Substitutional solution hardening of magnesium single crystals

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Abstract
Single crystals of magnesium containing varying amounts of In, Al, Pb and Bi in solid solution have been deformed in tension over a range of temperature between 4.2°k and 500°k. The critical resolved shear stress (CRSS) for basal slip has been examined in the light of the existing solution hardening theories. The earlier published data on Zn, Cd, Tl and Li solutes were included in arriving at a generalized solution hardening model for magnesium. The CRSS in the plateau region (above 295°k) can be described best with a C 2/3 relationship, where C is the atom fraction of solute. The strengthening mechanism was found to be one involving the interaction of solute atoms with edge dislocations. The extent of hardening is determined by the size and valency differences between the solute and the solvent. The valency term was found equivalent to the modulus interaction term of the statistical solution hardening theories. The CRSS at 0°k increases linearly with alloying at concentrations of solute above 0.2%. The rapid hardening non-linear region at low concentrations is a result of additional indirect strengthening due to an increased forest dislocation density. The extent of hardening at 0°k is determined by the size factor only, valency of the solute being of no consequence. The experimental data at 0°k are in quantitative agreement with the theory of Friedel (1964).