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. 相似文献
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. 相似文献
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. 相似文献
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. 相似文献