过共晶Al-7.5Ni-5Fe-xCo合金的组织特性与热学性能

Microstructure and Thermal Properties of Hypereutectic Al-7.5Ni-5Fe-xCo Alloys

利用金属型铸造工艺制备Al-7.5Ni-5Fe-xCo(x=0,0.3,0.6,1,2,%)合金,系统研究其组织演变和热学性能变化。结果表明,Co加入后合金中Al_(9)FeNi初生相细化,初生相周围析出的共晶组织含量逐渐增加。Co在Al-7.5Ni-5Fe合金中主要固溶于初生Al_(9)FeNi相。Co比Ni表现出更强的活性,易于置换Al_(9)FeNi中的Ni元素,形成Al_(9)M_(2)(M=Fe、Ni和Co)型结构。凝固热分析证实Co加入后Al_(9)FeNi相的析出凝固温度提前,而Al_(13)Fe_(4)相的析出温度降低,凝固初始阶段发生的固态扩散反应减少,凝固过程的改变使合金的组织结构细化。随着Co的加入,合金的热导率和热膨胀系数均有一定程度的降低,主要归因于Co原子在Al_(9)FeNi相中的固溶作用。

Al-7.5Ni-5Fe-xCo(x=0,0.3,0.6,1,2,%)alloys were prepared by permanent mold casting,and the evolution of microstructure and thermal properties were systematically investigated.The results indicate that the primary Al_(9)FeNi phase is refined,and the volume fraction of eutectic structure around the primary phase is gradually increased after Co addition.Co exists in the form of solution atom of Al_(9)FeNi phase in Al-7.5Ni-5Fe alloy,which is easy to replace Ni elements in Al_(9)FeN to form Al_(9)M_(2)(M=Fe,Ni and Co)phase due to the greater activity.Solidification heat analysis confirms that the precipitation solidification temperature of Al_(9)FeNi phase is advanced after Co addition,while the precipitation temperature of Al_(13)Fe_(4)phase is decreased.The solid diffusion reaction at initial stage of solidification is reduced,and the transformation of solidification process leads to the refinement of microstructure.With the addition of Co,the thermal conductivity and thermal expansion coefficient of the alloy are decreased to a certain extent,which is mainly attributed to the solid solution of Co atom in Al_(9)FeNi phase.