The friction stir welding process (FSW) was developed in the United Kingdomin the early 1990s. During FSW, the frictional heat that is generated is effectively utilized to facilitate material consolidation and eventual joining with the aid of axial pressure. The process is, therefore, a non-fusion welding process. FSW was applied in the current study in order to weld AZ31B-H24 alloy plates. Each of the different zones of the welded joint underwent optical metallographic characterization: the parent material, the Heat Affected Zone (HAZ), the Thermo-Mechanically Affected Zone (TMAZ), and the weld nugget. Optical metallography revealed deformation twinning at the TMAZ, grain refinement at the HAZ and evidence of heavy plastic deformation at the nugget. Creep tests at 100°C, 200°C and 300°C were conducted both on the parent material and on the friction stir welded specimens. Two different creep regimes seem to exist, a high stress regime in which creep is controlled by dislocation climb, and a low stress regime in which Grain-Boundary Sliding (GBS) becomes the dominant mechanism. Transmission electron microscopy of welded and non-welded specimens that underwent creep at 100°C revealed the existence of dislocation segments that do not lie on the basal planes. It is therefore assumed that other slip systems are active, in addition to the basal slip systems known to be the only ones active in pure magnesium up to about 180°C. The proposed deformation mechanism involves dislocation gliding on basal and non-basal planes assisted by twinning and GBS.
Cite this paper
M. Regev and S. Spigarelli, "Plastic Deformation Mechanisms of Base Material and Friction Stir Welded AZ31B-H24 Magnesium Alloy," Materials Sciences and Applications, Vol. 4 No. 6, 2013, pp. 357-364. doi: 10.4236/msa.2013.46046.
 S. S. Vagarali and T. G. Langdon, “Deformation Mechanisms in h.c.p. Metals at Elevated Temperatures I. Creep Behavior of Magnesium,” Acta Metallurgica, Vol. 29, No. 12, 1981, pp. 1969-1981.
 S. S. Vagarali and T. G. Langdon, “Deformation Mechanisms in h.c.p. Metals at Elevated Temperatures II. Creep Behavior of a Mg-0.8% Al Solid Solution Alloy,” Acta Metallurgica, Vol. 30, No. 6, 1982, pp. 1157-1170.
 K. Milicka, J. Cadek and P. Rys, “High Temperature Creep Mechanisms in Magnesium,” Acta Metallurgica, Vol. 18, No. 10, 1970, pp. 1071-1082.
 J. R. Davis and P. Allen, “ASM Handbook,” 10th Edition, ASM International, Ohio, 1990.
 A. Bussiba, A. Ben Artzy, A. Shtechman, S. Ifergan and M. Kupiec, “Grain Refinement of AZ31 and ZK60 Mg Alloys—Towards Superplasticity Studies,” Materials Science and Engineering A, Vol. 302, No. 1, 2001, pp. 56-62. doi:10.1016/S0921-5093(00)01354-X
 G. Ben Hamu, D. Eliezer and L. Wagner, “The Relation between Severe Plastic Deformation Microstructure and Corrosion Behavior of AZ31 Magnesium Alloy,” Journal of Alloys and Compounds, Vol. 468, No. 1-2, 2009, pp. 222-229. doi:10.1016/j.jallcom.2008.01.084
 L. Jin, D. Lin, D. Mao, X. Zeng, B. Chen and W. Ding, “Microstructure Evolution of AZ31 Mg Alloy during Equal Channel Angular Extrusion,” Materials Science and Engineering A, Vol. 423, No. 1-2, 2006, pp. 247-252.
 H. K. Kim and W. J. Kim, “Microstructural Instability and Strength of an AZ31 Mg Alloy After Severe Plastic Deformation,” Materials Science and Engineering A, Vol. 385, No. 1-2, 2004, pp. 300-308.
 S. Tian, L. Wang, K. Y. Sohn, K. H. Kim, Y. Xu and Z. Hu, “Microstructure Evolution and Deformation Features of AZ31 Mg-Alloy During Creep,” Materials Science and Engineering A, Vol. 415, No. 1-2, 2006, pp. 309-316.
