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The effects of additions of nickel to magnesium over the composition range from 0 to 40.41 and of copper, aluminium, and tin to magnesium by 15.10%, 18.40%, and 21.40%, respectively, on the internal friction and Young's modulus have been investigated by use of the flexural vibration method at room temperature. It was generally found that the Mg-Mg2Ni hypo-eutectic alloy samples had the well-defined amplitude-dependence of internal friction which resulted in a very high damping capacity at higher stress levels. The damping capacity of the eutectic and hyper-eutectic samples of the Mg-Mg2Ni alloy and also of the hypo-eutectic samples of the Mg-Mg2Cu, Mg-Mg17Al12, and Mg-Mg2Sn alloys was not so high as that of the hypo-eutectic samples of the Mg-Mg2Ni alloy. The effects of the size and shape of the magnesium phase, the solubility of the alloying elements in magnesium and the grain size on the behaviour of internal friction and Young's modulus were examined and discussed. The results were explained in terms of the vibrating string model of the dislocations in magnesium which were pinned weakly by impurity atoms. It is concluded that the very small solubility of nickel in magnesium and the dendritic or globular shape of the primary magnesium in the Mg-Mg2Ni hypo-eutectic samples are responsible for the much lower breakaway stress than that in other alloys and pure magnesium samples.

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