7050铝合金表面亚微米晶层摩擦磨损性能

采用增压喷丸方式在7050铝合金表面制备了亚微米晶层,观察并分析了亚微米晶层的组织结构,测试了喷丸前后的硬度,研究了亚微米化前后以及亚微米化后经退火处理3种状态下7050铝合金表面的滑动磨损特性,结果表明:由于增压喷丸使7050铝合金表面发生了严重的塑性变形而形成了一层厚度为30~40μm的亚微米晶层,硬度比未喷丸材料提高了2倍,喷丸后材料的磨损失重量明显减少,约为未喷丸处理试样的一半,特别是喷丸后经过退火的材料磨损量更小,表现出良好的耐磨性能。     

7050铝合金表面亚微米化及其显微硬度的研究

通过改进7050铝合金表面纳米化技术(调节喷丸压力、弹丸直径和喷丸时间)在材料表面获得亚微米晶层,利用OM、XRD、SEM等方法对亚微米结构表层进行了观察和分析。结果表明:喷丸使7050铝合金表面发生一定的塑性变形,表层亚微米晶尺寸约88 nm,显微硬度比基体提高2倍。     

7A04表面纳米化组织的热稳定性

用旋转辊压塑性变形方法在7A04铝合金表层获得纳米晶组织，用DSC和透射电镜研究了表面纳米晶组织的热稳定性。DSC测试结果表明7A04铝合金表面纳米晶的再结晶温度在473K左右，透射电镜分析表明表面纳米化样品473K退火后晶粒没有明显长大，平均晶粒尺寸约100nm。旋转辊压变形160min，表面层显微硬度由160HV升高到335HV，473K退火后显微硬度下降至250HV，但仍高于基体，573K退火后从表层到基体的显微硬度均明显下降。结果表明7A04表面纳米化组织的使用温度在473K以下。     

Al-Zn-Mg合金的表面纳米晶化及其热稳定性研究

利用高能喷丸技术在Al-Zn-Mg合金上制备出纳米晶结构表层，利用X-射线衍射仪、光学显微镜和透射电子显微镜研究由表层沿厚度方向的结构变化特征，并对纳米晶层的热稳定性进行分析。结果表明：高能喷丸处理后，在样品表层获得了等轴、随机取向的纳米晶粒，平均晶粒尺寸约为20nm；晶粒细化遵循逐渐细分原则；动态再结晶可能导致纳米晶粒组织最终形成；高应变量和应变速率及变形过程中的温升对表层纳米晶粒的形成起到了重要作用。表层纳米晶结构层在250℃真空退火后，有大量纳米级析出相析出，晶粒长至300nm左右，表现出较好的热稳定性。     

铝合金表面纳米晶化技术和机理研究

采用表面机械研磨的方法,在Al-Zn-Mg合金表面获得了厚20μm、晶粒尺寸为20～25 nm的纳米晶化层,使其表层硬度提高了约4倍。经透射电镜(TEM)观察发现,铝合金在表面机械研磨的过程中,原始粗晶粒内部出现位错墙和位错缠绕结构。随着变形量的增大,位错墙和位错缠绕结构逐步演变成小角度取向差的亚晶界,直至变成大角晶界,形成了纳米晶化层。     

7A52铝合金表面纳米晶层的电化学腐蚀性能

采用高速微粒轰击技术对7A52铝合金进行表面纳米化处理,利用OM、XRD和TEM研究了表面纳米晶层的微观结构特征,利用CHI660A型电化学工作站测试了样品表面纳米化处理前后电化学腐蚀性能,利用SEM和EDS分析了表面纳米样品电化学腐蚀机制。结果表明:纳米晶最表层晶粒尺寸约为8～20nm,平均晶粒尺寸约为16nm,表面纳米晶层的厚度为20μm左右;表面纳米晶层自腐蚀电流密度icorr由-4.07E-7A.cm-2变为-9.476E-7A.cm-2,明显降低且晶层无龟裂,表现出优异的耐腐蚀性能。表面纳米晶层耐腐蚀性能明显提高的主要原因是表面纳米化增加了样品表面活性,生成了质量优异的钝化膜。     

