The present study was performed on A356 alloy [Al-7 wt %Si 0.0.35 wt %Mg]. To that La and Ce were added individually or combined up to 1.5 wt % each. The results show that these rare earth elements affect only the alloy melting temperature with no marked change in the temperature of Al-Si eutectic precipitation. Additionally, rare earth metals have no modification effect up to 1.5 wt %. In addition, La and Ce tend to react with Sr leading to modification degradation. In order to achieve noticeable modification of eutectic Si particles, the concentration of rare earth metals should exceed 1.5 wt %, which simultaneously results in the precipitation of a fairly large volume fraction of insoluble intermetallics. The precipitation of these complex intermetallics is expected to have a negative effect on the alloy performance.

This paper presents a thorough study on the effect of rare earth elements, specifically La and Ce, on the microstructure characteristics of non-modified and Sr-modified A356 and A413 alloys. Several alloys were prepared by adding 1% La and 1% Ce either individually or in combination. Microstructural characterisation was carried out using optical microscopy, scanning electron microscopy and electron probe microanalysis as well as differential scanning calorimetry (DSC) analysis. The results showed that the individual and combined additions of La and Ce did not bring about any modification or even refinement in the eutectic Si structure. Moreover, these additions were found to negate the modification effect of Sr, particularly in the presence of La. The A356 and A413 alloys containing La and/or Ce displayed high phase volume fractions owing to the formation of Al–Si–La/Ce/(La,Ce) and Al–Ti–La/Ce intermetallic phases. DSC analysis revealed that the formation temperatures of these phases varied from 560 to 568 °C and 568 to 574 °C, respectively. This analysis also showed that the addition of La and Ce whether individually or in combination resulted in a depression in the eutectic temperature and a considerable increase in the solidification range, particularly for the A413 alloy.

The effect of transition elements, specifically Mn, Cr, V, and Mo, on dispersoid formation and mechanical properties in 6082 aluminum alloy was studied. The elevated-temperature mechanical properties were evaluated based on the compressive yield strength and creep resistance. The results indicated that the addition of Mn to the 6082 alloy resulted in the formation of a large number of the thermally stable α-Al(MnFe)Si dispersoids, thereby significantly improving the elevated-temperature mechanical properties of the alloy. Subsequent additions of Cr, V, and Mo increased the amount of Mn-bearing intermetallic phases, which decreased the supersaturation levels of Mn and Si in the α-Al, and consequently decreased the volume fraction of the dispersoids. The alloys containing Cr, V, and Mo exhibited similar yield strengths at 300°C and higher yield strengths at room temperature compared to the alloy containing only Mn. The size effect of the smaller dispersoids containing Cr, V, and Mo together with the solid-solution hardening of these elements could balance out the strength decrease resulting from the decreased volume fraction of the dispersoids. The additions of Cr, V, and Mo significantly increased the creep resistance of the Mn-containing 6082 alloy. Vanadium induced the highest creep resistance followed by Cr and Mo. Solute atoms of these elements with low diffusivity in the aluminum matrix contributed significantly to increasing the creep resistance at 300°C.