Influence Of Hot Extrusion On Microstructure And Mechanical Properties Of AZ91D Magnesium Alloy

This article take the cast condition AZ91D magnesium alloy as the object of study, carries on the analysis to its cast condition and the uniformized annealing organization performance, then in the different temperature, under the extrusion ratio condition carries on the compression test, after the determination extrusion pressure and the extrusion under the room temperature organization and mechanics performance.When the AZ91D as-cast alloy through uniform heat treatment 400℃×15h, the large brittleγ-Mg17Al12 phase both in the grain boundary and the dendrites are into most of theα-Mg (Al, Zn) matrix, essentially as a single-phase solid solution, crystal However, some uniform grain grown up than cast in favor of plastic deformation of the alloy.Regardless of the semifinished materials original state is the cast condition or the uniformized annealing condition, when extrusion needs the extrusion pressure reduces along with the extrusion temperature ascension, increases along with the extrusion ratio increases. At the same process parameters, the material after annealing by homogenization required extrusion pressure than squeeze cast direct extrusion pressure required for extrusion of small.The cast condition carries on the extrusion directly, in the extrusion temperature for 420℃, the extrusion compared toλis under 45 technological conditions, the room temperature tensile strength from before the extrusion 168 MPa to be able to enhance most greatly to 381MPa; Semifinished materials after uniformized annealing carries on the extrusion, in the extrusion temperature for 420℃, extrudes compared toλis under 45 technological conditions, the room temperature tensile strength may enhance most greatly before extrusion 232 MPa to 398 MPa. Under same extrusion temperature, when extrudes compared toλfrom 15 increases to 45, the thick crystal grain becomes the even tiny equiaxed grain, the alloy comprehensive mechanics performance is best, after and before discovery extrusion grain size and extrusion grain size related, when the initial crystal grain size is big, the dynamic recrystallization forms the new crystal grain size is also thick, vice versa. Therefore, after the long time uniformization annealing crystal growth, after the extrusion the crystal grain than the direct extrusion the cast condition to have to be big.Regardless of after is the uniformized annealing extrudes or the cast condition direct extrusion, compares with the extrusion before, the tensile strength, the yield strength, the elongation ratio obviously enhance. After cast condition extrusion, the alloy tensile strength may increase 381MPa before extrusion 168 MPa, the yield strength may increase before extrusion 93 MPa to 303 MPa, the elongation ratio from 4% enhances to 11%; Semifinished materials after uniformized processing extrudes the alloy tensile strength which obtains to be possible before extrusion 232 MPa to increase to 398 MPa, the yield strength may before extrusion 133 MPa increase to 288 MPa, the elongation ratio from 8% enhances to 11%. Before the extrusion, after the cast condition alloy and the uniformized annealing performance disparity is big, after but passes through the extrusion, between the two mechanics performance disparity reduces obviously.Through this compression test, the best extrusion craft parameter which obtains is: Time the cast condition semifinished materials direct extrusion best craft parameter for the extrusion temperature for 420℃, the extrusion ratio is 45; After uniformized processing time the semifinished materials extrusion best craft parameter for the extrusion temperature 390℃, the extrusion ratio is 45.