The Use of Rare Earth Metals in Al-Si-Cu Casting Alloys

In the current study, a series of forty-two cast Al-Si-Cu-Mg -based alloys with additions of transition metals (V, Cr, Ni) and rare earth (RE) metals (La, Ce) were prepared and mechanically tested in the as-cast, T5, T6 and T7 heat treatment conditions. The microstructures were investigated using optical microscopy, scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). The volume fraction, aspect ratio, and roundness of second phase constituents were determined by ImageJ analysis software. The microstructural observations show that the RE elements have a greater impact on the microstructure of cast alloys, resulting in the formation of new types of intermetallic phases containing RE, Al-Si-Cu-RE and Al-Ti-RE. With regard to the mechanical properties, it was found that the highest strength of the casting alloys was found with 0-0.2 wt% addition of Ce/La. However, the addition of more than 0.2 wt% induced a detrimental effect on the mechanical properties due to precipitation of a high volume fraction of insoluble intermetallic compounds containing RE. Excessive addition of RE elements leads to the formation of a coarse intermetallic compound along the grain boundary. Besides, RE elements have a marginal modification effect in terms of changing the morphology of the eutectic Si particles.