焊后时效处理对6082-T6铝合金搅拌摩擦焊接头的影响

对6082-T6铝合金搅拌摩擦焊接头进行自然时效和人工时效处理,通过透射电子显微镜、扫描电子显微镜、拉伸实验机和显微硬度计对组织演变和力学性能进行研究。结果表明:人工时效处理后显微硬度比焊态和自然时效高10~25HV,提高焊核区和热机影响区硬度效果明显好于自然时效。经过焊后自然时效、人工时效的焊接接头力学性能得到一定程度的提升,人工时效析出相比自然时效析出相抗拉强度提高12%,延伸率降低9%,人工时效提高拉伸强度效果更明显。人工时效处理后,焊核区组织发生显著变化,NZ主要为GP区,经过人工时效后NZ强化效应随团簇和GP区尺寸增大及数量增多而加强。HAZ主要为粗大的β′,经过人工时效后变化不大,硬度基本保持不变。通过对微观组织进行研究发现析出物的形状由界面能和应变能决定。     

焊后热处理对7055-0.1Sc铝合金搅拌摩擦焊接头的组织与力学性能的影响

对11 mm厚的7055-0.1Sc-T4铝合金板材进行搅拌摩擦焊接，研究了焊后热处理对接头的组织和力学性能的影响。结果表明，热处理前接头的硬度分布呈“W”形，接头前进侧和后退侧都有一个最低硬度区，强度系数为63.0%～73.8%，拉伸断口位于后退侧最低硬度区。焊后人工时效(120℃×24 h)热处理使焊核的硬度提高，但是不改变接头最低硬度区的硬度，对拉伸性能和断裂行为的影响甚微。焊后的固溶(470℃×1.5 h+水淬)+人工时效(120℃×24 h)(T6)热处理不改变低焊速接头的晶粒组织，但是使高焊速接头焊核区底部的晶粒异常长大；T6热处理使接头各区域原有的沉淀相溶解，重新生成细小均匀的η’和η(MgZn₂)沉淀相，使其硬度显著提高；T6热处理使接头沿“S”线附近出现微小的孔洞、在拉伸过程中沿“S”线开裂、其抗拉强度比焊接态大幅度提高，达到母材强度的87%，但是其塑性严重降低。     

热处理对2519铝合金接头组织及性能的影响

研究了焊后时效及固溶＋时效热处理对2519铝合金焊接接头组织和力学性能的影响．结果表明,时效处理后,处于欠时效态的焊缝析出强化相增加,硬度升高,而过时效态的热影响区软化区组织和硬度没有明显变化,焊接接头的强度略微提高,塑性下降．固溶＋时效处理后,焊缝中网状共晶减少,焊缝和热影响区软化区内的析出相形态变为细小的针状,且数量增加,焊缝金属硬度明显提高,热影响区的软化现象消失,焊接接头的强度和塑性显著增加．     

焊接速度对 7A52 铝合金 FSW 组织及力学性能的影响

目的在保证搅拌速度一定时,针对8 mm厚的7A52铝合金,在不同焊接速度下采用搅拌摩擦焊(FSW)进行焊接试验,研究其焊接接头的显微组织及力学性能。方法利用搅拌摩擦焊机进行对接焊接,焊后制取金相试样观察焊接接头宏观形貌和显微组织,并测定其力学性能。结果7A52铝合金FSW焊接接头焊核区的面积随着焊接速度的增大而增大,当焊接速度为250mm/min时,焊接接头的焊核区面积最大,焊核区的显微组织都为细小的等轴晶,焊接接头横截面的焊核区呈明显"洋葱环"的形貌,而热力影响区的结构特征则呈现出了较高的塑性变形流线层。焊接接头显微硬度分布都呈现出"W"形变化,在焊接速度为150 mm/min时,焊接接头的平均抗拉强度能达到452 MPa,达到了母材抗拉强度的89%。结论通过对不同焊接速度下7A52铝合金FSW焊接接头的组织和性能进行研究,得到了不同焊接速度下焊接接头组织和力学性能。     

