25Mg NMR site analysis in metals and intermetallics

Nuclear magnetic resonance (NMR) of the low abundance and low gyromagnetic ratio isotope 25Mg, I=5/2, 2.606 MHz/T, 10% abundant, is shown here to provide an informative probe for phase identification, site symmetry and site multiplicity of the intermetallic compounds which occur as strengthening precipitate phases in lightweight alloys. The intermetallics discussed here, Mg17Al12, MgZn2, Mg2Al3 and Al2CuMg, are the final equilibrium precipitate phases in a number of Mg- and Al-based heat-treatable alloys. The 25Mg spectra of Mg in Al-10 at%Mg alloy show the progressive precipitation of Mg2Al3 from Mg in solid solution as a function of annealing time at 150 °C. Also reported are 25Mg spectra for CuMg2, Mg44Al15Zn41 and Mg2Sn, along with the counter atom 67Zn and 63Cu NMR spectra for MgZn2 and CuMg2. All spectra are simulated to determine nuclear interaction parameters and confirm site occupancy.