Effects Of Micro-alloying On The Microstructures And Mechanical Properties Of Mg-Mn Alloys

In this work, Mg-Mn alloys with the addition of rare earth Er and Er/Al werestudied. Heat treatment, isothermal hot compression test, hot extrusion, etc. wereconducted to examine the effect by the addition of Er and Er/Al on the microstructures，deformation behaviors and mechanical properties.The results showed that, after solution treatment at450℃for4hours, there were alarge number of the black second phase Mn, microstructure was mainly composed ofcoarse columnar grains about800~1000um. Micro-alloying0.4Er/Al significantlyrefined grains of the alloy, the size was about150um.The hot compression tests of Mg-1.8Mn-0.4Er/Al alloy were carried out with strainrate0.01s-1~1s-1at250℃~450℃. The results showed that:1) with higher temperatureand lower strain rate, the critical stress of DRX was lower and critical strain was larger,there was no DRX in the microstructure of hot compression which were carried out at250℃and350℃with strain rate of1s-1.2) The lower the temperature and the largerthe strain rate were，the more amount of twin grains in the alloys; when strain rate wasin the range of0.01s-1~1s-1, there were still a certain number of twin grains in the alloyshot compressed at450℃.Mg-1.8Mn alloy hot extruded at450℃recrystallized thoroughly, the extent ofDRX both in the alloys that micro-alloyed with Er and Er/Al are decreased, in themeantime, the extent of DRX in the alloy with Er/Al was higher than that in the alloywith Er. Percentages of DRX grains of Mg-1.8Mn alloy with0.4%Er,0.7%Er,0.1%Er/Al,0.4%Er/Al and0.7%Er/Al were45%,51%,58%,60%and75%respectively.After heat treatment at390℃for an hour, Grain size of the DRX Mg-1.8Mn alloygrew up to about88um, and there was a larger static recrystallization in the alloys withmicro-alloying Er/Al. Alloys with micro-alloying Er/Al recrystallized fully.Results of the room temperature tensile tests on as-extruded alloys showed thataddition of4%Er significantly improved the strength of alloys: yield strength increasedfrom173MPa to224MPa，tensile strength increased from255MPa to276MPa, therewas little effect on strength of alloys by the addition of Er/Al. Addition of Er and Er/Alhad both improved the plasticity of alloys, elongation increased with the content of Erand Er/Al, but effect on enhance the plasticity by the addition of Er was moresignificant than addition Er and Al. By adding0.7%Er, elongation of alloy increased from5.0%to12.5%, while the elongation increased to19.0%with0.7%Er. in the earlyuniform plastic deformation process，strain hardening rate（）decreased by the additionof both Er and Er and Al, the decrease of of alloy with0.1%Er performed smallestvalue. When the plastic deformation reached certain extent，strain hardening rate（）increased by the addition of both Er and Er/Al, and the increase of was the largestwhen the content of addition reached7%.