铝合金表面纳米化处理及显微结构特征

采用高能喷丸技术在1420铝合金上制备出纳米晶结构表层,利用X射线衍射仪、透射电子显微镜及高分辨电子显微镜研究由表层沿厚度方向的结构变化特征,并对硬度沿厚度方向的变化进行分析.结果表明:经过表面高能喷丸处理,样品表面形成了厚度约为20μm的纳米晶层,平均晶粒尺寸由约20 nm逐渐增加到约100nm;距表层约20～50 μm为亚微细晶层;表面纳米化的程度与塑性变形量有关;表面纳米化是通过位错滑移的塑性变形方式实现的;与样品的内部相比,表面硬度显著提高.     

7A52铝合金焊接接头表面纳米化前后的性能分析

通过X射线、扫描电镜、显微硬度仪和摩擦磨损试验机等对7A52铝合金焊接接头高能喷丸处理前后的表面微观组织、晶粒尺寸、变形层厚度、显微硬度和耐磨性进行了测试分析.结果表明,经过20 min高能喷丸处理以后,母材、焊缝以及热影响区的表面平均晶粒尺寸分别为28.2,24.7和34.4 nm;表面变形层厚度约为36.5 μm材...     

45钢表面增压喷丸纳米化及其耐磨性研究

采用增压喷丸方式对45钢进行表面处理,在材料表面制得纳米结构表层,利用SEM、TEM、XRD等方法对纳米结构表层进行了观察与分析,采用盘一销式摩擦磨损试验机研究了纳米化前后表面的磨损性能.结果表明:增压喷丸使45刚表面发生严重的塑性变形,变形厚度约30μm,表层纳米晶尺寸约65nm,硬度比基体提高2倍:在低载油润滑条件下45钢表面纳米化后表现出优异的耐磨性能.     

钛合金TC4表面纳米化及其热稳定性

利用超音速微粒轰击技术(supersonic fine particles bombarding,SFPB)对钛合金TC4进行了表面纳米化处理,并对SFPB处理后的试样进行不同温度2 h退火处理。借助X射线衍射、显微硬度计、透射电子显微镜和差热分析对纳米化及热处理后的试样进行了组织和性能表征,研究钛合金表面纳米化机理及其热稳定性。结果表明:经过SFPB处理后的试样在表层形成了纳米结构层,随着处理时间的延长,变形层厚度不断增加,晶粒尺寸逐步细化,当SFPB处理30 min后晶粒尺寸趋于稳定,在表层形成了晶粒尺寸约为15 nm具有随机取向的纳米等轴晶。纳米化后的试样在750℃退火时,纳米晶未发生明显粗化,因而具有很好的热稳定性。     

Thermal stability of nanocrystalline in surface layer of magnesium alloy AZ91D

Isothermal and isochronal annealing was conducted to study the thermal stability of the nanocrystalline in the surface layer of Mg alloy AZ91D induced by high-energy shot peening(HESP) .Field emission scanning electron microscope(FESEM) and X-ray diffractometer were used to characterize the microstructure.Results showed that nanocrystalline produced by HESP on the surface layer of the magnesium alloy AZ91D was 60-70 nm on average.The nanocrystalline could remain stable at about 100℃,and grew up slowly between 100℃ and 200℃.When the annealing temperature reached 300℃,the growth rate of the nanocrystalline increased significantly.The kinetic coefficient n of the nanocrystalline growth was calculated to be 2-3 and the grain growth activation energy Q=39.7 kJ/mol,far less than the self-diffusion activation energy of magnesium atoms in the coarse polycrystalline material.     

