热轧对7055铝合金淬透性的影响

为研究热轧对7055铝合金淬透性的影响,采用末端淬火实验、硬度测试、光学显微镜和透射电镜研究了不同冷却速率处合金的组织和性能.实验结果表明:合金热轧后淬透性大大降低,淬透深度由约100 mm降至约45 mm,这主要与慢速淬火时析出的η平衡相的数量和尺寸的改变有关;热轧增加了η平衡相的形核位置,并引入大量的位错,增加了η平衡相的长大速率.因此,热轧合金固溶后慢速淬火时,析出的η平衡相的数量和尺寸都大大增加,时效后形成的η’沉淀强化相数量减少,硬度随冷却速率减小而下降的程度增加,合金的淬透性降低.     

Fe和Si杂质对Al-Zn-Mg-Cu合金淬火敏感性的影响EI北大核心CSCD

采用光学显微镜、扫描电子显微镜和透射电子显微镜等方法,研究了Fe和Si杂质对Al-Zn-Mg-Cu合金淬火敏感性的影响。结果表明:杂质含量的增加降低了合金的淬火敏感性,用硬度表征时最大降低3.29%。随杂质Fe和Si含量的增加,Al7Cu2Fe相和Mg2Si相含量明显增加,消耗了基体中的Cu和Mg原子,合金的过饱和度降低,从而引起合金淬火敏感性的降低;同时粗大的Al7Cu2Fe相和Mg2Si相有利于再结晶核心的形成,增加了合金的再结晶晶粒和(亚)晶界数目,促进慢速淬火过程中η平衡相的析出。过饱和度对合金淬火敏感性的影响大于晶粒结构对合金淬火敏感性的影响。     

淬火速率对Al-Zn-Mg-Cu-Cr合金挤压棒材组织及硬度的影响

通过硬度测试、扫描电镜、透射电镜研究淬火速率对Al-Zn-Mg-Cu-Cr合金挤压棒材组织及硬度的影响。结果表明:淬火速率低于100℃/s时,硬度开始明显下降;2℃/s淬火时,硬度下降了43%。淬火速率低于100℃/s时,随着淬火速率降低,冷却过程中(亚)晶界及晶内弥散粒子处非均匀形核析出η平衡相的数量和尺寸明显增加,时效强化效果明显降低。相同淬火速率时,晶内η平衡相尺寸大于晶界η平衡相尺寸。在所研究的淬火速率范围内建立起硬度值与η平衡相面积分数间的定量关系。     

7085铝合金剥落腐蚀的淬火敏感性

采用末端淬火实验、剥落腐蚀实验结合扫描和透射电镜分析,研究了7085铝合金剥落腐蚀的淬火敏感性。结果表明:7085铝合金的耐剥落腐蚀性能随淬火速率的降低而下降,腐蚀等级由EA级变为EB级,最大腐蚀深度从135μm增加至315μm,腐蚀深度与淬火速率的对数呈线性关系。淬火速率降低导致晶界析出相尺寸增加、无沉淀析出带宽化和在亚晶处也有η相析出,是造成剥落腐蚀淬火敏感性的主要原因。     

非等温回归再时效对7050铝合金组织与力学性能的影响

采用扫描电镜(SEM)、透射电镜(TEM)、硬度测试和拉伸测试研究了非等温回归再时效对7050合金组织和力学性能的影响。非等温回归处理的加热速率为5℃/min,回归终了温度包括160℃、190℃、220℃、260℃和300℃。结果表明:经120℃/24 h+RT■190℃+120℃/24 h的非等温回归再时效处理后,合金的力学性能最佳,其抗拉强度约为588 MPa,屈服强度约为558 MPa,延伸率约为23%,硬度值约为199HV。预时效态合金晶界平衡相η呈不连续分布,其尺寸约为49～70 nm,晶内析出相η'的平均尺寸约为5～6 nm;在190℃的非等温回归处理过程中,预时效态合金中的析出相发生了部分回溶,相的平均尺寸变小,其晶界相和晶内相的尺寸分别约为5～10 nm和3～6 nm,回归态合金晶界呈多列平行且无沉淀析出带(PFZ)不明显;再时效态合金的晶界相尺寸最大,约为91～108 nm,晶内相弥散,尺寸约为4～10 nm,无沉淀析出带变得明显,其宽度约为41 nm。     

