The grain size dependence of yield stress and flow stress in the quenched and aged magnesium-3 wt% zinc alloy was studied by the tensile test and the electron and optical microscopic observations in the temperature range from room temperature to −195°C. The main results obtained are as follows:
(1) This alloy does not clearly show the yield point in the stress-strain curve and parabolically harden irrespective of grain size and aging conditions.
(2) The change in the yield stress or flow stress with grain size conforms to the Hall-Petch relation in either case of the quenched and the aged stage.
(3) The coefficient, k_y, (corresponding to the yield stress) in the Hall-Petch relation depends largely on the testing temperature.
(4) The value of k_y, of precipitated alloys equals twice that of precipitates free alloys in the whole temperature range.
(5) The strain dependence of k (corresponding to the given plastic strain) is not very remarkable for the precipitates-free alloys as compared with the precipitated alloys. The value of k in the precipitated alloy is maximum at about 1 pct strain.
(6) It is possible that the value of k_y is the measure of difficulty of the prismatic slip.
(7) The friction stress σ₀, depends on the testing temperature and varies from 7 (at room temperature) to 1.5 kg/mm² (at −195°C) for the precipitates free state, from 6.5 (at room temperature) to 4.5 kg/mm² (at −195°C) in the precipitated state.