Inclusions in aluminum alloy can markedly affect thequality of the alloy. Therefore, several techniques ofthe treatment for cleaning of the molten aluminumalloy have been developed: e.g., chlorination, fluxtreatment, gas bubbling1, filtration2 and the combina-tion of the last two techniques. The evaluation of thesecleaning processes and the analysis of inclusions are ofsupreme importance. Therefore, several methods, e.g.,filtration3,4, centrifugation5,6, electric resistance7,8, ultra-sonic inspection9, etching or dyeing for microscopy10

and selective dissolution11, have been investigated forsuch evaluation. However, these methods can giveonly qualitative information or total mass concentrationof inclusions, but no quantitative evaluation of individ-ual compounds. Inclusions in molten aluminum alloydepend on its composition, used scrap, used cleaningprocess and its operational conditions, etc. Problemsdue to inclusions may be found by a user later on.Although simple and rapid methods for quantitativedetermination of individual compounds of inclusionsare necessary for avoiding troubles due to inclusionsand also for evaluating the used cleaning process, suchmethods are not found in the literature.

Glass cloth filters are used before casting for theremoval of inclusions in molten aluminum alloy. Thisfilter is replaced with a new one for each casting. Theinclusions collected on the filters without any addition-al apparatus will reflect the overall efficiency of themetal cleaning processes used and must have informa-tion on their sources. In the present report, an X-raydiffraction (XRD) method with selective dissolution ofmetallic aluminum has been developed for the determi-nation of inclusions collected on the filters, and suc-cessfully applied to the determination of spinel(MgAl2O4), periclase (MgO) and aluminum carbide,which were detected in an aluminum-magnesium alloy.

Experimental

Samples, reagents and filtersSamples were collected on glass cloth filters, so-

called “spout socks”, which were located at the inlet ofa mold during casting of the aluminum-magnesium5052 alloy, as shown in Fig. 1. The material collectedby the filter was cut to the size smaller than 3 mm witha nipper for the homogenization and ease of chemicaltreatment.

The following standard powders were used for recov-ery tests and the preparation of standard samples for theXRD determination: Spinel powder of 99.9% purity(Taimei Chemical, Nagano, Japan; aggregates of about1 mm particles, mainly 5 – 10 mm); periclase fine pow-der (1 – 15 mm, mainly 5 – 10 mm) which was preparedby pulverizing and sieving through a 20 mm sieve from100 – 200 mesh powder of 99% purity prepared byfusion (Soekawa Chemical, Tokyo, Japan); aluminumcarbide powder of 98% purity (Soekawa Chemical;aggregates of <=1 mm particles, mainly 5 – 10 mm).Reagents used for selective dissolution were of analyti-cal-reagent grade.

Hydrophilized poly(tetrafluoroethylene) membranefilters (Millipore, Omnipore JH, 0.45 mm in pore size,25 mm in diameter) were used for filtering off theresidue after the selective dissolution and as a support

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1998 © The Japan Society for Analytical Chemistry

Notes

Determination of Inclusions in Molten Aluminum Alloy by X-RayDiffractometry after Selective Dissolution

Masaaki IWATSUKI*, Shintaro NISHIDA* and Teruo KITAMURA**

*Department of Applied Chemistry and Biotechnology, Faculty of Engineering, Yamanashi University,Takeda, Kofu 400–8511, Japan

**Research and Development Department, Showa Aluminum Corporation,Kaisan-cho, Sakai, Osaka 590–8576, Japan

Keywords Inclusion, aluminum alloy, X-ray diffractometry, selective dissolution, glass cloth filter

Fig. 1 Schematic diagram of mounting of glass cloth filters.

for XRD measurements.

ApparatusA Rigaku X-ray diffractometer with a copper tube

and nickel filter was operated at 35 kV and 16 mA. Athin-layer specimen was inserted between a standardaluminum holder of 50´35´1.5 mm with a square aper-ture of 20´16 mm and a thin aluminum plate of35´28´0.4 mm with a round hole of 23 mm in diame-ter.

Recommended proceduresIn order to remove metallic aluminum, 0.8 g of the

sample is weighed out into a 200-ml beaker, 75 ml ofmethanol is added and the mixture is heated to 35°C ona hot plate. After 2.0 ml of bromine is added, theresulting solution is agitated by ultrasonication andkept at 35 – 45°C. After 15 min, additional 1.0 ml ofbromine is added, and the resulting solution is treatedin the same manner. Forty-five minutes after the firstaddition of bromine, the residue is filtered off through amembrane filter and washed with methanol until thebromine color disappears.

Integrated intensities of strong and non-overlappingdiffraction lines of the compounds in the residue, e.g.,(4 0 0) or (4 4 0) diffraction of spinel, (2 0 0) or (2 2 0)of periclase, (0 0 15–– ) of aluminum carbide, etc., aremeasured. The amounts of the compounds are deter-mined from working curves, which are obtained by thesame measurements of the standard samples preparedby filtrating the suspensions containing differentamounts between 0 and 1 or 2 mg of their standardpowders in methanol through the membrane filters.

