The influence of La and Ce additions on the solidification of alloys from the Al–Fe system

Abstract

Aluminium alloys are popular in modern applications due to their lightweight, high strength and ductility. Alloys in the 8xxx series have similar properties to those in the 1xxx series, but are stronger, are more malleable and have higher stiffness. The addition of rare earths (RE) can refine the as-cast microstructure and, as a result, can increase the corrosion resistance and mechanical properties of aluminium alloys at room and high temperatures. The effects of rare earth (Ce and/or La) additions to Al-1.4Fe alloys were investigated. Thermal analysis of the solidification behaviour of the reference alloy showed the occurrence of three reactions corresponding to the formation of α-Al, eutectic (α-Al + AlxFey) and Fe intermetallics, respectively. The results showed similar reactions for the Ce- and/or La-modified alloy, but at slightly different temperatures, indicating a change in the forming phases due to the addition of Ce and/or La. In all cases, the microstructures were typically hypoeutectic, consisting of the primary α-Al and the eutectic (α-Al + AlxFey). The effect of grain refinement of the primary α-Al grains of the as-cast alloy was observed by the addition of RE, while La showed the strongest effect. The effect of the RE additions showed no obvious differences in the morphology of the eutectic AlxFey, although they were present in these phases. When Ce and/or La were added, (α-Al + Al11Ce3) and/or (α-Al + Al11La3) eutectics were formed, while Fe was not detected in these eutectics.