The interpretation of the state chart of alloys is of outstanding importance in metallurgy, as it is possi ble to forsee the structure and the properties, above ali mechanical, of an alloy obtained by cooling a fusion of two or more metals in a known percentage.
Soldering alloys consist of Tin and Lead
Tin melts at 232 °C and lead at 327 'C.
Tin/lead alloys, whose characteristic is defined by the content of tin, are in fact commonly called "sol derings"; they have the property of melting at temperatures lower than those of tin/lead's fusion. On the abscissas of the shown chart are reported the composition in weight, and, on the ordinates the corresponding temperatures, as well as the melting point of the respective alloys which can be realised.
Each point in the chart represent therefore an alloy heated at a definitive temperature.
Of great importance is the eutectic composition E: it has a lower melting temperature, not only of the singie chemical species of which it is formed, but also of any other mixture of them. Even if it ha e well defined composition and fusion temperature, it isn't a chemical compound, as, when it is in the solid state, it is possible to distinguish the chrystal of both components by means of a microscope The eutectic composition E, which consists of 63% tin and 37% lead, is the one which is mainly taken into consideration for the employements stricly connected to the electronic field, just for its charac teristic of having the lowest melting point.