Variation of microstructure of RE-containing AlSi20Cu2Ni1RE0.6 alloy with different cobalt contents

Cobalt is generally considered as the element that can promote the high-temperature mechanical properties of Al–Si alloys. In order to develop new hypereutectic Al–Si alloys that can be used at high temperature, the changes of microstructure of Al–20Si–2Cu–1Ni–0.6RE–xCo alloy with different contents of Co were studied in this paper. The results show that, under P–RE complex modification of the alloy melt, the content of Co varying from 0 to 1.5% had little influence on the refining effect of primary Si and modification effect of eutectic Si, but the amount of acicular RE-bearing Al–RE–Ni–Co–Si compounds gradually increased with the increase of Co content. In addition, Co could also modify the morphology of Fe-bearing phases, which solidified as particles instead of long needles. The addition of Co even has an adverse effect on the tensile strength of this RE-containing hypereutectic Al–Si alloy.

Research highlights▶ In this manuscript, the changes of microstructure and mechanical property of Al–20Si–2Cu–1Ni–0.6RE alloy with different Co contents were firstly studied. ▶ The microstructure and compositions of Co-containing phases were also characterized by optical microscopy, electron microscopy, and energy dispersive X-ray spectrometer. ▶ The results show that, under P–RE complex modification of the alloy melt, the content of Co varying from 0 to 1.5% has little influence on the refining effect of primary Si and modification effect of eutectic Si, but the amount of acicular RE-bearing compounds gradually increases with increase of Co content. ▶ In addition, Co could also modify the morphology of Fe-bearing phases, which solidified as particles instead of long needles. ▶ The addition of Co even has an adverse effect on the tensile strength of this RE-containing hypereutectic Al–Si alloy.