Abstract
Three transient and one stable phase precipitate sequentially during isochronal annealing 30K/30 min and 20K/20 min in solution heat-treated Mg4Tb2Nd and Mg3Tb2Nd alloys (nominal composition in wt.%). The precipitation of the transient phases is characterized by measurable heat release. Quenched-in vacancies bond to Tb and/or Nd atoms up to 120 °C probably contribute to relatively well-developed early precipitation stages. The dense triangular arrangement of the coherent D0₁₉ phase plates is responsible for the peak age hardening observed after annealing up to ∼ 220 °C – 270 °C. The peak hardening temperature depends on solute concentration and on solution heat treatment conditions. Following loss of particle coherency during a sequent precipitation of β₁ (fcc structure, lattice parameter a = 0.74 nm) and β (fcc structure, Mg₅Gd-type) phases leads to developing of open volume defects at matrix-precipitate interfaces.

Key words
Mg alloys, electrical resistivity, DSC, TEM, positron annihilation spectroscopy

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