Microstructure and mechanical properties of friction stir welding of AZ31B magnesium alloy added with cerium

The AZ31B magnesium alloy sheet added with 0.5 wt.% Ce was welded with friction stir welding(FSW).The microstructures and mechanical properties of the welded joint were investigated.The results showed that the microstructures in the weld nugget zone were uniform and with small equiaxed grains.The grains in the heat-affected zone and the thermo-mechanical affected zone were coarser than those in the base metal zone and the weld nugget zone.The ultimate tensile strength of AZ31B magnesium alloy added with 0.5...     

Effect of surface preparation on the corrosion resistance of friction stir linear lap welded AZ31B-H24

The effect of surface preparations on the atmospheric (continuous NaCl salt fog) corrosion resistance of bare (uncoated) linear friction stir lap welded magnesium (Mg) alloy AZ31B-H24 joints was investigated. The surface preparations evaluated included as-received (as-welded for the weld zones), mechanically abraded and acid-cleaned. Electrochemical potentiodynamic polarisation, X-ray photoelectron spectroscopy and Auger electron spectroscopy measurements were made to elucidate the link between the surface preparation and the relative corrosion resistance observed across the microstructural zones of the joints. Heavy metal surface contamination of the as-received material, rather than the air-formed oxide or differences in alloy grain size resulting from variations in thermo-mechanical processing history, was found to be the controlling factor affecting the corrosion mode observed and, in turn, the relative corrosion resistance across the joint. Removal of the heavy metal contamination changed the corrosion mode from pit-like to filament-like, which in turn homogenised the corrosion resistance across the joint in the continuous salt fog exposure.     

The Effect of Cutting Speed and Depth of Cut on Surface Roughness During Machining of Austempered Ductile Iron

In this paper, the influence of process parameters on microstructural characteristics & mechanical properties of AZ80A Mg alloy during friction stir welding (FSW) are investigated in a detailed manner. The tensile fracture surfaces obtained from successfully fabricated joints are subjected to tensile tests and microstructural investigations were done using scanning electron microscope. From the experimental results, the joints produced under a 5 kN axial force value at 1000 rpm and at a feed rate of 1.5 mm/min were found to exhibit superior mechanical properties and metallurgically defect free weldments when compared with other joints. The chemical compositions of these defect free joints were analyzed using energy dispersive spectrometry. Moreover, ideal level of heat generation, uniform flow of the plasticized material and formation of fine grain structure with uniform distribution in the FSW zone were found to be the main reasons for these superior mechanical properties and flawless joints.     

Process Parametric Dependency of Axial Downward Force and Macro- and Microstructural Morphologies in Ultrasonically Assisted Friction Stir Welding of Al/Mg Alloys

Metallurgical and Materials Transactions A - An elementary analysis is proposed to quantify the effects of ultrasonic vibrations during friction stir welding (FSW) of AA6061-T6 to AZ31B Mg alloy....     

镁-铝异种合金搅拌摩擦焊的研究现状及展望

镁合金具有高的比强度和比刚度,被广泛应用于各种工程领域。然而镁合金存在易腐蚀和成形性能差等缺点,极大地制约了镁合金的广泛应用。铝合金密度低,强度高,接近或超过优质钢,塑性好,可加工成各种型材,具有优良的导电性、导热性和抗蚀性,在工业上得到了广泛使用,使用量仅次于钢。在航空航天、轨道交通及汽车等精密工业中,异种合金间的焊接被认为是最复杂的工程之一。通过镁-铝异种合金的焊接,有效结合两种合金的优点,从而满足一些特殊工作环境对零件的使用要求。与此同时,镁-铝异种合金的焊接可显著节省材料从而降低成本,极大拓展了镁合金和铝合金的应用。搅拌摩擦焊可以显著改善传统熔焊工艺中存在的许多冶金问题,从而获得高质量的焊接接头。因此,不同牌号的镁-铝搅拌摩擦焊既有重大的科学研究价值又有巨大的工业应用价值。本文总结了镁-铝合金搅拌摩擦焊的研究进展,特别关注了搅拌摩擦焊工艺参数对微观组织演变、力学性能及相关缺陷的影响,并对后续的研究热点进行了展望。     

Effect of Scandium on Corrosion Resistance of Welded Joint of Al-6Mg-Zr Alloy

Al Mgalloyshavebeenwidelyusedinmanyin dustries,especiallyinmarineandaircraftapplica tions,duetotheirgoodweldability,ductilityandex cellentcorrosionresistance.Beingthenon heattreat ablealloys,thesematerialsderivetheirstrengthpri marilyfromsolidsolutio…     

