1、Designation: B 953 07Standard Practice forSampling Magnesium and Magnesium Alloys forSpectrochemical Analysis1This standard is issued under the fixed designation B 953; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of la
2、st revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice describes the sampling of magnesium andmagnesium-base alloys to obtain a chill-cast sample suitablefor qu
3、antitative atomic emission spectrochemical analysis. Thedisk in the region to be excited is representative of the melt andgives a repeatability of results that approach that of thereference materials used.1.2 This practice describes the procedure for representativesampling of molten metal.1.3 The va
4、lues stated in SI units are to be regarded as thestandard. The values given in parentheses are for informationonly.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate
5、safety and health practices and determine the applica-bility of regulatory limitations prior to use. Specific precau-tionary statements are given in 5.12. Referenced Documents2.1 ASTM Standards:2E 401 Practice for Bonding Thin Spectrochemical Samplesand Standards to a Greater Mass of MaterialE 1257
6、Guide for Evaluating Grinding Materials Used forSurface Preparation in Spectrochemical AnalysisB 954 Standard Test Method for Analysis of Magnesiumand Magnesium Alloys by Atomic Emission Spectrometry3. Summary of Practices3.1 Molten metal representative of the furnace melt ispoured directly into a s
7、pecified mold (described in 5.2.1)toproduce a chill-cast disk. The disk is machined to a specificdepth that represents the average melt composition and pro-duces an acceptable surface for excitation.3.2 Fabricated, cast, or wrought products may be exciteddirectly without remelting; however, accuracy
8、 of results maysuffer in highly alloyed samples due to the potential forelemental segregation.4. Significance and Use4.1 This practice, used in conjunction with the followingquantitative atomic emission spectrochemical test method,B 954, is suitable for use in manufacturing control, material orprodu
9、ct acceptance, certification, and research and develop-ment.5. Apparatus5.1 Ladle, capable of holding a minimum of 400 g (7.7 oz)of molten metal, with a handle of sufficient length to reach intoa furnace, trough, or crucible sufficiently deep to obtain asample representative of the melt being cast.
10、The ladle may belightly coated with a tightly adhering ladle wash that will notcontaminate the sample. Boron nitride can be applied atelevated temperatures to form a tenacious coating.WarningTrace moisture in the coating or on the tool may causedangerous spattering. Preheat all sampling tools and mo
11、ldsprior to use.5.2 Sample Molds, capable of producing homogeneouschill-cast disks having smooth surfaces, free of surface pocketsand porosity. These castings should have a spectrochemicalresponse similar to the reference materials used in preparingthe analytical curves and must have a repeatability
12、 fromexcitation-to-excitation of no more than 2% relative on majoralloying elements. They must be representative of the melt inthe region excited. Several types of molds have been foundacceptable:5.2.1 Type A, open cavity mold, is shown in Fig. 1. Theadvantage of this mold is its simple design and a
13、bility toproduce a sample disk that can be excited around the entireannular area. Mold dimensions can be modified to produce adisk size ranging from approximately 44 to 64 mm (1.75 to 2.5in.) in diameter by 10 to 15 mm (0.4 to 0.6 in.) in thickness. Acircular central recess 10 to 20 mm (0.4 to 0.8 i
14、n.) in diameter1These practices are under the jurisdiction of ASTM Committee B07 on LightMetals and Alloys and are the direct responsibility of Subcommittee B07.04 onMagnesium Alloy Cast and Wrought Products.Current edition approved June 1, 2007. Published July 2007.2For referenced ASTM standards, v
15、isit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428
16、-2959, United States.on one side of the disk (analytical side) facilitates machining ofthat side in preparation for excitation. It also promotes a moreuniform freezing of the raised peripheral area. The moldmaterial should be mild steel and should weigh approximately2 to 3 kg (4.5 to 6.5 lb).5.2.2 T
