0 S.-W.Lee et al.Materials Science and Engineering A 464 (2007)76-84 (a) Mg-15Al-1Zn alloys of 10-pass Tested at275℃ Untested =1x10351 516% E=2x103s1 1270% i=5x103s1 728% E=1x102s 370% E=2x102s1 285% E=5x102s 261% 2cm () Mg-15Al-1Zn alloys of 10-pass Tested at300℃ Untested 2=1x108 1093% i=2x103r' 1406% =5x103g1 1087% E=1×102g 986% E=2x102s1 623% E=5x102s1 2cm 417% (c) Mg-15Al-1Zn alloys of 10-pass Tested at325'℃ Untested E=1x103s1 695% e=2x103g1 963% e=5x103s1 1297% E=1×102g1 1610% E=2x103g4 608% E=5x10251 2 cm, 227% Fig.6.Untested and tested Mg-15Al-1Zn specimens tested at:(a)275C:(b)325C:(c)325C. that these regions had underwent a high-strain-rate superplas- thus the amount of B phase.The second is the fact that B tic deformation [43].Based on this,the morphology evolution phase has a melting point of 450C much lower than that of of a grain from equiaxed shape to filament shape on the sur- a phase,about 650C,and hence a higher mobility of dis- face of the superplastic tensile sample is proposed as shown in location during plastic deformation.Fig.10 shows two direct Fig.9.Two reasons conclude that B phase is the most prob- evidences to support the proposed mechanism by examin- able phase contributing these filaments.The first is the fact ing the surface and center regions of the fractured portion that the amount of filaments increases with Al content and which was mounted with the resin and polished to reveal the80 S.-W. Lee et al. / Materials Science and Engineering A 464 (2007) 76–84 Fig. 6. Untested and tested Mg–15Al–1Zn specimens tested at: (a) 275 ◦C; (b) 325 ◦C; (c) 325 ◦C. that these regions had underwent a high-strain-rate superplas￾tic deformation [43]. Based on this, the morphology evolution of a grain from equiaxed shape to filament shape on the sur￾face of the superplastic tensile sample is proposed as shown in Fig. 9. Two reasons conclude that phase is the most prob￾able phase contributing these filaments. The first is the fact that the amount of filaments increases with Al content and thus the amount of phase. The second is the fact that phase has a melting point of 450 ◦C much lower than that of phase, about 650 ◦C, and hence a higher mobility of dis￾location during plastic deformation. Fig. 10 shows two direct evidences to support the proposed mechanism by examin￾ing the surface and center regions of the fractured portion which was mounted with the resin and polished to reveal the