Tensile behavior of friction-stir-welded AZ31-H24 Mg alloy

In the present study, tensile behavior of friction-stir-welded AZ31 (Mg-3.6Al-1Zn-0.6Mn in wt pct)-H24 Mg alloy was investigated. It was found that the tensile property, particularly tensile elongation, of AZ31-H24 alloy was significantly degraded with friction stir welding (FSW). The tensile fracture always occurred at the boundary between the thermomechanically affected zone (TMAZ) and the stir zone (SZ) on the advancing side. The fractographic examination on the tensile-fractured AZ31-H24 alloy specimen showed a mixed mode of cleavage and dimpled rupture. The AES analysis suggested that the significant reduction in tensile elongation of friction-stir-welded AZ31-H24 Mg alloy was attributable to the entrapped oxides along the boundary between the TMAZ and SZ.     

单轨列车用镁合金与铝合金在NaCl溶液中的电偶腐蚀行为研究

采用浸泡失重、SEM、XRD等方法研究了AZ31镁合金与A6N01S-T5铝合金偶接后在3.5%NaCl溶液中电偶腐蚀行为。结果表明,浸泡腐蚀试验时间越长,偶对中AZ31镁合金、A6N01S-T5铝合金的腐蚀失重量越大,但是平均腐蚀速率则呈下降趋势。在偶对中AZ31镁合金作为阳极腐蚀加速,A6N01S-T5铝合金作为阴极,与镁合金接触的部分得到保护,而暴露在溶液中的部分发生了严重的阴极腐蚀。     

铝锂合金的搅拌摩擦焊接技术研究与应用现状

对铝锂合金搅拌摩擦焊的焊接区宏观形貌、析出相等微观组织和拉伸、疲劳等力学性能进行了综述和分析,介绍了铝锂合金搅拌摩擦焊接在航空航天领域的最新应用,提出了下一步铝锂合金搅拌摩擦焊的发展方向。     

Corrosion Behavior of Welded Joints of Al-6Mg Alloy with Trace Scandium Addition

Al-6Mg alloy with trace Sc addition was prepared by means of melting-casting.The samples of the welded joints of Al-6Mg alloy with trace Sc addition were made by method of manual argon-arc welding.Neutral salt spray test was carried out by referring to GB/T10125-1997 and GB6384-1986 practice.Exfoliation testing was carried out in accordance with the method of Al-Mg alloy exfoliation corrosion test.The corrosion behaviors of the welded joints of AlMg alloy with high level of Mg and trace Sc addition were studied.The microstructures of the welded joints were observed by using optical microscope and transmission electron microscope.The corrosion resistance mechanism of the alloy was also involved.This work intended to determine if the welded joints of Al-6Mgalloy with trace Sc addition can have excellent corrosion resistance, when their strength are clearly improved.The results show that trace content of Sc refines the grains of alloys effectively, raises remarkably the corrosion resistance of the welded joints of Al-6Mg alloy with trace Sc addition.The corrosion resistance mechanisms are that there is free of continuous grain boundary precipitation or network which could be susceptible to corrosion in the microstructure of welded joints.     

Friction Stir Welded AZ31 Magnesium Alloy: Microstructure, Texture, and Tensile Properties

This study was aimed at characterizing the microstructure, texture and tensile properties of a friction stir welded AZ31B-H24 Mg alloy with varying tool rotational rates and welding speeds. Friction stir welding (FSW) resulted in the presence of recrystallized grains and the relevant drop in hardness in the stir zone (SZ). The base alloy contained a strong crystallographic texture with basal planes (0002) largely parallel to the rolling sheet surface and $ \langle {11\bar{2}0} \rangle $ directions aligned in the rolling direction (RD). After FSW the basal planes in the SZ were slightly tilted toward the TD determined from the sheet normal direction (or top surface) and also slightly inclined toward the RD determined from the transverse direction (or cross section) due to the intense shear plastic flow near the pin surface. The prismatic planes $ (10\bar{1}0) $ and pyramidal planes $ (10\bar{1}1) $ formed fiber textures. After FSW both the strength and ductility of the AZ31B-H24 Mg alloy decreased with a joint efficiency in-between about 75 and 82 pct due to the changes in both grain structure and texture, which also weakened the strain rate dependence of tensile properties. The welding speed and rotational rate exhibited a stronger effect on the YS than the UTS. Despite the lower ductility, strain-hardening exponent and hardening capacity, a higher YS was obtained at a higher welding speed and lower rotational rate mainly due to the smaller recrystallized grains in the SZ arising from the lower heat input.     

