Microstructure Distribution Characteristics of High-Strength Aluminum Alloy Thin-Walled Tubes during Multi-Passes Hot Power Backward Spinning Process

The microstructure of the thin-walled tubes with high-strength aluminum alloy determines their final forming quality and performance. This type of tube can be manufactured by multi-pass hot power backward spinning process as it can eliminate casting defects, refine microstructure and improve the plasticity of the tube. To analyze the microstructure distribution characteristics of the tube during the spinning process, a 3D coupled thermo-mechanical FE model coupled with the microstructure evolution model of the process was established under the ABAQUS environment. The microstructure evolution characteristics and laws of the tube for the whole spinning process were analyzed. The results show that the dynamic recrystallization is mainly produced in the spinning deformation zone and root area of the tube. In the first pass, the dynamic recrystallization phenomenon is not obvious in the tube. With the pass increasing, the trend of dynamic recrystallization volume percentage gradually increases and extends from the outer surface of the tube to the inner surface. The fine-grained area shows the states of concentration, dispersion, and re-concentration as the pass number increases. .

Process of friction-stir welding high-strength aluminum alloy and mechanical properties of joint

The process of friction-stir welding 2A12CZ alloy has been studied. And strength and elongation tests have been performed, which demonstrated that the opportunity existed to manipulate friction-stir welding parameters in order to improve a range of material properties. The results showed that the joint strength and elongation arrived at their maximums (331 MPa and 4%) at 37.5 mm/min and 300 rpm. As welding parameters changing, joint tensile strength and elongation had similar development. Hardness measurement indicated that the weld was softened. However, there was considerable difference in softening degree for different joint zone. The weld top had lower hardness and wider softening zone than other zone of the weld. And softening zone at advancing side was wider than that at retreating side.

High-strength aluminum alloys hollow billet prepared by two-phase zone continuous casting

The two-phase zone continuous casting(TZCC)technique was used to continuously cast high-strength aluminum alloy hollow billets,and a verified 3D model of TZCC was used to simulate the flow and temperature fields at casting speeds of 2-6 mm·min^(-1).Hollow billets under the same conditions were prepared,and their macro/microstructures were analyzed by an optical microscope and a scanning electron microscope.During the TZCC process,a circular fluid flow appears in front of the mushy zone,and the induction heated stepped mold and convective heat transfer result in a curved solidification front with depressed region near the inner wall and a vertical temperature gradient.The deflection of the solidification front decreases and the average cooling rate in the mushy zone increases with increasing casting speed.Experimental results for a 2D12 alloy show that hot tearing periodically appears in the hollow billet accompanied by macrosegregation near the inner wall at casting speeds of 2 and 4 mm·min^(-1),while macroscopic defects of hot tearing and macrosegregation weaken and the average size of columnar crystals in the hollow billets decreases with further increasing casting speed.2D12 aluminum alloy hollow billets with no macroscopic defects,the finest columnar crystals,and excellent mechanical properties were prepared by TZCC at a casting speed of 6 mm·min^(-1),which is beneficial for the further plastic forming process.

Recent progress in corrosion protection of friction stir welded high-strength aluminum alloy joints

Friction stir welding （FSW） has been widely used in many industries, with which high-strength aluminum alloys can be well joined. However, the corrosion resistance of FSW high-strength Al alloy joints is relatively poor, which limits their industrial applications. The joints shall be protected against corrosion. In this review, therefore, the current status and development of corrosion protection for FSW high-strength Al alloy joints are presented. Particular emphasis has been given to different protection methods ： lowering heat input, post-weld heat treatment, surface modification and spray coatings. Finally, opportunities are identified for further research and development in corrosion protection of FSW high-strength Al alloy joints.

Influence of pre-stretching on quench sensitive effect of high-strength Al-Zn-Mg-Cu-Zr alloy sheet

The influence of pre-stretching on quench sensitive effect of high strength Al-Zn-Mg-Cu-Zr alloy AA 7085 sheet was investigated by tensile testing at room temperature,transmission electron microscopy(TEM)and differential scanning calorimetry(DSC).The water-cooled and aged alloy exhibits higher strength than the air-cooled and aged alloy;2.5%pre-stretching of tensile deformation exerts little effect on strength of water-cooled and aged alloy but increases that of air-cooled and aged one,and therefore the yield strength reduction rate due to slow quenching decreases from about 3.8%to about 1.0%,reducing quench sensitive effect.For the air-cooled alloy,pre-stretching increases the sizes ofη'strengthening precipitates but also increases their quantity and the ratio of diameter to thickness,resulting in enhanced strengthening and higher strength after aging.The reason has been discussed based on microstructure examination by TEM and DSC.

