Mg-9Gd-4Y-O.6Zr合金的二次时效

摘要

对Mg-9Gd-4Y-0.6Zr合金挤压态和挤压T5态在275～350℃的高温下时效0～96 h,测试两种状态在时效过程中的硬度变化,并用透射电镜观察析出相的组织演变.结果表明:合金挤压T5态比挤压态在275～350℃高温时效中的硬度高,并具有较好的耐热性.合金挤压T5态在275～350℃的高温二次时效过程中产生回归现象,二次时效的温度越高,回归现象越明显,形成β1相的速度越快,达到平衡相(β1相)所需的时间也越短.β'相向β1相转变所需的相变时间最长;β1相向β相转变所需相变时间最短,组织内会出现β'相、β1相和β相三相共存;因此,β'相向β1相的转变一旦完成,合金的硬度和耐热性急剧地下降.%The as-extruded and extruded-T5 Mg-9Gd-4Y-0.6Zr alloys were aged in the temperature range of 275-350 ℃ for 0-96 h, the hardness was tested and the microstructure evolution was studied by transmission electron microscope.The results show that the extruded-T5 alloy has higher hardness and better heat resistance than the as-extruded alloy during high temperature ageing. The retrogression phenomenon occurs during the secondary ageing of the extruded-T5 alloy. The higher the secondary ageing temperature is, the more significant the retrogression phenomenon is, the faster the β1 formation is, the shorter the time of transforming to the equilibrium phase β is. The time ofβ' phase transforming into β1 phase is the longest during secondary ageing, while that ofβ1 phase transforming to β phase is the shortest and three phases of β', β1 and β can co-exist in the aged microstructure. The hardness and heat resistance drop sharply once the β' phase transforms toβ1 phase.