日本金属学会誌

J. Japan Inst. Metals, Vol. 53, No. 8 (1989),
pp. 759-763

Stress Relaxation Behaviour of 7075-Al Alloy during Discontinuous Deformation

Katuo Saitou1, Junji Kihara2 and Yasuo Otoguro1

1Department of Mechanical Engineering, Faculty of Technology, Gunma University, Kiryu
2Department of Metallurgical Engineering, Faculty of Technology, The University of Tokyo, Tokyo

Abstract:

Information about the dislocation behaviour is necessary for the investigation of the discontinuous deformation, and the stress relaxation test is one of the method to obtain it. This study is intended to provide the stress relaxation behaviour of 7075-Al alloy, which exhibits nearly regular load drops in the stress-strain curve. The stress relaxation tests are done at the positions just before (Max position) and after (Min position) the load drop. The relaxed stress Δ R at each position is discussed. In addition, a strain gauge is attached to the specimen in order to keep the specimen strain constant during the relaxation for the sake of obtaining the true telaxation properties of the specimen.
The main results obtained are as follows:
(1)  In the case of the strain control, the Δ R is the value obtained when the stiffness of the machine is infinite, and corresponds to the effective stress.
(2)  The stress relaxation at a Min position is due mainly to the deformation band formed when the load dropped.
(3)  The stress fluctuations during the discontinuous deformation correspond to the internal stress fluctuations by the formation of the deformation band.


(Received 1989/1/18)

Keywords:

discontinuous deformation, Portevin-LeChatelier effect, stress relaxation, effective stress, internal stress, deformation band, aluminum-zinc-magnesium-copper alloy


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