A Process Of Augmenting Cold-Drawability Of The Magnesium + 1.5 Per Cent Manganese Alloy

MAGNESIUM and its alloys have long been characterized as possessing limited capacity for mechanical forming at atmospheric temperatures prior to rupturing despite their outstanding performances in this respect at elevated temperatures. Responsible for this behavior are the fundamental facts that these hexagonal-type metals have comparatively few slip elements at low temperatures for any extensive deformation and that, at high temperatures, additional slip elements become operative, thus enhancing greater plasticity under strain. The transitional point has been set at 225°C by Schmid1 for single crystals, and at 250°°C by Morell and Hanawalt2 for extruded magnesium metal. In a recent X-ray investigation on polycrystalline magnesium-alloy sheets, Barrett and Haller3 have revealed that, below the transitional temperature, the initial plastic deformation proceeds mostly by a twinning action; that, above such a temperature, the action is mostly by slip. The deep-drawing performance of the magnesium + 1.5 pct alloy sheett over a wide range of temperatures has been investigated by Weber and Vanden Berg,' and their results are presented in Fig r. It should be noted from this work that a maximum drawability of about 25 pct at room temperature has been obtained on this alloy under the conventional deep-drawing operations. For the same alloy, it is now possible to augment the cold drawability to about 40 pct by a process to be disclosed. Hitherto, this value has been obtained only by deep-drawing the alloy at around 230°C. That greater plastic flow is attainable at atmospheric temperatures on magnesium under certain deformational techniques was discovered by the authors6 in their analyses of plastic-deformational behaviors of pure magnesium. This fact is best illustrated in Fig 2 from the Hargreaves analysis6 performed by the authors under two different modes of loading. For direct test, a separate unstrained specimen was used for each load duration, whereas for the integrated test the same specimen was employed for all the five intermittent loadings so that the load duration was made additive throughout the investigation. The higher plastic flow-rate at room temperature, as designated by the Hargreaves constant S, was obtained by the integrated or intermittent loading procedure. The authors5 in further tests showed that, under such a procedure greater plastic flow was also realized with a progressive increase in deformational loads. These findings have been applied