Developing an Empirical Relationship to Predict Corrosion Rate of AZ31B Magnesium Alloy under Sodium Chloride Environment

Magnesium alloys have gained considerable interest as a structural material for automotive and aerospace applications due to their low-density, high specific strength and good castability. As a consequence, these light alloys have a promising future. The limitation of low corrosion resistance restricts their practical applications. Corrosion behaviour of the AZ31B magnesium alloy was evaluated by conducting immersion corrosion test in NaCl solution at different chloride ion concentrations, pH value and immersion time. An attempt was also made to develop an empirical relationship to predict the corrosion rate of AZ31B magnesium alloy. Three factors, five level, central composite rotatable design matrix was used to minimize the number of experimental conditions. Response surface methodology was used to develop the relationship. The developed relationship can be effectively used to predict the corrosion rate of AZ31B magnesium alloy at 95 % confidence level.     

Corrosion Behavior of Top and Bottom Surfaces for Single-Side and Double-Side Friction Stir Welded 7085-T7651 Aluminum Alloy Thick Plate Joints

Thick plate joints of 7085-T7451 aluminum alloy were obtained through both single-side and double-side friction stir welding (SS or DS-FSW). The chloride ions effects on the corrosion behavior of the top and bottom surfaces of the joints were examined by cyclic potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM). Results show that the corrosion susceptibility was suppressed significantly in the weld nugget zone, while the base material and heat-affected zone were prone to be corrosion attacked. For the SS-FSWed joint, the top surface showed a higher corrosion resistance than that of the bottom surface, but the larger corrosive heterogeneity was observed between the top and bottom surfaces compared with the two welds of DS-FSWed joint, which was confirmed by the morphology of corrosion attack. A deep insight on the microstructure of the joints indicates that the intermetallic particles played a key role in the corrosion behavior of the FSWed AA7085 aluminum alloy joints in chloride solution.     

300M超高强钢在中性盐雾环境中的腐蚀行为及机制

摘要：为了研究300M超高强钢在中性盐雾环境中的腐蚀行为及腐蚀机制，采用失重法，宏观、微观腐蚀形貌分析，三维表面轮廓分析及电化学分析的研究方法，来表征腐蚀实验现象并进行分析。结果表明：300M超高强钢在中性盐雾环境中的腐蚀产物为FeOOH、Fe2O3、Fe(OH)3和Fe3O4；腐蚀速率随着腐蚀时间逐渐降低，腐蚀后期（72h）腐蚀速率降低50%；腐蚀初期以点蚀为主，点蚀坑通过横向扩展，逐渐发展为后期的均匀腐蚀，腐蚀表面形貌呈沟壑状；外腐蚀层对基体的保护能力很弱，Cr元素在锈层靠近基体的一侧偏聚使内腐蚀层具有一定的抗腐蚀性。     

应力作用下Al-Li合金的腐蚀行为研究

通过测量动电位极化曲线,并用扫描电镜（SEM）、透射电镜（TEM）观察,分析应力作用下峰时效的2195、1420Al-Li合金在3．5％NaCl溶液中的腐蚀行为。结果表明,无应力时1420Al-Li合金发生蚀孔较大且不连续的均匀腐蚀,2195Al-Li合金发生局部腐蚀为晶间腐蚀和孔蚀的均匀腐蚀;施加应力时1420Al-Li合金蚀孔增多、尺寸减小,2195Al-Li合金晶间腐蚀加重,大量孔蚀连接成片形成严重的均匀腐蚀。     

对不同环境的2D70铝合金低周疲劳性能研究

对2D70铝合金在试验室空气、湿空气、盐雾及盐雾+SO四种环境下进行低周疲劳试验,对比四种环境下的循环σ-ε2曲线及应变-寿命曲线,得出结论:相同应变下,2D70铝合金随腐蚀环境增强,循环应力降低;相同应变下,2D70铝合金在盐雾及盐雾+SO两种环境下低周疲劳寿命相近,并且随着腐蚀环境的增强,低周疲劳寿命降低;腐蚀环境越强,材料疲劳损2伤程度越大。研究结果为预测飞机不同环境的低周疲劳寿命提供了参考,对飞机腐蚀防护及耐久性设计具有重要意义。     

