| A method of Equal Channel Angular Processing(Equal Channel Angular Pressing,ECAP)is used on the extrusion of WE43 magnesium alloy along Bc path under the temperature of 220 C.Fine grained WE43 magnesium alloy were fabricated by Equal Channel Angular Processing(ECAP),microstructure evolution of WE43 magnesium alloy in different passes were examined by optical microscopy(OM),scanning electron microscopy(SEM),transmission electron microscopy(TEM)are used to study the internal texture and the evolution of the grain boundary in the extrusion process.The mechanical properties of the alloy before and after ECAP deformation,as well as the corrosion resistance were detected at room temperature,and the mechanism was analyzed.After 4 passes of ECAP extrusion,the grain size was refined,from 50?m to 1.1 ?m,The eutectic phase of the rod like phase is precipitated in the matrix after the extrusion.After 4 passes of extrusion,the eutectic phase is broken into spheroid and dispersed in the matrix,the dislocation density increases with the increase of extrusion passes and reaches the peak at the third pass.After 4 passes,the dislocation density in the alloy decreases as a result of dynamic recrystallization.After extrusion,the texture density increased gradually,but the typical magnesium alloy extruded silk texture was not formed because of the extrusion conditions.With the increase of extrusion passes,the tensile strength of the alloy increased gradually.From the as cast 198MPa to 295MPa after four passes,the elongation of the material increased.After 4 passes of extrusion,the elongation of the sample increased from 8%to 16%.After extrusion,the hardness of the alloy reached the highest at the fourth pass and the hardness value was 101.3,which was mainly caused by the change of the microstructure of the specimen.The corrosion resistance of WE43 magnesium alloy before and after extrusion is studied.It is found that the solid solution alloy has the best corrosion resistance abilities.This is mainly due to the dissolution of the eutectic phase to the matrix during the heating process.With the increase of extrusion passes,the corrosion resistance of the alloy decreased gradually,the weight loss rate after 3 passes comes to the peak which is 90%,corrosion solution pH was 9.65,that means 3 passes of WE43 magnesium alloy has the worst corrosion resistance abilities,this is mainly due to the distribution of eutectic phase in the matrix and the high level of dislocation density.After 4 passes,the corrosion resistance of the alloy increases,and the weight loss rate and the pH value of the alloy decrease obviously after corrosion.This is mainly due to the homogeneous distribution of eutectic phase in the matrix and the decrease of dislocation density in the alloy.Electrochemical corrosion tests of 1 to 4 passes of equal channel corner extrusion showed that the corrosion current of the alloy extruded from different passes was basically the same and the corrosion resistance of the alloy was not affected by the extrusion pass,With the increase of squeezing pass,the eutectic phase disperses in the matrix,but does not disappear,so the galvanic corrosion on the alloy surface still exists.It doesn't affect the corrosion resistance of the alloy.However,after four passes of extrusion,the eutectic phase is evenly distributed in the matrix,resulting in a uniform film of Mg(OH)2 on the surface of the sample,resulting in uniform corrosion of the alloy surface and an improved corrosion resistance. |
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