Research on microstructure in as-cast 7A55 aluminum alloy and its evolution during homogenization

The microstructure of the as-cast 7A55 aluminum alloy and its evolution during homogenization were investigated by means of optical microscopy （OM）, scanning electron microscopy （SEM）, energy dispersive spectroscopy （EDS）, X-ray diffraction （XRD）, and differential scanning calorimetry （DSC） analysis. The results indicate that the microstructure of the as-cast 7A55 aluminum alloy mainly consists of the dendritic network of aluminum solid solution, Al/AIZnMgCu eutectic phases, and intermetaUic compounds MgZn2, Al2CuMg, Al7Cu2Fe, and Al23CuFe4. After homogenization at 470℃ for 48 h, Al/AlZnMgCu eutectic phases are dissolved into the matrix, and a small amount of high melting-point secondary phases were formed, which results in an increasing of the starting melting temperature of 7A55 aluminum alloy The high melting-point secondary phases were eliminated mostly when the homogenization time achieved to 72 h. Therefore, the reasonable homogenization heat treatment process for 7A55 aluminum alloy ingots was chosen as 470℃/72 h.

Effect of connection processes on mechanical properties of 7B04 aluminum alloy structures

The static and fatigue properties of 7B04 aluminum alloy structures connected by riveting and refill friction stir spot welding(refill FSSW)were compared and analyzed.Results show that the static compression load of the typical structure connected by riveting and refill FSSW fluctuated in the range of 117-124 kN,and the shear load was in the range of 89-95 kN.Welds spacing had a small influence on the static load of the structures joined by refill FSSW.However,the fatigue life of riveted structures was lower than that joined by refill FSSW.For the welded structure,the heterogeneous microstructures of the welded joint led to the uneven microhardness,and the hook at the lap interface bent upwards at the same time.These factors made the welded structures during the fatigue test failure along the path of sleeve moving.

Effect of heat treatment on mechanical properties of thixoformed 7A09 aluminum alloy

The effects of solution-ageing treatment on the mechanical properties of semi-solid metal(SSM)products were studied by the method of orthogonal experiment.The microstructure and tensile properties at different treatment conditions were analyzed.The results show that the effects of solution-ageing treatment were obviously influenced by the original microstructure of the SSM billet. Higher temperature is favorable for the sufficient solution of alloy elements,but the grains will grow up when treated at a higher temperature or soaked for a longer time.There is a contradiction between the maximum tensile strength and elongation percentage. Under the condition of solution treatment at 475℃for 12 h and at 133℃for 20-22 h ageing,better properties including about 540 MPa of tensile strength and more than 6.3%of elongation can be obtained in general.The surplus phases not melted in the substrate and the solution precipitated supersaturated elements are the main factors influencing the properties of the alloys.

Investigation of Stress Corrosion Cracking Initiation of 7A52 Aluminum Alloy

The stress corrosion cracking（SCC） behaviour of 7A52 aluminum alloy in air and in 3.5% NaCl solution was researched by slow strain rate test（SSRT） and SEM-EDS. The SCC susceptibility was estimated with the loss of the reduction in area. The experimental results indicate that the SCC susceptibility of 7A52 aluminum alloy in 3.5% chloride solution is the highest at strain rate of 1×10-6 s-1. The lowest one is under the condition of 1×10-5 s-1. Stress concentration and anode dissolving around Al-Fe-Mn intermetallics initiate micropores which will result in microcracks. The existence of intermetallics in the microstructure may play an important role in understanding the SCC initiation mechanisms of 7A52 aluminum alloy.

Volta Potential Analysis of Intermetallics in 7A52 Aluminum Alloy

In order to study the effect of intermaetallics on the corrosion behaviour of 7A52 aluminum alloy, the alloy was characterized by means of SEM-EDS and scanning Kelvin probe force microscopy（SKPFM）. The experimental results indicate that there are two different intermetallics：A1-Mn-Fe and Mg2Si. Both intermetallics exhibite the negative volta potential relative to the matrix indicating an anodic behaviour. Hereby, they are easy to be dissolved and corroded under the erosive environment, and there become the corrosion initiation sites. The A1-Mn-Fe intermetallics show stronger anodic behaviour than those of Mg2Si intermetalics. It means that A1-Mn-Fe intermetalics are easier to be corroded.

Cutting properties of water vapor plasma arc on 7A52 aluminum alloy plate

7A52 aluminum alloy was cut with an integrated equipment for welding and cutting using water vapor plasma arc. Various cutting mediums were tested. The arc force, electron density and cutting speed in each medium were tested and calculated. The fractography and microstructure of the cuts were also analyzed. Results show that the arc force, electron density and cutting speed #wreased with increasing acetone concentration. However, above a certain value （40%）, higher acetone concentrations contribute little to the arc force and cutting speed. The microstrueture of material near the cut was greatly influenced by the water vapor plasma arc. While the microstructure of the material beyond 10 mm from the cut was hardly influenced by the cutting heat. It was demonstrated that the water vapor plasma arc can be used for cutting of aluminum alloys in open field or emergency situations.

