Effect Of Composition Optimization On Microstructure And Mechanical Properties Of WE43 Magnesium Alloy

In order to solve the problems of poor plasticity and low potential for improving mechanical properties of WE43 magnesium alloy,the composition of WE43 alloy was optimized by multiple rare earth compound strengthening and adding modified elements,and its microstructure evolution and mechanical properties change rules and mechanisms were analyzed.According to the composite strengthening effect of multiple rare earth components,the precipitation efficiency of dispersion strengthened phase and the volume of brittle eutectic phase can be improved by adding Gd element and adjusting rare earth component,so as to optimize the mechanical properties of the alloy.The results show that the total amount of rare earth in the alloy is between WE43 and we54,and the precipitation efficiency of strengthening phase is better than WE alloys by multiple rare earth compound strengthening.The addition of Gd is controlled at 1.0 wt.%,which not only improves the effect,but also avoids the formation of sharp massive phase.Based on the optimization of the main strengthening rare earth elements,the different characteristics of the alloy are regulated by adding different micro alloying modifiers to meet the different requirements of practical application.According to the research results,the following conclusions are drawn:?1?The results show that adding Gd into WE43 alloy and adjusting rare earth component can increase nucleation density and increase precipitation efficiency of the strengthening phase.After adding Gd,the grain size of the alloy is refined,and the morphology of brittle eutectic phase is reduced.There is no sharp block phase with large size which is harmful to the mechanical properties.The main precipitate of the alloy is??phase,its size increases with the increase of aging temperature,while the density and quantity decrease correspondingly.The main reason for the improvement of mechanical properties is the increase of precipitation efficiency of precipitates and grain refinement by adding Gd.Lower aging temperature leads to more compact and fine precipitates,which has more obvious effect on the strength of the alloy;with the increase of aging temperature,the plasticity of the alloy is improved and the strength does not decrease due to the limited low density precipitation area.?2?The grain size of the modified alloy was refined by adding Zn.At low Zn content,there are a small amount of Mg₅RE phase and lamellar Mg₁₂REZn phase in the microstructure of the alloy;when the Zn content increases,the number and volume of LPSO phase increase rapidly.The results show that the modified alloy has obvious aging hardening effect,and the time to reach the peak of aging is obviously shortened after adding Zn.When the content of Zn is low,the size of??precipitates is reduced by the replacement of rare earth elements,the number and density of precipitates are increased,the precipitation strengthening effect is further enhanced,and the strength of the alloy are significantly improved.The further increase of Zn will lead to the formation of coarse LPSO phase,inhibit the formation of??precipitates,and lead to the decrease of strength.?3?After adding Ag,the dispersion state of Gd element in the matrix is reduced,and the composite strengthening effect of multi rare earth elements is weakened.Ag-rich phase with small size and round edge can be formed in the microstructure.One is Mg₂₄?RE,Ag?₅ phase,and the other is close to?phase,which only exists when the Ag content is high and the amount is small.Ag inhibits the growth of intermetallic phases and the formation of harmful precipitates,which improves the plasticity of the alloy.The plasticity of the alloy does not decrease significantly due to the increase of low precipitation density regions in the microstructure.However,the Ag containing intermetallic phase consumes more rare earth elements and inhibits the quantity density of??phase and?phase,resulting in the precipitation strengthening effect of the alloy is not significantly improved compared with the unmodified alloy.?4?After the addition of Sc,the microstructure of the alloy is obviously modified,and the grain size and precipitation morphology of the alloy are significantly refined.With the increase of Sc content,the tensile strength first increases and then decreases,the yield strength increases,and the elongation decreases.The refinement of microstructure and the increase of precipitation density caused by Sc are the main reasons for the improvement of strength and plasticity of the alloy.The results show that the size of precipitates in Sc containing alloy is slightly larger,the amount of precipitates is larger,and the precipitation density is more dispersed.Therefore,the effect of strengthening grain boundary and improving strength is more obvious.At the same time,because of the refinement of microstructure and precipitate phase,the alloy has good plasticity.?5?With Sm addition,the total amount of eutectic phase in as-cast alloy does not change,but the volume and morphology change obviously.With the increase of Sm content,the tensile strength,yield strength and elongation of as cast alloy increase firstly and then decrease.The room temperature mechanical properties of the peak aged alloy increase first and then decrease with the increase of Sm content,and reach the highest value when the content of SM is 1.5 wt.%.The main strengthening phases increase first and then decrease with the change of Sm content,and the microstructure of the alloy is refined and then coarsened.