Cyclic deformation of dispersion-strengthened aluminum alloys

The cyclic deformation behavior of two dispersion-strengthened aluminum alloys produced by mechanical alloying is examined. The materials studied include an AlMg alloy (IN-9052) and a similar alloy containing an addition of lithium (IN-905XL). The results of plastic strain-controlled low cycle fatigue tests are compared with those obtained for a conventional 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 moderate hardening to failure. These observations suggest that the residual stresses induced during processing may influence the initial cyclic response, but that the dispersoids are resistant to shear as expected. The dispersion-strengthened alloys also exhibit a substantial asymmetry in the tension and compression peak stresses due to the presence of the dispersoids. This result is similar to that for the AA7075-T6, but no such asymmetry was detected in the solid solution-strengthened alloy (AA5083-H321). The cyclic lifetime of IN-9052 is slightly greater than that of the other materials examined in this study. This result is attributed to the role of the dispersoid particles in promoting homogeneous deformation. Finally, the importance of incorporating a non-linear elastic strain calculation in low cycle fatigue testing of high-strength materials is discussed.