Three-dimensional size and orientation of the precipitates in AZ91 magnesium alloys measured by TEM techniques

Knowledge of the microscopic structure, including three-dimensional(3-D) size and orientation of the precipitates, is essential tofully understand the mechanical properties of the magnesiumalloys and designing the alloys with better performance. AnalyticalTEM with high spatial resolution offers the simultaneousmeasurements of 3-D size, structure, orientation, composition of theprecipitates from one typical sample along an establishedcrystallographic axis. Besides popular Burgers orientationrelationship (OR), other ORs such as Pitsch--Schrader OR, CrawleyOR, Potter OR and a new OR with the form of [0001]_α 1.0° from [311]_γ and (11bar 20)_α 2.0° from (03bar 3)_γ between the magnesiummatrix and the precipitate γ -Mg₁₇Al₁₂ areidentified by TEM imaging and diffraction techniques. As a case study,the thicknesses of the individual precipitates with Burgers OR arefurther measured to be 100--200~nm through both electron energy-lossspectroscopy and x-ray energy dispersive spectroscopy combiningdifferential x-ray absorption and extrapolation, which are inagreement with the overall 3-D size statistic distribution resultsobtained through analysing various samples along various directions.Furthermore, the fabricated wedge-shape structure provides aplatform on which to study the dependence of the interfacial strain on thevariation of the thickness.