SiC_p/ZA27复合材料在预变形-半固态等温热处理过程中的组织演变

Microstructural Evolution of SiC_p/ZA27 Composite During Pre-deformation-Semisolid Isothermal Heat Treatment

对 Si Cp/ ZA2 7复合材料锭料在 2 5 0℃进行了不同程度的压缩变形 ,研究了经变形的复合材料在半固态温度 4 6 0℃等温热处理过程中组织的演变过程。结果表明 :随变形量的增大 ,复合材料原来发达的树枝晶逐渐变为粗短枝晶和等轴晶 ;在热处理过程中 ,变形的树枝晶因晶间共晶组织的溶入而快速合并长大 ,形成无晶界或少晶界的相互连接的组织 ,将原晶界处的 Si Cp裹入晶粒内 ,随后 ,剩余共晶组织开始熔化并向回复与再结晶所形成的多边形晶界浸渗 ,造成组织分离 ,当压缩比大于 10 %时 ,形成相互独立的多边形晶粒 ,后经球状化形成球状晶粒 ,同时 ,将 Si Cp返还于固态晶粒间的液相中 ;而压缩比小于 10 %时 ,则形成相互连接的不规则组织 ;随着变形量的增大 ,上述演变过程加快 ,球状化刚完成时的晶粒尺寸变小、圆整度提高 ;球状化完成之后 ,因有效液相率低 ,晶粒的粗化现象较为明显。

The SiC p/ZA27 composite was compressed at 250℃ by different ratio.The microstructural evolution of these deformed composites were investigated during isothermal heat treatment at semisolid temperature of 460℃.The results indicated that the initial developed dendrites of the composite gradually became into short-coarsened dendrites and equiaxed grains with the increasing of the compressing ratio.During the subsequent heat treatment, the deformed primary dendrites of the composite rapidly merged and coarsened and became into the interconnected structure with a few or without boundaries,resulting in the entrapping of the SiC p into grains.Following,the residual boundaries (eutectics) began melting and penetrated along the polygon boundaries formed from the recovery and recrystallizatio,thus the interconnected structure disintegrated into independent grains with polygon boundaries which evolved into globular grains through spheroidizing when the compressed ratio was over 10%.and into irregular interconnected solid grains when the ratio below 10%.Simultaneously,the SiC p was returned back to the liquid between solid grains.With the increasing of the compressed ratio,the structureal evolution accelerated,and the size of the solid grains formed when the spheroidization just completed decreased and their sphericity increased.After the spheroikization completed,the coarsening phenomenon of the solid grains was obvious because the effective liquid fraction was much lower.