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1、Grain size measurement -By Xia Outline Sampling Grinding and polishing Etching Microscope operating Grain size measurement Sampling TP1 Casting billets 38 mm 12 mm Evaluation position Surface Centre Evaluation position Grinding polish with few drops 1m suspension for 23 minutes. (10N force or by han
2、d) Al: Grind with 600#-800#-1200#-2400#-4000# sand paper, polish with 1m suspension for 1030 minutes. (20N force for pure Al) Polarized metallurgy Light input Polarizer Compensator Etched sample Analyzer Detector Etchant and etching procedure Etchant Etching condition Mg alloys Distilled water 50 ml
3、 Anhydrous ethyl alcohol 150 ml Glacial acetic acid 1 ml Immerse for about 4 min at room temperature Rinsed with ethanol AZ91 or macro etching Picric acid 4.2g Ethanol 140ml Acetic acid 10 ml Distilled water 10 ml Immerse for 13 seconds Rinsed with ethanol For sensitive Mg alloys (Pure Mg, MgZn et.
4、al) Picric acid 4.2g Ethanol 70ml Acetic acid 10 ml Distilled water 10 ml Immerse for 13 seconds Rinsed with ethanol For normal Mg alloys (AZ91D, AZ31 et. al) Al alloys Molybdic acid solution No information HCl (concentrated) 45 ml HNO3 (concentrated) 15 ml HF (48%) 15 ml Water 25 ml (Tuckers) Immer
5、se for 1015 seconds Macro etching Electrolyte: 200 ml water, 10 ml fluoroboric acid (35%) (Bakers) 1520 v for 30s-2 min Anodizing Typical etched samples AZ91D samples Al-Zn alloys Pure Al Grain size measurement Standard test methods: ASTM E112 (Log normal size distribution) ASTM E1382 (For automatic
6、 analyzers) ASTM E1181 (Duplex size distribution) ASTM E930 (Coarse grains in fine matrix) Methods stated in E112: Comparison methods; Grain counting methods (Planimetric or Jeffries procedure); Intercept methods. Terminology ASTM grain size number G NAE=2G-1, NAE is the number of grains per square
7、inch at 100x magnification. Grain boundary intersection count (GBIC), the number of times a test line cuts across, or is tangent to, grain boundaries (triple point intersections are considered as 1.5 intersections). Grain intercept count (GIC), determination of the number of times a test line cuts t
8、hrough individual grains on the plane of polish (tangent hits are considered as 0.5 interception; test lines that end within a grain are consider as 0.5 intersection). Intercept length (IL), the distance between two opposed, adjacent grain boundary intersection points on a test line segment. GBIC/GI
9、C/IL Intercept length Intercept grain boundaries GBIC: 4+1.5 GIC: 0.5+4+0.5 BCAST-Procedure 1. Magnification, Test Line and Fields Ideally, the length of a single test line and the magnification should be such that 50 intercepts can be counted. The use of multiple fields to obtain 50 intercepts is d
10、iscouraged, although permitted, due to the bias which will decrease the accuracy as the number of fields increases. The suggested magnification should be 100x although the other magnifications are permitted and 5 fields is encouraged. 2. Count the intercepts. An intercept is the segment of the test
11、line which overlays one grain. Count 1 for each intercept and for each time an end of the test line falls on a grain. Or count the interceptions An intersection is the point where the test line cuts a grain boundary. Count 1 for each intersection, 1 for each tangential intersection, when an end of t
12、he test line ends exactly on a grain boundary and 1 when the intersection occurs at a triple point. 3. Measurement Strategy Make counts on 3 to 5 blindly selected and widely separate fields to obtain a reasonable average for the specimen. Additional counts may be required to obtain the desired accur
13、acy. Use 68 uniformly distributed test lines, for an independent field for equiaxed structure. At least 500 grains need to be count for an approximation estimate of a sample. Select typical samples but do not attempt to choose fields that appear to be typical ! Measurement under Axio system Spatial diameter of grains: Planar diameter of grains: , mean lineal intercept length Grain size measurement form End Thank you for your attention !