ZA27合金及其复合材料的半固态非枝晶组织制备研究

【作者】 狄杰建；

【导师】 郝远； 陈体军；

【作者基本信息】 甘肃工业大学 ， 材料加工工程， 2001， 硕士

【摘要】 本文分别以ZA27合金和SiC_p/ZA27复合材料为研究对象，以K₂ZrF₆为变质剂，采用半固态等温热处理的方法，研究了ZA27合金的相变、Zr含量对ZA27合金半固态组织影响以及对演变速率的影响和SiC_p/ZA27复合材料的组织演变过程。 结果发现，ZA27合金经0.01～1％Zr处理时，随Zr含量的增加，生成的Zr（Al，Zn）₃高熔点化合物增多，促进初生相非均质形核，使初生相得以细化。在460℃保温30min时，Zr含量越高，铸态组织越细小，越容易熔化，非枝晶化的速率越快，所获得的半固态组织越细小，半固态极限尺寸越小。当Zr含量达到0.04％时，就能获得符合触变成形所需的半固态组织。但Zr量超过0.2％时，圆整度下降，Zr含量为0.2％时，其半固态组织的圆整度最好。 0.4％Zr处理的ZA27合金在半固态等温热处理时，主要发生了以下相变：首先是晶界处或枝晶臂间的共晶组织η相中的Zn原子和初生α’相的Al原子通过β相互相扩散溶解，分别生成富Zn和富Al的过饱和固溶体，经淬火保留到室温，又分别发生分解反应：β→β+η，α’→α+η。随着保温时间的延长，10min后，成分已均匀化，基本上成为单相组织，未溶于α’相的共晶η相和β相中的η相开始熔化。10～20min，η相熔化数量增多且彼此连接，把块状组织分成了许多小的近球状组织。20min后，温度趋于恒定，再没有什么特殊的相变，固、液两相处于动态平衡中。 另外，0.6％Zr处理的SiC_p/ZA27复合材料在460℃保温30～40min时，可以获得组织细小、圆整度好的半固态非枝晶组织。其组织的演变同ZA27合金的演变相似，由于SiC_p的加入，阻碍了晶粒的合并，避免了均一的大组织的形成，增加了位错密度，加速了原子的扩散。因此，复合材料的演变速率快与基体合金。SiCp/ZA27复合材料的组织粗化现象不如基体合金明显。更多还原

【Abstract】 Both effects of Zr on semi梥olid structure of ZA27, its evolutional rate and transformation , and structural evolution of SiC~/ZA27 composite were investigated during semi梥olid isothermal heat treatment, with K2ZrF6as a modifier. As a result, with the increasing of Zr content, more Zr(Al, Zn)3 compounds with high melting point were obtained , which promoted the heteronucleus of primary phase and made it finer. The higher the content of Zr was, the finer the as梒ast structure was, the easier the melting was , the faster the evolution of non梔endritized structure was, the smaller the semi梥olid structure and its extreme dimension were .Setnisolid structure suitable to thixoforming was obtained when Zr reached 0. 04%. But roundness decreased when Zr was over 0. 2%, thus the roundness of semisolid structure with 0. 2%Zrwas best. ?Such transformations of ZA27 alloy with 0.4% Zr were as follows during semi梥olid isothermal heat treatment. Zn atoms in rjphase of eutectic on boundary or between dendritic arms and Al atoms in a - phase dissolved each other through P phase. Zn梤ich and Al梤ich supersaturated solid solution were formed and kept unchanged to room temperature by quenching , such decompositions -.P+rl, a 棏~a+~occurred sequentially. Composition homogenized and single phase was formed after 10 mm. rlphase undissolved into a - phase and in P phase began melting. llith the increasing and connecting with each other of melting riphase, block structures were divided into many small near globular particles within 10?0 mm. There were no special transformations with temperature unchanged after 20mm. The solid and liquid lay in dynamic equilibrium. Moreover, semi梥olid non梔endritic structure with fine structure and better rounder of SiC~/ZA27 composite was obtained at 460 Cfor 30?0min. Addition of SiC~ can prevent annexation of particles and formation of homogenous big structure, increase density of dislocation and make diffusion of atoms faster. Thus evolutional rate of SiC,/ZA27 composite was faster than that of ZA27 alloy. Structural coarsing of SiC~/ZA27 composite was not more apparent than that of ZA27 alloy.更多还原