Mn、Fe含量对3003铝合金铸锭均匀化行为的影响

通过电导率测试、扫描电子显微镜等观察分析,研究了不同Mn、Fe含量对3003合金铸锭和均匀化组织的影响。3003合金铸锭中有明显的波纹状Mn偏析,晶界处有粗大的α-Al(Fe,Mn)Si或Al₆(Fe,Mn)初生相。Fe含量由0.12%(质量分数)升高至0.30%,铸锭平均晶粒尺寸由257 μm减小为108 μm,初生相面积分数由1.28%升高至3.75%;Mn含量越高,合金电导率值越低。均匀化升温阶段,析出相主要受形核和长大过程控制,并伴随较高温度下析出相的部分回溶;600 ℃保温阶段,析出相以Ostwald熟化和原子长程扩散两种机制发生粗化,尺寸不断增大,数量减少;合金均匀化晶界附近有无析出带形成。合金Mn含量由1.15%升高至1.60%,析出相回溶温度由500 ℃升高至550 ℃,600 ℃保温12 h完成后,析出相尺寸也由149.0 nm升高至342.5 nm;高Fe低Mn(0.30%Fe,1.15%Mn)合金晶内析出相分布均匀,而低Fe高Mn(0.12%Fe,1.60%Mn)合金晶内析出相呈不均匀分布,晶粒心部及枝晶干处贫Mn区析出相数量较少。     

固溶处理对Al-7.9Zn-2.5Mg-1.0Cu合金淬火敏感性的影响

采用末端淬火-硬度测试、差示扫描量热法、透射电镜、扫描电镜等方法,研究了固溶处理对Al-7.9Zn-2.5Mg-1.0Cu合金淬火敏感性的影响。结果表明:随着距淬火端面距离的增加,合金试样的硬度逐渐降低,处理制度为475℃/2h试样的淬火敏感性明显比处理制度为450℃/8h+475℃/2h试样的低,其淬透层深度超过100mm,而处理制度为450℃/8h+475℃/2h试样的淬透层深度仅为65mm。固溶处理制度对合金过饱和度的影响不大,但是与处理制度为475℃/2h的试样相比,处理制度为450℃/8h+475℃/2h试样的再结晶晶粒和(亚)晶界数目大大增加,促进了慢速淬火过程中η平衡相的析出,且尺寸相对粗化,导致了淬火敏感性的提高。     

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.     

Zr在7050铝合金中的行为与作用的电镜观察

本文研究了含Zr的高强7050铝合金中Zr化合物的存在形态,尺寸和分布特点。TEM观察表明,锭铸中的Zr以ZrAl_3初晶和固溶体两种形式存在;均匀化处理的铸锭中,球形的ZrAl_3在基体上呈共格与非共格形式弥散析出,尺寸约为10～30nμ,热轧变形后,ZrAl_3大都钉轧在位错线和小角晶界上,其形态和尺寸没有明显改变;淬火后,可观察到大量存在的亚结构和亚晶粒,球形ZrAl_3质点分布在亚晶界、晶内以及位错线上,非共格的ZrAl_3周围有η相非均质成核;与含Cr的该系合金相比较,可看到E相尺寸远大于含Zr合金中的ZrAl_3质点,而ZrAl_3周围非均质成核的η相的尺寸和数量要比E相周围的小得多;淬火后经时效和双级过时效热处理,ZrAl_3质点的形态、尺寸和分布,均无显著变化。利用上述实验结果,可以园满地解释Zr对7050铝合金细化晶粒、提高再结晶温度、降低淬火敏感性以及提高强度和抗应力腐蚀性能的作用。     

挤压AM50(-Ca)镁合金的显微组织与力学性能研究

研究了挤压AM50(-Ca)镁合金的微观组织和力学性能.研究发现添加钙在AM50合金中生成新的Al2Ca相,并细化合金的晶粒尺寸.大于2wt.%的钙使铸态AMS0的晶粒尺寸从200 μm减小到40 μm,使挤压态AM50的晶粒尺寸从15 μm减小到7.5 μm.含钙量较少时,晶粒内仍含有少量的Mg17Al12相,Al2Ca相主要分布在晶界;含钙量多于2wt.%时,合金中的Mg17Al12完全消失,除晶界处的Al2Ca相外,在晶粒内部出现大量的针状Al2Ca相.加钙提高了AM50合金的低温抗拉强度,同时在所有试验温度下合金的屈服强度得到提升.     

