Question $1$

a$)$ Explain the mechanisms for the formation of the three$-$zone grain structure found in a cross$-$section of a cast alloy ingot. Use sketches to illustrate your answer.

$[11$ marks$]$

b$)$ Explain the influences of alloy content, cooling rate and pouring temperature on the final microstructure of an ingot.

$[6$ marks$]$

c$)$ Describe two casting defects $($Pipe formation and Gas holes$)$ in the ingot and the corresponding remedies to avoid such defects.

$[8$ marks$]$