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.

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 ℃.

Microstructure,mechanical and corrosion behavior of high strength AA7075aluminium alloy friction stir welds-Effect of post weld heat treatment

High strength aluminium alloy AA7075(Al-Zn-Mg-Cu) is a precipitate hardenable alloy widely used in the aerospace,defense,marine and automobile industries.Use of the heat treatable aluminium alloys in all these sectors is ever-increasing owing to their excellent strength-toweight ratio and reasonably good corrosion resistance.The shortage in corrosion resistance,however,usually poses negative concern about their reliability and lifetime when they service in the variable marine environments.These alloys also exhibit low weldability due to poor solidification microstructure,porosity in fusion zone and lose their mechanical properties when they are welded by fusion welding techniques.Friction stir welding(FSW) is a reliable technique to retain the properties of the alloy as the joining takes place in the solid state.The welds are susceptible to corrosion due to the microstructural changes in the weld nugget during FSW.In this work,the effect of post weld treatments,viz.,peak aging(T6) and retrogression & reaging(RRA),on the microstructure,mechanical properties and pitting corrosion has been studied.Friction stir welding of 8 mm-thick AA7075 alloy was carried out.The microstructural changes of base metal and nugget zone of friction stir welds were studied using optical microscopy,scanning electron microscopy and transmission electron microscopy.Tensile and hardness test of base metal and welds has been carried out.Pitting corrosion resistance was determined through dynamic polarization test.It was observed that the hardness and strength of weld were observed to be comparatively high in peak aged(T6) condition but the welds showed poor corrosion resistance.The resistance to pitting corrosion was improved and the mechanical properties were maintained by RRA treatment.The resistance to pitting corrosion was improved in RRA condition with the minimum loss of weld strength.

Effect of post weld heat treatment on tensile properties and microstructure characteristics of friction stir welded armour grade AA7075-T651aluminium alloy

This paper reports the effects of post weld heat treatments, namely artificial ageing and solution treatment followed by artificial ageing, on microstructure and mechanical properties of 12 mm thick friction stir welded joints of precipitation hardenable high strength armour grade AA7075-T651 aluminium alloy. The tensile properties, such as yield strength, tensile strength, elongation and notch tensile strength, are evaluated and correlated with the microhardness and microstructural features. The scanning electron microscope is used to characterie the fracture surfaces. The solution treatment followed by ageing heat treatment cycle is found to be marginally beneficial in improving the tensile properties of friction stir welds of AA7075-T651 aluminium alloy.

Microstructure and pitting corrosion of armor grade AA7075 aluminum alloy friction stir weld nugget zone-Effect of post weld heat treatment and addition of boron carbide

Friction stir welding(FSW) of high strength aluminum alloys has been emerged as an alternative joining technique to avoid the problems during fusion welding.In recent times FSW is being used for armor grade AA7075 aluminum alloy in defense,aerospace and marine applications where it has to serve in non uniform loading and corrosive environments.Even though friction stir welds of AA7075 alloy possess better mechanical properties but suffer from poor corrosion resistance.The present work involves use of retrogression and reaging(RRA) post weld heat treatment to improve the corrosion resistance of welded joints of aluminum alloys.An attempt also has been made to change the chemical composition of the weld nugget by adding B4C nano particles with the aid of the FSW on a specially prepared base metal plate in butt position.The effects of peak aged condition(T6),RRA and addition of B4C nano particles on microstructure,hardness and pitting corrosion of nugget zone of the friction stir welds of AA7075 alloy have been studied.Even though RRA improved the pitting corrosion resistance,its hardness was slightly lost.Significant improvement in pitting corrosion resistance was achieved with addition of boron carbide powder and post weld heat treatment of RRA.

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.

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.

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 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.

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

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.

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.

基于BSO-BP神经网络的型材搅拌摩擦焊PWHT工艺参数优化

为获取焊后热处理最优工艺参数组合,进一步消减地铁型材焊接残余应力,提出一种基于BSO-BP神经网络的搅拌摩擦焊焊后热处理工艺参数优化方法。首先,基于有限元理论对型材结构搅拌摩擦焊及焊后热处理过程进行数值模拟,通过分析焊后热处理各工艺阶段对残余应力的影响确定待优化工艺参数;其次,基于头脑风暴算法对BP神经网络的权值和阈值进行优化,从而改进BP神经网络;再次,结合试验设计与有限元分析,得出不同工艺参数组合的热处理后型材结构焊接残余应力值,利用所得试验数据建立BSO-BP神经网络;最后,基于BSO-BP神经网络构建焊后热处理工艺参数优化模型,采用粒子群算法对其寻优求解,并与传统设计方案进行对比。结果表明:BSO-BP神经网络的预测误差更小且与试验数据的拟合效果更佳;采用最优工艺参数组合可增强焊后热处理对残余应力的消减作用;本研究可为实际工艺过程提供参考。

焊后热处理对SA-182F1和SA-106C钢接头显微组织和力学性能的影响

采用钨极氩弧焊和焊条电弧焊焊接SA-182F1和SA-106C钢.对焊接接头进行了615℃保温8h的消除应力处理.检测了焊接接头热处理前、后的显微组织和力学性能.结果表明:热处理前、后焊接接头的拉伸和冲击性能均满足要求,消除应力处理使接头拉伸性能降低、冲击韧度提高;热处理前后焊接接头的显微组织没有差异.