2195铝合金中温变形条件下的静态再结晶机理及动力学

具有高强度、低密度的2195铝合金是航空航天构件减重的首选材料。2195铝合金在中温热变形过程中常会伴随着静态再结晶的发生,静态再结晶晶粒对材料最终的力学性能有着重要影响。因此,本工作采用热压缩试验、硬度测试、EBSD和XRD测试技术研究了静态再结晶晶粒判别方法,研究了不同变形温度(160~240℃)和不同保温时间(0~30 s)对静态再结晶行为和位错演变行为的影响,探明了静态再结晶的演变机理。结果表明,晶粒平均取向差角度分布值(GOS值)小于或等于0.4°的晶粒为静态再结晶晶粒;当变形温度为160~240℃、应变速率为0.01 s^(-1)以及变形程度为30%时,随着保温时间t(t<20 s)延长,静态再结晶增加,晶粒尺寸逐渐增大。然而,当变形温度为240℃、保温时间大于20 s时,静态再结晶晶粒没有明显增加,仅有略微长大。在静态保温过程中,160℃的变形样品比200℃的变形样品能够更快、更易形成细小静态再结晶晶粒。基于以上研究规律,建立了2195铝合金中温变形条件下的静态再结晶动力学模型,该模型具有良好的预测效果。本研究对优化2195铝合金热变形和热处理工艺参数具有重要的理论价值和实际意义。

Discrete element and finite element coupling simulation and experiment of hot granule medium pressure forming

The granule medium of discreteness is supposed to be continuous（Drucker-Prager model） in the existing finite element simulation analysis on the hot granule medium pressure forming（HGMF） process, so the granule medium may produce tensile stress in the process of pressure-transferring and flowing, which does not coincide with the reality. The analysis method, discrete element and finite element（DE-FE） coupling simulation, is proposed to solve the problem. The material parameters of simulation model are obtained by the pressure-transfer performance test of granule medium and the hot uniaxial tensile test of sheet metal. The DE-FE coupling simulation platform is established by adopting Visual Basic language. The features in the process that AA7075-T6 conical parts are formed by the HGMF process are analyzed and verified by the process test. The studies show that the results of DE-FE coupling simulation coincide well with the test results, which provides a new analysis method to solve the mechanics problem in the coupling of discrete and continuum.

2219中厚铝合金VPTIG深熔焊接熔池行为与组织性能

针对2219-T87铝合金双频复合脉冲变极性TIG(DP-VPTIG)深熔焊接过程,采用高速图像采集和多物理场数值仿真技术对熔池传热传质行为进行研究,解耦了双频脉冲电流和方波变极性电流的作用机制,并探究了DP-VPTIG电弧对接头组织性能的影响。结果表明:双频脉冲能有效激发熔池内小孔,方波变极性电流能保证焊接过程稳定,DP-VPTIG可实现中厚板铝合金的高效高质量深熔焊接。相比常规VPTIG接头,DP-VPTIG接头焊缝组织更加细小,接头抗拉强度、屈服强度和延伸率分别提高了8%、17%和22%。

4032铝合金活塞在中高温氨水环境中的腐蚀行为研究

近年来,氨(NH_(3))作为内燃机燃料得到广泛关注。氨燃烧会产生大量的水,然而未完全燃烧的氨在有水存在的中高温环境中对发动机活塞部件可能会产生腐蚀。以4032铝合金活塞材料为研究对象,研究其在恒温200℃下25%(质量分数)氨水溶液中的腐蚀行为,着重探讨了在不同时间尺度下铝合金的腐蚀失重、腐蚀产物形态、腐蚀电化学性质。结果表明,4032铝合金在中高温氨水环境中的腐蚀速率随浸泡时间的延长呈先增强后减弱的变化趋势,腐蚀产物主要以Al(OH)_(3)为主。随着浸泡时间的延长,4032铝合金的腐蚀电位Ecorr和极化电阻Rp均逐渐增大,腐蚀电流密度Jcorr逐渐减小,并进一步解析了其腐蚀机理。

