Li对Al-Zn-Mg-Cu系合金GP区转变动力学的影响

Al-Zn—Mg—Cu系合金在较低温度时效时，形成2种类型的GP区：GP(Ⅰ)区和GP(Ⅱ)区。选用7075，7075 0．58％Li，7075 0．89％Li和7075 1．0％Li4种合金进行343K，240h和393K，24h时效，以获得GP区，并通过DSC实验结果，用Avrami—Johnson—Mehl(AJM)表达式计算了GP区溶解动力学参数，从而定量地研究Li对7075合金GP区转变的影响。结果表明：经过343K，240h时效后，含Li的7075合金的GP(I)区溶解激活能较7075合金的略低，Li促进GP(I)区的形成；经过393K，24h时效后，2种合金GP区溶解激活能相差不大。     

预变形对7075-T6铝合金时效成形回弹及力学性能的影响

为评价铝合金预变形-时效成形工艺的可行性,试验研究了预变形对7075-T6铝合金时效成形性能的影响。研究表明:预变形能显著降低7075-T6铝合金的时效成形回弹率,并在一定程度上提高其塑性,但对其拉伸强度产生不利影响。随着预变形程度的增加,合金的屈服强度和抗拉强度降低,初始强化相GP区减少,η'相向粗大η相的转变,并形成较宽的无沉淀析出带,从而弱化其时效成形强度。     

时效时间对7075-T6铝合金组织与性能的影响

通过硬度测试、拉伸、导电率测试等方法，并借助金相显微镜、X衍射分析仪和扫描电镜等手段，系统研究时效时间对7075-T6铝合金组织和性能的影响。结果表明，随着时效时间的延长，7075-T6铝合金组织出现显著变化，时效18 h后晶粒尺寸由初始状态的88.76μm细化为35.78μm,时效24 h后粗化为67.88μm。7075-T6铝合金的硬度和导电率随着时效时间的延长出现了上升的趋势，分别在时效4 h和24 h时出现极大值。由微观组织变化可见，时效时间的延长会使合金G.P.区减少和η′(MgZn₂)相增多，而G.P.区和η′相均可阻碍位错运动，使得合金的强度和导电率提升。当时效时间过长，出现过时效，晶粒再度粗化，合金的力学性能降低。     

含银7055铝合金回归再时效过程中的组织与性能变化

研究了回归温度(180℃，200℃，220℃)及预时效时间(12h，18h，24h)对含Ag的7055铝合金回归再时效后的强度和微观组织的影响。结果表明，由于微量Ag的添加，120℃，l8h预时效处理后180℃回归再时效的强度稳定性较高，而随着回归温度的提高，再时效强度下降较快，这种现象归因于Ag的添加提高了GP区和η′相的稳定性，使得GP区溶解温度升高，因而180℃回归时只发生GP区和η′相的缓慢粗化，而200℃和220℃回归时发生GP区的溶解并促进，η′相快速粗化形成η相；实验结果显示，预时效时间对回归再时效后的强度也有较大的影响：预时效时间较长或较短时(12h，24h)，再时效强度随回归时间的变化较大，而经18h预时效，再时效强度稳定性较高。这种差别是由于预时效后析出相的种类和体积分数不同所致。     

双级时效对1973铝合金组织和性能的影响

采用透射电子显微镜(TEM)、选区电子衍射(SADP)和硬度测试等手段研究1973高强高韧铝合金在不同温度下的单级时效析出及硬化行为。结果表明:1973铝合金在120和140℃有很强的抗过时效能力,峰时效过后,硬度在长时间内基本保持在195 HV附近。1973铝合金的析出序列为:α过饱和固溶体(SSS)→GPⅠ区/GPⅡ区→η'亚稳相→η平衡相→T相。在140℃单级时效过程中,GPⅡ区和η'相一直都存在于时效合金中,对合金起着最大的强化作用。     

电流场对7B04铝合金时效析出行为的影响

采用示差扫描量热分析(DSC)研究了固溶、时效阶段施加电流场对7B04铝合金时效析出行为的影响。试验结果表明:固溶阶段施加500 A直流电抑制了η'相和η'+η相的析出,促进了GPⅠ区的析出;时效阶段施加600 A直流电促进了η相的析出和长大,η相的最大析出速率较常规时效的提高了67.6%,形成激活能由常规时效的233.8 k J/mol降低至162.9 k J/mol。     

7075铝合金“双峰”时效研究

采用硬度测试、拉伸力学性能测试、XRD衍射物相分析以及α(A l)基体点阵常数的测量等方法对7075铝合金超长时间时效行为、力学性能、应力腐蚀(SCC)敏感性及组织进行了研究。结果表明,7075铝合金的硬度及强度都具有时效双峰特征。两个时效峰的硬度和强度相差不多,但对应第二峰时效的合金具有高强度低SCC敏感性等优异性能。第二峰强化相主要是充分析出的η′相(MgZn2)。     

