The impact of Ce-containing precipitates on the solidification behavior, microstructure, and mechanical properties of Al-6063

The present study investigates the effects of 1.0 wt% cerium (Ce) addition on the solidification behavior, microstructure, and mechanical properties of 6063 aluminum alloy. Thermal analysis exhibited four reaction points during the solidification of the reference 6063 alloy corresponding to the formation of α-Al, Al13Fe4, α-AlFeSi, and Mg2Si, respectively. Similar reactions were also observed for the Ce-modified alloy along with two additional reactions corresponding to the formation of Al-Ce and Al-Si-Ce precipitates. Microstructure examination revealed a grain size reduction of 25% due to Ce addition. In regards to the formed phases, the addition of Ce caused the formation of both Al-Ce and iron-free Al-Si-Ce precipitations. This suggested that the Si consumed during the formation of Al-Si-Ce precipitates was at the expense of Mg2Si rather than the silicon contained in Al-Fe-Si compounds. As for the mechanical properties, Vickers hardness measurements for samples in the T6 condition revealed an increase, in comparison to the as-cast condition, by 83% and 40% for the reference and Ce-modified alloys, respectively. The lower strengthening for the Ce-modified alloy was attributed to the less availability of Mg2Si due to silicon depletion. Compression test results for samples in the T6 condition exhibited a decline of both the yield and ultimate strength for the Ce-modified alloy, in comparison to the reference alloy. This was also attributed to the silicon depletion due to the formation of Al-Si-Ce precipitates, which impaired the precipitation hardening process.