Al-Li合金的研究进展

Al-Li合金是一种综合性能好、具有巨大开发潜力的轻质合金,被认为是21世纪飞行器和舰船理想的结构材料.简要回顾了Al-Li合金的发展历史,重点介绍了铝锂合金的制备方法、微合金化、焊接等方面的研究进展.提出了对Al-Li合金研究今后的发展方向:组合优化现有制备工艺,提出新的制备技术;进一步探寻更有效的合金化途径,增加基体相与δ'相界面的错配度,引入新的时效强化相;不断改进焊接工艺,使合金的接头强度系数提高.     

Al-Li合金强韧化机理及途径

概述了Al-Li合金强韧化的内部机理和外部机理，并在此基础上阐述了提高Al-Li合金强韧性的主要途径。     

阳极氧化处理增强Al-Li合金胶接板剪切强度的机理

为揭示磷酸阳极氧化处理后Al-Li合金胶接接头剪切强度大幅度增强的机理,分别对其进行机械打磨和磷酸阳极化表面处理,并选用不同的分析仪器对表面处理后的Al-Li合金表面微观形貌、粗糙度、表面润湿性和表面自由能进行测试计算和分析。结果表明,机械打磨后仅在Al-Li合金表面留下纵横交错的沟槽,而磷酸阳极化处理后使得Al-Li合金表面产生了微观粗糙的多孔膜,增加了胶层与合金表面的接触面积,改善了胶质分布的均匀性;磷酸阳极化处理后Al-Li合金表面自由能明显提高,改善了粘接界面的润湿性能。两方面的共同作用,使得胶接界面的抗剪切能力大幅提高。     

铝锂合金电子束焊接数值模拟分析及工艺优化

采用组合热源模型对Al-Li合金电子束焊接温度场分布进行数值模拟分析,通过热-力耦合,模拟计算得到接头区域的残余应力分布.结果表明,Al-Li合金电子束焊接温度场沿焊接方向呈椭圆形分布,电子束热源中心的温度最高,其附近区域的等温线分布密集,随着与热源中心的距离增大,等温线分布逐渐稀疏,焊缝区存在较大的温度梯度,较好地模拟出了电子束焊缝的钉形分布特征.接头的残余应力分布模拟结果显示,残余应力主要集中于焊缝区,由于修饰焊的热作用,焊缝上部具有相对较大的应力值.利用模拟计算得到的结果进行焊接工艺及参数优化,焊接工艺试验表明,试验焊缝形貌与模拟熔池形貌相吻合,进一步验证了模拟计算结果的可靠性.     

1420Al-Li合金超塑特性及微成形

采用最大载荷法研究了1420Al-Li合金的超塑特性,根据试验获得的超塑特性参数,采用两种形式的模具对1420Al-Li合金的微成形性进行了研究.分析了成形压力、保压时间对微成形的影响,采用扫描电镜和金相显微镜分析了成形件的微观形貌,更好地理解了材料在微成形时的行为.     

Al-Li合金的短横向断裂和晶界脆性

一、引言 Al-Li合金因具有明显高于传统高强铝合金的比强度和比刚度而受到了人们的重视。许多国家已经投入大量人力、物力进行Al-Li合金的研究专题国际Al-Li合金会议已连续召开6次。目前,国外已有商业规模不同牌号、不同类型Al-Li合金半成品的生产能力和销售。 经过多年努力研究,当前Al-Li合金半成品(板材、挤压型材、锻件等)的纵向强韧配合已经达到或者超过了传统高强铝合金,尤其是纵向长裂纹疲劳扩展抗力明显高于传统合金。但是,几乎所有Al-Li合金半成品的短横向断裂性能都明显低于传统合金,短横向断裂韧度值通常只有纵向的1/3～1/2。这就大大地限制了Al-Li合金作为新一代结构材料的应用,成为当前研究与发展所必须要解决的关键问题之一。 Al-Li合金的短横向断裂均为沿晶断裂。短横向断裂性能差是由其晶界脆性所决定的。虽然,人们从一开始就已经认识到与晶内强烈的平面滑移一样,弱晶界也是Al-Li合金塑性低、韧性差的一个重要原因。但是,     