柱形光头搅拌针搅拌摩擦焊接铝锂合金接头组织及力学性能

采用柱形光头搅拌针搅拌摩擦焊接5mm厚的铝锂合金轧制板,并对接头组织和力学性能进行了分析.焊后接头形成了三个组织差异明显的区域:焊核区,热机影响区和热影响区.焊核区微观组织呈鱼鳞状;热影响区组织在焊接热循环作用下,发生回复反应,形成棒状的回复晶粒;前进侧和后退侧热机影响区内为颗粒较大的等轴晶晶粒,且后退侧晶粒尺寸大于前进侧.力学性能测试结果表明,焊接速度υ＝40mm/min时,接头获得最高拉伸强度(296MPa);焊接速度υ＝80mm/min时,接头获得最大延伸率(8.6%).硬度测试结果表明,焊缝区发生了软化,前进侧和后退侧材料的软化区间大致相同,但后退侧软化程度高于前进侧.     

铝铜复合板搅拌摩擦焊接接头组织性能研究

采用搅拌摩擦焊接对铝铜层状复合板进行了焊接,研究了接头组织性能。结果表明,焊接接头焊核区(Nugget zone,NZ)产生了细小等轴状的动态再结晶晶粒,铝层、铜层平均晶粒尺寸分别为4μm、3μm。NZ铝层、铜层平均显微硬度为29.21HV、86.9HV。抗拉强度为154.6 MPa,为母材的61.6%,延伸率为6%。铜颗粒在铝层中形成夹杂是拉伸性能下降的主要原因。     

Mg-Y-Nd-Zr镁合金焊接接头的显微组织与力学性能研究

目的研究Mg-Y-Nd-Zr镁合金焊接接头显微组织和力学性能。方法采用钨极氩弧焊工艺制备Mg-Y-Nd-Zr合金焊接接头,采用金相显微镜、扫描电子显微镜观察焊接接头显微组织,采用能谱测试主要合金元素含量,采用电子万能实验机测试焊接接头的力学性能,采用维氏硬度计测试焊接接头的硬度。结果Mg-Y-Nd-Zr合金母材、焊缝区与热影响区平均晶粒尺寸分别为80, 30, 95μm。焊接接头的抗拉强度、屈服强度和断后伸长率分别为295 MPa, 188 MPa和3.0%。结论 Mg-Y-Nd-Zr合金母材、焊缝和热影响区晶粒均为等轴晶,与母材相比,热影响区未发生晶粒粗化,焊缝区晶粒明显细化,析出相Mg24Y5增多。Mg-Y-Nd-Zr合金焊接接头经525℃×12 h固溶+225℃×12 h时效处理后,各区域的硬度差异不大。抗拉强度达到母材的93%,断后伸长率达到母材的67%。     

热循环、腐蚀和自然时效对 2024 铝合金搅拌摩擦焊接头力学性能的影响

研究了焊接过程中热循环、焊后腐蚀和自然时效对2024铝合金搅拌摩擦焊(FSW)接头力学性能的影响。结果表明,同一焊缝不同位置的力学性能存在一定的差异,靠近插入点位置的屈服强度和抗拉强度明显低于其他位置,之后不断升高,趋于稳定,屈服强度和抗拉强度的最大值分别约为310 MPa和415 MPa;随着自然时效时间的增加,接头屈服强度和抗拉强度在前2个月增长较快,增长率最大分别为2%和1.5%,之后趋于稳定,而伸长率的增长率先较快,增长率最大为6%,之后变缓;在不同的自然时效时间下,腐蚀均明显降低2024铝合金FSW接头的屈服强度、抗拉强度和伸长率,减小率的最大值分别为6.5%,6.1%和19.8%;随着自然时效时间的增加,腐蚀后接头的力学性能下降更严重。     

热处理工艺及Ce对1420铝锂合金焊接接头力学性能的影响

研究了不同热处理状态对不同Ｃｅ含量的１４２０铝锂合金焊接接头力学性能及焊缝凝固组织的影响。结果表明；微量Ｃｅ添加到１４２０合金中，可阻焊缝热影响区的晶粒粗化并使焊缝凝固组织细化。采用焊后固溶＋人工时效的热处理工艺，可使焊接接头强度第数有明显提高。     

