Hydride formation and its impact on SPS magnesium alloys with yttrium and neodymium

Gas-atomised binary magnesium alloys Mg-2wt.% Nd (N2) and Mg-4wt.%Y (W4), derived from the WE43 system, were consolidated using spark plasma sintering (SPS) at temperatures between 450 and 550 °C. The influence of sintering temperature on the microstructure, mechanical properties, and corrosion behaviour was systematically investigated. Both alloys achieved nearly full densification (<0.1% residual porosity). TEM analyses confirmed the presence of fine hydrides (NdH 2 or YH 2 ) and oxides (Nd 2 O 3 or Y 2 O 3 ) as the dominant secondary phases. Increasing sintering temperature promoted secondary phase coarsening and alloying-element segregation at former powder particle boundaries, while grain growth remained limited (14 – 19 µm). The mechanical response showed a decrease in compressive yield strength from 132 MPa at 450 °C to 112 MPa at 550 °C for both alloys, primarily due to grain coarsening, reduced precipitation strengthening, and lower dislocation density. Corrosion performance revealed opposing trends between the alloys: N2 compacts exhibited the lowest corrosion rates at 450 and 500 °C, whereas W4 compacts showed improved stability only at 550 °C due to the formation of protective Y-enriched oxide layers of former powder particles. The results highlight the key role of hydride and oxide phase evolution during SPS in governing both mechanical and corrosion behaviour of low-rare-earth Mg alloys. • Spark plasma sintering of gas-atomised Mg-2wt.% Nd (N2) and Mg-4wt.% Y (W4) alloys achieved nearly full consolidation while preserving the powder microstructure. • Sintered compacts contained only hydrides (NdH 2 /YH 2 ) and oxides (Nd 2 O 3 /Y 2 O 3 ), highlighting the crucial role of hydrogen uptake during powder atomisation. • Both alloys exhibited similar compressive yield strength, which decreased with increasing sintering temperature due to microstructural coarsening and reduced hydride particle density. • Corrosion behaviour was strongly influenced by the interaction between hydride formation and the stability of the surface corrosion layer. • N2 alloys sintered at 450-500 °C showed the best corrosion resistance, forming compact protective layers, while W4 alloys experienced severe degradation at lower temperatures but partial protection at 550 °C due to yttrium segregation and Y-enriched oxide layer formation.