The solidification process and matrix microstructure

Shrinkage experienced during solidification is the main culprit for the occurrence of porosity [146,165-167,173,175,199]. 

West et al [200] state that there are three types of microstructure  

A network of dendrites much smaller than the fibers 

The dendrites nucleate on the fibers and grow into the interfiber spaces (occurring with hypereutectic Al-Si alloys, AfiSi and AlsNi) 

After growth, a primary phase is formed, found on the fibers and between dendrite branches. 

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