CONSTITUTION OF THE ALLOYS OF ALUMINIUM AND ZINC. 343 



PLATE 7. 



Fig. 28. Alloy 75, quenched from 470 C., showing y crystals surrounded by " liquid." Etched with 

 nitric acid. x 150. 



29. Alloy 75, annealed for 30 minutes and quenched at 430 C., showing absence of " liquid " and 

 approach to homogeneity, x 150. 



30. Alloy 75, annealed for 2 hours and then quenched at 430' C., showing homogeneous S. x 150. 



.. 31. Alloy 75, annealed at 430 C., showing " pearlitic " structure of decomposed S. x 300. 



32. Alloy 70, slowly cooled, showing cores of y, sheaths of partly decomposed ft, and residues of 



eutectic. x 150. 



33. Alloy 70, slowly cooled after annealing at 430 C., showing " pearlitic " structure, x 170. 



.. 34. Alloy 40, slowly cooled, showing cores, x 150. 



35. Alloy 50, quenched at 467 C., showing presence of " liquid." x 150. 



36. Similar alloy to fig. 35, quenched just above the solidus, showing slight traces of liquid. 

 x!50. 



