Reversion after ageing in an Mg–Y–Gd–Zr alloy

• Published in: Journal of alloys and compounds Vol. 635; pp. 173 - 179
• Main Authors: Lukyanova, E.A., Rokhlin, L.L., Tabachkova, N.Yu, Dobatkina, T.V., Nikitina, N.I.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 25.06.2015
• Subjects: Age hardening; Aging; Annealing; Decomposition; Magnesium; Magnesium alloys; Magnesium base alloys; Precipitation; Rare earth metals; Reversion; Softening; Solid solution decomposition; Solid solutions; Rare earth metals; Solid solution decomposition; Reversion; Magnesium alloys; Age hardening
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2015.02.115

•The ageing behaviour of the hot deformed Mg–Y–Gd–Zr alloy was investigated.•In the peak-aged Mg–Y–Gd–Zr alloy the reversion after ageing was observed.•The reversion is caused by the dissolution of the precipitates formed during ageing.•The reversion phenomenon is accompanied by softening of the Mg–Y–Gd–Zr alloys. Decomposition of the magnesium supersaturated solid solution during ageing and reversion after ageing in the commercial wrought magnesium alloy containing two rare earth metals (Mg–4.7%Y–4.6%Gd–0.3%Zr (wt.%)) were investigated using Brinell hardness, electrical resistivity measurements and transmission electron microscopy observation. The Mg–4.7%Y–4.6%Gd–0.3%Zr (wt.%) alloy is significantly hardened during ageing in the hot extruded condition owing to the decomposition of the magnesium supersaturated solid solution. The decomposition process in the alloy has been found to consist of precipitation sequence: β″(D019)→β′(cbco)→β(bcc). The maximum hardness is achieved after ageing at 200°C, 64h and caused by precipitation of the metastable β′(cbco) phase. It has been found that the Mg–4.7%Y–4.6%Gd–0.3%Zr (wt.%) alloy tends to the reversion after ageing when is subjected to annealing at temperatures higher than the ageing temperature. Dependence of the reversion after ageing on the annealing temperature and time has been established. During the reversion treatment the dissolution of the precipitates occurs, which leads to the softening of the alloy. The reversion effect increases with increasing annealing temperature.