Aluminium is commonly alloyed with copper. Based in the phase diagram below, describe the formation of microstructures in an alloy containing $4\%$ Cu by weight, under the following conditions:

I. Slow cooled $($equilibrium cooling$)$ from the solidification temperature.

II$.$ Solution treated, then rapidly cooled $($quenched$),$ then re$-$heated and held $($aged$)$ at $160\backslash$deg C for $16$h followed by air cooling to room temperature.

III. Explain why is Il$)$ preferable to l$)?$

C

IV$.$ If the alloy now contains $25\%$ Cu by weight, explain the main differences

expected in l$).$