The Effect On Microstructure And Properties Of 0.6 Wt.% MgO/Mg-3Zn-0.2Ca By Equal Channel Angular Pressing

As one of the several plastic deformation processes,equal channel angle pressing(ECAP)is a rapidly developing deformation technology for preparing fine grain materials.Magnesium matrix composite has become one of the most important materials for biological application due to its good biodegradability.Some oxides can be used as reinforcers for Mg matrix composites due to their high chemical stability.Among them,MgO has excellent thermal stability,which is especially suitable for the preparation of biological magnesium alloys.With the increased MgO content,the properties of the material are improved.But when the content is more than 0.5 wt.%,MgO agglomeration occurs and has an adverse effect on the material.In addition,it cannot meet the requirements of biological implants for the poor plasticity and fast corrosion rate of magnesium alloy.Therefore,ECAP is adopted to resolve the disadvantages for better properties.In this study,the Mg-3Zn-0.2Ca composite added 0.6 wt.%MgO was processed by ECAP with the route B_C at 300?,aiming at implanting the components in the human body.The evolution of microstructure,mechanical properties and the mechanism after ECAP process were analyzed and explored.The results are as follows:(1)After 8 passes ECAP at the mold angle of 120°,the grains of the composite material were homogenized significantly.Under the condition of maintaining the ultimate compressive strength,the compressive yield strength decreased slightly by less than 10%,but the compressive elongation increased from 14.17%to 34.18%.At the same time,with the increase of ECAP passes,the sizes of MgO and the other second phase decreased and they became more evenly distributed in the matrix.It was found that the recrystallized grain had preferred orientation during the deformation at higher temperature.The non-basal plane slip systems were activated,which is beneficial to the improvement of its plasticity.(2)Considering the limited effect of ECAP on grain refinement of composite materials under the angle of the mold of 120°.The mold angle was changed to 90°,and it was found that the grain was significantly refined after 8 passes of ECAP.The compressive yield strength decreased to 81.56 MPa after one pass ECAP.With the increase of passes,the compressive yield strength increased gradually,and the compressive elongation at failure almost remains unchanged.(3)In order to improve the problem of the subsequent grain refinement effect is limited when ECAP at high temperature,the ECAP at lower temperature was used to treat the composite.It was found that the average grain size was refined to 1.93?m.Compared with the ECAP at 300?,the texture was changed significantly,and the(0001)basal plane texture was formed.Due to the fine grain strengthening effect,its compressive yield strength had been improved.(4)Considering the performance of composites under different ECAP parameters the extruded and 8-pass ECAP-ed samples were carried out the biological immersion test.Compared with the extruded material,the biological corrosion resistance of ECAP-ed samples was improved.The corrosion rate of the sample by 8 passes ECAP at 300?was the slowest,with the electrochemical corrosion potential of-1.325 V and the self-corrosion current density of 5.359?A/cm~2.This is because the fine grains,more grain boundaries and evenly distributed MgO and the other second phase in the structure formed a dense layer of corrosion products on the surface of the matrix to protect the matrix.This reduced the corrosion rate of the material and improved its corrosion resistance.