Effect of high-temperature pre-precipitation on microstructure and properties of 7055 aluminum alloy

1　INTRODUCTIONAl Zn Mg Cuserieshigh strengthaluminumal loyswithhighstrength to densityratioandexcellentmechanicalpropertieshavebeentheprimarystruc turalmaterialsofaerocraftinthespaceandgroundtransportationvehicles.Thedevelopmentandexten siveutilizationofhigh strength 7xxxseriesareham peredby poorcorrosionresistance ,especiallystresscorrosioncracking (SCC )resistance .Overthe pastfewyears ,thestudiesaboutstresscorrosioncrackingandageingtreatmentprocesshavebeenproceedinginordertoobtainma…     

晶界结构在不同热处理下对铝镁合金腐蚀规律的研究现状

铝镁合金是未来应用汽车领域发展具有很大潜力的一类重要材料.通常,在商品中的铝镁合金,镁的质量分数在0.5%～13%.汽车制造商通常选用镁的质量分数在4.5%以上,然而研究发现,当镁的质量分数超过3%的时候,会引起晶界间腐蚀,从而造成应力腐蚀开裂.此现象未见文献对其进行系统的分析和研究.本文主要介绍铝镁合金在不同的热处理...     

Al-Zn-Mg-Cu系铝合金中不同区域电子结构及应力腐蚀机理分析

利用计算机编程建立了Al--Zn--Mg--Cu合金 (7175铝合金) 中α--Al, η相及α--Al大角度晶界原子集团模型, 采用递归法计算 合金中Zn, Mg, Cu和H的环境敏感镶嵌能、原子间相互作用能、Fermi能级和态密度等电子结构参数, 分析了合金的应力腐蚀机理. 计算 结果表明: Mg, Cu和H容易在晶界偏析. Mg对H具有吸引作用, 促进H在晶界偏析, 引起晶界氢脆; Zn增大晶界与晶内的电位差, 降低合 金抗腐蚀性; Cu能减小晶界与晶内Fermi能级差, 降低晶界与晶内的电位差, 具有减缓合金腐蚀的作用. 计算结果还表明: η相的Fermi能 级最高, 腐蚀过程中作为阳极优先溶解. 由于η相俘获H, 当晶界析出断续η相时可减弱晶界H的偏析, 提高抗腐蚀性; 但晶界连续分布η相则形成腐蚀通道, 加速腐蚀进程.     

Correlations among stress corrosion cracking,grain-boundary microchemistry,and Zn content in high Zn-containing Al–Zn–Mg–Cu alloys

The correlations among the corrosion behaviour, grain-boundary microchemistry, and Zn content in Al–Zn–Mg–Cu alloys were studied using stress corrosion cracking (SCC) and intergranular corrosion (IGC) tests, combined with scanning electron microscopy (SEM) and high-angle angular dark field scanning transmission electron microscopy (HAADF-STEM) microstructural examinations. The results showed that the tensile strength enhancement of high Zn-containing Al–Zn–Mg–Cu alloys was mainly attributed to the high density nano-scale matrix precipitates. The SCC plateau velocity for the alloy with 11.0 wt.% Zn was about an order of magnitude greater than that of the alloy with 7.9 wt.% Zn, which was mainly associated with Zn enrichment in grain boundary precipitates and wide precipitates-free zones. The SCC mechanisms of different Zn-containing alloys were discussed based on fracture features, grain-boundary microchemistry, and electrochemical properties.     

Al-xMg-3.1Zn铝合金的应力腐蚀开裂行为及其机制

通过慢应变速率拉伸实验和动态电解充氢实验分别研究了Al-x Mg-3.1Zn铝合金的应力腐蚀开裂行为及其氢脆行为。结合宏观断口和微观断口形貌分析研究了合金发生应力腐蚀开裂的进程。通过对合金应力腐蚀开裂的机制进行分析阐明了合金中Mg元素含量对合金应力腐蚀开裂行为的影响。结果表明:在该合金体系中存在应力腐蚀开裂,且合金的应力腐蚀敏感性随合金中Mg含量的降低而降低,这与合金的阳极溶解行为与氢脆行为随Mg元素含量降低而减弱有着直接的关系。在这当中,合金中晶界析出相的数量随Mg元素含量降低而减少起到了至关重要的作用。     

