【摘要】 研究了铸态和挤压态Mg₉₇Y₂Zn₁合金中长周期堆垛有序结构在高温退火时的组织演化.结果表明,铸态合金由网状的18R-LPSO相、堆垛层错、α-Mg和少量的Mg₂₄Y₅颗粒组成.经过挤压后,第二相沿挤压方向呈带状分布,同时在基体内析出大量尺寸细小的14H层片.铸态合金退火初期,14H结构在18R周围的层错区内大量形核,随后18R沿着层错向14H层片转变,14H层片不断增厚和增长,并在退火30 h时体积达到最大.此后继续退火时,18R向14H的转变和14H的溶解同时进行,在退火200 h的样品基体内部几乎不存在14H层片,只在18R相周围有少量残余14H结构.对于挤压态合金,由于挤压时大量形核位置的引入,14H晶核在合金中已大量存在.退火时,18R结构不断溶解于基体中直至全部消失,14H层片则随退火时间的延长连续增长和增厚.当14H层片覆盖基体后,继续延长退火时间,14H层片的增长受到α-Mg晶界阻碍,只发生粗化以及溶解过程.在退火200 h的挤压态样品中,只剩下粗化的14H结构.更多还原

【Abstract】 Recently,there has been increasing interest in the transformation process between 18R and 14H long period stacking ordered（LPSO） structures in Mg-Y-Zn alloys.However,the detailed phase transformation associated with 18R and 14H structures remains to be established.In this work,the effects of high temperature annealing on the microstructure evolutions of LPSO structure of ascast and as-extruded Mg₉₇Y₂Zn₁ alloy were investigated by OM,SEM and TEM.The results show that the as-cast alloy is mainly composed of network-shaped 18R-LPSO phase,stacking faults（SFs）,Q-Mg matrix and a small number of Mg₂₄Y₅ particles.After extrusion,the 18R phase is rearranged in lines along the direction of extrusion and plenty of fine 14H lamella is precipitated in the matrix.During the early stage of annealing,the 14H phase in the as-cast alloy is nucleated massively in the SFs regions around 18R structure.With transformations from the 18R phase,the 14H lamella develops along the directions of length and thickness,and their volume fraction reaches to the maximum when the alloy is annealed for 30 h.As the annealing process continues,the dissolution of 14H phase into thematrix proceeds at the same time.There is almost no 14H lamella present in the center of α-Mg matrix but a few remains near the 18R phase in the microstructure of the specimen annealed for200 h.In case of the as-extruded alloy,however,abundant fine 14H lamella has already been introduced during the hot extrusion.When the annealing treatment is operated,the 18R phase keeps dissolving into the matrix until disappearing completely,while the 14H lamella grows continuously.When the whole matrix is covered by 14H lamella,the development of 14H lamella along the length direction is hindered by the grain boundaries.And only coarsening 14H lamella is observed in the as-extruded alloy sample annealed for 200 h.更多还原