JOURNAL OF RARE EARTHS 25 (2007) 744 - 748JOURNAL OFRARE EARTHSwww. elsevier. com /locate/jreStudy on the Deformation Behavior of M g23. 6%Er Magnesium AlloyW ang Zhongjun (王 忠 军 ) 1 3 , J ia W eip ing (贾 维 平 ) 1 , Cui J ianzhong (崔 建 忠 ) 2(1. School of M aterials Science and Engineering, U n iversity of Science and Technology L iaoning, A nshan 114051,China; 2. The Key L aboratory of E lectrom agnetic P rocessing of M aterials, M inistry of Education, N ortheasternU niversity, Shenyang 110004, China)Received 9 May 2007; revised 22 August 2007Abstract: The deformation behaviour of a casting Mg23. 6% Er magnesium alloy after T6 treatment was studied in tensiletests from room temperature to 450 under different strain rates ranging from 1. 0 10 - 4 to 6. 0 10 - 3 s- 1. Obtained lo2cal p lateau in the temperature dependence of the ultimate strength ( b ) and yield strength ( 0. 2 ) under constant strainrate indicated the p resence of dynam ic strain ageing (DSA). Serrated flow was observed at the temperature of 200, 250,and 300 . The observed negative strain rate sensitivity suggested that the serrated flow behavior arose from DSA. Thetemperature and strain rate dependence of the critical strain for the onset of serrated flow was analyzed using a phenomeno2logical DSA equation, and the apparent activation energy Q for the serrated flow was obtained by calculation.Key words: Mg23. 6% Er alloy; deformation behavior; serrated flow; dynam ic strain aging; rare earthsCLC number: TG146. 2; TG249; TG166. 3 Document code: A Article ID : 1002 - 0721 (2007) 06 - 0744 - 05It is well2known that rare earth (RE) can purifymelt and imp rove the mechanical p roperties of magne2sium especially at elevated temperatures. H igh per2formance M g2RE alloys have several app lications inaerospace and automotive industry 1 3 . Desp ite be2ing used for decades, scientific understanding of theflow behavior ofMg2RE alloys is incomp lete. Serratedflow has been observed and investigated in M g2Nd orM g2Y2Nd system alloys, for examp le, G rtnerov Vet al 4 observed serrated flow in M g2017% Nd mag2nesium alloy under T6 condition at the temperaturesof 200 300 . Zhu S M and N ie J F 5 also foundserrated flow in W E54 magnesium alloy after T6 treat2ment at the temperature range of 150 225 . Butthese studies are lim ited only in Mg2Nd and Mg2Y2Ndalloys, and further researches with regard to the serra2ted flow of other magnesium alloys containing rareearth elements should be carried out. The serratedflow in Mg23. 6% Er alloy at elevated temperatures wasreported and the results obtained were analyzed andexp lained.1 Exper im en ta lMagnesium of commercial purity with 3. 6% Eringot ( 50 mm 100 mm ) was used in this study.The ingot was subjected to T6 treatment, that is, thesolution was treated at 500 for 8 h, then quenchedinto warm water of 65 with subsequent ageing treat2ment at 200 for 8 h. Flat tensile specimens withgauge dimensions of 2 mm 6 mm 15 mm were ma2chined from ingots, the tensile direction of specimenswas parallel to the axes of ingots, and all tensile speci2mens were machined from the 1 /2 radius locations ofingots. The tensile specimens were tested using a3 Corresponding author( E2mail: zhongjunwang126. com)Foundation item: Project supported by the National Natural Science Foundation of China (50374025) and the“ 863” p rogram (2003AA331110)B iography: W ang Zhongjun (19692) , Male, Doctor; Major field of interest : advanced p rocessing of magnesium alloysCopyright 2007, by Editorial Comm ittee of Journal of the Chinese Rare Earths Society. Published by Elsevier B. V. A ll rights reserved.screw2driven INSTRON testing machine equipped witha heating chamber. The tests were performed at a tem2perature interval from 25 to 450 under differentstrain rates ranging from 1. 0 10 - 4 to 6. 0 10 - 3s- 1. For tests at elevated temperatures, specimenswere heated up to the selected temperatures within 15m in and maintained at that temperature for 5 m in be2fore testing. The temperature was controlled within 1 . Tensile test data were collected by a comput2er data2acquisition system, from which tensile p roper2ties such as yield strength ( 0. 2 ) , ultimate tensilestrength ( b ) , and critical strain ( c ) for serratedflow were determ ined. Two specimens were used forsome test conditions to ensure the rep roducibility of da2ta. M icrostructures were observed using an op tical m i2croscope (OM, LE ICA DMR) and a transm ission elec2tron m icroscope ( TEM, TECNA I G2).2 Results and D iscussionFig. 1 ( a ) shows the m icrostructure of unde2formed samp les after T6 treatment. The m icrostructureis composed of 2Mg solid solution of Er in Mg matrixand some particles in the solid solution. The structureof these particles are determ ined by the selected areaelectron diffraction ( SAD ) pattern of TEM , which be2longs to 2Mn crystal type having body2centered cubic(B. C. C. ) structure ( Fig. 1 ( b