日本金属学会誌

J. Japan Inst. Metals, Vol. 67, No. 4 (2003),
pp. 149-152

Grain Size Dependence of Active Slip Systems in an AZ31 Magnesium Alloy

Takayuki Kobayashi1,, Junichi Koike1, Yu Yoshida2,, Shigeharu Kamado2, Mayumi Suzuki1, Kouichi Maruyama1 and Yo Kojima2

1Department of Material Science, Tohoku University, Sendai 980-8579
2Department of Mechanical Engineering, Nagaoka University of Technology, Nagaoka 940-2188

Abstract:

Polycrystalline Alloys of Mg-3Al-1Zn (AZ31) were obtained by equal channel angular extrusion and subsequent annealing at 300°C} for 24 h or at 500{°C for 4 h. These samples had average grain sizes of 7 μm and 50 μm, respectively. Tensile tests were performed at room temperature at an initial strain rate of 1 × 10-3 s-1.

The microstructure of the deformed samples at 2% strain was observed by transmission electron microscopy. Active slip systems were determined from the ratio of resolved shear stress (plastic anisotropy factor, PAF) for non-basal/basal slip systems. In the material with large grains (PAF=15.4), non-basal a dislocations were active near grain boundaries, while basal a dislocations were dominant in the grain interior. In the material with fine grains (PAF=0.88), non-basal a dislocations were active in all regions. The density of non-basal a dislocation segments was found to be 40% of the total dislocation density.

The activation of non-basal a dislocations is attributed to induced stresses induced to maintain grain-boundary compatibility. In large grains this effect is limited near the grain boundary. In fine grains, this effect occurs within the entire grain.


(Received December 2, 2002)

Keywords:

magnesium, microstructure, dislocation, grain boundary, grain size


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