Al-Zn-Mg-Cu系超高强度铝合金的研究现状与发展趋势

分析了近年来超高强度Al-Zn-Mg-Cu系铝合金的成分设计、工艺优化、显微组织分析、力学性能测试及微量元素的作用，对今后的发展动向提出了一些新的看法：采用传统铸造技术得到的铝合金，Zn含量的最大值在8wt％左右，抗拉强度低于700MPa；采用喷射成形技术，Zn含量最大值能够超过12wt％，同时抗拉强度可达800MPa以上，大大提高了铝合金的强度；超高强度铝合金的固溶强化相主要为MgZn2相；经回归时效处理(RRA)后，合金同时具有T6的强度和T7X的抗应力腐蚀性能；微量元素对超高强度铝合金的组织和性能具有显著的影响。     

微量Mg元素添加对Cu-Cr合金析出行为及性能的影响

通过熔炼铸造工艺制备了Cu-Cr和Cu-Cr-Mg合金,评价了Mg元素对Cu-Cr合金硬度、导电和抗软化性能的影响,研究了Mg元素对Cu-Cr合金析出相的细化作用,探讨了Mg元素的迁移行为。结果表明,相比于Cu-Cr二元合金,时效态Cu-Cr-Mg合金具有更高的硬度和软化温度,且保持较高的导电性能。两种合金的主要时效强化相均为纳米Cr析出相,Mg元素的加入抑制了纳米沉淀相的长大和结构转变,峰时效态Cu-Cr-Mg合金的析出相与基体可能仍保持共格界面关系,过时效态合金中出现与Heulser相结构相同的析出相,且峰时效态Cu-Cr-Mg合金经过高温保温处理后,其强化相的尺寸明显小于Cu-Cr合金析出相。EDS的结果表明,在时效初期Mg和Cr共存于析出相内部,而在时效后期析出相内部只有Cr元素存在,Mg元素发生迁移,同时理论估算结果显示,Mg元素可明显降低Cu(fcc)/Cr(bcc)之间的界面能,导致其偏聚于基体/析出相界面处,这可能是Mg元素能够细化析出相和提高合金性能的主要原因。     

Zn/Mg比及时效温度对Al-Zn-Mg-Cu系合金析出行为的影响

采用热力学模拟软件中的铝合金模块研究了Al-Zn-Mg-Cu系合金中不同Zn/Mg比及时效温度对析出相GP区及η'相的析出规律的影响。结果表明,GP区含量随Zn/Mg比的增加而降低,低温时效能够促进GP区的形成;而η'相含量随Zn/Mg比的增加略微降低,时效温度对η'相含量影响不大;与120℃相比,合金在160℃时效时η'相含量达到6.5%的时间缩短16 h;在相同温度下时效时,随Zn/Mg比的增加,η'相含量达到6.5%的时间先缓慢增加,当Zn/Mg比大于2.91时则快速增加。合金的淬火敏感性随Zn/Mg比的增加有所降低;随Zn/Mg比从2.46提高到3.20,GP区和η'相的鼻尖温度分别从150℃和330℃降低到140℃和320℃;临界冷却速率随Zn/Mg比的增加而逐渐降低。     

合金元素对Al-Mg合金抗腐蚀性能及拉伸性能的影响

为了在保证力学性能的基础上提高铝合金的抗腐蚀性能,采用拉伸试验、浸泡腐蚀、动电位极化曲线和形貌观察对添加了Mg、Cr元素的Al-Mg合金的拉伸性能和抗腐蚀性能进行了分析.结果表明:与Al-2.03Mg合金相比,Al-2.90Mg合金的屈服强度和抗拉强度提高,但抗腐蚀性能明显降低;而添加了少量Cr的Al-2.90Mg-0.15Cr合金,其屈服强度和抗拉强度进一步增大,且抗腐蚀性能与Al-2.03 Mg合金相比没有明显下降,甚至在模拟海水腐蚀液中浸泡1 500h后,Al-2.90Mg-0.15Cr合金具有比Al-2.03 Mg合金更低的平均腐蚀速率,说明适量添加Mg和Cr元素,能够在保证抗腐蚀性能的基础上,有效提高铝合金的屈服强度和抗拉强度.     