时效温度对轧制态7075铝合金组织及性能的影响

对轧制态7075铝合金采用固溶和时效处理,观察并研究了显微组织、扫描断口。研究发现:不同时效温度下,轧制态7075铝合金晶内和晶界处不同程度析出第二相组织η相,基体晶粒大小有较大差异。其中时效温度为200℃时,晶内和晶界均匀弥散分布着大量第二相,基体晶粒细化;时效温度为220℃时,弥散分布在晶内和晶界的第二相明显减少,并且基体晶粒粗化。时效温度为200℃时,断口韧窝最大最深,表现出典型的韧性断裂。     

Al-Zn-Mg-Cu合金时效过程动力学分析

根据升温差热扫描量热分析( DSC)曲线,对Al-Zn-Mg-Cu系合金的时效过程进行了动力学分析,并利用Ozawa、Takor、Kissinger和Starink方法计算出GP区、η′相、平衡相η的激活能分别为:50、122、90 kJ/mol,这表明GP区的形成主要与Mg原子的迁移相关;η′相的形成是Mg和Zn原子共同迁移的结果,主要与Zn原子的迁移相关.     

烘烤时间对AA7075高强铝合金组织和性能的影响

采用透射电镜、万能试验机和电化学测试等试验手段，研究了烘烤时间对AA7075高强铝合金组织和性能的影响。结果表明，随着烘烤时间的延长，η′相的数量先上升后下降，3 h烘烤样品主要析出相为粗大的η相。同时，η′相是合金的主要强化相，η′相数量的增加和η′相向η相的转变促使合金的强度先上升后下降，2 h烘烤下的合金强度最高，屈服强度和抗拉强度分别达到392 MPa和458 MPa。3 h烘烤样品的粗大晶界析出相可降低晶界敏感性，阻碍腐蚀沿晶界扩展，显著提高合金耐腐蚀性。     

Classification of the role of microalloying elements in phase decomposition of Al based alloys

The fundamental role of microalloying elements in several aluminium alloys such as Al–Cu, Al–Li–Cu and Al–Cu–Mg has been investigated using a Monte Carlo computer simulation. All the utilized simulation parameters, e.g. pair interactions between same atoms species, between different atom species and between an atom and a vacancy, were derived from known thermodynamic or kinetic quantities. A small addition of Mg to Al–Cu alloys exhibits a strong tendency to form Mg/Cu/Vacancy complexes in the atom configurations, which is more remarkably revealed in Al–Li–Cu alloys. The combined addition of Ag or Si with Mg significantly increases the number of Mg/Cu/Vacancy complexes in Al–Cu–Mg alloys. From the comparison with experimentally reported results, these complexes are reasonably regarded as an effective heterogeneous nucleation site for GP zones, GPB zones and/or the Ω phase. The utilized simulation model, furthermore, permits the role of microalloying elements to be well classified in terms of the characteristic features of each element.     

Corrosion Evolution of High-Strength Aluminum Alloys in the Simulated Service Environment of Amphibious Aircraft in the Presence of Chloride and Bisulfite

The corrosion evolution of 2024-T351 and 7075-T651 aluminum alloys in the thin electrolyte layer (TEL) and wet-dry alter-nating cycle (WDAC) environment is studied in this work.The results show that in the TEL environment,the competitive effect between H+ that accelerates corrosion reactions and deposition of aluminum sulfate that impedes corrosion attacks exists during the corrosion exposure.The difference is that with increasing HSO3-,subsurface intergranular corrosion on 2024-T351 is promoted to form exfoliation corrosion eventually and the degree of exfoliation corrosion begins to decrease because the blocking effect of aluminum sulfate exceeds the expediting effect of H+.For 7075-T651,the corrosion area and the corrosion diameter decrease gradually,which is attributed to the HSO3-enhanced deposition of corrosion products and their blocking effect.In the WDAC environment,the corrosion processes of 2024-T351 and 7075-T651 are the acidic dissolution of the matrix during the soaking phase.When the HSO3-concentration is high enough (0.1 M),the inhibiting effect of aluminum sulfate becomes the dominant factor.     