Surface nanocrystallization of 7A52 aluminum alloy welded joint

As a means of surface modification process, metal surface nanocrystallization （MSN） has attracted widespread attention and enjoyed a great prospect. However, currently little research is carried out regarding MSN of welded joint. The processes of high energy shot peening （HESP） technology and ultrasonic impact treatment （UIT） were carried out to achieve joint surface nanocrystallization. The grain size of before and after the welded joint surface nanocrystallization were comparatively analyzed with X-ray diffractometer, the surface deformation layer thickness of before and after the welded joint surface nanocrystallization were comparatively analyzed with optical microscopy, the surface hardness of before and after the welded joint surface nanocrystallization were comparatively analyzed with micro hardness machine. The results show that both of the processes can achieve welded joint surface nanocrystaUization and the weld after HESP have smaller grain size, larger deformation layer thickness and higher hardness values than those after UIT. However, HESP is restrained by the shapes and sizes of welding materials, so the UIT process is preferred to use in the general engineering practical applications.

Effects of in-situZrB_2 nanoparticles and scandium on microstructure and mechanical property of 7N01 aluminum alloy

In this study, the in-situ synthesized ZrB_(2) nanoparticles and rare earth Sc were introduced to enhance the strength and ductility of 7N01 aluminum alloy, via the generation of high-melting and uniform nanodispersoids. The microstructure and mechanical property evolution of the prepared composites and the interaction between ZrB_(2) and Sc were studied in detail. The microstructure investigation shows that the introduction of rare earth scandium(Sc) can promote the distribution of ZrB_(2) nanoparticles, by improving their wettability to the Al melt. Meanwhile, the addition of rare earth Sc also modifies the coarse Al Zn Mg Mn Fe precipitated phases, refines the matrix grains and generates high-melting Al_3(Sc,Zr)/Al_3Sc nanodispersoids. Tensile tests of the composites show that with the combinatorial introduction of ZrB_(2) and Sc, the strength and ductility of the composites are improved simultaneously compared with the corresponding 7N01 alloy, ZrB_(2) /7N01 composite and Sc/7N01 alloy. And the optimum contents of ZrB_(2) and Sc are 3 wt% and 0.2 wt% in this study. The yield strength, ultimate strength and elongation of(3 wt% ZrB_(2) +0.2 wt% Sc)/7N01 composite are 477 MPa, 506 MPa and 9.8%, increased about 18.1%, 12.2%and 38% compared to 7N01 alloy. Furthermore, the cooperation strengthening mechanisms of ZrB_(2) and Sc are also discussed.

7×××系铝合金时效处理工艺的研究进展

概括了7×××系高强铝合金的时效热处理工艺,重点分析了T6时效、双级时效、RRA时效、双峰时效以及非等温时效等时效热处理工艺对7×××系铝合金微观组织和性能的影响以及强化机理,并评述了针对具体牌号的7×××铝合金在不同的时效制度下析出相演变以及性能(强度、伸长率、耐腐蚀性等)规律,阐述了时效热处理在7×××铝合金强化及耐腐蚀性能方面研究的不足以及实际应用中存在的问题,提出了未来时效热处理工艺研究重点和方向,为7×××系铝合金时效工艺在实际生产中的应用提供参考。

7系高强铝合金力学性能研究现状及发展趋势

高强铝合金材料在土木工程领域具有较为广泛的应用前景,然而关于7系高强铝合金材料尚无系统的研究,限制了其在大跨度空间结构、特种结构、极端环境等复杂工程中的应用。本文对比了几种较为常用的7系铝合金材料力学性能,并详细阐述了高强铝合金材料高温力学性能、构件承载性能以及焊接连接性能等方面的研究进展。从国内研究现状看出,目前已开展较为充分的高强铝合金材料力学性能研究,但是关于7系高强铝合金构件轴压稳定、抗弯、压弯下构件稳定性能的研究尚且不足,搅拌摩擦焊接连接节点受力性能的研究突破对高强铝合金材料的工程应用具有重要意义。本文基于现有研究的不足之处,展望了7系高强铝合金材料与构件性能研究的发展方向,以期推动高强铝合金材料的工程应用。

Impact of cooling rate on exfoliation corrosion resistance of a Li-containing 7xxx aluminum alloy

The impact of cooling rate after solution heat treatment on exfoliation corrosion resistance of a Li-containing 7xxx aluminum alloy was investigated by accelerated immersion and electrochemical impedance spectroscopy test,optical microscope,electron backscatter diffraction and scanning transmission electron microscope.With the decrease of cooling rate from 1700℃/s to 4℃/s,exfoliation corrosion resistance of the aged specimens decreases with rating changing from EA to EC and the maximum corrosion depth increasing from about 169.4μm to 632.1μm.Exfoliation corrosion tends to develop along grain boundaries in the specimens with cooling rates higher than about 31℃/s and along both grain boundaries and sub-grain boundaries in the specimens with lower cooling rates.The reason has been discussed based on the changes of the microstructure and microchemistry at grain boundaries and sub-grain boundaries due to slow cooling.

