In the present paper, the possibility of occurrence of HDDR (hydrogenation disproportionation desorption recombination) phenomena were studied in an Au-2 mass%Mg alloy. Cathodic hydrogen-charging at R.T. in the alloy resulted in causing disproportionation reaction which formed MgH2 embedded in an Au matrix. After the heat-treatment in vacuum for 4 h at 500°C, MgH 2 decomposed into Mg and hydrogen. Mg resolved into Au matrix phase again. The original Au-Mg solid-solution alloys with size of 20-100 nm fine grains were obtained. This is the first observation of occurrence of HDDR phenomena in the Au-Mg alloys. The HDDR treated sample shows the slightly higher hardness in comparing with those of as-quenched samples.
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