Micro Compression Behavior And Microstructural Evolution In An Ultrafine-grained Pure Aluminum

The plasticity micro-forming technology is a method of manufacturing microparts in low cost and batch production, and has wide application prospect in the fieldof MEMS. However, size effect is so obvious in conventional coarse grain materialsthat influences the forming properties and dimensional accuracy of micro parts inmicro forming process. Micro forming technology has brought a new challenge inmaterial selection. Ultra-fine grained materials that made by severe plasticdeformation can catch sub-micron or even nanometer. Compared with theconventional coarse grain materials, ultra-fine grain material not only has highermechanical properties in the room temperature, but also has good plasticity formingperformance, and especially suitable for application in plastic microformingtechnology. Ultra-fine grained materials and micro forming technology has becomean important research direction of micro manufacturing field.The paper is studying on ultra-fine grained high pure aluminum material thatmade by the ECAP method, detects the mechanical properties and microstructure, andobserves the microstructure after micro compression test under different strain rate,grain size and sample size.Through the8pass ECAP extrusion, we can obtain the grain size of about1.27μm ultrafine grained high purity aluminum material. In ECAP extrusion process, withthe increase of extrusion passes, a large number of small angle grain boundary firstappears in the grain interior, then the small angle grain boundary transfor m to thelarge angle grain boundary, and finally forms the fine equiaxed grains. In mechanicsperformances, the microhardness and tensile strength increases firstly, and thendecreases, finally remains stable with the number of pass increases.The results of micro compression tests on ultrafine grained show that: flow stressof ultrafine grain material is highly influenced by strain rate, and the flow stressgradually increases with the increases of strain rate while the flow stress of coarsegrain sample is not obviously affected. The floe stress of ultrafine grained materialgradually decreases with the decrease of sample size while the flow stress of coarsegrain gradually increases with the decrease of sample size. With decrease of grainsize, the flow stress of ultrafine grained material increases gradually, and the workhardening phenomenon is weaker and weaker, but the flow stress of the coarse grainmaterial appeared abnormal, which is because of the poor deformation compatibilityof coarse grain sample. Observed by SEM, the results show that the slip bandsobviously appear in the coarse grain interior, and with the decrease of the grain size,the slip bands are less obvious, and no obvious slip bands can be found in ultra-fine grain, but the shear deformation along the grain boundary can be found.The results of the observation of microstructure of compression samples byEBSD technique shows that with the increase of the strain, the substructure in thecoarse grain interior increases gradually, and the misorientation of small angle grainboundary has the gradually increasing tendency, but the microstructure of ultra-finegrained does not obvious change before and after deformation. In the coarse graincondition, with the decrease of sample size, the deformation uniformity of coarsegrain interior is getting worse, while the deformation of ultra-fine grain is gettingmore coordination.