含Li的Al-Zn-Mg-Cu合金的研究进展

对含Li的Al-Zn-Mg-Cu合金的研究进展进行了回顾与总结.含Li量大于1.8%的Al-Zn-Mg-Cu合金基体中主要沉淀相是δ'相、S相和T'相,塑性和韧性较差.含Li量不大于1.0%的Al-Zn-Mg-Cu合金基体上析出η'相或T'相,二级时效或多级时效则可使其达到较高的硬度.最后,指出含Li的Al-Zn-Mg-Cu合金目前存在的问题,并提出了进一步研究的方向.     

多级时效热处理对7056铝合金析出组织与耐蚀性的影响

利用透射电子显微镜(TEM)、扫描电子显微镜(SEM)、力学性能测试、电导率测试以及剥落腐蚀、慢应变速率拉伸应力腐蚀(SSRT)、Tafel循环极化曲线等手段研究多级时效热处理对7056铝合金析出组织及耐蚀性的影响。结果表明:过时效再时效热处理后溶质原子二次析出,晶内析出相体积分数增大,晶界析出相粗化断开,无沉淀析出带宽化。与120℃/24h相比,采用120℃/6h预时效工艺有利于晶内细小析出相回溶和粗大相长大。再时效热处理可提高过时效合金的强度和电导率,与峰时效和回归再时效相比,合金的抗拉强度损失不大,电导率明显提升。过时效再时效热处理后,合金晶界处连续阳极溶解被有效避免,抗剥落腐蚀和抗应力腐蚀性能增强。     

800MPa级Al-Zn-Mg-Cu系合金

通过采用在线精炼、在线细化、热顶铸造等技术手段,成功在直接水冷半连续铸造设备上制备出了合金化元素总量达20%的Al-Zn-Mg-Cu系合金,打破了7000系铝合金合金化元素总量不高于14%的极限。利用金相显微镜、透射电镜进行微观组织观察,采用差热分析仪测试相转变温度,测试了硬度、拉伸性能并利用扫描电镜进行断口分析。该合金经过挤压、RRA热处理后,其抗拉强度、屈服强度和伸长率分别达到810.3,799.3MPa和3.4%。通过对单级时效动力学和三级时效动力学进行研究,确定了合金的最佳时效温度为120℃,而时效时间的可选择范围较大。Zn含量高达16.1%的铝合金中主要由未溶第二相和时效析出相η′相共同强化,未发现其他新析出相。     

Mg与Ag含量对Al-Cu-Mg-Ag新型耐热铝合金晶间腐蚀性能的影响

采用晶间腐蚀性能测试研究Mg与Ag含量对Al-Cu-Mg-Ag合金抗腐蚀性能的影响,结合透射电子显微分析技术与电化学分析技术等探讨了不同成分合金的晶间腐蚀机理。结果表明:增加Mg与Ag含量能够提高合金的时效硬化速率。随Mg含量的增加,强化相Ω相尺寸逐渐减小,体积分数逐渐增大,晶界析出相增多,无沉淀析出带(PFZ)中溶质原子减少,PFZ与基体的电位差增大,合金的抗晶间腐蚀能力逐渐降低。随Ag含量的增加,合金中的强化相由大量的θ′相和少量的Ω相,逐渐转变为大量的Ω相和少量的θ′相。Ag含量的改变对PFZ的电位差影响不大,合金的耐蚀性主要取决于PFZ的宽度。增加Ag含量能够细化晶界析出相,减小PFZ宽度,腐蚀通道变窄,合金的抗晶间腐蚀性能得到提高。     

