Rapid Assessment of Hardening Behavior of Al-Ce-Mg Ternary Alloys Enabled by Directed-Energy Deposition

Abstract

Al-Ce-based alloys are promising candidates for additive manufacturing (AM) due to their hot cracking resistance and because they do not require heat treatment to obtain precipitation strengthening. The rapid solidification characteristic of AM can lead to enhanced mechanical properties; however, the strengthening mechanisms over large composition ranges are unclear. Here, combinatorial synthesis by directed-energy deposition (DED) and hardness measurements were used to rapidly map the composition-dependent strength of the ternary Al-Ce-Mg system. Tensile testing and microstructure characterization of selected compositions were performed to elucidate the compositional dependence of the strengthening mechanisms. Al11Ce3 precipitates were present in all cases, and the maximum hardness (1.25 GPa) was measured for the Al-8Ce-10Mg composition. A combination of (i) Hall-Petch strengthening, based on the FCC matrix phase cell size; (ii) precipitation strengthening, based on Al11Ce3 volume fraction and size; and (iii) solid solution strengthening, based on Mg composition of the matrix phase, were used to account for the measured strengths. Hardness is shown to correlate well with ultimate tensile strength in alloys with substantial work-hardening, highlighting the value of surface-based techniques for rapid screening.

Keywords: Al-Ce alloys, Directed energy deposition, combinatorial approach, additive manufacturing, mechanical properties