Effects of Strain Hardening and Alloying on the Strength of Al-Mg-Si Alloys

Strain hardening through cold working and solid solution strengthening through alloying are common mechanisms for improving the mechanical properties of aluminum alloys. Multiple strengthening mechanisms are at play in Al alloys including strain hardening, the Hall Petch relationship, precipitation strengthening, and solid solution strengthening. When multiple strengthening mechanisms are involved, it is often unclear which contribute most to the material’s strength making physics-based model less accurate. It is more useful to build models with known contributions of the competing mechanisms. Experimentally determining these contributions is time consuming but results in a more refined and calibrated model. We surmise that there exists a balance between additional experimental rigor and model improvement, but the necessary dataflow and limit of diminishing returns remain unclear. In the present study, 99.999 wt%Al, 97 wt%Al-3 wt%Mg, 99 wt%Al-1 wt%Si, 99 wt%Al-0.5 wt%Mg-0.5 wt%Si and AA7075 were examined focusing on strain hardening and solid solution strengthening to map out the trade-off between experimental resources and model refinement. Comparable grain sizes were selected for each alloy to control the contribution of the Hall Petch effect, and solution annealed AA7075 was selected to achieve a single-phase microstructure. Our methods include microstructural analysis, compression testing, X-Ray Diffraction, and micro-hardness testing.