Of Za27 Alloy And Its Composite Semi-solid Non-sticks Preparation Of Grain Structure Research

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�'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.