CYCLIC DEFORMATION OF DISPERSION-STRENGTHENED ALUMINUM-ALLOYS

The cyclic deformation behavior of two dispersion-strengthened aluminu m alloys produced by mechanical alloying is examined. The materials st udied include an Al-Mg alloy (IN-9052) and a similar alloy containing an addition of lithium (IN-905XL). The results of plastic strain-contr olled low cycle fatigue tests are compared with those obtained for a c onventional Al-Mg alloy (AA5083-H321) and a conventional precipitation -strengthened alloy (AA7075-T6). The dispersion-strengthened materials exhibit a small amount of initial cyclic softening followed by modera te hardening to failure. These observations suggest that the residual stresses induced during processing may influence the initial cyclic re sponse, but that the dispersoids are resistant to shear as expected. T he dispersion-strengthened alloys also exhibit a substantial asymmetry in the tension and compression peak stresses due to the presence of t he dispersoids. This result is similar to that for the AA7075-T6, but no such asymmetry was detected in the solid solution-strengthened allo y (AA5083-H321). The cyclic lifetime of IN-9052 is slightly greater th an that of the other materials examined in this study. This result is attributed to the role of the dispersoid particles in promoting homoge neous deformation. Finally, the importance of incorporating a non-line ar elastic strain calculation in low cycle fatigue testing of high-str ength materials is discussed.