Al-Zn-Cu-Mg及Al-Cu-Mg在氯化物水溶液中应力腐蚀开裂的扫描电镜断口形貌

本文研究了Al—Zn—Cu—Mg及Al—Mg—Cu在氯化物水溶液中用慢应变速率方法得到的应力腐蚀开裂的扫描电镜断口形貌。结果发现两种铝合金在氯化物水溶液中的应力腐蚀开裂断口复盖着—层腐蚀产物,这层腐蚀产物可以呈现不同的扫描电镜断口形貌,如类似解理的“平滑”形貌,“龟裂泥巴状”形貌等等。遮盖了应力腐蚀开裂固有的真实形貌;应力腐蚀开裂固有的真实形貌是相同的,呈典型的沿晶开裂形貌,盖有腐蚀产物层的形貌则取决于介质pH和电位。因此,应该根据铝合金应力腐蚀开裂固有的真实扫描电镜断口形貌来鉴别铝合金的应力腐蚀。将断口进行化学去膜处理可以得到铝合金应力腐蚀开裂的固有的真实的扫描电镜断口形貌。     

Interkristalline,Kornflächen- und Spannungsriß-Korrosion von ausgehärteten AlZnMg 1-Legierungen

Intercrystalline corrosion, grain-phase corrosion and stress-corrosion cracking of aged AlZnMg1 alloys Potentiostatic polarisation curves and stress corrosion crack propagation of a pure and a commercial AlZnMg1-alloy, both peakhardened either by warm or by double ageing, were investigated in airsaturated sodium halide and sulfate solutions at a temperature of 303 K. For this, propagation of crack tips was observed microphotographically under potentiostatic conditions and under constant stress using specimens precracked by fatique corrosion. The pure alloy contents (weight percent): Zn 4,4; Mg 1,26; Fe 0,05; Si 0,006; balance Al, the commercial alloy: Zn 5,05; Mg 1,2; Fe 0,23; Si 0,1; Mn 0,23; Cr 0,2; Cr 0,2; Ti 0,074; Zr 0,12; Cu 0,056; balance Al. In sodium halide solutions either grain boundary and grain attack or only grain attack occurs at a potential region more positive than the respective breakdown potential. At the more negative restpotential no attack can be observed. The influence of concentration of chloride ions on the velocity of discontinuous crack propagation in the pure alloy, which starts without any initiation stage, is different for both heat treatments. No crack propagation is observed in the commercial alloy and in any case in sulfate solutions. The obtained stress corrosion cracking results may be explained by hydrogen embrittlement of the area around the crack tip.     

铝合金在海洋环境中的腐蚀研究(Ⅱ)--海水全浸区16年暴露试验总结

总结了铝合金在青岛海域海水全浸区暴露16年的腐蚀结果，防锈铝LF2Y2，LF6M（BL），F21M，180YS在海水全浸区有好的耐蚀性，工业纯铝L4M，锻铝LD2CS的耐蚀性较差，无包铝层的硬铝LY12CZ和超硬铝LC4CS在海水中的耐蚀性很差，硬铝，超硬铝的包铝层起牺牲阳极作用，使基体受到保护，海生物污损对铝合金在海水中的腐蚀有明显影响，镁、锰能提高铝的耐海水腐蚀性，硅明显降低铝的耐蚀性，铜严重损害铝的耐蚀性，腐蚀电位较负的铝合金耐海水腐蚀性较好，腐蚀电位较正的铝合金耐海水腐蚀性较差。     

Effects of Sn and Ca additions on microstructure,mechanical properties,and corrosion resistance of the as‐cast Mg‐Zn‐Al‐based alloy

Effects of Sn and Ca additions on microstructure, mechanical properties, and corrosion resistance of the as‐cast Mg‐6Zn‐2Al‐based alloy were investigated by SEM, XRD, tensile tests, electrochemical measurements, etc. The higher the Sn content, the higher the yield strength of the Mg‐6Zn‐2Al‐based alloy. Trace Ca addition refined both grains and divorced eutectics in the Mg‐Zn‐Sn‐Al alloys, leading to the best combination of strength and plasticity. Moreover, its influence was more significant for the alloy with a higher Sn content. Furthermore, the combined addition had a beneficial effect on the corrosion resistance improvement of the Mg‐6Zn‐2Al alloy. The Mg‐6Zn‐2Al‐3Sn‐0.2Ca alloy was the most corrosion‐resistant alloy among the nine alloys studied, better than AZ91 and ZA85. It could be ascribed to the decrease and the refinement of divorced eutectics, the higher hydrogen overvoltage of Sn and the Ca grain refinement.     