Microstructure characteristics of as-surface nanocrystallized 1420 aluminum alloy by high-energy shot peening

A nanostructured surface layer was fabricated on 1420 aluminum alloy by high-energy shot peening.Microstructures were characterized by X-ray diffractometer (XRD), transmission electron microscope (TEM) and high-resolution electron microscope(HRTEM), and microhardness measurement was conducted along the depth from top surface layer to matrix of the sample peened for 30 rain. The results show that a nanocrystalline layer about 20μm in thickness is formed on the surface of the sample after high-energy shot peening, in which the grain size is changed from about 20 nm to 100 nm. In the surface layer of 20-50μm in depth, the microstructure consists of submicron grains. The surface nanocrystallization is accomplished by dislocation slip. The microhardness of the top surface nanostructured layer is enhanced obviously after high-energy shot peening(HESP) compared with that of the coarse-grained matrix.     

TEM study on microstructures and properties of 7050 aluminum alloy during thermal exposure

The microstructures of 7050 aluminum alloy under different thermal exposure conditions were investigated by means of transmission electron microscopy (TEM), high resolution electron microscopy (HREM) and tensile test. Guinier preston (GP) zone and η′ phase are the main precipitates in original 7050 alloy. The orientation relationship between η′ and matrix is

and

. When the alloy is exposed at different temperatures for 500 h, with the thermal exposure temperature increasing, it can be seen under TEM that the precipitates become larger and the width of precipitate free zones (PFZ) becomes larger. The higher temperature the alloy is exposed at, the more the strength is reduced. Both GP zones and η′ precipitates getting coarser and the PFZ getting wider should be responsible for the strength decline and elongation rise of 7050 alloy during thermal exposure.     

7050铝合金均匀化过程中组织转变

采用光学显微镜、扫描电镜和差示扫描量热法等研究7050合金均匀化过程中的显微组织与化合物的演变。结果表明,7050合金铸态为典型的枝晶网状组织,其中片层状共晶组织由α(Al)和T相(Al Zn Mg Cu)组成,并存在少量含Fe相(Al7Cu2Fe)。均匀化温度在460℃以上,共晶相发生分解,且由T相向S相(Al2Cu Mg)发生转变,480℃以上S相发生溶解并逐渐减少,而含Fe相的形状和尺寸基本不发生变化。随均匀化时间的延长和温度的升高,T相逐步向S相完全转变,且S相逐渐溶解于基体中,残留很少。对于所采用的7050合金铸锭,为了消除共晶组织,减少残留化合物和合金元素均匀分布,460℃×24 h+480℃×8 h双级均匀化工艺为较合理的均匀化工艺。     

Constituents evolution of LFEC 7050 aluminum alloy during processing

The d 120 mm ingots of 7050 aluminum alloy were made by low frequency electromagnetic casting （LFEC） and conventional DC casting process, respectively. After homogenization treatment the ingots were extruded to rods and the solution and aging treatment were carried out for the rods. Constituents evolution during processing and effects of LFEC on constituents and remnant constituents were studied. The results show that 7050 aluminum alloy mainly contains Al-Zn-Mg-Cu type and Al-Cu-Fe type constituents. Al-Zn-Mg-Cu type constituents dissolve during homogenization, while Al-Cu-Fe type constituents could not dissolve. After homogenization treatment, the main remnant constituent is A17Cu2Fe which crushes and orients along the extrusion direction after extrusion. Compared with DC process, by the process of LFEC, the constituents or remnant constituents are smaller in size and less in content. The LFEC process shows significant improvement in elongation by LFEC in both as-cast state and final state.     

7050高强铝合金锻件的热处理工艺模拟

通过有限元模拟分析,研究了7050高强铝合金锻件的热处理工艺过程,获得了热处理过程中的温度场分布与变化规律,并计算了热处理过程中的残余应力分布.结果表明,固溶过程能有效去除锻件成形过程中的残余应力,但淬火过程又会在锻件表面形成较大的拉应力,这与淬火过程中较大的锻件内外温度梯度有关.按照工艺要求,在随后对锻件进行的不同变形程度的冷压缩后发现,3％的压缩量不但能消除锻件表面的应力,还能使锻件残留有非常有益的压应力,从而能够有效地抑制后续处理过程中的裂纹产生.通过研究验证了7050高强铝合金锻件热处理工艺设计的合理性,具有一定的工程参考价值.