铝-锂合金平面应力断裂韧性的研究

一、前言 Al-Li合金因具有低密度、高弹性模量、高比强度等优点而引起宇航工业的广泛重视。但由于滑移局部化及无沉淀区的存在,导致Al-Li合金塑性较差。Sanders,Grig-son等人认为,共面滑移是导致Al-Li合金塑性较差的重要原因。加入某些合金元素如Cu、Mg、Zr等或改善热处理制度,形成非剪切沉淀相或促进均匀滑移可使合金的断裂韧性和塑性有较大提高,和Al-Li-Cu-Mg-Zr合金中存在的S’(Al_2CuMg),β’(Al_3Zr),T_1(Al_2LiCu)等析出相均可有效地提高合金的断裂韧性。所以,对Al-Li合金断裂韧性进行测试具有十分重要意义。通常能够反映材料本身属性的断裂韧性K_(IC)是对厚板的测试得到的,而实际应用的Al-Li合金多为薄板(厚为1～3mm),而通常情况下薄板的平面应力K_C估均高于厚板的平面应变K_(IC)值,因此,宇航工业的薄壁构件如用K_(IC)作依据则过于保守,于是Al-Li合金平面应力K_C值就显得更为重要,本文运用阻力曲线(R曲线)法对薄板8090Al-Li合金、LC4合金和LY12合金面应力K_C值进行测试。     

Al-Li合金高温抗氧化性能的研究

一、前言 Al-Li合金具有密度低、比强度和比钢度高等优点,在航空航天等领域有着广泛应用的前景。但由于Al-Li合金中含有Li、Mg等活泼元素在有氧的环境,特别是在温度较高的情况下,表面会发生严重氧化,形成一表面脱锂层。表面氧化会引起表面敏感性能的变化,使合金的拉伸强度、疲劳强度和硬度下降。从而影响了合金在高温下的使用。Be,Ca,Bi等元素可改善一般铝合金的抗氧化性能,为改善Al-Li合金的抗氧化性能,有人尝试在Al-Li合金中添加以上元素和La+Ce等,但都未取得明显效果。稀土元素作为我国的一种富有资源,在铝合金中已广泛应用,在Al-Li中的应用近几年国内也有所开展。Y是稀土族中密度较小的元素,我们的工作表明,加Y可明显改善Al-Li合金的室温和高温性能。本工作是在Al-Li-Cu-Mg-Zr合金中,添加了不同量的轻稀土元素Y,并采用高温氧化法研究了Y对合金抗氧化性能的影响。 二、实验方法     

用玻璃粉末强化的混凝土

一个由摩擦搅拌焊接、旋压成型的铝－锂（Al-Li）合金液体燃料推进剂圆顶罐首次在NASA马歇尔太空飞行中心亮相。据说它是为大型液体燃料推进剂设计的第一个标准尺寸的摩擦搅拌焊接、旋压成型的圆顶罐。     

冷轧 Al-Li 合金的再结晶

对 Al-Li 合金的再结晶温度和再结晶形核机制进行了研究。结果表明:所研究的 Al-Li 合金的再结晶开始温度为250℃,终了温度为400℃。再结晶形核有亚晶聚合和亚晶长大两种机制。     

Gas tungsten arc welding of fine-grained AZ31B magnesium alloys made by powder metallurgy

AZ31B magnesium alloys with various grain sizes and oxygen contents were prepared by powder metallurgy (P/M) combined with hot extrusion, and the P/M magnesium alloys were subjected to gas tungsten arc welding (GTAW). Porosities are observed in weld joints of the P/M AZ31B alloys with high oxygen contents. Gas composition analysis of porosity shows that the porosity originates mainly from the decomposition of magnesium hydroxide formed during the fabrication of magnesium alloys. The porosity can be decreased or prevented by reducing the amount of magnesium hydroxide (which is expressed as oxygen content in the present study) in the base materials, through controlling the P/M processing time. Use of a filler rod and/or an insert sheet containing rare earth element La tends to decrease the porosity in weld joints. When oxygen content in P/M AZ31B alloys is reduced to 440 ppm or less, sound weld joints without porosity are obtained. Mechanical test demonstrates that tensile strength of the sound weld joints of P/M AZ31B alloys is at the same level as that of weld joint of a commonly hot-extruded AZ31B alloy.     

