The corrosion behaviour of friction stir welded AZ31B-H24 and -T4 Mg alloys in 3?5%NaCl solution was examined based on potentiodynamic test and constant immersion test results. For friction stir welded AZ31B-H24 specimens, the corrosion potential was higher compared with as received (i.e. parent) specimens, while the trend was reversed for AZ31B-T4 specimens. The present corrosion test results appear to be closely related to the grain size of the friction stir welded specimens. The effects of prior T4 heat treatment, and subsequent microstructural evolution, with friction stir welding on the corrosion behaviour is discussed based on potentiodynamic tests, constant immersion tests and micrographic observation.
In this study, the linear elastic fracture mechanics (LEFM) approach, including use of the equivalent initial flaw size (EIFS) concept and fatigue crack propagation (FCP) rates, da/dN, as a function of either DK or DK eff , was used to predict the fatigue life of a porosity-containing 319-T7 specimen. The uniaxial fatigue tests were conducted on a 319-T7 specimen at a stress ratio (R) of À1. For the LEFM-based fatigue life prediction, da/dN-DK data were obtained for the 319-T7 specimen at R = 0.1. The shape and the size of the porosity were analyzed based on the fractographic and the micrographic analyses for each fatigued specimen. The LEFM concept, including the use of the EIFS value, back-calculated by using da/dN-DK eff data, successfully predicts the porosity-affected stress vs the number of cycles to failure (S-N) fatigue behavior of cast 319-T7 specimens. The LEFM models presently available for predicting the fatigue life of porosity-containing alloys were evaluated and a simple modification was proposed based on extensive fractographic analysis results.
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