材料期刊网

用硬度、拉伸、金相及X射线等方法研究了镁-锌合金的时效硬化机制.研究结果指出:镁-锌(5％)合金在200℃时效时,析出具有六角结构、垂直于镁基体的基面且和基体共格的杆状β′过渡相.其主要作用是提高合金的屈服强度,而对其应变硬化率却几乎沒有影响.当这种时效合金受到范性变形吋,由于位错不能切过β′相而塞积于β′相之前.存在于β′相周围的共格畸变应力場是合金在时效状态屈服强度提高的基本原因.必须提高外加应力才能迫使位错克服这种畸变应力場的作用而交滑移到柱面上去.

The mechanism of age-hardening of magnesium-zinc alloy has been investigated by means of hardness measurement, tensile test, metallographic examination and X-ray analysis. It is shown that when the magnesium-5%zinc alloy is aged at 200℃ for not too long a period, a hexagonal transition phase β' is precipitated, which is rod-like, orientated perpendicularly to the basal plane of the magnesium matrix and coherent to it. The existence of such transition β' precipitates raises the yield strength of the alloy but does not change appreciably its rate of strain hardening in tension test at 77°K. It is presumed that when this age-hardened alloy was plastically deformed, the gliding dislocations were unable to cut through the β' rods but piled-up against them. The coherent stress field accompanying the β' phase is the principal reason to account for the rise of yield strength of the alloy after aging. Additional external stress must be applied in order to overcome such coherent stress field and to force the constricted gliding dislocations to cross-slip into the prismatic planes of the matrix.