Drawing-upsetting-extrusion-clinching of high-strength steel and aluminum alloy

To realize good point connection between high-strength steel and aluminum alloy,a process of drawing-upsetting-extrusion-clinching was proposed.First,the sheets were drawn;then,the bottom of the protrusion part was extruded,forming the necessary initial interlock;and finally,the protrusion part was reverse press clinched,forming a certain height of the clinched head.Taking DP980 high-strength steel and A15083 aluminum alloy as the connection objects and using the method of numerical simulation combined with experimental test,the mold was made,and the experiment was carried out on the basis of numerical simulation.The experimental results proved the feasibility of the process and the effectiveness of the numerical model.The simulation and experimental results show that the necessary interlock in the drawing-upsetting-extrusion stage is the premise of effective connection.The relative protrusion height should be around 55.6%after reverse-press-clinching.The best comprehensive mechanical properties measured by strength test were shear resistance of 2644 N,fatigue life of 24,535 times and peel resistance of 1522 N.Through failure analysis,the relationship between the interlock Tu and the neck thickness Tn of the joint with the best comprehensive mechanical properties was established as Tu=0.35Tn.The design method of die and process parameters when the sheet thickness changes was researched by numerical simulation.The results show that the clearance between the punch and the die and the bottom thickness are directly proportional to the sheet thickness,and the drawing depth is directly proportional to the punch radius.

Hot Granules Medium Pressure Forming Process of AA7075 Conical Parts

High strength aluminum alloy plate has a low elongation at room temperature, which leads to the forming of its components need a high temperature. Liquid or gas is used as the pressure-transfer medium in the existing flexible mould forming process, the heat resistance of the medium and pressurizing device makes the application of aluminum alloy plate thermoforming restricted. To solve this problem, the existing medium is replaced by the heat-resisting solid granules and the general pressure equipments are applied. Based on the pressure-transfer performance test of the solid granules medium, the feasibility that the assumption of the extended Drucker-Prager linear model can be used in the finite element analysis is proved. The constitutive equation, the yield function and the theoretical forming limit diagram（FLD） of AA7075 sheet are established. Through the finite element numerical simulation of hot granules medium pressure forming（HGMF） process, not only the influence laws of the process parameters, such as forming temperature, the blank-holder gap and the diameter of the slab, on sheet metal forming performance are discussed, but also the broken area of the forming process is analyzed and predicted, which are coincided with the technological test. The conical part whose half cone angle is 15° and relative height H/d0 is 0.57, is formed in one process at 250℃. The HGMF process solves the problems of loading and seal in the existing flexible mould forming process and provides a novel technology for thermoforming of light alloy plate, such as magnesium alloy, aluminium alloy and titanium alloy.

Heat treatment and granule medium internal highpressure forming of AA6061 tube

The new forming process of AA6061 alloy tube, including solution treatment, granule medium internal high-pressure forming and aging treatment, was developed. The AA6061 alloy tube via heat treatment satisfied the forming requirement, and the granule medium internal high pressure forming method for AA6061 alloy tube was also realized by using convenient implementation with low requirement of equipment and flexible design of product. At a solution temperature of 560℃ and time of 120 min, the elongation of the AA6061 extruded tube increases by 300% and the strength and the hardness dramatically decrease too. Therefore, the AA6061 alloy tube meets the requirement of internal high-pressure forming because of the improvement of formability. The experiments shows that the strength and hardness of AA6061 alloy workpiece recover to that of the as-received alloy at an aging temperature of 180℃ and time of 360 min, and the strength of AA6061 alloy workpiece is equal to the base alloy. The typical parts of convex ring tube, stepped shaft tube and hexagonal tube were successfully produced in lab by using the present forming method. The forming tests show that the maximum expansion ratio(MER) of the AA6061 extruded tube increases by 25.5% and the material properties of formed AA6061 alloy tube reached the performance of as-received alloy.

