Modern notions about the structure of liquid metals and alloys are considered. It is shown, that several types of micro-inhomogeneity and micro-heterogeneity can exist in liquid metal solutions. Their structural state can be changed as a result of composition, prehistory, temperature or pressure variations or under the influence of other external factors. These changes can be saved while subsequent cooling down to liquidus with a suitable rate and influence the structure and properties of the hardened alloy. The main attention is drawn to the influence of temperature of liquid metal heating. It is shown the possibility to develop optimal thermal smelting modes using the results of the structure and properties of melts investigation. Such optimized heat treatment of melts is an effective way to improve the quality of aluminum-based alloys.