17、ype B, center pour mold, is shown in Fig. 2. Theadvantage of this mold is that the sample obtained may beexcited around the entire annular area. This mold produces ahorizontally cast disk with the sprue over the center on thebackside. The mold dimensions are such as to produce a diskapproximately 64
18、 mm (2.5 in.) in diameter by 13 mm (0.5 in.)in thickness. A circular central recess 10 to 13 mm (0.4 to 0.5in.) in diameter on one side of the disk (analytical side)facilitates machining of that side in preparation for excitation.It also promotes more uniform freezing of the raised peripheralarea, b
19、ut the corresponding raised portion of the mold must notbe so large as to restrict the throat for the sprue. A slight taper,1 to 2, on the hinged portion of the mold facilitates openingwhen a disk has been cast. The mold material should be mildsteel and should weigh approximately 3.5 to 4.5 kg (8 to
20、 10 lb).5.2.3 Type U, U-Block mold, is shown in Fig. 3. This sidegated block mold produces a cylindrical block sample ofapproximately 40 mm (1.6 in.) in diameter by 60 mm (2.4 in.)high. The mold is placed on top of a massive 150 mm (5.9 in.)diameter by 50 mm (2.0 in.) thick copper chill plate with a
21、knurled working surface. The mold material is mild steel. Thedownsprue directionally choked side gate promotes a con-trolled fill. The strong directional solidification provided by thechill plate produces a spectrochemically homogenous samplefor at least the first third and usually up to two thirds
22、of thelength of the U-block sample from chill the cast face (Note 1).NOTE 1To improve the performance and durability of the moldsdescribed above, prepare the surface of the mold cavity to minimize theformation of gas pockets on the surface of the castings and to resist rustingof the mold cavity surf
23、ace. To do this, blast the inner surface with a sharpgrit that cuts rather than peens. The resulting finely roughened face isessential for obtaining a smooth and uniform surface on the cast disk.Next, degrease the mold, place in a cold furnace, and raise the temperatureto 400C (752F).At this tempera
24、ture and throughout the remainder of theFIG. 1 Type A Mold Open Cavity Mold and SampleFIG. 2 Type B Mold Center Pour Mold and SampleFIG. 3 Type U Mold U-Block Mold and SampleB953072heating cycle, introduce steam into the furnace. Raise the temperature to540C (1004F) and maintain for 4 h. The resulti
25、ng black oxide coating istenacious and of a dull black appearance.5.2.4 Other Types of MoldsOther molds of different types,materials, and dimensions may be substituted provided that theuniformity of the samples so obtained is comparable to theuniformity of samples obtained from the Type A, B, or Umo
26、lds, and furthermore that such samples have a spectro-chemical response similar to the reference materials used forpreparing the analytical curve.5.3 Lathe, capable of machining a smooth, flat surface onthe reference materials and samples. A milling machine mayalso be used.5.4 Tool Bits ,Either allo
27、y steel, carbide-tipped, or carbideinsert tool bits are recommended. The best shaped of toolvaries with the type and speed of the lathe, but in general, softmetals require less top and side rake than steel.5.5 Metallographic Polisher/Grinder, A metallographicpolisher/grinder may also be used to prep
28、are the sample surfaceprovided care has been taken in selecting a non-contaminatingabrasive compound. Metallographic grade wet/dry silicon car-bide discs of 120 grit or higher will produce a good samplesurface with essentially no silicon carryover to the sample.This must be verified by making a comp
29、arison between freshlyprepared surfaces on a polisher/grinder and that of a lathe ormilling machine. Reference Guide E 1257 for a description ofcontamination issues with various abrasive compounds.6. Preparation of Samples6.1 Molten Metal:6.1.1 Chill-Cast Disk by Molds A, B, or U:6.1.1.1 When a furn
30、ace or crucible of molten metal is to besampled, the temperature must be well above the point atwhich any solid phase could be present. Using the ladle or aseparate skimming tool, optionally coated with a dry, tightlyadhering mold wash (described in 5.1) and free of anyremaining previous metal, push
