Effect of rare earth element Ce on hot tearing susceptibility of Al-Si-Mg alloy

Abstract

Al-Si-Mg alloys exhibit significant application potential in aerospace, automotive, and power transmission fields due to their low density and favorable combination of properties. To investigate the effects and mechanisms of cerium (Ce) on the hot tearing susceptibility (HTS) of these alloys, a series of Al-1.5Si-0.35Mg-xCe, A356-xCe, and Al-ySi-0.35Mg alloys were prepared using a constrained rod casting (CRC) mold. The microstructure, solidification parameters, and hot tearing fracture surfaces were characterized via optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and focused ion beam (FIB) techniques. The results indicate that: (1) The HTS of the Al-1.5Si-0.35Mg alloy increased with Ce additions of 0.1–0.5 wt.%, peaking at a value of 71 with 0.3 wt.% Ce. This increase is attributed to an expanded solidification temperature range (ΔT), earlier dendrite coherency, and the formation of plate-like phases oriented vertically at grain boundaries, which impeded interdendritic liquid feeding. (2) In contrast, although the addition of 0.1–0.5 wt.% Ce to A356 alloy also widened the ΔT and raised the dendrite coherency temperature (T_DCP), it concurrently refined the secondary dendrite arm spacing (SDAS). Moreover, the relatively high eutectic Si content in A356 provided sufficient liquid for crack healing, resulting in no observed hot tearing in any A356-xCe alloys. (3) For Al-ySi-0.35Mg alloys, HTS decreased monotonically with increasing Si content (1.5–7.0 wt.%). This reduction is ascribed to the enhanced crack-healing capacity of the eutectic Si phase and a general decreasing trend in both the ΔT and T_DCP at higher Si levels. Collectively, these findings provide a foundation for rationally determining processing parameters and optimizing the castability of Al-Si-Mg alloys.