The Effect of Specimen Size and Test Procedure on the Creep Behavior of ME21 Magnesium Alloy

Lightweight constructions and materials offer the opportunity to reduce CO2 emissions in the transport sector. As components in vehicles are often exposed to higher temperatures above 40% of the melting temperature, there is a risk of creep. The creep behavior usually is investigated based on standard procedures. However, lightweight constructions frequently have dimensions not adequately represented by standardized specimen geometries. Therefore, comparative creep experiments on non-standardized miniature and standardized specimens are performed. Due to a modified test procedure specified by a miniature creep device, only the very first primary creep stage shows a minor influence, but subsequently, no effect on the creep process is detected. The creep behavior of hot extruded and heat treated ME21 magnesium alloy is investigated. It is observed that the creep parameters determined by the miniature and standard creep tests are different. As the deviations are systematic, qualitatively, evidence of the creep behavior is achieved. The creep parameters obtained, and particularly the creep strain and the strain rate, show a higher creep resistance of the miniature specimen. An initial higher number of twinned grains and possible multiaxiality in the gauge volume of the miniature specimen can be responsible.

Indenter misalignment in impression creep test: Uncertainty, correction and recommendation

The impression creep test (ICT) method, as a miniature specimen test technique, has been used extensively to determine the in-service creep properties of power plant components. However, the experiment results of the ICT can be affected by some uncertainties associated with the inaccuracies of measurement, which have not been studied before. This paper presents some results of finite element analyses, to evaluate the effect of indenter misalignment on the results of the ICT, such as the steady-state creep deformation rate and the conversion parameters. The results obtained have shown that the angular misalignments of the indenter around horizontal directions have a relatively significant influence on the conversion parameters, and the misalignment around vertical direction has a much less significant effect. Empirical formulas were developed for the possible correction of the conversion factors. Finally, some recommendations on the control of the indenter and specimen alignment were given.