Microstructure and Thermal Properties of Hypereutectic Al-7.5Ni-5Fe-xCo Alloys
Al-7.5Ni-5Fe-x Co(x=0,0.3,0.6,1,2,%)alloys were prepared by permanent mold casting,and the evo-lution of microstructure and thermal properties were systematically investigated.The results indicate that the primary Al9FeNi 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 Al9FeNi phase in Al-7.5Ni-5Fe alloy,which is easy to replace Ni elements in Al9FeN to form Al9M2(M=Fe,Ni and Co)phase due to the greater activity.Solidification heat analysis confirms that the precipitation solidification temperature of Al9FeNi phase is advanced after Co addition,while the precipitation temperature of Al13Fe4 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 Al9FeNi phase.
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