28.69% when compared with the conventional welding process. The peak value of hardness is observed at a frequency of 4,450 Hz. This is because of fine grain structure at this frequency, which is observed through the microstructure analysis.Originality/valueA novel technique is introduced to refine the weld-pool through electrode vibrations. To improve the hardness of the welded joints, vibrations play a major role by refining the grain structure. The vibrations are imparted with the help of a special equipment attached to the electrode.

Effect of post weld heat treatment and welding parameters on mechanical and corrosion characteristics of friction stir welded aluminium alloy AA2014-T6

This paper addresses the effect of post weld heat treatment methods on the mechanical and corrosion characteristics of friction stir welded aluminum alloy AA2014-T6. Aluminum alloy AA2014 is mainly used in applications that demand high strength to weight ratios, such as aerospace, marine, and industrial applications. In this work, AA2014-T6 plates of 6 mm thick were butt welded using a tool with a square profile. Tensile strength, hardness, and corrosion characteristics were compared between the samples as welded and post weld heat treated. Welded samples that were heat treated for a shorter ageing period (8 h) showed improved tensile strength irrespective of welding process parameters, compared to as-welded samples. The samples heat treated for a longer ageing period (9 h) showed a decline in tensile strength for low tool rotation speed. Hardness increased in welded samples heat treated for 8 h. Welded samples heat treated for 9 h show high passivity in corrosion media.

Effect of Local Post Weld Heat Treatment on Tensile Properties in Friction Stir Welded 2219-O Al Alloy

To improve the formability of the aluminum alloy welds and overcome the size limitation of the bulk post weld heat treatment (BPWHT) on large size friction stir welded joints, a local post weld heat treatment method (LPWHT) was proposed. In this method, the resistance heating as the moving heat source is adopted to only heat the weld seam. The temperature field of LPWHT and its influence on the mechanical properties and formability of FSW 2219-O Al alloy joints was investigated. The evaluation of the tensile properties of FSW samples was also examined by mapping the global and local strain distribution using the digital image correlation methodology. The results indicated that the formability was improved greatly after LPWHT, while the hardness distribution of the FSW joint was homogenized. The maximum elongation can reach 1.4 times that of as-welded joints with increase the strength and the strain of the nugget zone increased from 3 to 8% when annealing at 300 °C. The heterogeneity on the tensile deformation of the as-welded joints was improved by the nugget zone showing large local strain value and the reason was given according to the dimple fracture characteristics at different annealing temperatures. The tensile strength and elongation of LPWHT can reach 93.3 and 96.1% of the BPWHT, respectively. Thus, the LPWHT can be advantageous compared to the BPWHT for large size welds.

Influences of local PWHT from different criteria at home and abroad on the residual stress of the under-matching welded joint

The under-matching welded joint is more commonly used in engineering practice now and the post-weld heat treatment (PWHT) is the common method to reduce the residual stress of the welded joint, while the research on the under-matching welded joint after PWHT is few. And the different influences of the local PWHT from different criteria haven't been specifically analyzed by the researcher. The finite element software-ABAQUS is used to simulate the welding process and PWHT process of the under-matching welded joint which is the combination of CF62(base metal) and 316L(weld) in this paper. The discussion of the influences of local PWHT from different criteria at home and abroad on the residual stress of the under-matching welded joints are based on the experimental verification and the proposal criterion has been given in this paper. The numerical simulation by finite element has been proved to be useful to predict the residual stress of the under-matching welded joint after local PWHT from different criteria by the comparison between residual stress results of experiment test and numerical simulation in this paper. The local PWHT method of ASME-Ⅷ is the best and it is recommended in this paper. The criteria PD5500 and EN13445 are at the second place while the old criterion GB150-1998 is conservative. The new criterion GB150-2011 have been promoted very much than the old criterion GB150-1998 of the local PWHT method.

Local Postweld Heat Treatment of Heterogeneous Welded Joint

A concept of heterogeneous welded joint is proposed for researching and describing the characteristics of local postweld heat treatment (PWHT) temperature field for asymmetric thermal conductivity welded joint. Its three types have been classified according to thermal conductivity direction around the weld, separately, welded joint with transverse unidirectional thermal conductivity, transverse bidirectional thermal conductivity, transverse and longitudinal thermal conductivity. Compared with the temperature field of symmetric thermal conductivity welded joint, the highest temperature point of heterogeneous welded joint deviates from the heat device center, and uniform temperature area shrinks. In addition, longitudinal temperature difference and dramatic temperature change zone have arisen for the third type heterogeneous welded joint. In order to improve the temperature distribution, two PWHT methods called temperature compensation method and power compensation method have been put forward and developed. Several engineering applications of two methods are illustrated as examples.

