The document discusses the structure and solidification of pure metals and alloys during casting. It provides information on: 1. The formation of equiaxed and columnar grains near mould walls during solidification for pure metals. 2. Alloys solidify over a range of temperatures, forming a mushy state within this temperature range. 3. The size and distribution of grains throughout a casting depends on the rate and direction of heat flow during solidification. 4. Shrinkage and porosity occur during solidification as metals contract, which can lead to dimensional changes and cracking in castings.