Effect of Cyclic Stress Reduction on the Creep Characteristics of AZ91 Magnesium Alloy

doi:10.1007/s40195-015-0296-7

Abstract

Abstract:

The creep deformation behavior of aged AZ91 magnesium alloy under the cyclic stress reduction has been investigated in the temperature range 353-383 K. The microstructural evolution of the AZ91 magnesium alloy at different heat treatment conditions has been studied using optical microscopy and scanning electron microscopy. The minimum strain rate, $ε ? min$ , was found to be higher under cyclic stress reduction condition than that under static creep condition for the same maximum stress. Cyclic creep acceleration is interpreted using the interaction of moving dislocations with the existing β-phase (Mg₁₇Al₁₂) precipitates. The mean value of the activation energy of secondary creep stage was found to be equal to that quoted for lattice self-diffusion of magnesium mechanism.

Key words: Magnesium alloys, Microstructure, Cyclic stress, Dislocations

Alaa Farag Abd El-Rehim. Effect of Cyclic Stress Reduction on the Creep Characteristics of AZ91 Magnesium Alloy[J]. Acta Metallurgica Sinica (English Letters), 2015, 28(8): 1065-1073.

Figures/Tables 8

Table 1 Chemical composition of the alloy used in the present study (in wt%)

Al	Zn	Mn	Si	Cu	Fe	Mg
8.9	0.8	0.09	0.05	0.006	0.004	Bal.

Fig. 1 Stress time variation for fluctuating stress

Fig. 2 Optical micrographs of AZ91 alloy after aging for 4 h at different temperatures: a 423 K, b 473 K, c 523 K, d 573 K, e 623 K (X500)

Fig. 3 SEM micrographs of AZ91 alloy after aging at for 4 h at different temperatures: a 423 K, b 523 K, c 623 K

Fig. 4 Representative creep strain dependence of strain rate for AZ91 wire samples aged at 423 K for 4 h and crept at 353 K subjected to different amplitudes of cyclic stress reduction, σ cy, at a constant frequency of 0.36 Hz

Fig. 5 The aging temperature, T a, dependence of the minimum strain rate, ε?min , at different amplitudes of cyclic stress reduction, σ cy. Creep temperatures, T, are indicated

Fig. 6 Effect of cyclic stress reduction amplitude, σ cy, on the minimum strain rate, ε?min , at different aging temperatures, T a. Creep temperatures, T, are indicated

Fig. 7 Plots of ln ε?min versus 103/T for different amplitudes of cyclic stress reduction, σcy, at different aging temperatures. Aging temperatures, T a, are indicated

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