X-ray and electrical resistivity studies of a silver-magnesium alloy containing 25 atomic per cent, of magnesium are described. From the results, it is concluded that a superlattice exists at this composition, the order-disorder transformation occurring between 386 and 389 O C .

SummaryMatthiessen's rule has been tested by, determining the slopes of the electrical resistivity-temperature curves for wires of eight common metals and alloys in various states of deformation by wire-drawing. The results show that the slope is independent of deformation, i.e. the rule is true, to within 0·5 per cent. for nickel, copper (two purities), iron, and 80/20 brass, and to within 1 per cent. for aluminium. However, for 75/25 brass and an aluminium bronze, deformations corresponding to logarithmic strains of 2·3 decrease the slopes by 1 and 3 per cent. respectively. As an explanation of this behaviour, it is suggested that deformation causes an increase in the characteristic temperature.

Efforts were undertaken jointly between PCC Airfoils and PCC Structurals Division to simulate solidification conditions and predict the occurrence of shrinkage and microporosity defects in Alloy 7 18 structural castings. The approach used finite element thermal analysis validated by experiments.An engine rail was selected as the demonstration part. A finite element thermal model was used to generate data on solidification conditions (i.e., solidification sequence, isochron, temperature gradient (G) and solidification rate (R)). A baseline condition was first established by matching model-predicted shrinkage locations with known inspection results for actual gating and casting conditions. A second model was then built for a casting with a different gating system to predict shrinkage locations prior to inspection. It was found that the shrinkage locations predicted by the second model match reasonably well with casting inspection results.