7075和2024铝合金的固溶组织与力学性能

研究了升温固溶处理对提高７０７５和２０２４铝合金的结晶相固溶程度和力学性能的影响,升温固溶可使最终固溶温度超过多相共晶温度而不产生过烧组织,提高结晶相固溶程度。７０７５合金的结晶相较２０２４合金的易于固溶,两种合金的力学性能与固溶程度密切相关。强化固溶的７０７５合金强度提高约２０％,断裂和屈服强度可达６６０ＭＰａ和６０６ＭＰａ,其性能提高的幅度大于强化固溶的２０２４合金。     

Al-Zn-Mg-Cu合金在时效过程中η相沿小角晶界的析出序列

采用高分辨透射电子显微镜和高角环形暗场扫描透射电子显微镜结合X射线能谱仪,研究Al-Zn-Mg-Cu合金叩相沿小角晶界的析出序列。试样在135℃分别时效5min到6h。结果表明,η相在小角晶界的析出序列是：SSS→VRC→GPⅡ区→η’→η。基于非平衡晶界偏析和非平衡晶界共偏析理论,在Al-Zn-Mg-Cu合金时效过程中,通过溶质一空位对的扩散,大量的沉淀形成元素偏析到晶界。这种晶界偏析在VRC、GPⅡ区、η’相和η相的形核和生长中起重要作用。     

Investigation on Behavior of Rare Earth Element Cerium in Aluminum-Lithium Alloys by Internal Friction Method

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Effect of Be on aging behavior of an Al-Si-Cu-Mg cast alloy

The effect of Be addition on the aging behavior of UNS 03370 (Al11Si3Cu0.3Mg) was investigated by micro-hardness measurement, differential scanning calorimetry (DSC) and transmission electron microscope (TEM) analysis. Age hardening analysis shows Be additions to an Al11Si3Cu0.3Mg alloy accelerates the age hardening rate and increases the peak hardness by 15 HV during aging at 160°C. DSC shows that Be additions lead to an endothermic peak corresponding to the dissolution of Gunier Preston zones (GP I) disappear with exothermic peaks corresponding to precipitation of GP II zones and the λ′ and/or ϑ′ phases shift to low temperature. DSC and TEM analyses show that GP II zones are more effective than λ′ and/or θ′ on hardening the alloy, and Be addition increases the homogeneous nucleation density of GP II zones. The possible Be atoms participating in the precipitation process during aging and the high Be-vacancy binding energy can explain the effect of Be on aging behavior of Al11Si3Cu0.3Mg alloy.     

Si含量对Mg-8Zn-4Al-0.3Mn镁合金时效过程的影响

采用光学显微镜、扫描电镜(附EDAX能量分散光谱系统)和差示扫描量热仪(DSC)等分析手段研究了不同Si含量(0～1.61wt%)对Mg-8Zn-4Al-0.3Mn(ZA84)合金时效过程的影响。结果表明,合金经固溶处理后显微硬度较铸态下提高了8%左右,其Mg2Si、τ(Mg32(Al,Zn)49)等相基本未溶入基体中。随着ZA84合金中加入Si量的增加,合金的析出相形成激活能呈增加趋势,峰值时效时间由ZA84合金的2h左右推迟至8h左右,析出相粗化时间较ZA84合金推迟4h以上。合金中加入不同含量Si后其峰值时效显微硬度提高幅度为4%～12%。     

Exfoliation corrosion testing of aluminium alloys

Abstract

The exfoliation corrosion behaviour of sheet and plate materials of various conventional aluminium and Al–Li alloys has been evaluated using accelerated tests. Results are .compared with atmospheric exposure data published in the literature to assess the applicability of the testing techniques employed. For damage tolerant Al–Li based sheet and plate, the cyclic acidified salt fog (Mastmaasis) test according to ASTM G85, Annex A2 indicated susceptibility to exfoliation corrosion, reproducing the limited outdoor corrosion data for the Al–Li alloys 8090–T81 and 2091–T84 as well as marine exposure results reported for the conventional alloys 2024–T351 and 7075–T7351. Therefore, it appears to be a promising testing technique for predicting the service performance of high strength aluminium alloys. Compared with the ratings determined following the cyclic acidified saltfog tests, the standard Exco test according to ASTM G34 indicated better exfoliation corrosion behaviour of the alloys investigated, except for 8090–T6 sheet and 7075–T7351 plate, which exhibited severe and mild exfoliation respectively. In the modified Exco test suggested by Lee and Lifka, 7075–T7351 panels were susceptible to pitting, whereas the other alloys studied generally suffered more severe exfoliation than in the standard Exco test.     

PRECIPITATION IN BINARY Al-Li ALLOYS

Studies were carried out on the precipitation in two sets of binary Al-Li alloys by means ofhardness tests,DSC analyses and TEM observations.When the alloys were aged for constanttime,a peak appeared on the plot of temperature dependence upon their hardness in the rangeof low temperatures,and the endothermic dissolution peak was quite distinct on the DSCcurve also at low temperatures.These are believed that an Li-rich GP zone formed in the al-loys aged at low temperatures,but no more GP zone if aging at elevated temperatures.Thehardness of the alloys raises rapidly with coarsening of δ′-phase grains.The two endothermicpeaks of δ′ dissolution on the DSC curve relate to the structural adjustment at twice of the δ′precipitation.The equilibrium δ-phase,being of higher thermal stability,nucleates and growsdirectly from the supersaturated solid solution with the aid of the gram boundary.