热处理对同质异态TC17钛合金线性摩擦焊接头的影响

对TC17(α+β)和TC17(β)钛合金进行线性摩擦焊及焊后热处理试验,运用光学显微镜(OM)、扫描电镜(SEM)观察接头各区域的微观组织变化,采用轮廓法测试接头残余应力分布情况,分析了热处理对接头的微观组织、残余应力及力学性能的影响。结果表明:焊接过程中焊缝区发生了相变及动态再晶界过程,形成亚稳定β相;两侧热力影响区初生α相严重变形,针状α相完全溶解。经过热处理,亚稳定β相分解为稳定的α+β相,板条状α相在晶界析出,针状α相在晶粒内部析出,变形α相发生不同程度的分解。轮廓法测试结果表明,接头沿振动方向的应力呈双峰分布,接头热力影响区处拉应力峰值达到最大约360 MPa,焊缝中心拉应力值约140 MPa,经过热处理,接头沿振动方向拉应力值降低至50 MPa以下。经过热处理后接头微观组织更加均匀,并且接头残余应力得到消除,接头拉伸及疲劳性能得到明显改善。

热处理温度对1000 MPa级高强钢熔敷金属组织和性能的作用机制

采用丝级埋弧焊方法制备1000 MPa级高强钢熔敷金属,利用SEM、EBSD、XRD和TEM等微观分析方法研究了焊后热处理温度(500~620℃)对1000 MPa级高强钢熔敷金属组织演变的影响,并通过拉伸和冲击试验评估其力学性能.结果表明,随着热处理温度升高,1000 MPa级高强钢熔敷金属抗拉强度和屈服强度对比焊态(as welded,AW)先升高后降低,熔敷金属热处理后比AW韧性降低.1000 MPa级高强钢熔敷金属在540℃热处理时获得较好强韧匹配效果,抗拉强度1030MPa,屈服强度970 MPa,-40℃冲击韧性58 J.1000 MPa级高强钢熔敷金属在500~620℃热处理过程中M/A组元中的A逐渐分解为碳化物和铁素体,M在620℃热处理时生成逆转变奥氏体并保留至室温.碳化物对于位错具有钉扎作用,但随热处理温度升高碳化物对位错的钉扎作用减弱,位错通过滑移和攀移不断减少.熔敷金属析出的碳化物对位错的钉扎作用强于位错滑移的软化作用时,熔敷金属强度提高,碳化物对位错的钉扎作用弱于位错滑移的软化作用时基体组织软化,熔敷金属强度降低.析出的碳化物导致位错塞积,产生的应力集中区域成为裂纹源,使热处理态熔敷金属韧性低于AW.

管式加热炉用TP347H与P5炉管异种钢GTAW焊接工艺研究

针对ASME SA312 TP347H奥氏体不锈钢管与ASTM SA335 P5铁素体耐热钢管的异种钢焊接存在金属稀释、碳迁移和残余应力等问题,在考虑稀释影响的基础上,选择ER309和ERNiCr-3两种焊接材料根据是否焊后热处理以及是否堆焊隔离层制定了6种焊接工艺方案,并通过焊接试验、力学性能试验和金相检验,对比分析了不同工艺下焊接接头的性能。结果表明:外观检查和RT结果均符合相关标准要求;所有试件的抗拉强度均达到标准规定的415 MPa以上,其中最大值达到505 MPa,且断后伸长率在25%以上,TP347H侧热影响区的冲击吸收功平均值为54.0~70.5 J,均满足标准规定;直接焊接法未经焊后热处理的焊接接头P5侧母材热影响区附近硬度超标,而经焊后热处理的焊接接头硬度值均满足标准要求;经焊后热处理的焊接接头碳扩散更明显,而采用ERNiCr-3焊丝进行堆焊隔离层,并进行后热处理的焊接接头碳扩散程度最小。综合分析,ERNiCr-3堆焊隔离层+后热工艺方案得到的焊接接头性能最佳,满足标准要求,且无需进行焊后热处理,更适合现场焊接。

焊后热处理对核反应堆压力容器用16MND5钢组织和性能的影响

采用光学显微镜、透射电子显微镜,通过拉伸、冲击和落锤试验等方法研究了焊后热处理温度和保温时间对16MND5钢的组织和力学性能的影响。结果表明:经模拟焊后热处理后16MND5钢的室温和350℃抗拉强度和屈服强度都呈下降趋势,且下降幅度随焊后热处理温度的升高和保温时间的延长而增大;焊后热处理时间的延长导致钢的冲击性能小幅度下降,焊后热处理温度对冲击性能的影响并不明显;焊后热处理后的钢基体中弥散分布的细小第二相粒子数量减少、尺寸增大,导致钢的强度降低。

碳钢管道焊后热处理要求分析

碳钢是可焊接性较好的钢种,选择适当的焊接材料和工艺,焊接接头不易产生淬硬组织或冷裂纹。分析了碳钢管道的焊接及预热要求、焊后热处理规定,以及免除焊后热处理的条件。认为在应力腐蚀工况条件下,为避免发生腐蚀破裂,全壁厚范围内的碳钢管道焊后应进行热处理。