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BELL SYSTEM TECHNICAL JOURNAL 



composition should be easily within 0.5 per cent. Whether the possible 

 usefulness of the test could be realized economically in engineering 

 practice has not as yet been ascertained. 



180 



170 



160 



150 



140 



130 



120 



110 



10 



20 



30 40 , 50 . 60 



TIME (minutes) 



70 



80 



90 



Fig. 6 — A group of plasticity curves illustrating the effect of composition upon 



plasticity. 



Segregation 

 Experimental Deiermination 



The plastic deformation of a material composed of solid and liquid 

 phases, such as a solder during wiping, presents a condition favorable 

 to segregation, and this phenomenon has often been thought to play 

 an important role in determining the quality of a solder. Especially 

 has this been true in regard to porosity. Now, if a sample of solder 

 which has a tendency to segregate is subjected to a plasticity test, a 

 considerable amount of liquid phase should be pushed to the outer 

 edges of the sample during the first part of the run. Since the liquid 

 phase always contains that part of the sample which later solidifies as 

 the eutectic, it follows that after the sample has been allowed to cool, 

 the outer edges should be richer in eutectic than the central portion. 



This, as a matter of fact, was found to be true, and measurements 

 of segregation were made upon a number of samples taken from the 

 plastometer. These samples were usually about 5 cm. in diameter. 

 They were cut diametrically, polished and etched. 



