Strengthening mechanisms of an Al-Mg-Sc-Zr alloy

As a step toward developing an Al-Mg-Sc-Zr alloy for use up to 200 degreesC, the mechanisms responsible for alloy strengthening were identified for Al-6Mg-2Sc-1Zr (wt%) (Al-6.7Mg-1.2Sc-0.3Zr (at%)). The current work quantifies the active strengthening mechanisms at room temperature and explicitly considers solid solution strengthening, grain boundary strengthening, and Al-3(Sc,Zr) precipitate strengthening. Existing strengthening models, together with data from microstructural characterization were used to determine the magnitude of individual contributions. Strengthening due to the sub-micron grain size was the largest contribution to alloy strength, followed in decreasing order by precipitate strengthening and solid solution strengthening. Tensile yield strengths, 540-640 MPa (78-93 ksi), measured at room temperature agree well with predicted values. Model predictions showed that increasing the precipitate size from 7.5 nm to 20-25 nm and increasing the volume fraction of these particles from 0.015-0.025 up to 0.035 could produce a material with a yield strength of 865 MPa (125 ksi). Published by Elsevier Science Ltd. on behalf of Acta Materialia Inc.