31、 any dross away from thesampling area. Next, dip the ladle sideways into the clear areawell below the surface and stir momentarily. Then turn theladle upright, and quickly withdraw. Two things are thusaccomplished, namely, heating the ladle prevents metal freez-ing on the wall and obtaining metal we
32、ll beneath the surfaceminimizes the risk of inclusion of small particles of oxide.6.1.1.2 Unless the mold is already hot, cast a preliminarydisk into the clean mold in order to preheat it and discard thisdisk. Remove excess metal from the ladle, dip into the moltenmetal as before, and fill the mold
33、with an even rate of pour thatallows the escape of air from the mold. Do not dump the metalinto the mold. Avoid overfilling the sprue, if applicable,otherwise the mold may be difficult to open.Allow the metal tofreeze quietly without jarring. The surface of the disk must befree of any shrinkage, inc
34、lusions, cracks, or roughness.6.1.1.3 For samples obtained from the Type A mold, using alathe or milling machine remove a 2- to 3-mm (0.1- to 0.15-in.)layer from the mold-chilled surface of the sample to eliminatethe oxidized and contaminated area. For samples obtained fromthe Type B mold, cut off t
35、he sprue from the back of the sampleand using a lathe or milling machine remove a 2- to 3-mm (0.1-to 0.15-in.) layer from the mold-chilled surface of the sampleto eliminate the oxidized and contaminated area. For samplesobtained from the Type U mold, cut off the side gate from thesample and using a
36、lathe or milling machine remove a 5-mm(0.2-in.) layer from the mold-chilled surface of the sample toeliminate the oxidized and contaminated area. This cut depthwill be deep enough to eliminate contamination pick up fromthe mold surface while remaining within the most rapidlycrystallized region of th
37、e disk. The final cut on each of thesample types should be a fine cut of approximately 0.2 mm(0.01 in.) in depth. The machined surface must be smooth andfree of scuffs, pits, or inclusions. The ideal surface is neitherpolished nor visibly grooved but should be a surface showingvery fine tool marks o
38、r a standard machine finish. A surfacemuch finer or much coarser may result in an apparent analyticaldifference. Furthermore, it is important that both sample andreference material have the same machine finish. Note thatTypes A, B, and U disks may be excited around the entireannular area. For these
39、disk types, the outer 5 mm (0.2 in.) tothe edge and the inner region up to approximately 12-mm(0.48-in.) radius should be avoided. The shaded zone in Fig. 4illustrates the approximate area suitable for excitation.6.1.2 Other Accepted MoldsIf molds other than Types A,B or U are used, the same instruc
40、tions given in 6.1 wouldapply. In addition, since a mold of different dimensions mayresult in a different freezing pattern, each new type of moldmust be evaluated in order to ascertain the proper depth ofmachining to represent the true composition of the melt.6.2 Fabricated and Cast Products:6.2.1 D
41、irect Excitation Without Casting a SampleWhenthe sample preparation procedures described in 6.1 cannot befollowed, for example, where the samples are sheet, plate,extrusions, or cast parts, usually only approximate analyses canbe made. For best results the sample must be (1) sufficientlymassive to p
42、revent undue heating, (2) allow machining toprovide a clean, flat surface which creates a seal between thespecimen and the spark stand, and (3) reference materials of asimilar metallurgical condition (spectrochemical response) andchemical composition must be available. On sheet and platesamples, mac
43、hine off approximately 0.8 mm (0.03 in.) or onefourth of the sample thickness, whichever is the smaller. Onother products, machine a flat surface approximately 1.5 mm(0.06 in.) below the original surface. Choose the depth,location, and number of areas to be analyzed to provide arepresentative analys
44、is of the product. In accordance withPractice E 401, thin flat material may also be bonded by meansof a heat and electrically conducting epoxy-type adhesive to amore massive section to provide a heat sink.FIG. 4 Disk Excitation Area is ShadedB9530737. Keywords7.1 alloys; magnesium; spectrochemical;
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48、o the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).B953074
