A relationship between the liquid and solid states of AK21M2.5N2.5 aluminum alloy being used in the automotive manufacture was investigated. The kinematic viscosity was measured in the process of the specimens heating up to 1250°C and subsequent cooling. In the regime of cooling from 1200 to 450°C the alloy density polytherms were studied and a metallographic analysis of as-cast alloy was made. The results of DTA enable to determine the intervals of phase transformations during alloy crystallization. Influence of the alloy heating maximum temperature in the process of smelting on the structure and properties of chill castings was determined.