Effects of adding Ti on microstructure and properties of Al-Bi immiscible alloy

Abstract

Immiscible alloy, as a kind of special metallurgy characteristic alloy, has been investigated for decades. The fabrication of immiscible alloy with a homogeneous microstructure remains a challenge due to the liquid-liquid phase separation. The microstructure and the properties of Al-Bi immiscible alloy with an addition of Ti are investigated, and the effect of adding Ti on mechanical behavior for self-lubricating performance is measured. The pure Al and Ti are first melted in graphite crucible under argon gas protection. An appropriate amount of Bi is added into the melt. After melting and homogenizing the immiscible alloy, the melt is maintained at 1150 ℃ for 10 min, and then it is quenched. The scanning electron microscope analysis results show that the addition of Ti leads to a significant reduction of Bi-rich droplet size and an increase of particle number. The Bi-rich droplets of the ternary Al-Bi-Ti alloy are more homogeneously distributed throughout the Al matrix than the microstructure of binary Al-Bi alloy. The results from X-ray diffraction and energy disspersive spectrometer indicate that Al3Ti compounds, which are the transformation products between Al and Ti elements, disperse in the Al matrix. The needle-like Al3Ti compounds suspend in Al-Bi melt and impede the Bi phase in the liquid miscibility gap from being segregated. This is conducible to refining the microstructure of Al-Bi alloy. The Al3Ti compounds form before the initial nucleation of the Bi phase in the Al matrix, and impede the Bi phase from being segregated. Al-Bi immiscible alloy is effectively fabricated with dispersed fine second phase droplets by the addition of Ti. For the Al-Bi alloy, the coarse and non-uniform distribution of Bi-rich droplets can be easily broken. The improvement in the wear resistance of Al-Bi immiscible alloy by adding Ti can be attributed not only to the dispersion and size of the Bi soft phase but also to the in-situ formation of Al3Ti compounds. The addition of Ti is effective for refining the microstructure and improving the wear properties, which simultaneously improves the practical applications of self-lubrication bearing material with low coefficient of friction i.e., reducing the energy loss.