金属间化合物Ni3Al基合金结构焊工研究

对Ｎｉ３Ａｌ基合金结构焊接的工艺进行了研究，对焊缝显微组织及性能进行了分析，结果表明：采用合理的焊接工艺参数，用Ｎｉ８１８焊条能够实现Ｎｉ３Ａｌ工个的结构焊接。     

Microstructure of Al-Mg-Si Weld Joints Produced by Pulse TIG Welding

Al-Mg-Si alloys (6000 series) are heat-treatable aluminum alloys and are extensively used in various sectors such as aerospace, automobiles, and general construction. Fabrication of these alloys often requires welding. Pulse TIG offers many advantages over conventional TIG welding as far as control of microstructure is concerned. This research investigated the effect of pulsed TIG welding parameters such as pulse duration, peak current, pulse frequency on the microstructure of heat-affected zone, and fusion line and weld metal of Al-0.5%Mg-0.5%Si weld joints. It was observed that a significant change in microstructure takes place in moving from the base metal to weld centerline. Dissolution of phases present along the grain boundary occurs as the fusion line is approached. Grain structure of heat-affected zone, fusion line, and weld metal appears to have tangible relationship with pulse parameters.     

Review: Low transformation temperature weld filler for tensile residual stress reduction

An attractive, alternative approach for the reduction of harmful residual stresses in weld zones is reviewed, which utilises low temperature, solid-state, displacive phase transformations in steel. The theory, latest concepts and practice for the design of such low transformation temperature (LTT) filler alloys are considered. By engineering the phase transformation temperature of the weld metal so as to take advantage of transformation expansion, the residual stress state within the weld zone can be significantly altered, most particularly where the weld thermally contracts with any movement of base parts constrained. To date, the technique has been shown to increase fatigue strength for some common weld geometries, which may enable engineering design codes to be favourably re-drafted where such LTT filler alloys are used.     

Effect of ultrasonic welding parameters on microstructure and mechanical properties of dissimilar joints

Ultrasonic spot welding has received significant attention during past few years due to their suitable applications in comparison to conventional fusion welding techniques. Fusion welding of dissimilar Aluminum and Stainless steel alloys is always a challenging task because of poor control on grain size and formation of undesirable brittle intermetallic compounds in the weld metal, which have deleterious effect on mechanical properties. In the past, welding of dissimilar alloys has been performed using electron beam welding, laser beam welding and friction stir spot welding, resistance spot welding, etc. However, little work has been reported on dissimilar welding of Aluminum and Stainless steel alloys using ultrasonic spot welding. The objective of the present work is to optimize ultrasonic spot welding parameters for joining 3003 Aluminum alloy with 304 Stainless steel. Welding was performed at various clamping pressures (i.e. 30, 40, 50 and 60 psi) and energy levels for investigating its effect on microstructure, mechanical properties and bond quality of the weld. Different levels of weld quality i.e. ‘under weld’, ‘good weld’ and ‘overweld’ were identified at various welding parameters using physical attributes. The weld specimens prepared with energy 125 and 150 J showed the maximum bond strength and were rated as “good” weld. It was also revealed that for a good quality weld, the maximum tensile strength is achieved once a reasonable amount of bond density and material thinning (required for the formation of metallurgical bonds) is attained.     

The mechanical properties related to the dominant microstructure in the weld zone of dissimilar formed Al alloy joints by friction stir welding

The joint properties of dissimilar formed Al alloys, cast Al alloy and wrought Al alloy, were examined with various welding conditions. Friction stir welding method could be applied to join dissimilar formed Al alloys which had different mechanical properties without weld zone defects under wide range of welding condition.The weld zone of dissimilar formed Al alloy exhibited the complex structure of the two materials and mainly composed of the retreating side material.The mechanical properties also depended on the dominant microstructure of the weld zone with welding conditions. The different mechanical properties of the weld zone with welding conditions were related to the behavior of the precipitates of wrought Al alloy and Si particles of cast Al alloy. The higher mechanical properties of the weld zone were acquired when a relatively harder material, wrought Al alloy, was fixed at the retreating side.     