亚微米Al2O3P/Al-Mg-Si复合材料时效行为

为了研究亚微米级Al₂O₃颗粒对基体合金时效过程的影响规律,在 6061 铝合金基础上调整Mg、Si含量,采用压力浸渗法,制备了Al₂O₃体积分数为30%的亚微米级Al₂O_3P/Al-2.26Mg-0.63Si复合材料。通过硬度试验、SEM和TEM等手段,研究了复合材料及其基体合金的时效行为。结果表明,Al-2. 26Mg-0.63Si 合金的时效过程比较明显,随时效温度的提高峰时效时间提前,190℃时出现时效软化现象。亚微米Al₂O₃颗粒的加入强烈抑制复合材料的时效过程,时效曲线未出现明显时效峰。分析认为,由于大部分Mg 元素被消耗在界面形成MgAl₂O_4,且基体中位错稀少,不利于溶质原子扩散,因此复合材料中沉淀相在过时效阶段仍停留在GP区状态,没有充分长大,时效析出受到抑制。     

Al-Zn-Mg-Cu系超高强铝合金的研究进展

评述了国内外超高强铝合金的研究及应用概况,介绍了Zn、Mg、Cu等主要元素与Zr、Sc、Li、Ag、Be及稀土等微量元素对Al-Zn-Mg-Cu系超高强铝合金组织与性能的影响,介绍了Al-Zn-Mg-Cu系合金制备技术、热处理工艺及其最新进展,讨论了超高强铝合金主要强化机制以及微观组织与性能之间的关系.针对超高强铝合金现存的问题,提出了今后研究开发的方向.     

Effects of the enhanced heat treatment on the mechanical properties and stress corrosion behavior of an Al–Zn–Mg alloy

In this article, the effects of the enhanced solution treatment (EST) and high-temperature pre-precipitation (HTPP) on the microstructures, mechanical properties, and stress corrosion cracking resistance of an Al–Zn–Mg alloy have been investigated. The results indicated that EST and HTPP can substantially affect the microstructures of the alloy. The width of the continuously distributed grain boundary precipitates decreases after the EST, while the continuous grain boundary precipitation changes to a discontinuous precipitation structure after both the EST and HTPP. The yield strength, tensile strength, elongation, and fracture toughness of the specimens after the EST are much higher than those of the specimens only after traditional solution treatment, since the EST substantially decreases the size and volume fraction of the constituents. The stress corrosion cracking resistance of the specimens after both the EST and HTPP has been greatly improved due to the discontinuous distribution, and high Cu and low Mg concentrations of the grain boundary precipitates.     

蠕变时效对7050铝合金板材组织与性能的影响

通过金相显微、透射电子显微、电子拉伸和剥落腐蚀实验研究了7050铝合金板材蠕变时效与人工时效的微结构及性能。结果表明:蠕变时效过程中施加的应力使板材不断产生变形,为η′析出相提供了大量形核点,析出相尺寸更加细小,特别是晶界无沉淀带较人工时效明显变窄,晶界析出相不连续。与人工时效相比,蠕变时效试样的抗拉强度和抗剥落腐蚀性能略有提高。     

微量Ge对7056铝合金组织和淬火敏感性的影响

通过力学拉伸、末端喷淋淬火实验,结合金相观察、硬度测试、电导率测试、扫描电镜(SEM)和透射电镜(TEM)等测试分析方法,研究微量Ge元素对7056铝合金组织和淬火敏感性的影响。结果表明:添加微量Ge细化了合金晶粒,晶粒尺寸由137μm减小到114μm;添加微量Ge在晶界上形成了粗大的Mg_2Ge相,并抑制了T相的形成;与无Ge合金相比,添加Ge后无沉淀析出带(PFZ)宽度变窄,从190nm减小到90nm,同时晶界析出相尺寸减小;添加微量Ge显著降低了合金的淬火敏感性,合金淬透深度提高了约25%,这与慢速淬火时析出的η平衡相的数量和尺寸有关;Ge降低了合金中的空位浓度,η平衡相在缺陷处的非均匀形核及长大被抑制,时效后η′沉淀强化相数量增多,慢速冷却时合金强度下降程度减小,合金淬透性提高。     

Effect of stamping deformation on microstructure and properties evolution of an Al–Mg–Si–Cu alloy for automotive panels