Effect of minor Sc and Zr on microstructures and mechanical properties of Al-Zn-Mg based alloys

1　ＩＮＴＲＯＤＵＣＴＩＯＮＡｌｕｍｉｎｕｍａｌｌｏｙｃｏｎｔａｉｎｉｎｇｍｉｎｏｒＳｃａｎｄＺｒｉｓａｎｅｗ ｇｒｏｕｐｏｆｓｔｒｕｃｔｕｒｅｍａｔｅｒｉａｌｓ ,ｗｈｉｃｈｈａｓｈｉｇｈｓｔｒｅｎｇｔｈ ,ｈｉｇｈｄｕｃｔｉｌｉｔｙ ,ｇｏｏｄｃｏｒｒｏｓｉｏｎｒｅｓｉｓｔａｎｃｅａｎｄｗｅｌｄａｂｉｌｉｔｙ[1～ 5] .Ｉｔｉｓｍａｉｎｌｙａｐｐｌｉｅｄｉｎａｅｒｏｓｐａｃｅ ,ｎｕｃｌｅａｒｅｎｅｒｇｙａｎｄｓｈｉｐｓｉｎｄｕｓｔｒｙ .Ｔｈｅｓｉ ｍｕｌｔａｎｅｏｕｓａｄｄｉｔｉｏｎｏｆＳｃ ,ＺｒｏｒＴ…     

铝合金在海洋环境中的腐蚀研究（Ⅰ）：——海水潮汐区16年暴露试验总结

总结了铝合金在青岛海域海水潮汐区暴露16年的腐蚀试验结果，防锈铝LF2Y2、LF6M（BL）、F21M、180YS在海水潮汐区有好的耐蚀性，工业纯铝L4M、锻铝LD2CS的耐蚀性较差，硬铝LY11CZ（BL）、LY12CZ（BL）和超硬铝LC4CS（BL）的包铝层起着牺牲阳极作用，使基体受到保护，海生物污损对铝合金的腐蚀有明显影响，镁，锰能提高铝在海水潮汐区的耐蚀性，硅明显降低铝的耐蚀性，铜严重损害铝的耐蚀性。     

7050铝合金晶界偏析与应力腐蚀,腐蚀疲劳行为的研究

研究了不同时效状态的７０５０铝合金晶界偏析与应力腐蚀开裂及湿空气环境下疲劳裂纹扩展的关系，并采用修正的化学方法计算了晶界偏析对断裂应力的影响。结果表明：随着时效程度的增加，晶界上Ｍｇ偏析浓度减小，捕获Ｈ的能力减弱，晶界断裂应力的百分数随之下降，因而合金的抗应力腐蚀和腐蚀疲劳性能提高。     

Stress-corrosion cracking of aged AlCuMg alloys in NaCl solution

Pitting potentials and stress corrosion life-times of AlCuMg alloys (mainly 2024 alloy) with various ageing structures have been measured in a de-aerated 1M NaCl solution under conditions of controlled potential. The aged alloy, which has the higher susceptibility to stress-corrosion cracking, showed two pitting potentials corresponding to pitting at the grain boundaries and within the grains. The susceptibility of the alloys to intergranular stress-corrosion cracking occurred at potentials above the pitting potential of the grain boundaries. The intergranular stress-corrosion cracking is caused not by the dissolution of the grain boundary precipitates (S phase) but by the pitting dissolution of the solute-denuded zones along the grain boundaries. Aspects of SCC in the alloys are similar to those in the Al-4%Cu alloy without Mg.     

铝合金应力／应变时效机制的第一性原理研究

基于第一性原理计算方法探讨了铝合金应力／应变时效的可能机制,综合评估了时效温度和外加应力／应变对Al-Sc合金中Al3Sc固溶边界和A1-Cu合金中Al／θ＇＇界面能的潜在影响。计算结果表明：在传统时效过程中引入外加拉应力／应变,声子态密度在高态区有红移现象,可以明显降低溶解熵;同时,导致相图中固溶线上移,表明外加拉应力／应变可降低Al3-Sc在Al-Sc合金中的极限固溶度,从而增加析出相的最大可能体积分数。外加应力／应变对Al-Cu合金中不同取向的Al／θ＇＇,界面形成能有不同程度的影响,这种差别可以通过泊松效应进一步放大,从而影响到Al-Cu合金中析出相的择优取向。这2种机制在应力／应变时效中均可能发挥重要作用。     

Influence of Zn Content on Microstructures,Mechanical Properties and Stress Corrosion Behavior of AA5083 Aluminum Alloy

To enhance the stress corrosion cracking (SCC) resistance, Zn was utilized as an alloy element to add in the AA5083 aluminum alloys. The effects of Zn content on the microstructures, mechanical properties and SCC resistance were systematically evaluated. The results demonstrate that in the studied range adding Zn can significantly improve the SCC resistance of the AA5083 alloys. This is related to the relatively low amount of continuous β (Al₃Mg₂) phase along grain boundary and the formation of Zn-containing phase such as Al₅Mg₁₁Zn₄ phase. Based on the results, the optimal Zn content with respect to SCC resistance is approximately 0.50 wt.%. Further increasing Zn content results in coarse precipitates discontinuously distributed along grain boundaries.     

