The alloy shear yield stress can be roughly times the stated pure-aluminium critical resolved shear stress. Strengthening raises the stress required for dislocation glide rather than requiring homogeneous shearing of a perfect crystal.
- Solid-solution strengthening: substitutional solutes create elastic and chemical disturbances that interact with dislocations. A moving dislocation must escape or drag these disturbances.
- Precipitation hardening: suitably spaced second-phase particles obstruct glide. Small shearable precipitates resist cutting; larger nonshearable obstacles require dislocation bowing and bypass. Particle spacing and coherency matter, so overaging can reduce strength.
- Work hardening: prior plastic deformation increases dislocation density. Intersections, junctions and forest dislocations impede subsequent glide; a common scaling is .
- Grain boundary strengthening: smaller grains shorten the distance over which dislocations can pile up and make slip transfer across differently oriented grains more difficult. In its ordinary regime, the Hall-Petch relation is .
These mechanisms can coexist. The numerical comparison is an order-of-magnitude comparison of shear strengths; it is not a conversion of the alloy's shear yield stress directly into a tensile yield stress.
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