Materials Transactions Online

Materials Transactions, Vol.58 No.05 (2017) pp.728-733
© 2017 The Japan Institute of Metals and Materials

Improvement of Strength-Elongation Balance of Al-Mg-Si Sheet Alloy by Utilising Mg-Si Cluster and Its Proposed Mechanism

Ken Takata1, Kohsaku Ushioda2, Ryutaro Akiyoshi3, Ken-ichi Ikeda4, Jun Takahashi5, Satoshi Hata6 and Kenji Kaneko7

1Steel Research Laboratories, Nippon Steel & Sumitomo Metal Corporation, Futtsu 293-8511, Japan
2Technical Development Bureau, Nippon Steel & Sumitomo Metal Corporation, Futtsu 293-8511, Japan
3Department of Materials and Molecular Sciences, Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, Kasuga 816-8580, Japan
4Division of Materials Science and Engineering, Faculty of Engineering, Hokkaido University, Sapporo 060-8628, Japan
5Advanced Technology Research Laboratories, Nippon Steel & Sumitomo Metal Corporation, Futtsu 293-8511, Japan
6Department of Engineering Sciences for Electronics and Materials, Faculty of Engineering Sciences, Kyushu University, Kasuga 816-8580, Japan
7Department of Materials Science and Engineering, Faculty of Engineering, Kyushu University, Fukuoka 819-0395, Japan

The tensile properties of an Al-Mg-Si alloy with Mg-Si clusters were compared with those of an Al-Mg-Si alloy with β″ precipitates of the same strength. The elongation of the alloy with Mg-Si clusters was found to be greater than that of the alloy with β″ precipitates because of the high work hardening rate of the former alloy, particularly in the high-strain region. Decomposition of Mg-Si clusters into solute Mg and Si atoms during the tensile deformation was revealed by differential scanning calorimetry. Transmission electron microscopy revealed three types of dislocation characteristics in these alloys: homogeneous distribution of dislocations with β″ precipitates, cell structures in the alloy with solute Mg and Si, and a combination of these two types in the alloy with Mg-Si clusters. In the case of the alloy with Mg-Si clusters, the yield strength increased significantly owing to the dislocation cutting mechanism; simultaneously, the elongation of this alloy improved greatly because of the presence of solute Mg and Si atoms formed by decomposition via plastic deformation, which were inferred to prevent dynamic recovery in the later stage of tensile deformation. Consequently, a comparison of conventional 6000 series and 7000 series Al alloys revealed that the alloy with clusters had advantages over the alloy with precipitates and the alloy with solutes in terms of the balance between strength and elongation.

This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 79 (2015) 391-397.

[doi:10.2320/matertrans.M2016258]

(Received 2016/07/14; Accepted 2017/02/03; Published 2017/04/25)

Keywords: aluminium-magnesium-silicon alloy, magnesium-silicon cluster, dissolution, repartition of solute, cell structure

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