Results and Discussion

Dissolution of metallic aluminumIt has been found that metallic aluminum in the filter

collection can be practically dissolved by thebromine–methanol treatment within 45 min by cutting itto the size smaller than 3 mm and by adding dividedvolumes of bromine twice under ultrasonication, asshown in Fig. 2.

XRD qualitative analysis of the residueFigure 3 shows the XRD pattern of the residue

obtained from a filter collection of a molten aluminumalloy containing magnesium. Spinel, periclase and alu-minum carbide were identified from the pattern.

Recovery testsStandard powders of 3.0 mg each were treated sepa-

rately in the same manner as the recommended proce-dure and the residues were weighed, as shown in Table1. Recoveries of these powders on the bromine–methanol treatment were 94 – 96%, except for fine peri-clase powder whose recovery was 89%. This suggeststhat very fine particles of periclase may be lost duringthe treatment, but coarse particles which strongly affectthe quality of alloys can be recovered.

Working curvesTable 2 shows that linear working curves of spinel,

periclase and aluminum carbide were obtained withgood precisions.

Analysis of real samplesSpinel, periclase and aluminum carbide in the

618 ANALYTICAL SCIENCES JUNE 1998, VOL. 14

Fig. 2 Relation between treatment time and residue.

Fig. 3 X-Ray diffraction pattern of the residue after bromine–methanol treatment. AC: aluminum carbide; Sp: spinel; Pe:periclase.

Table 1 Recoveries of standard powders on bromine-methanol treatment

Standard powder n

Spinel 5 96.2 2.2Periclase (100 – 200 mesh) 4 94.2 2.9 (fine) 4 88.9 0.4Al4C3 5 94.9 1.1

Recovery, %

Av. s

residues after the bromine–methanol treatment of realsamples of about 0.8 g were repeatedly determined bythe present method. These compounds of 0.07, 0.08and 0.20%(m/m), respectively, were found in the filtercollection, together with satisfactory results of a stan-dard addition test, as shown in Table 3. Concentrationsof inclusions in the molten aluminum alloy can be cal-culated from these results by multiplying the ratio ofthe total amount of the sample in the spout socksagainst that of the molten aluminum passed through thespout socks.

In summary, an X-ray diffractometric method hasbeen developed for the determination of inclusions,e.g., spinel (MgAl2O4), periclase (MgO) and aluminumcarbide, which were collected on a glass cloth filter inmolten aluminum alloy just before casting. The pro-posed method can give useful data for the evaluationsof the quality of the obtained ingot and of the usedcleaning process.

References

1. Y. Ohno, D. T. Hampton and A. W. Moores, Light Metals,1993, 915.

2. J. E. Dore and J. C. Yarwood, Light Metals, 1977, 171.3. N. J. Keegan and J. M. McCollum, Light Metals, 1992,

1085.4. R. B. Blackburn, Aluminium, 56, 585 (1980).5. F. R. Mollard, J. E. Dore and W. S. Peterson, Light Metals,

1972, 483.6. C. J. Simensen, Metallurgical Trans., 12B, 733 (1981).7. C. Dupuis and R. Dumont, Light Metals, 1993, 997.8. J.-P. Martin and F. Painchaud, Light Metals, 1994, 915.9. T. L. Mansfield, Light Metals, 1984, 1085.

10. S. Masiyama, K. Arai, T. Onishi and M. Goto, Keikinzoku(J. Jpn. Inst. Light Metals), 25, 129 (1975).

11. C. J. Simensen and G. Strand, Fresenius’ Z. Anal. Chem.,308, 11 (1981).

(Received November 4, 1997)(Accepted March 12, 1998)

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Table 2 Working curves of spinel, periclase and aluminum carbide

Diffraction line Equationa Correlation factor s(x)/mg

Spinel (4 0 0) y=26.4x–0.69 0.996 0.013 Periclase (2 0 0) y=77.7x+5.7 0.995 0.029 Al4C3 (0 0 15) y=10.3x–0.12 0.997 0.012

a. y, integrated intensity /cps·deg; x, content /mg.

Table 3 Determination of spinel, periclase and aluminum car-bide in filter collection

Sampletaken/g

0.798 0.60 0.68 1.6 0.075 0.085 0.200.801 0.59 0.66 1.5 0.074 0.082 0.190.808 0.57 0.66 1.7 0.071 0.082 0.210.804 0.56 0.65 1.5 0.070 0.081 0.190.797 a 0.58 0.67 1.5 0.073 0.084 0.19

Av. 0.57 0.66 1.6 0.073 0.083 0.20 s 0.01 0.01 0.1 0.002 0.002 0.01

Content,%(m/m)Found/mg

MgAl2O4 MgO Al4C3 MgAl2O4 MgO Al4C3

a. Standard powders of spinel and aluminum carbide of 0.50 mg each were added and the corresponding values were subtracted from the analytical results.