Microstructural Study and Mechanical Properties of Dissimilar Friction Stir Welded AA5083-H111 and AA6082-T6 Reinforced with SiC Nanoparticles

Dissimilar friction stir welds were produced in 3 mm thick plates of AA6082-T6 and AA5083-H111 aluminum alloys using SiC as reinforcing material. The optimum weld presents a good distribution of nanoparticles in the weld nugget and mechanical mixing of the two alloys as well as further grain refinement compared to the one without nanoparticles. Higher hardness in the weld nugget is also evidenced, followed by enhanced ultimate tensile strength and elongation values. All specimens, after the tensile test, were lead to fracture at the heat affected zone of AA6082-T6 and specifically at the region of the lowest hardness.     

Process parameters/material location affecting hooking in friction stir lap welding: Dissimilar aluminum alloys

Influence of spindle and weld speeds, metal location, direction of spindle rotation, and tool pin length on hooking in lap FSW of dissimilar aluminum alloys and the effect of hook on tensile and fatigue weld strength was studied. Optical images of the cross-section of the specimen welded at different process parameters were analyzed. The results indicate that increased spindle speed, reduced weld speed, higher tool pin length, clockwise spindle rotation, and locating the stronger material at the bottom of the joint increased the size of the hooking defect. Higher weld speeds and very high spindle speeds resulted in lower hook size on the advancing side (AS) compared to the retreating side (RS) of the joint. Welding with low weld speed would result in higher advancing side hook size compared to the retreating side. Friction stir weld joints fabricated with anti-clockwise spindle rotation has been found to have extremely low hook both on the AS and the RS of the joint. The tensile and fatigue strengths of the weld joints and plates are degraded by the hook. The fatigue strength of welded alloys could be improved by a double pass weld, the second pass welded immediately adjacent to the first pass.     

Comparative experimental study on the modification of microstructural and mechanical properties of friction stir welded and gas metal arc welded EN AW‐6061 O aluminum alloys by post‐weld heat treatment

In this paper, the effects of post‐weld heat treatment on modification of microstructures and mechanical properties of friction stir welded and gas metal arc welded AA6061‐O plates were compared with each other. Gas metal arc welding and friction stir welding were used as the applicable welding processes for AA6061‐O alloys. The applied post‐weld heat treatment consisted of solution heat treatment, followed by water quenching and finally artificial aging. The samples were classified as post‐weld heat treated and as‐welded joints. The microstructural evolution, tensile properties, hardness features and fracture surfaces of both as‐welded and post‐weld heat treated samples were reported. The results clearly showed that friction stir welding process demonstrated better and more consistent mechanical properties by comparison with the gas metal arc welding process. The weld region of as‐welded samples exhibited a higher hardness value of 80 HV0.1 compared to the base material. In addition, the feasibility of post‐weld heat treatment in order to enhance the mechanical properties and to obtain more homogeneous microstructure of 6061‐O aluminum alloys was evaluated.     

Influence of heat input/multiple passes and post weld heat treatment on strength/electrochemical characteristics of friction stir weld joint

The V-95 and D-19 precipitation hardened Russian aluminum alloys are widely used in the Russian aircraft industry and these alloys are not weldable by conventional fusion weld techniques. This paper intends to evaluate the effect of spindle and weld speed on joint strength characteristics of a single pass (SP) and double pass (DP) friction stir lap weld through a common heat index and to analyze the effect of retrogression and re-ageing treatment (RRA) on joint strength and corrosion characteristics. The strength characteristics were analyzed by welding and shear testing of specimens and corrosion susceptibility of joint through immersion in EXCO solution as per ASTM G34. The trials revealed that the joint strength of the welded alloy is inversely proportional to the heat index and the DP weld provided significantly higher strength than an SP weld. The heat affected zone of the joint was found most sensitized to corrosion. The RRA treatment was found to improve the strength of the joints welded with higher heat input while it slightly degraded the joint strength for low heat input welds. The corrosion characteristics of the welded joint is also significantly improved by the post weld RRA treatment.