Abstract
The structural ageing process of lead–0.4 wt% magnesium alloy at room temperature has been examined by means of various X-ray diffraction methods. Results obtained are as follows: (1) It has been confirmed from Laue photographs of single-crystalline specimens and small-angle scatter photographs of polycrystalline specimens that G.P. zones are formed in the early stage of ageing at room temperature. Distribution of solute atoms inside G.P. zones seems to be initially disordered and ordered after ageing. (2) The shape of the zones is plate-like, being formed on {100} planes of matrix lead solid solution. (3) From the Debye-Scherrer photograph of the polycrystalline specimens which had been aged for a long time (3500 hr), it has been shown that the stable phase Mg2Pb is formed in the prolonged stage of ageing at room temperature. The Laue photographs obtained for the single-crystalline specimens in this stage of ageing can be well explained by the following orientation relationships between the matrix Pb lattice and the stable precipitate Mg2Pb lattice: (100)Pb⁄⁄(001)Mg2Pb and [110]Pb⁄⁄[010]Mg2Pb.