Industrial aluminum alloys with scandium additive

Deformable alloys of the system Al - Zn - Mg possess a number of advantages over other aluminum alloys. The main advantage is the possibility of obtaining high strength properties in combination with good plastic and resource characteristics and good weldability, high technological adaptability in metallurgical production, and general corrosion resistance. However, these alloys have not found wide application due to the corrosion under stress exhibited by welded joints. The present work concerns the possibility of improving this characteristic by additional alloying of alloys of the Al - Zn - Mg system.Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 7, pp. 21 – 23, July, 1995.     

Influence of scandium on weldability of 7010 aluminium alloy

Abstract

The commercial 7000 series aluminium alloys are based on medium strength Al–Zn–Mg and high strength Al–Zn–Mg–Cu systems. The medium strength alloys are weldable, whereas the high strength alloys are non-weldable. This is because the amount of copper present in these alloys gives rise to hot cracking during solidification of welds. As a result, the high strength Al–Zn–Mg– Cu base alloys are not used for applications where joining of components by welding is an essential step. In the present study, using a combination of qualitative Houldcroft test and quantitative Varestraint test, it is shown that a small addition of scandium to the commercial 7010 alloy reduces the hot cracking susceptibility during solidification of welds produced by the gas tungsten arc welding process. The improvement in weldability is found to be the result of the considerable grain refinement in the weld structure following the scandium addition. The results of microhardness and tensile tests are further described within the context of the present work to demonstrate that the 7010+Sc welds also exhibit a combination of improved strength and ductility.     

Comparison of microstructure and corrosion properties of Al-Zn-Mg-Cu alloys 7150 and 7010

The influence of coarse Cu-bearing particles, matrix and subgrain boundary precipitates on the stress corrosion susceptibility of the Al-Zn-Mg-Cu alloys was investigated. The strength of 7150 alloy is about 15 MPa higher than that of 7010 alloy. The 7010 alloy exhibits higher resistance to stress corrosion cracking as compared with the 7150 alloy. The coarse Cu-bearing particles are detrimental to the resistance to stress corrosion cracking. The increase of size of matrix and subgrain boundary precipitates decreases the susceptibility of stress corrosion. The anodic dissolution and hydrogen embrittlement govern the cracking process. The severity of stress corrosion cracking is shown to be related to the coarse Cu-bearing particles, matrix and subgrain precipitates in Al-Zn-Mg-Cu alloys.     

Effect of nano Al (Scx−1Zrx) precipitates on the mechanical and corrosion behavior of Al‐2.5 Mg alloys

Microanalytical, mechanical, and corrosion studies were undertaken to investigate the effect of nano‐precipitates of Al(Sc_x−1Zr_x) on the mechanical and corrosion characteristics of Al 2.5 alloy containing 0, 0.15, 0.3, 0.6, and 0.9 wt% of Sc with 0.15 wt% Zr. Addition of 0.3% Sc significantly increased the yield strength due to small precipitates sizes (5–19 nm) and the high coherency of the nano‐particles. Largest contributor to the strength was grain boundary strengthening caused by pinning of grain boundary precipitates. The alloys showed a good resistance to corrosion in 3.5 wt% neutral chloride solution. The alloy offered a high passivation tendency because of homogeneous coherent nano Al(Sc_x−1Zr_x) precipitates. The nano precipitates interfaces and homogeneously distributed Al₃Sc precipitates offer a high degree of corrosion resistance to Al 2.5 Mg Sc alloys compared to conventional aluminum alloys, such as Al 6061 and Al6013.     

Corrosion product force measurements in the study of exfoliation and stress corrosion cracking in high strength aluminium alloys

Exfoliation corrosion was assessed in three high strength aluminium alloys by measuring the force generated by voluminous corrosion products and their stress corrosion behaviour was studied in tests on double cantilever specimens. There was an inverse linear relationship between the corrosion product forces and the K_ISCC values for stress corrosion cracking in these materials, providing further evidence for a common corrosion mechanism. Exfoliation and SCC were both dependent on the rate of intergranular corrosion, which is controlled in these alloys by the grain boundary precipitates and the resistance to both forms of corrosion was improved in alloys with an over-aged heat treatment condition.