Determination of Optimum Post Weld Heat Treatment Processes on the Microstructure and Mechanical Properties of IS2062 Steel Weldments

This study investigates the effect of post heat treatment on the microstructure and mechanical properties of IS2062 steels. Similar metal joints of IS2062 weldments are prepared by using MIG welding process. This melting is occurring at edges of the plates because of sufficient amount of heat energy is passing over the plate per unit time and density of energy is supplied to the wire. In this connection, heating and cooling of weldment some of the disturbances in metallurgical and mechanical point of view. To overcome we will choose suitable post weld heat treatment to avoid the disturbances and improve industrial requirement irrespective of the mechanical, microstructure of the weldment. The objective is to determine the optimum post weld heat treatment method for the IS2062 steel. After welding, the effects of post weld heat treatment on weld metal microstructure and mechanical properties including weldment tensile strength, impact and hardness over the room temperature range 32°C are investigated. In particular this study the effect of these properties to understand estimate heat treatments on the tensile impact, Hardness materials are considered as weldments before heat treatment and after post weld heat treatment.

Residual Stress Reduction in Single Pass Welds Using Parallel Line Reheating

Current postweld heat treatment (PWHT) methods rely mainly on static thermal sources or line heating using dispersed beams which require significant capital investment and often pose limits on weldment size. In the current study, an alternative PWHT method based on line heating is presented and analyzed. The method, which is intended to perform low temperature stress relief, employs parallel oxyacetylene torches to induce a tensile stress in the vicinity of the weld toe. X-ray diffraction (XRD) measurements taken from bead-on-plate (BOP) welds made using ASTM A572-50 showed a 37% decrease in the peak longitudinal stress after parallel line reheating was performed. A corresponding reduction in the stress gradient on the plate surface was also observed. Welding and reheating were also modeled in sysweld to assess how torch placement affected the longitudinal stress distribution and an optimum offset was identified for the 8-mm plate thickness used. Analysis of the thermomechanical history in the vicinity of the weld toe indicates that a tensile stress is superposed during reheating and is concurrent with the reduction in the peak longitudinal stress.

Novel postweld heat treatment method for improving mechanical properties of resistance spot weld

A novel postweld heat treatment method by applying cross-direction welding current (cross-current) was applied on the resistance spot weld. The effect of cross-current on the nugget shape, microstructure and mechanical properties was investigated. The results show that the cross-current postweld heat treatment enhances the efficiency of postweld heat treatment and improves the mechanical performance of nugget. The cross-current promotes the recrystallisation of nugget microstructure, which induced the transformation of microstructure from column crystal to quasi equiaxed grain. The quasiequiaxed grains of martensite in the weld nugget significantly increase the microhardness of weld nugget and the tensile shear force of weld joint.

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 °C, 30 min), water quenching and artificial aging (175 °C, 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.

Investigations on the influence of post weld heat treatment on fatigue crack growth behaviour of electron beam welded AA2219 alloy

This paper reports the influence of post weld heat treatment on fatigue crack growth behaviour of electron beam welded AA2219 aluminium alloy. An attempt has been made to enhance the fatigue crack growth resistance of the electron beam welded joints through post weld heat treatment methods such as solution treatment (ST), artificial aging (AA), solution treatment and artificial aging (STA). Electron beam welding machine with 100 kV capacity has been used to fabricate the square butt joints. Servo hydraulic controlled fatigue testing machine with a capacity of 100 kN has been used to evaluate the fatigue crack growth behaviour of the welded joints. Of the three post weld heat treated joints, the solution treated and aged (STA) joints are offering better resistance against the growing fatigue cracks. The superior mechanical properties, preferred microstructures in the weld metal region and favourable residual stress field of the weld region are found to be the reasons for superior fatigue performance of the STA joints compared to other joints.

Fatigue behaviour of post weld heat treated electron beam welded AA2219 aluminium alloy joints

This paper reports the effect of post weld heat treatment on fatigue behaviour of electron beam welded AA2219 aluminium alloy. An attempt has been made to enhance the fatigue strength of the electron beam welded joints through post weld heat treatment methods such as solution treatment, artificial aging, solution treatment and artificial aging. Electron beam welding machine with 100 kV capacity has been used to fabricate the square butt joints. Servo hydraulic controlled fatigue testing machine with a capacity of 100 kN has been used to evaluate the fatigue life of the welded joints. Of the three post weld heat treated joints, the solution treated and aged joints are enduring higher number of cycles under the action of cyclic loads.