Effect of processing parameters on quench sensitivity of an AA7050 sheet

Secondary precipitation takes place in alloy 7050 during slow quenching after solution and results in a significantly decreased content of Mg, Zn elements. Optical microscopy, transmission electron microscopy (TEM), and electron backscatter diffraction (EBSD) study showed the distribution of Al₃Zr particles plays a vital role in quenching process. The equilibrium η phases mainly precipitate at Al₃Zr particles within the recrystallized grains and other high energy areas (primarily grain boundaries). The influence of the processing (homogenization, hot rolling and solution) parameter on the quench sensitivity is also investigated by mechanical property examination (T6 temper). A ramping heat homogenization, controlled hot rolling (67% rolling reduction and 3-5 s⁻¹ deformation rate) and two-stage solution treatment result in lesser recrystallization and fewer high angle grain boundaries, and lower the boundary angles within sub-structures. The decreasing number of heterogeneous precipitation sites endows the study alloy with good quenching sensitivity and better mechanical properties.     

Zn对铸态Mg-Y-Nd-Zr合金组织和力学性能的影响

采用光学显微镜(OM)、扫描电子显微镜(SEM)、X射线衍射分析及力学性能测试等研究Zn元素对Mg-Y-Nd-Zr铸态合金显微组织及力学性能的影响。结果表明:随着Zn含量的增加,Mg-Y-Nd-Zr-xZn(x=0.0%,0.5%,1.0%,1.5%,质量分数)合金的晶粒逐渐细化,平均晶粒尺寸由(57±0.8)μm细化至(30±0.3)μm,晶界处共晶相的体积分数也逐渐增加。Mg-Y-Nd-Zr铸态合金中主要存在Mg12Nd相和Mg24Y5相,加入0.5%Zn后,合金中出现Mg12YZn相。随Zn含量的增加,Mg12YZn相的体积分数不断增大,合金的力学性能逐渐提高。当Zn含量为1.0%时,合金具有最优的力学性能,其抗拉强度、屈服强度和伸长率分别为(208±5.9),(159±3.9)MPa和(7.5±0.2)%,较未加Zn的合金分别提高了18,42MPa和1.2%。     

7075-H18铝合金板材的淬火敏感性与等温转变行为EI北大核心CSCD

以2 mm厚的7075-H18高强度铝合金板材为研究对象,采用微观组织分析、显微硬度测试、动力学建模与计算相结合的方法,对板材的淬火敏感性、等温相变行为及转变动力学进行系统研究,构建"时间-温度-性能"关系图。结果表明:7075-H18板材具有较高的淬火敏感性。"时间-温度-性能"关系图的鼻尖温度约为350℃,孕育期仅为0.23 s,淬火敏感温度区间为271~404℃,转变量为0.5%的曲线对应的临界线性冷却速率为969.7℃/s,超过了冷模淬火所能达到的冷却速率。板材在等温淬火过程中主要形成粗大的η平衡相,等温时间越长,晶内与晶界的η相尺寸越大,晶界η相越趋于连续分布,且无沉淀析出带变宽。基于实验数据构建的等温转变动力学模型,对7075-H18板材的等温相变过程进行准确预测,板材在350℃等温过程中沉淀相的析出速率最大,等温相变类型为"形核-长大"型相变,相变过程为层片状沉淀相的长大、增厚及互相吞并。理论计算结果与透射电子显微镜下观测到的η相特征以及"时间-温度-性能"关系图相一致。     

Effect of minor Sc addition on microstructure and stress corrosion cracking behavior of medium strength Al–Zn–Mg alloy

