.7 A04 Surface Nanocrystallization And Its Influence On Ion Implantation,

The surface nanocrystalline microstructure of 7A04 aluminum alloy was obtained by means of circulation rolling plastic deformation (CRPD). Optical microscope(OM), X-ray diffraction (XRD) , transmission electron microscopy (TEM), microhardness tester and differential scanning calorimeter(DSC) were applied to characterize the microstructure and property of the surface layer. Experimental evidences showed that the microstructure of the surface layer of sample was refined into nanoscale after the CRPD treatment. The mean grain size in the surface layer was about 50nm, and the depth of deformed layer was about 500μm. The microhardness of the nanostructured surface layers was enhanced significantly after CRPD compared with that of the matrix, which can primarily be attributed to the grain refinement. The surface microhardness had improved from 160HV0.05 of the initial sample to 335HV0.05 after CRPD.The DSC measurement showed that the synthesis of a nanostructured surface layer had influence on the phase transformation of the 7A04 aluminum alloy. It also could be found that the degree of deformation is enhanced with the increasing of the CRPD treating time and the onset temperature of recrystallization was about 473K by using the DSC measurement.In order to study the thermal-stability of the nanocrystalline layer, different temperature annealing behavior of the sample after the CRPD treatment was investigated. The microstructure observation and microhardness testing showed that the best using temperature of the nanocrystalline layer of 7A04 aluminum alloy is below 473K. Under this temperature, the average grain is fine and the microhardness is still higher than that of origin sample.Ion implantation behavior of the sample after CRPD treatment was investigated in comparison with that of the origin sample. XPS results showed that N could be implanted into 7A04 aluminum alloy, and the N depth profile is close to Gaussian distribution in the implanted layers of the CRPD treated sample and the origin sample. But the N concentration peak in the CRPD treated sample is lower than that in the origin sample.