Microstructure and mechanical properties of friction stir welded powder metallurgy AA2024 alloy

The extruded plate of powder metallurgy AA2024 aluminum alloy was successfully solid-state joined by friction stir welding(FSW) to demonstrate potential applications in the aerospace and automotive industries. For determining the optimal processing parameters of FSW, the microstructure, mechanical properties, and fracture behavior of FSW joints were evaluated. When the processing parameters were optimized with 2000 r/min rotation speed and100 mm/min traverse speed, high quality welds were achieved. The ultimate tensile strength yield strength and elongation of the joint can reach 415 MPa(85% of the base metal strength), 282 MPa, and 9.5%, respectively. The hardness of the joint gradually decreased from the alloy matrix to the heat-affected zone. The lowest strength and hardness appeared near the heat-affected zone because of the over-aging caused by heat flow from repeated stirring during FSW. The average grain size of the stir zone(2.15 μm) was smaller than that of the base metal(4.43 μm) and the heat-affected zone(5.03 μm), whose grains had <110> preferred orientation.

Research on technological parameters of pressure forming with hot granule medium on AA7075 sheet

Hot granule medium pressure forming （HGMF） process is a new process in which granule medium replaces the medium in existing flexible-die hot forming process, such as liquids, gases or viscous medium. Hot forming of light alloy sheet parts can be realized based on the properties of granule medium, such as withstanding high temperature and pressure, filling well, sealing and loading easily. In this work, the forming of AA7075 cylindrical parts by HGMF process is taken as an example to establish the constitutive relation and forming limit diagram （FLD） of AA7075 sheet which is related to temperature by hot uniaxial tensile test of sheet metal. Based on the assumption that granule medium is applied to extended Drucker-Prager linear material model, the finite element model of HGMF process is established and the effect of technological parameters, such as forming temperature, blank-holder gap and drawing ratio, on the sheet metal formability, is studied. The limit drawing ratio curve of AA7075 cylindrical parts at forming temperature of 175-300 ℃ is obtained by HGMF process test, and the limit drawing ratio reaches the maximum value of 1.71 at 250 ℃. The results of numerical simulation are consistent with the results of process test, and the forming force, distribution of wall thichness and form of instability are predicted correctly, which provides reference for the application of HGMF process.

Stress-strain analysis on AA7075 cylindrical parts during hot granule medium pressure forming

Hot granule medium pressure forming(HGMF) is a technology in which heat-resistant granules are used to replace liquids or gases in existing flexible-die forming technology as pressure-transfer medium. Considering the characteristic of granule medium that seals and loads easily, the technology provides a new method to realize the hot deep-drawing forming on high strength aluminum alloy sheet. Based on the pressure-transfer performance test of granule medium and the material performance test of AA7075-T6 sheet, plastic mechanics analysis is conducted for the areas, such as the flange area, force-transfer area and free deforming area, of cylindrical parts deep-drawn by HGMF technology, and the function relation of forming pressure is obtained under the condition of nonuniform distribution of internal pressure. The comparison between theoretical result and experimental data shows that larger deviation occurs in the middle and later period of forming process, and the maximum theoretical forming force is less than the experimental value by 24.6%. The variation tendency of the theoretical thickness curve is close to the practical situation, and the theoretical value basically agrees well with experimental value in the flange area and the top area of spherical cap which is in the free deforming area.

Effects of electrolyte components on properties of Al alloy anode

The effects of Na2SnO3, In(OH)3 and Na2SnO3+In(OH)3 on the properties of Al alloy anode were studied in alkaline medium at 25 ℃. The self-corrosion rate of Al alloy anode was studied by method of H2 immersed in aqueous medium, and the electrochemical properties of Al alloy anode were tested via galvanostatic discharge and dynamic potential methods. The results show that the self-corrosion rate of Al alloy anode in 4 mol/L NaOH+3 mol/L NaAlO2 medium can be minimized by adding Na2SnO3, In(OH)3 and Na2SnO3+ In(OH)3. Na2SnO3, In(OH)3 and Na2SnO3+In(OH)3 make Al anodic potential shift positively in galvanostatic discharging. The most effective additive of Al alloy anode in 4 mol/L NaOH+3 mol/L NaAlO2 medium is 0.075 mol/L Na2SnO3+0.005 mol/L In(OH)3, integrating self-corrosion rate and electrochemical properties.

