Effect of Enhanced Cooling on the Microstructure and Mechanical Properties of Friction Stir Spot-Welded AZ31 Magnesium Alloy

Abstract:

AZ31 magnesium alloy was friction stir spot welded in air and cooling in water. The effect of the enhanced cooling rate on the microstructure and mechanical properties of the joint was analyzed. The results showed that flowing water had obvious cooling effect instantaneously, which significantly restrained the growth of dynamic recrystallized grains. The average grain size in stir zone was 1.3μm in cooling water condition, which is far smaller than that of the joint prepared in air cooling condition. Under the condition of enhanced cooling, the microhardness in stir zone significantly increased, the ultimate tensile load (~ 3.99kN) increased by 15.7%, and the tensile deformation value (~ 3.65 mm) increased by 62.2%. Dimples in SEM fracture morphologies indicated the better plastic deformation capacity of joints prepared by cooling water, which failed through a mixture mode of ductile and brittle fracture.

• Periodical: Materials Science Forum (Volume 850)
• Pages: 784-789
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.850.784
• Online since: March 2016
• Authors: Song Lin Chen, Da Tong Zhang
• Keywords: AZ31 Magnesium Alloy, Mechanical Properties, Microstructure, Submerged Friction Stir Spot-Welded

References

[1] Yuan-Ching Lin, Ju-Jen Liu, Ben-Yuan Lin, et al. Effects of process parameters on strength of Mg alloy AZ61 friction stir spot welds[J]. Materials and Design, 2012, 35 : 350–357.

DOI: 10.1016/j.matdes.2011.08.050

[2] Y.S. Sato, S.H.C. Park, M. Michiuchi, et al. Constitutional liquation during dis- similar friction stir welding of Al and Mg alloys [J]. Scripta Mater, 2004, 50: 1233− 1236.

DOI: 10.1016/j.scriptamat.2004.02.002

[3] D.Q. Sun, B. Lang, D.X. Sun, et al. Microstructures and mechanical properties of resistance spot welded magnesium alloy joints, Mater Sci Eng A, 2007, 460–461: 494–8.

DOI: 10.1016/j.msea.2007.01.073

[4] Mumin Tutar, Hakan Aydin, Celalettin Yuce, et al. The optimisation of process parameters for friction stir spot-welded AA3003-H12 aluminium alloy using a Taguchi orthogonal array [J]. Materials and Design, 2014, 63: 789-797.

DOI: 10.1016/j.matdes.2014.07.003

[5] Tian-jiao LUO, Bao-liang SHI, Qi-qiang DUAN, et al. Fatigue behavior of friction stir spot welded AZ31 Mg alloy sheet joints [J]. Transactions of Nonferrous Metals of Society of China, 2013, 33: 1949−(1956).

DOI: 10.1016/s1003-6326(13)62682-5

[6] M. Hosseini, H. Danesh Manesh. Immersed friction stir welding of ultrafine grained accumulative roll-bonded Al alloy [J]. Materials and Design, 2010, 31 : 4786–4791.

DOI: 10.1016/j.matdes.2010.05.007

[7] M.A. Mofid, A. Abdollah-zadeh, F. Malek Ghaini. The effect of water cooling during dissimilar friction stir welding of Al alloy to Mg alloy [J]. Materials and Design, 2012, 36: 161–167.

DOI: 10.1016/j.matdes.2011.11.004

[8] Darras B, Omar M, Khraisheh M. Experimental thermal analysis of friction stir processing. Mater Sci Forum, 2007, 539–543: 3801–6.

DOI: 10.4028/www.scientific.net/msf.539-543.3801

[9] Basil Darras, Emad Kishta. Submerged friction stir processing of AZ31 Magnesium alloy. Materials and Design, 2013, 47: 133–137.

DOI: 10.1016/j.matdes.2012.12.026

[10] Hofmann DC, Vecchio KS. Submerged friction stir processing (SFSP): an improved method for creating ultra-fine-grained bulk materials. Mater Sci Eng A, 2005, 402: 234–41.

DOI: 10.1016/j.msea.2005.04.032

[11] Fang Chai, Datong Zhang, Yuanyuan Li. High strain rate superplasticity of a fine-grained AZ91 magnesium alloy prepared by submerged friction stir processing. Mater Sci Eng A, 2013, 568: 40–48.

DOI: 10.1016/j.msea.2013.01.026

[12] Yong Zhao, Zhengping Lu, Keng Yan. Microstructural characterizations and mechanical properties in underwater friction stir welding of aluminum and magnesium dissimilar alloys. Materials and Design, 2015, 65: 675–681.

DOI: 10.1016/j.matdes.2014.09.046

[13] Miao Q, Hu L, Wang X, Wang E. Grain growth kinetics of a fine-grained AZ31 magnesium alloy produced by hot rolling. J Alloys Compd, 2010, 493: 87–90.

DOI: 10.1016/j.jallcom.2009.12.049

[14] Darras B. A model to predict the resulting grain size of friction stir processed AZ31 magnesium alloy. J Mater Eng Perform, 2012, 21: 1243–8.

DOI: 10.1007/s11665-011-0039-5