Creep-Rupture Behavior of Die-Cast Magnesium Alloys (original) (raw)
2017
It is found that the relationship between the time-to-rupture t r and the time to the onset of tertiary creep t οt ( t r / t ot ) in die-cast Mg-9Al alloy is equal to 1.3 and independent of stress, test temperature and diecasting parameters over the range examined. It is shown that the introduction of creep-rupture strain into Monkman-Grant relation modified by Dobes and Milicka demonstrates only the deviation range of the minimum creep rate from the average creep rate. The apparent activation energy E c of creep is below the value of magnesium self-diffusion energy ESD up to 175°C. At higher temperatures, E c > E SD , and creep deformation may be controlled by diffusion processes (dislocation climbing, etc.). The established magnitude of stress exponent n in the power law (the modified Arrhenius rate equation) within the stress range from 20 to 50 MPa is close to the value of n ≅ 3 typical of solid-solution alloys. The increase in n values at higher stresses up to ~ 5 is caused,...
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Internal stresses during creep of magnesium alloys at 523K
Materials Science and Engineering: A, 2007
ABSTRACT Strain transient dip tests have been used for the measurement of internal and effective stresses in minimum creep rate stages of several magnesium-based alloys at 523K. Values of the internal stresses well reflect the creep resistance levels of the investigated alloys. The applied stress exponent n of the minimum creep rate ε˙min equals or exceeds values of six in all the investigated alloys. On the other hand, a very low value of two for the effective stress exponent m of ε˙min was obtained independent of alloy structure. The experimental internal stress in creep is comparable with the internal stress determined by means of stress relaxation tests in the course of stress–strain tests under similar stresses at the testing temperature.
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