Surface nanocrystallization of 7A04 aluminium alloy induced by circulation rolling plastic deformation

The surface nanocrystalline microstructures of 7A04 aluminium alloy was obtained by means of circulation rolling plastic deformation（CRPD）, the grain refinement behavior and the hardness variation were examined. X-ray diffraction（XRD） and transmission electron microscopy（TEM） were applied to characterize the microstructure of the surface layer. The experimental evidences show that, after the CRPD treatment, the mean grain size in the surface layer is about 50 nm. The microhardness of the nanostructured surface layers is enhanced significantly after CRPD compared with that of the matrix, which can be attributed primarily to the grain refinement. The microhardness at the top surface can reach about HV0.05335, while the value of the matrix is HV0.05160 or so. The surface hardening effect is obtained obviously. Besides, the thermal stability of nanocrystalline layer was investigated. The results of the XRD analysis and the microhardness measurement show that the nanocrystalline layer has better thermal-stability than the matrix. And the DSC measurement shows that the synthesis of nanostructured surface layer has influence on the phase transformation of 7A04 aluminum alloy.     

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.