Thermal Stability of Nanocrystalline AZ31 Magnesium Alloy Fabricated by Surface Mechanical Attrition Treatment

doi:10.1007/s40195-015-0308-7

Abstract

Abstract:

A nanocrystalline layer (NL) was fabricated on the surface of AZ31 magnesium (Mg) alloy sheet by surface mechanical attrition treatment (SMAT). The microstructure of the Mg alloy was characterized by optical microscopy, X-ray diffraction and microhardness test. The results showed that both the microstructure and microhardness of AZ31 Mg alloy sheet after SMAT revealed a gradient distribution along depth from surface to center. The thermal stability of the NL was investigated through characterizing the microstructure evolution during the post-isothermal annealing treatment within the temperature range from 150 to 250 °C. The NL exhibits a certain degree of thermal stability below 150 °C, while it disappears quickly when annealing at the temperature range of 200-250 °C. The grain growth kinetics of the nanocrystalline of AZ31 Mg alloy induced by SMAT was investigated. The activation energy of nanocrystalline AZ31 Mg alloy was obtained with a value of 92.8 kJ/mol.

Key words: Magnesium alloy, Thermal stability, Surface mechanical attrition treatment, Nanocrystalline structure, Gradient structure

Jiang-Man Xu, Yong Liu, Bin Jin, Jia-Xin Li, Shi-Ming Zhai, Xiang-Jie Yang, Jian Lu. Thermal Stability of Nanocrystalline AZ31 Magnesium Alloy Fabricated by Surface Mechanical Attrition Treatment[J]. Acta Metallurgica Sinica (English Letters), 2015, 28(9): 1162-1169.

Figures/Tables 8

Fig. 1 XRD patterns of the AZ31 Mg alloy sheet surface layers before and after SMAT. The inset is the Mg (002) peak.

Fig. 2 Cross-sectional microstructures of the AZ31 magnesium alloy samples: a before SMAT, b after SMAT.

Fig. 3 Variations of the grain size and the microhardness along depth from the center of AZ31 Mg alloy after SMAT.

Fig. 4 Comparison of the surface layer microstructure of AZ31 alloys under heat treatment: a 150 °C/10 min, b 150 °C/30 min, c 200 °C/10 min, d 200 °C/30 min; e 250 °C/10 min, f 250 °C/30 min.

Fig. 5 Thickness of the gradient layers with the increase in annealing time at different temperatures.

Fig. 6 Variations of the microhardness along depth from the center of AZ31 Mg alloy by SMAT under annealing at different temperatures: a 150 °C, b 200 °C, c 250 °C.

Fig. 7 Variations of the grain size with annealing temperature and time in the top treated surface of AZ31 Mg alloy sheet samples induced by SMAT.

Fig. 8 Plot of ln k (rate constant) versus 1000/T of nanocrystalline AZ31 induced by SMAT.

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