高压扭转变形Mg-Zn-Y合金的组织演化和时效行为

采用透射电镜(TEM)、扫描电镜(SEM)、X射线衍射(XRD)仪和显微硬度计研究了高压扭转(HPT)变形Mg-Zn-Y合金的微观组织演变和时效行为。结果表明,在HPT变形前后,合金中的第二相颗粒是W相和Mg₂₄Y₅相,且在HPT处理后没有观察到任何新沉淀物的形成,说明HPT变形并未导致合金发生相变。同时,发现HPT变形过程是伴随着形变孪晶的产生和大量位错增殖而进行的,其中形变孪晶在HPT处理过程中被第二相颗粒所细分。与未变形合金相比,HPT变形可以加速时效进程,即在更短的时效时间达到相对高的峰值硬度。对HPT变形7圈的试样进行175 ℃×8 h时效处理后,峰值显微硬度达到约114 HV0.1。经过时效处理后,析出相优先在位错和孪晶界处形核,说明位错和孪晶界充当析出相优先形核位点。

Microstructure evolution and aging behavior of Mg-Zn-Y alloy processed by high pressure torsion

Microstructure evolution and aging behavior of high-pressure torsion(HPT)deformed Mg-Zn-Y alloy were studied by using transmission electron microscope(TEM),scanning electron microscope(SEM),X-ray diffraction(XRD)instrument and microhardness tester.The results show that before and after HPT deformation,the second phase particles in the alloy are W phase and Mg₂₄Y₅ phase,and the formation of any new precipitates is not observed after HPT processing,indicating that HPT deformation does not lead to phase transformation of the alloy.At the same time,it is found that the HPT deformation process is accompanied by the generation of deformation twins and the multiplication of a large number of dislocations.The deformation twins are subdivided by the second phase particles during the HPT process.Compared with undeformed alloys,HPT deformation can accelerate the aging process,that is,reach a relatively high peak hardness under a shorter aging time.The specimens after HPT deformed 7 turns of are aged at 175℃ for 8 h,the peak microhardness reaches about 114 HV0.1.After aging treatment,the precipitated phase preferentially nucleates at the dislocations and twin boundary,indicating that dislocations and twin boundary act as preferential nucleation sites for the precipitated phases.