铝合金搅拌摩擦焊接头微观组织和力学性能分析

目的 研究7020铝合金搅拌摩擦焊(FSW)的结构和机械性能。方法 采用搅拌摩擦焊对铝板进行对接焊试验,具体形式为单面焊双面成型。采用拉伸机和显微维氏硬度仪对试样进行力学性能测试;利用蔡司金相、光谱仪、扫描电子显微镜、X射线衍射仪研究母材和焊接接头的微观组织。结果 在硬度上,母材>热影响区>焊核区,热影响区平均硬度约为94HV,母材平均硬度为99HV,焊核区平均硬度最低为78HV,焊核区出现“S”缺陷,在一定程度上弱化了焊核区性能;7020铝合金搅拌摩擦焊接头的抗拉强度为235 MPa,屈服强度为158 MPa,屈强比为0.67,伸长率为7%,焊接系数可以达到73.8%;母材的抗拉强度为325 MPa,屈服强度为278 MPa,屈强比为0.86,伸长率为25%;焊接接头中心显微组织主要由胞状树枝晶体组成,显微结晶依次呈现为平面晶、胞状晶、树枝状晶、等轴晶;铝合金母材和焊接接头的金属相组成均为α?Al+Mg2Si;焊接接头断口呈现比较明显的韧性断裂特征。结论 铝合金搅拌摩擦焊可以获得性能比较优良的焊接接头,为其他铝合金材料的FSW焊接提供技术参考。     

Effects of ultrasonic assisted friction stir welding on flow behavior,microstructure and mechanical properties of 7N01-T4 aluminum alloy joints

Conventional friction stir welding(FSW) and ultrasonic assisted friction stir welding(UAFSW) were employed to weld 6-mm thick 7 N01-T4 aluminum alloy plates. Weld forming characteristics and material flow behavior in these two different welding processes were studied and compared. Ultrasonic vibration was applied directly on the weld in axial direction through the welding tool. Metal flow behavior,microstructure characteristics in the nugget zone(NZ) and evolution of the mechanical properties of naturally aged joints were studied. Results show that the ultrasonic vibration can significantly increase the welding speed of defect-free welded joint. At the rotation speed of 1200 rpm, the UAFSW can produce defect-free welded joints at a welding speed that is 50% higher than that of the conventional FSW.Ultrasonic vibrations can also improve surface quality of the joints and reduce axial force by 9%. Moreover, ultrasonic vibrations significantly increase the volume of the pin-driven zone(PDZ) and decrease the thickness of the transition zone(TZ). The number of subgrains and deformed grains resulting from the UAFSW is higher than that from the FSW. By increase the strain level and strain gradient in the NZ,the ultrasonic vibrations can refine the grains. Ultrasonic energy is the most at the top of the NZ, and gradually reduces along the thickness of the plate. The difference in strengths between the FSW and the UAFSW joints after post-weld natural aging(PWNA) is small. However, the elongation of the UAFSW is8.8% higher than that of the FSW(PWNA for 4320 h). Fracture surface observation demonstrates that all the specimens fail by ductile fracture, and the fracture position of the UAFSW joint changes from HAZ(PWNA for 120 h) to NZ(PWNA for 720 and 4320 h).     

Effect of heat treatment on tensile properties of friction stir welded joints of 2219-T6 aluminium alloy

Abstract

The effect of post-weld heat treatment (PWHT) on the tensile properties of friction stir welded (FSW) joints of 2219-T6 aluminium alloy was investigated. The PWHT was carried out at aging temperature of 165°C for 18 h. The mechanical properties of the joints were evaluated using tensile tests. The experimental results indicate that the PWHT significantly influences the tensile properties of the FSW joints. After the heat treatment, the tensile strength of the joints increases and the elongation at fracture of the joints decreases. The maximum tensile strength of the joints is equivalent to 89% of that of the base material. The fracture location characteristics of the heat treated joints are similar to those of the as welded joints. The defect free joints fracture in the heat affected zone on the retreating side and the joints with a void defect fracture in the weld zone on the advancing side. All of the experimental results can be explained by the hardness profiles and welding defects in the joints.     