环境温度对船用耐蚀钢腐蚀行为的影响

 采用国际海事组织（IMO）模拟油轮货油舱内底板环境试验方法,对比分析了传统船板和耐腐蚀船板的腐蚀失重与腐蚀形貌,深入研究了环境温度对船用耐蚀钢腐蚀行为影响规律。结果表明,环境温度对船板腐蚀行为存在显著影响,随着环境温度（30~50℃）的升高,点蚀坑的数量逐渐增多,点蚀坑深度先增大后减小,在45℃时达到峰值。2种钢点蚀行?畋鸾洗螅炒甯值闶纯拥纳疃戎本侗龋╤/D）随环境温度的增大而增大,而耐蚀船板则呈现逐步下降的趋势。耐蚀合金元素的加入有效降低了船板钢在不同温度下的腐蚀速率,减小了钢的点蚀坑数量,改善了点蚀坑的扩展方式。即点蚀坑由纵向深度方向扩展,转为横向表面方向扩展,有效提高了船板的安全性。     

Modelling Corrosion Behavior of Friction Stir Processed Aluminium Alloy 5083 Using Polynomial: Radial Basis Function

Aluminium alloy 5083, widely used in marine applications, undergoes accelerated corrosion in sea water due to the aggressive reaction of chloride ions with the secondary phase particles and other intermetallics present in the alloy matrix. The corrosion rate of the alloy is also influenced by the temperature difference between the alloy and its environment. Friction stir processing (FSP) is a recent solid state processing technique for improving the surface properties of metals and alloys. In this study, an attempt has been made to explore the possibility of improving the corrosion resistance of AA5083 by FSP. FSP trials were performed by varying the tool rotation speed, tool traverse speed and shoulder diameter of the tool, as per face centered central composite design. The corrosion potential and the corrosion rate of friction stir processed AA5083 was studied using potentiodynamic polarization studies, at three different temperatures. Mathematical models based on polynomial—radial basis function were developed and used to study the effect of process parameters on the corrosion potential and the corrosion rate of friction stir processed AA5083. FSP resulted in refinement of the grain structure, dispersion and partial dissolution of secondary phase particles in the matrix, which increased the corrosion resistance of the alloy.     

盐雾腐蚀对HRB400E抗震钢筋低周疲劳和力学性能的影响

摘要：采用质量分数为5%的NaCl溶液在盐雾腐蚀箱进行30~90d加速腐蚀试验,研究了盐雾腐蚀对HRB400E钢筋低周疲劳行为和拉伸性能的影响。然后采用轴向位移控制模拟地震载荷对腐蚀钢筋开展了低周疲劳和拉伸试验,获得循环响应特征曲线和应变 寿命曲线。结合SEM断口形貌观察,分析钢筋的低周疲劳断裂机制。结果表明：盐雾腐蚀对钢筋的质量和尺寸有明显影响,钢筋表面产生腐蚀坑;钢筋的力学性能随腐蚀时间增加而降低,腐蚀90d的断裂伸长率下降率达461%,屈服强度在腐蚀30d以后可能就不再满足标准要求;腐蚀明显削弱了钢筋的抗循环载荷性能,导致低周疲劳寿命下降;腐蚀会减小钢筋的裂纹扩展区面积并加速裂纹扩展。     

Microstructure and Fatigue Properties of a Friction Stir Lap Welded Magnesium Alloy

Friction stir welding (FSW), being an enabling solid-state joining technology, can be suitably applied for the assembly of lightweight magnesium (Mg) alloys. In this investigation, friction stir lap welded (FSLWed) joints of AZ31B-H24 Mg alloy were characterized in terms of the welding defects, microstructure, hardness, and fatigue properties at various combinations of tool rotational rates and welding speeds. It was observed that the hardness decreased from the base metal (BM) to the stir zone (SZ) across the heat-affected zone (HAZ) and thermomechanically affected zone (TMAZ). The lowest value of hardness appeared in the SZ. With increasing tool rotational rate or decreasing welding speed, the average hardness in the SZ decreased owing to increasing grain size, and a Hall–Petch-type relationship was established. Fatigue fracture of the lap welds always occurred at the interface between the SZ and TMAZ on the advancing side where a larger hooking defect was present (in comparison with the retreating side). The welding parameters had a significant influence on the hook height and the subsequent fatigue life. A relatively “cold” weld, conducted at a rotational rate of 1000 rpm and welding speed of 20 mm/s, gave rise to almost complete elimination of the hooking defect, thus considerably (over two orders of magnitude) improving the fatigue life. Fatigue crack propagation was basically characterized by the formation of fatigue striations concomitantly with secondary cracks.