Abstract
Although fluorescent X-ray analysis of a variety of elements in aluminum alloys have been reported, little is known about magnesium analysis. This is because of anomalous behavior of this element under conventional technique and thus an individual calibration curve is necessary for each alloy type. An investigation of the effect of the coexisting heavy elements was intended since the MgKα line (9.89 Å) is easily absorbed by such elements. Zinc (16%), copper (15%) and nickel (13%) were chosen as examples of the coexisting elements because they are often contained in commercially available aluminum alloys at higher concentrations.
Measurements were made for the MgKα intensities from aluminum alloys containing 110% Mg. The relationship between the Mg concentration and the MgKα intensity in Al-Mg binary alloy was linear within the above Mg concentration range. However, the MgKα intensity decreased upon the presence of the heavy metals (See Fig. 1 for Al-Mg and Al-Mg-Zn alloys). This is apparently due to an absorption of the fluorescent X-ray by the heavy metals. Therefore, Matsumura's equation and Andermann's equations were used and the reported values of the mass absorption coefficients were introduced in order to correct the absorption. The results, however, were unsatisfactory except those for Zn; the magnitude of correction was too large for the Al-Mg-Cu and Al-Mg-Ni alloys, whereas the corrected MgKα intensity from Al-Mg-Zn alloys agreed with that from Al-Mg alloys (See Fig. 2 for Al-Mg-Cu alloys). This is presumably due to an inaccuracy of the mass absorption coefficients for Cu and Ni because the equation successfully corrected the absorption by Zn which is the adjacent element to Cu and Ni on the periodic table. Incidentally, the mass absorption coefficients at 9.89 Å calculated from our experimental results were 34703950 and 31603100 for Cu and Ni, respectively, while the values obtained by an interpolation of the reported coefficients were 5800 and 5400.
Correction without using the mass absorption coefficients was then intended. A correction equation (eq. 7), composed of weight fractions of the absorbing components and constants, was deriven from Beattie's equations. This equation is convenient for the practical analytical work (The weight fractions of the absorbing heavy metals can be easily determined by an X-ray fluorescent analysis). An assumption, verified by experiments, was made in order to derive the equation. It is based on the fact that major component of the sample is aluminum and that the difference between the mass absorption coefficients of Al and Mg, (μAl-μMg), is much smaller than (μZn-μMg), (μCu-μMg) and/or (μNi-μMg). The constants were calculated from the experimental results. The equation thus determined was successfully applied for the analysis of multi-component commercial alloys. Addition of another correction term was recommended when more than 2% of Fe is present.
