Effect Of Equal Channel Angular Pressing On Microstructure And Properties Of ZAM63-xSi Alloys

Magnesium alloys show excellent room temperature performance,however,when the temperature exceeds 393K,the high temperature performance significantly decreases and its application is extremely limited.Added low-cost Si element to the magnesium alloys can form a high temperature stable phase Mg₂Si,which can improve the mechanical behavior under high temperature of the alloys.It is of great significance to overcome the limitation of high cost associated with the alloys containing RE and expend the application of magnesium alloy.In this paper,effect of different passes and route on microstructural and mechanical properties of the as-cast ZAM63-1Si alloy are systematiclly investigated on the basis of the optimization of the Si content in the ZAM63 alloy.In addition,compared the creep properties of as-cast containing Si and the creep resistance of the alloys by different passes and different routes was optimized.Finally,the high-temperature creep mechanism of the optimal alloy was systematically studied.The main conclusions are as follows:（1）The as-cast ZAM63-xSi（x=1,2,3）alloy is mainly composed ofα-Mg,Mg₃₂（Al,Zn）₄₉,MgZn and Mg₂Si phases.With the increase of Si content,the Mg₂Si phase gradually changes from the Chinese script to block.The yield strength and tensile strength of the alloy are increased and then decreased,while the elongation decreased.ZAM63-1Si alloy has the best mechanical properties,tensile strength and elongation reached 128MPa and 1.8%,respectively.（2）ECAP can significantly refine the grains and change the second phase’s distribution of ZAM63-1Si alloy.The mechanism is mechanical shear crushing and continuous dynamic recrystallization.After the first pass by the B_C route,the grain size of the alloy is obviously refined and the second phase is basically crushed,however,it was still distributed near in situ.The room temperature properties is obviously improved.After 2 passes,the average grain size of the alloy was more refined,the distribution of the second phase was more uniform and the distribution is strip-like.After 4 passes,part of grains in the alloy began to grow and and the second phase is more dispersed.Among them,the yield strength of the alloy was the highest after 1 pass,reaching 147MPa.After 4times,the comprehensive performance of the alloy was the best,and the tensile strength and elongation reached 283MPa and 25.8%respectively.The second phase distribution was changed after the 4 passes by route B_C-m,but the dispersion degree did not change very much.The number of large grains in the alloy was increased,and the tensile strength and elongation were 288MPa and13.7%,respectively.（3）The high temperature creep resistance of the ZAM63-1Si alloy extruded by B_C route is obviously better than that of as-cast alloy.In addition,the creep resistance of the alloy increases gradually with the increase of the extrusion pass,and the steady creep rate of the alloy after 4 passes is 1.41e-6s-1.Compared with the 4 passes by B_C route,the creep resistance of B_C-m-m route was decreased,and the steady creep rate increased to 1.93e-6s-1.（4）Under the creep conditions of（448⁴98K）/（50⁷0MPa）,The creep stress exponent values of 4 passes by route B_C were 4.76;5.55 and 6.22,respectively.and the creep activation energy values were 62;71 and 84,respectively.The creep mechanism of the alloy is the dislocation climbing mechanism controlled by diffusion at low temperature,and gradually transitions to the creep mechanism of dislocation climbing and enhanced control of the second phase at high temperature.