Microstructure and properties of additively manufactured Al-Ce-Mg alloys

Surface Defect Mitigation of Additively Manufactured Parts Using Surfactant-Mediated Electroless Nickel Coatings

The emergence of defects during the early production phases of ferrous-alloy additively manufactured (AM) parts poses a serious threat to their versatility and adversely impacts their overall mechanical performance in industries ranging from aerospace engineering to medicine. Lack of fusion and gas entrapment during the manufacturing stages leads to increased surface roughness and porosities in the finished part. In this study, the efficacy of employing electroless nickel-boron (Ni-B) deposition to fill and level simulated AM defects was evaluated. The approach to levelling was inspired by the electrochemical deposition techniques used to fill vias in the electronics industry that (to some extent) resemble the size and shape of AM-type defects. This work investigated the use of surfactants to attenuate surface roughness in electroless nickel coatings, thereby achieving the preferential inhibition of the coating thickness on the surface and promoting the filling of the simulated defects. A cationic surfactant molecule, CTAB (cetyltrimethyl ammonium bromide), and a nonpolar surfactant, PEG (polyethylene glycol), at different concentrations were tested using a Ni-B electrolyte for the levelling study. It was found that the use of electroless Ni-B to fill simulated defects on ferrous alloys was strongly influenced by the concentration and nature of the surfactant. The highest levelling percentages were obtained for the heavy-molecular-weight PEG-mediated coatings at 1.2 g/L. The results suggest that electroless Ni-B deposition could be a novel and facile approach to filling defects in ferrous-based AM parts.

Comparing evolution of precipitates and strength upon aging of cast and laser-remelted Al-8Ce-0.2Sc-0.1Zr (wt.%)

The microstructural evolutions, upon solidification and subsequent aging, and associated hardening effects for both cast and laser-surface-remelted Al-8Ce-0.2Sc-0.1Zr (wt.%) hypo-eutectic alloy are investigated with focus on precipitation and coarsening behavior of their Al₁₁Ce₃ and L1₂-Al₃(Sc,Zr) precipitates. Laser surface remelting, which produces solidification conditions typical of additive manufacturing (AM) processes, suppresses formation of undesirable primary Al₁₁Ce₃ and Al₃(Sc,Zr) precipitates on solidification. It also greatly refines the interlamellar spacing of the eutectic Al₁₁Ce₃ phase, thus enhancing the Orowan strengthening effect as compared to the cast alloy, beyond the load-transfer effect from the Al₁₁Ce₃ phase. Subsequent aging at 325 °C leads to further hardening of both alloys due to secondary Al₃(Sc,Zr) nanoprecipitation, with much more pronounced hardness increases in the laser-remelted alloy, owing to a higher number density of finer Al₃(Sc,Zr) nano-precipitates, as compared to the cast alloy. This improvement is rationalized by an enhancement of Al₃(Sc,Zr) nucleation rate upon aging of laser-remelted alloy, as compared to the cast alloy, considering differences in elemental supersaturation within the α-Al regions of these alloys. Prolonged aging, up to 1000 h, at 325 °C causes the hardness of both alloys to decline relatively slowly, implying that this alloy is suitable for AM processes and subsequent applications where high strength and good heat resistance are needed.