增材制造中高强铝合金的缺陷与力学性能研究进展

铝合金是一种重要的轻质金属结构材料,广泛应用于航空航天和交通运输等领域。行业的快速发展对铝合金零件的服役性能和制备过程都提出了更高的要求,传统减材制造已难以满足对铝合金零件高效敏捷、绿色环保的制备要求。增材制造作为一种新兴的快速成形技术,为铝合金零件的制备提供了一个崭新的思路。然而,由于增材制造的工艺特点和铝合金的本征性质,通过增材制造技术制备的中高强铝合金零件中易形成诸多缺陷,严重损害其力学性能,限制其实际生产应用。本文综述了增材制造中高强铝合金零件中的缺陷类型及其成因,并从优化工艺参数、合金成分和添加形核剂三个方面,重点讨论了目前消除增材制造中高强铝合金零件中缺陷,改善其力学性能的进展及发展趋势,并指出未来改善增材制造中高强铝合金微观组织和力学性能的努力方向应为综合调控工艺参数和合金成分,进一步探索增材制造铝合金的最佳热处理工艺,从而获得高强塑性增材制造铝合金。

6063铝合金阳极氧化膜中温无镍封孔工艺

以醋酸镁和醋酸锂为主盐,聚乙二醇600(PEG600)为表面活性剂,对6063铝合金阳极氧化膜进行封孔处理。研究了封孔时的pH、温度和时间对阳极氧化膜耐蚀性的影响,得到较优的封孔工艺参数为:Mg(CH_(3)COO)_(2)·4H_(2)O 3g/L,CH_(3)COOLi 7 g/L,三乙醇胺2 g/L,PEG 6006 g/L,苯并三氮唑(BTA)5 g/L,温度75℃,pH 6.1,时间30 min。采用扫描电子显微镜(SEM)、X射线光电子能谱(XPS)、电化学测试等手段分析了阳极氧化膜封孔前后的微观形貌、元素组成和耐蚀性,并简要分析了封孔机理。在较优工艺条件下封孔后阳极氧化膜的微观表面更加粗糙,耐蚀性良好,封孔产物主要由Mg、Li和Al的氧化物与氢氧化物所组成。

6082铝合金中厚板高频脉冲MIG对接焊工艺及接头的残余应力

采用高频脉冲MIG焊和常规脉冲MIG焊进行了6082-T6铝合金8 mm厚板的对接焊工艺试验(焊接接头条件:焊接间隙1 mm,钝边为0.5 mm、坡口角度分别为50°和60°),对比分析了焊缝成形规律及焊后焊趾处的残余应力值。研究结果表明:两种焊接方法的焊缝成形质量良好,与常规脉冲MIG焊相比,高频脉冲MIG焊根部熔深较大,坡口角度为50°时,在相同的热输入(10.7 kJ/cm)条件下,根部熔宽增加约20%,坡口角度60°时,根部熔宽增加约16%;与常规脉冲MIG焊相比,高频脉冲MIG焊的气孔敏感性较小,焊接残余应力较小。坡口角度为60°时,横向残余应力(σy)降低约为18.5%,纵向残余应力(σx)下降约为8.3%;坡口角度为50°,横向残余应力(σy)降低约为18%,纵向残余应力(σx)下降约为7%;坡口角度由60°减小为50°,高频脉冲焊焊趾处的残余应力下降约6%。

基于电磁加载的新型中应变率动态拉伸测试系统与试验方法

以轻金属和复合材料为代表的新型航空航天结构材料在中应变率环境下的动态力学行为和相关失效机理研究受到越来越多的关注。为了充分探究新型结构材料性能与应变率之间的对应关系,在电磁铆接系统的基础上研发了一种可以实现中应变率动态拉伸测试的新型试验系统,为金属和复合材料及其连接结构进行动态性能测试提供了一种科学高效的试验方法。首先介绍了电磁加载装置的基本原理和功能特点,分别对加载系统、控制系统和数据采集系统进行了详细说明;其次介绍了动态加载测试过程不同参数下对应力学响应的变化及其重复试验下的一致性结果,进而验证了整个测试系统的稳定性和可靠性;最后采用该系统测试了不同应变率下2024–T6铝合金的力学特性。测试结果表明,电磁加载动态拉伸测试系统可以准确地反映出应变率变化对2024–T6铝合金性能的影响,这为新型航空材料进行服役环境下的结构安全性研究提供了有力的技术支撑。