Influence of Sc content on microstructure and stress corrosion cracking behavior of medium strength Al–Zn–Mg alloy have been investigated by optical microscopy, scanning electron microscopy, electron backscatter diffraction, transmission electron microscopy and slow strain rate test. The results indicate that the addition of Sc results in the formation of the quaternary coherent Al_3(Sc, Zr, Ti) dispersoids during homogenization treatment, which will inhibit the dynamic recrystallization behavior. The number density of Al_3(Sc, Zr, Ti) particles increases with the increase of Sc content, and thus the recrystallization fraction of hot-extruded alloy is reduced and the peak strength in two-stage artificial aging sample is enhanced. At the same time, the wide of precipitation free zone is reduced, and the content of Zn and Mg in grain boundary particles and precipitation free zone is increased with the increase of Sc content. In peak-aged state, the 0.06 wt% Sc added alloy shows the better stress corrosion cracking resistance than the Sc-free alloy because of the reduction of recrystallization fraction and the interrupted distribution of grain boundary precipitates along grain boundary. However, the further addition of Sc to 0.11 wt% will result in the deterioration of stress corrosion cracking resistance due to the increase of electrochemical activity of grain boundary particles and precipitation free zone as well as hydrogen embrittlement.     

Effects of germanium on quench sensitivity in Al–Zn–Mg–Zr alloy

Effects of the trace element germanium (Ge) on the quench sensitivity of an Al–Zn–Mg–Zr alloy were investigated in the present work. The results showed that the Ge-bearing alloy exhibited lower quench sensitivity as compared to the Ge-free alloy. This phenomenon could be reasonably interpreted in terms of the stability of supersaturated solid solution of alloys after quenching from an elevated temperature. The apparent vacancy formation energies for the Ge-free and Ge-bearing alloys were determined to be 0.49 and 0.58 eV respectively. This suggested that the addition of a small amount of Ge was able to trap excess vacancies, leading to a decrease in the amount of coarse dispersoids and resultant low quench sensitivity in Ge-bearing alloys. Therefore, Ge could be used in alloy productions, which require a slow cooling rate to reduce the residual stresses and distortions.     

Effect of Microstructure on Thermal Expansion Coefficient of 7A09 Aluminum Alloy

The relationship between microstructure evolution and coeffcient of thermal expansion (CTE) of 7A09 alu- minum alloy was investigated in this paper. Differential scanning calorimetry (DSC) was combined with transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) to investigate microstructure evolution taking place in 7A09 aluminum alloy during heating and cooling process. The corresponding CTE curves of the 7A09 alloy were recorded by thermal dilatometer. Results indicated that GPII zones and η phase were main precipitates in the highest strength tempered (T6) 7A09 alloy. The η phase was the main participate in 7A09 alloy during the cooling process. The nonlinear dependency existed between CTE and temperature in both changing temperature processes. During the heating process, obvious additional contraction of alloy volume was directly caused by phase transition, such as dissolution of η phase, transition from η to η phase and dissolution of η phase. The additional contraction could slow down the increase of CTE greatly and be expressed in the nonlinearity of CTE curve. Volume and energy changes of alloy system inffuenced the variation trend of CTE directly, which was caused by the precipitation of η phase during the cooling process. These effects were revealed by the corresponding nonlinear change of CTE.     

Structure of grains and grain boundaries in cryo-mechanically processed Ti alloy

A Ti5Ta1.8Nb alloy with the major phase as α (hcp) Ti has been subjected to severe plastic deformation by means of cryo-rolling. Significant grain refinement (from ~5 μm to ~60 nm) has been observed. The mechanism of grain refinement was studied by analysis of lattice strain variations with increase in cold work using XRD technique. Various intermediate stages, such as hardening, alignment of dislocations, cell formation and criticality before new grain formation, were identified. Formation of cells with dislocations alignment at the boundaries and then finally forming an ultra-fine grain structure was confirmed by transmission electron microscopy studies. Detailed grain boundary characterisation has been carried out using high-resolution transmission electron microscopy studies and crystallographic texture analysis. The grain-refined structure was found to possess a large fraction of high angle boundaries identified also as special boundaries by evaluating the misorientation angle/axis sets for a pair of adjacent grain boundaries.