Behaviour of quenched-in defects in magnesium alloys and its effect on flow stress

Abstract

Magnesium specimens containing aluminium, zinc or silver have been tested in tension after air cooling or water quenching from temperatures in the solid solution range. All materials exhibited an increment in flow stress (compared with air-cooled specimens) after water quenching that tended to increase with quenching temperature and alloy content. Variations in the flow stress on subsequent ageing at temperatures up to 280°C are consistent with hardening by the precipitation of further loops of dislocation and subsequent softening as vacancies are lost to sinks.

Whatever the heat-treated condition or composition of the specimens, the flow stress increase over the air-cooled value can be interpreted in terms of the concentration and size of dislocation loops, and all alloys display a linear dependence on the square root of the product of loop density and diameter until the mean distance between loops decreases to less than six loop diameters. Beyond this point there is a more complex dependence upon the same parameters.