Microstructures
by George Langford, Sc.D., Massachusetts Institute of Technology, Cambridge, MA, 1966
Copyright©
2005 by George Langford
Non Ferrous Alloys - Lesson 4 - Fifth specimen
Aluminum - 4.5% copper casting at 50X
This is the same alloy as the previous specimen, but it has been heat treated subsequently.  Examine both photomicrographs carefully to find out what microstructural changes have taken place.  The image at left was made at 50X; and the photomicrograph below it was made at 200X.  Keller's etch was used again.
Aluminum - 4.5% copper casting at 200X
Form an opinion before proceeding to the explanation.












The precipitated impurities have been dissolved, the alpha etches more smoothly, and the coring has disappeared.

Specimen 6 is a fractured casting.