Abstract
Serration phenomena, in which stress fluctuates in a saw-tooth shape, occur when a uniaxial test is performed on an aluminum alloy containing a solid solution of solute atoms. The appearance of the serrations is affected by the strain rate and temperature. Indentation tests enable the evaluation of a wide range of strain rates in a single test and are a convenient test method for evaluating serration phenomena. Previously, the serrations caused by indentation at room temperature were clarified using strain rate as an index. In this study, we considered ambient temperature as another possible influential factor. We clarify, through experimentation, the effect of temperature on the serration phenomenon caused by indentation. An Al–Zn–Mg–Cu alloy (7075 aluminum alloy) was used as the specimen. The aging phenomenon was controlled by varying the testing temperature of the solution-treated specimen. Furthermore, the material properties obtained by indentation were evaluated. By varying the testing temperature, the presence and amount of precipitation were controlled and the number of solute atoms was varied. Additionally, the diffusion of solute atoms was controlled by maintaining the displacement during indentations, and a favorable environment for the occurrence of serrations was induced. The obtained results reveal that the variations in the serrations formed in the loading curvature obtained via indentation are attributed to the extent of interaction between the solute atoms and the dislocations.
Highlights
A phenomenon called serration—stress fluctuations in a saw-tooth shape—occurs when a uniaxial test is performed on aluminum alloys containing solute atoms in the solid solution [1,2,3,4].Dynamic strain aging gives rise to the Portevin–Le Chatelier effect [3,5,6]
We extend our previous work [8,18] to clarify the effects of testing temperature on the serration behavior during indentation tests
The serration phenomenon during indentation was varied by controlling the number of precipitated phases based on the effect of natural and artificial aging
Summary
A phenomenon called serration—stress fluctuations in a saw-tooth shape—occurs when a uniaxial test (e.g., tensile test) is performed on aluminum alloys containing solute atoms in the solid solution [1,2,3,4]. Previous studies [8,18] indicated that the serration phenomenon in indentation could possibly be evaluated using the concept of effective strain rate. It was discovered that there is a test evaluation limit called critical strain [19] and that serrations could be used as an index to evaluate this effect [18]. These previous studies were conducted only in an ambient temperature environment, the effect of temperature on the serration behavior during indentation was not investigated. Indentation was established as a new method of evaluating material properties through the evaluation of the serration behavior related to the microstructure
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