The effect of 5 % tensile deformation, which simulates the stamping process of Al–Mg–Si–Cu automotive outer panels, on the microstructural evolution during age strengthening, has been investigated. In addition, its benefit on key mechanical properties including hardness, yield strength, ductility, and corrosion resistance has been linked to the microstructural features. It was found that the aging precipitation sequence, SSSS → clusters and G.P. zones → β″ → β′ + Q′ → Q, was not influenced by the dislocations introduced through the stamping deformation prior to aging. On the other hand, stamping deformation could promote the formation of precipitates and refine the precipitates because of the enhanced heterogeneous nucleation and the accelerated precipitation kinetics, leading to superior strength of the alloy at the early stage. Meanwhile, the larger amount of Cu incorporated into nanoprecipitates leads to better intergranular corrosion resistance of the stamped alloy compared with the unstamped one. Due to the reduction in free Si amount at grain boundaries, the formation of fine subgrain structures and the increase of dislocation accumulation, the ductility of the stamped alloy was increased.     

Effect of creep-aging processing on corrosion resistance of an Al–Zn–Mg–Cu alloy

Creep-aging forming, combining both the aging treatment and forming process, has recently drawn much attention of researchers. In this study, the effects of creep-aging processing on the corrosion resistance of an Al–Zn–Mg–Cu alloy are studied. Results show that the corrosion resistance of the studied Al–Zn–Mg–Cu alloy is sensitive to creep-aging processing parameters (creep-aging temperature and applied stress). With the increase of creep-aging temperature, the corrosion resistance first increases and then decreases. Increasing the applied stress can deteriorate the electrochemical corrosion resistance and improve the exfoliation corrosion resistance. The creep-aging processing can change the size and distribution of precipitates in the aluminum matrix, which significantly affects the corrosion resistance. The discontinuous grain boundary precipitates and narrow precipitate-free zones can enhance the corrosion resistance.     

7075铝合金脉冲变极性等离子弧焊接头的双级时效行为EI北大核心CSCD

通过力学性能、电导率测试和TEM分析,对10 mm厚7075铝合金脉冲变极性等离子弧焊(pulse variable polarity plasma arc welding,PVPPAW)接头的双级时效行为特征进行研究,并确定了较为合理的双级时效工艺。结果表明:7075铝合金PVPPAW接头的抗拉强度随着终时效温度的升高和终时效时间的延长先增大后减小。经160℃,12 h终时效处理后的接头抗拉强度为545.1 MPa,比焊态时提高了37%。此时接头的电导率为27.9%IACS,抗应力腐蚀性能有所提高。焊缝中心主要强化相为η′相和η相,随着终时效温度的升高和终时效时间的延长,晶内与晶界的析出相逐渐长大和粗化,晶界的无沉淀析出带变宽。     

淬火速率对7055铝合金组织和力学性能的影响

通过常温力学性能测试和透射电镜(TEM)研究了淬火速率对7055铝合金组织和力学性能的影响.结果表明,一定时效条件下,合金的力学性能随淬火速率降低而下降.组织观察发现,淬火速率小时,合金在冷却过程中于A l3Zr粒子和晶界非均匀形核析出粗大η平衡相,降低固溶体过饱和程度,削弱时效强化效果.时效时这些粗大η平衡相继续长大并在周围形成无沉淀析出带.晶界无沉淀析出带宽度随淬火速率降低而增大.对合金力学性能下降的原因进行了分析和探讨.     

Reasons for superior mechanical and corrosion properties of 2219 aluminum alloy electron beam welds

Electron beam welds of aluminum alloy 2219 offer much higher strength compared to gas tungsten arc welds of the same alloy and the reasons for this have not been fully explored. In this study both types of welds were made and mechanical properties were evaluated by tensile testing and pitting corrosion resistance by potentio dynamic polarization tests. It is shown that electron beam welds exhibit superior mechanical and corrosion properties. The weld metals have been characterized by scanning electron microscopy; transmission electron microscopy and electron probe micro analysis. Presence of partially disintegrated precipitates in the weld metal, finer micro porosity and uniform distribution of copper in the matrix were found to be the reasons for superior properties of electron beam welds apart from the fine equiaxed grain structure. Transmission electron micrographs of the heat affected zones revealed the precipitate disintegration and over aging in gas tungsten arc welds.