Effect of Rotation Rate on Microstructures and Mechanical Properties of FSW Mg-Zn-Y-Zr Alloy Joints

Friction stir welding (FSW) of Mg-Zn-Y-Zr plates with 6 mm in thickness was successfully carried out under a wide range of rotation rates of 600-1200 r/min with a constant traverse speed of 100 mm/min. After FSW, the coarse grains in the parent material (PM) were changed into fine equiaxed recrystallized grains at the nugget zone (NZ). Furthermore, the coarse Mg-Zn-Y particles (W-phase) were broken up and dispersed homogenously into the Mg matrix. With increasing rotation rates, the size of the W-phase particles at the NZ significantly decreased, but the recrystallized grain size tended to increase. The hardness values of the NZs for all the FSW joints were higher than those of the PM, and the lowest hardness values were detected in the heat affected zone (HAZ). The fracture occurred in the thermo-mechanical affected zone (TMAZ) on the advancing side for all the FSW joints in the tensile test, due to the incompatibility of the plastic deformation between the NZ and TMAZ caused by remarkably different orientation of grains and W-phase particles. The strength of FSW joint reaches 90% of that of its PM.     

焊后时效对7046铝合金搅拌摩擦焊接头力学性能的影响

对厚度为3.5mm的7046铝合金挤压板材进行搅拌摩擦焊接并对焊接接头进行人工时效,研究了焊后时效对接头力学性能的影响.结果 表明,焊接接头时效前的硬度分布大致呈"W"形,抗拉强度为406.5 MPa,焊接系数为0.8,拉伸时在后退侧热影响区与热机影响区的过渡位置出现断裂,此处的硬度值最低,断裂面上有大量的韧窝;进行1...     

Fatigue properties of friction stir welded particulate reinforced aluminium matrix composites

Few papers have discussed the friction stir welding (FSW) of particulate reinforced aluminium matrix composites and most of them focused on the set-up of the welding process parameters and their effect on microstructure, hardness and tensile behaviour. The aim of this study was to investigate the fatigue resistance of FSW joints on an as-cast particulate reinforced aluminium based composite (AA6061/22 vol.%/Al₂O_3p). The welding process was performed using different process parameters, also investigating their effect on joint microstructure. The mechanical properties of the FSW composites were compared with those of the base material and the results were correlated to the microstructural modifications induced by the FSW process on the aluminium alloy matrix and the ceramic reinforcement. FSW reduced the size of both particle reinforcement and aluminium grains, and also led to a significant increase in interparticle matrix microhardness, for all process parameters. The FSW specimens belonging to a different set of parameters, tested without any post-weld heat treatment, exhibited a very high joint efficiency (ranging from 90% to 99%) with respect to the ultimate tensile strength of the base material. The stress controlled fatigue test showed a high spread both for the base and FSW composites. Statistical analysis disclosed that all FSW specimens belonging to different process parameters showed apparently slightly worse fatigue behaviour than that of the base composite. Statistical processing applied to the different welding parameters revealed that all the welded specimens belonged to the same population. Therefore it can be concluded that the parameters used produced joints with similar microstructure and comparable fatigue behaviour. The slight difference in the fatigue behaviour of the FSW specimens whose process parameters differed form those of the unwelded composite was explained by the different microstructural homogeneity in the transition from the base to the FSW zone.     

Evolution of microstructures and mechanical properties in similar and dissimilar friction stir welding of AA5086 and AA6061

In this work, thermo-mechanical behavior and microstructural evolution in similar and dissimilar friction stir welding of AA6061-T6 and AA5086-O have been investigated. Firstly, the thermo-mechanical behaviors of materials during similar and dissimilar FSW operations have been predicted using three-dimensional finite element software, ABAQUS, then, the mechanical properties and the developed microstructures within the welded samples have been studied with the aid of experimental observations and model predictions. It is found that different strengthening mechanisms in AA5086 and AA6061 result in complex behaviors in hardness of the welded cross section where the hardness variation in similar AA5086-O joints mainly depends on recrystallization and generation of fine grains in weld nugget, however, the hardness variations in the weld zone of AA6061/AA6061 and AA6061/AA5086 joints are affected by subsequent aging phenomenon. Also, both experimental and predicted data illustrate that the peak temperature in FSW of AA6061/AA6061 is the highest compared to the other joints employing the same welding parameters.     

