Microstructures
by George Langford, Sc.D., Massachusetts Institute of Technology, Cambridge, MA, 1966
Copyright©
2005 by George Langford
Non Ferrous Alloys - Lesson 4 - Second specimen
Aluminum - 12% silicon alloy at 50X
When the silicon content of the aluminum is raised to 12% as shown at left at 50X (same HF etchant) an excessive amount of coarse eutectic silicon forms.
Aluminum - 12% silicon alloy at 200X
At left the same specimen is shown at 200X.

This microstructure gives poor mechanical properties because of the platelike shape, brittleness and poor bonding of the silicon particles in the aluminum matrix.


Specimen 3 has been improved by a key elemental addition.