 J. Liu, D. Chen, Z. Chen and H. Yan, “Deformation Behavior of AZ31 Magnesium Alloy during Tension at Moderate Temperatures,” Journal of Materials Engineering and Performance, Vol. 18, No. 7, 2009, pp. 966-972.
 J. Koike, N. Fujiyama, D. Ando and Y. Sutou, “Roles of Deformation Twinning and Dislocation Slip in the Fatigue Failure Mechanism of AZ31 Mg Alloys,” Scripta Materialia, Vol. 63, No. 7, 2010, pp. 747-750.
 H. Somekawa, K. Hirai, H. Watanabe, Y. Takigawa and K. Higashi, “Dislocation Creep Behavior in Mg-Al-Zn Alloys,” Materials Science and Engineering A, Vol. 407, No. 1-2, 2005, pp. 53-61. doi:10.1016/j.msea.2005.06.059
 J. C. Tan and M. J. Tan, “Dynamic Continuous Recrystallization Characteristics in Two Stage Deformation of Mg3Al-1Zn Alloy Sheet,” Materials Science and Engineering A, Vol. 339, No. 1-2, 2003, pp. 124-132.
 H. Watanabe, H. Tsutsui, T. Mukai, M. Kohzu, S. Tanabe and K. Higashi, “Deformation Mechanism in a CoarseGrained Mg-Al-Zn Alloy at Elevated Temperatures,” International Journal of Plasticity, Vol. 17, No. 3, 2001, pp. 387-397. doi:10.1016/S0749-6419(00)00042-5
 A. Mwembela, E. B. Konopleva and H. J. McQueen, “Microstructural Development in Mg Alloy AZ31 during Hot Working,” Scripta Materialia, Vol. 37, No. 11, 1997, pp. 1789-1795. doi:10.1016/S1359-6462(97)00344-8
 M. M. Myshlyaev, H. J. McQueen, A. Mwembela and E. Konopleva, “Twinning, Dynamic Recovery and Recrystallization in Hot Worked Mg-Al-Zn Alloy,” Materials Science and Engineering A, Vol. 337, No. 1-2, 2002, pp. 121-133. doi:10.1016/S0921-5093(02)00007-2
 M. Regev, E. Aghion, M. Bamberger, S. Berger and A. Rosen, “Dislocation Analysis of Crept AZ91D Ingot Castings,” Materials Science and Engineering A, Vol. 257, No. 2, 1998, pp. 349-352.
 T. D. Massalski, “Binary Alloy Phase Diagrams,” 2nd Edition, ASM, Ohio, 1987.
 M. Regev, A. Rosen and M. Bamberger, “Qualitative Model for Creep of AZ91D Magnesium Alloy,” Metallurgical and Materials Transactions A, Vol. 32, No. 6, 2001, pp. 1335-1345. doi:10.1007/s11661-001-0224-5
 M. Regev, H. Rosenson and Z. Koren, “Microstructure Study of Particle Reinforced AZ91D and AM50 Magnesium Alloy,” Materials Science and Technology, Vol. 23, No. 12, 2007, pp. 1485-1491.
 H. Sato and H. Oikawa, “Transition of Creep Characteristics of HCP Mg-Al Solid Solutions at 600-650K,” In: D. G. Brandon, R. Chaim and A. Rosen, Eds., Strength of Metals and Alloys, Freund, London, 1991, pp. 463-470.
 S. Spigarelli, M. Regev, M. El Mehtedi, G. Quercetti and M. Cabibbo, “Analysis of the Effect of Friction Stir Welding on the Minimum Creep Rate of an Mg-3% Al1% Zn Alloy,” Scripta Materialia, Vol. 65, No. 7, 2011, pp. 626-629. doi:10.1016/j.scriptamat.2011.06.042
 J. A. del Valle, F. Penalba and O. A. Ruano, “Optimization of the Microstructure for Improving Superplastic Forming in Magnesium Alloys,” Materials Science and Engineering A, Vol. 467, No. 1, 2007, pp. 165-171.
 J. A. del Vall, M. T. Perez-Prado and O. A. Ruano, “Deformation Mechanisms Responsible for the High Ductility in a Mg AZ31 Alloy Analyzed by Electron Backscattered Diffraction,” Metallurgical and Materials Transactions A, Vol. 36, No. 6, 2005, pp. 1427-1438.