氧化膜对6082铝合金搅拌摩擦焊接头疲劳性能的影响

对6 mm厚的6082-T6铝合金进行两种表面处理然后实施搅拌摩擦焊接,研究了对接面氧化膜对接头组织和疲劳性能的影响。结果表明,进行速度为1000 mm/min的高速焊接时,对接面未打磨和打磨的接头焊接质量都良好,接头强度系数达到81%;两种接头的疲劳性能基本相同,疲劳强度均为100 MPa;少数样品在焊核区外断裂,大部分样品在热影响区断裂。与接头相比,两种接头焊核区的疲劳性能有所提高,均为110 MPa,在疲劳测试中裂纹并未沿“S”线萌生和扩展。     

Microstructure and mechanical properties of double-side friction stir welded 6082Al ultra-thick plates

In the present work, 80 mm thick 6082Al alloy plates were successfully double-side welded by friction stir welding(FSW). The relationship between the microstructures and mechanical properties was built for the double-side FSW butt joint with more attention paid to the local characteristic zones. It was shown that a phenomenon of microstructural inhomogeneity existed in the nugget zone(NZ) through the thickness direction. The grain size presented an obvious gradient distribution from the top to the bottom for each single-pass weld, and the microhardness values decreased from both surfaces to the middle of the NZ.The lowest hardness zone(LHZ) exhibited a "hyperbolical"-shaped distribution extending to the middle of the NZ. Similar tensile properties were obtained in the three sliced specimens of the FSW joint, and the joint coefficient reached about 70% which achieved the same level as the conventional FSW Al alloy joints. Finite element modeling proved that the "hyperbolical"-shaped heat affected zone(HAZ) was beneficial to resisting the strain concentration in the middle layer specimen which helped to increase the tensile strength. Based on the analysis of the hardness contour map, tensile property and microstructural evolution of the joints, an Isothermal Softening Layer(ISL) model was proposed and established, which may have a helpful guidance for the optimization on the FSW of ultra-thick Al alloy plates.     

A review of friction stir welding of steels: Tool,material flow,microstructure, and properties

Considerable progress has been achieved in friction stir welding (FSW) of steels in every aspect of tool fabrication, microstructure control and properties evaluation in the past two decades. With the development of reliable welding tools and precise control systems, FSW of steels has reached a new level of technical maturity. High-quality, long welds can be produced in many engineering steels. Compared to traditional fusion welding, FSW exhibits unique advantages producing joints with better properties. As a result of active control of the welding temperature and/or cooling rate, FSW has the capability of fabricating steel joints with excellent toughness and strength. For example, unfavorable phase transformations that usually occur during traditional welding can be avoided and favorable phase fractions in advanced steels can be maintained in the weld zone thus avoiding the typical property degradations associated with fusion welding. If phase transformations do occur during FSW of thick steels, optimization of microstructure and properties can be attained by controlling the heat input and post-weld cooling rate.     

Effect of a post-weld heat treatment on the mechanical and microstructure properties of AA6061 joints welded by the gas metal arc welding cold metal transfer method

This work studies the effect of a post-weld heat treatment (PWHT) on the mechanical and microstructure properties of an AA6061 sample welded using the gas metal arc welding (GMAW) cold metal transfer (CMT) method. The CMT method was used because the method provides spatter-free welding, outstanding gap bridging properties, low heat input and a high degree of process flexibility. The welded samples were divided into as-welded and PWHT samples. The PWHTs used on the samples were solution heat treatment, water quenching and artificial aging. Both welded samples were cut according to the ASTM E8M-04 standard to obtain the tensile strength and the elongation of the joints. The failure pattern of the tensile tested specimens was analysed using scanning electron microscopy (SEM). A Vickers microhardness testing machine was used to measure the hardness across the joints. From the results, the PWHTs were able to enhance the mechanical properties and microstructure characteristics of the AA6061 joints welded by the GMAW CMT method.