Fe和Si杂质元素对7×××系高强航空铝合金组织及性能的影响

综述了Fe、Si杂质元素对7×××系高强航空铝合金的微观组织及力学性能的影响。Fe、Si主要是以粗大难溶杂质相形式存在。形成含Fe杂质相的种类较多,在含Cu量较高的合金中主要是形成Al7Cu2Fe相;形成含Si杂质相主要是Mg2Si相。Fe、Si杂质元素含量增加对合金强度的影响不大,但形成的富Fe、富Si粗大难溶杂质相含量的增加明显降低合金的塑性、断裂韧性和抗应力腐蚀性能。降低Fe、Si杂质元素含量是发展高综合性能航空铝合金的重要方向。

7×××系超高强铝合金的强韧化研究进展及发展趋势

总结了国内外关于7×××系超高强铝合金的强韧化方面研究进展及其现状,概述了提高超高强铝合金综合性能而开发的各种新技术和新工艺,探讨了超高强铝合金的强韧化途径,展望了强韧化的发展趋势,对提高高强铝合金强韧化性能提出了优化合金成分、改善制备工艺和开发新型的热处理技术等主要研发方向,概括了未来需要着重开展研究的内容。

7×××系超高强铝合金板材各向异性的研究现状

较为系统地介绍了7×××系铝合金的合金化原理、板材各向异性的影响因素及其研究现状。铝合金厚板各向异性及其不同厚度层性能变化的特征成为近年来重要研究方向,指出在厚板的轧制、热处理及微合金化元素等对合金组织、性能均匀性及各向异性的影响规律方面应投入更多力量进行研究,以便解决各向异性的同时,为未来合金开发和工艺升级提供参考。

7×××系铝合金双级双峰时效工艺研究

采用洛氏硬度计、显微硬度测试仪、扫描电镜(SEM)等手段系统地研究了7003、7050和7075铝合金双级双峰时效过程中时效硬化特性和微观组织结构等。结果表明,7×××系铝合金双级时效与单级时效一样存在硬度双峰现象,且第二峰的硬度比第一峰的硬度略高,从而验证了7×××系铝合金双级双峰的普遍性。

解读航空航天7×××系铝合金材料的状态

7×××系铝合金材料是制造大型飞机所用的关键材料,也是变形铝合金中状态代号最多的。详细介绍7×××系铝合金材料的状态代号及其定义,对状态代号适用的合金及产品种类作了举例说明。

7A60铝合金杯形件等温压扭关键工艺参数分析

以7A60铝合金杯形件为研究对象,通过工艺实验和有限元模拟研究了杯形件在等温压扭成形过程中关键工艺参数对其成形性能的影响。结果表明:坯料高径比对累积变形量的影响主要在镦粗变形阶段,下模扭转速度增大,成形载荷降低,扭矩增加;但当下模转速太大时,压扭件盘面过渡圆角区域损伤值将大于1,边缘易于产生破裂缺陷;成形温度的变化对成形载荷和扭矩的影响较为显著;成形过程中对压扭件施加小于1圈的扭转剪切变形,合金的连续性不会遭到破坏,且合金强度相比传统挤压件有所提高。

几种常用7×××系铝合金成分设计规律分析

高强度7×××系铝合金是航空航天工业的主要结构材料。对常用的五种7×××系铝合金的化学成分、不同厚度的板材以及其对应的力学性能进行了对比分析。通过Thermo-Calc热力学软件计算和试验验证,分析研究了合金中的元素配比、析出相与力学性能以及淬火性能之间的关系。结论是:对于7×××系铝合金,提高合金元素添加量可以获得更多的沉淀析出相,从而提高合金的强化效果;而减少沉淀析出相的总量可以降低7×××系铝合金的淬火敏感性;减少强化效果差的析出相,获得更多有效的强化相,则既有利于提高强化效果又有利于降低7×××系铝合金的淬火敏感性。

强化固溶处理对7×××铝合金型材组织与性能的影响

采用力学性能测试、金相和透射电子显微分析,研究了固溶处理工艺对7×××铝合金力学性能和显微组织的影响。结果表明,强化固溶处理可使最终固溶温度超过多相共晶温度而不产生过烧组织,提高残余可溶结晶相的固溶程度和基体的过饱和程度。与常规固溶处理相比,经强化固溶处理的合金时效后抗拉强度和屈服强度分别提高44N/mm2和52N/mm2,而伸长率仍然保持在14%的高水平。

7A04铝合金热顶铸造圆锭裂纹问题的探讨

裂纹是铝合金铸锭或加工制品成为废品的重要原因之一,铸造时形成的微裂纹会导致挤压制品失效。7A04铝合金的有效结晶范围宽,线收缩率大,因此热顶铸造时易产生热裂纹,而且,随着铸锭直径的增大,裂纹的倾向性更高。以热应力理论为基础,分析了影响7A04铝合金热顶铸造圆锭裂纹的因素,结合生产实际进行探索,掌握了7A04铝合金产生裂纹的一般规律,通过控制化学成分、设计结构合理的结晶器等措施,减少了7A04铝合金热顶铸造圆锭裂纹废品。