Copper alloys with up to 9 wt% Sn are used in the automotive industry and in electrical/electronic applications for their electrical, mechanical and tribological properties in the form of hot and cold rolled thin strip.
An other application in Europe is the "Nordic Gold" monetary alloy, used in 10,20 and 50 eurocents coins. It is a quaternary Cu, 5Zn, 5Al, 1Sn (all wt%) alloy whose merit is first not to contain any nickel and second to combine specific physical properties, a gold like aspect and a reasonable corrosion resistance. The composition was also selected in view of its poor processability to limit counterfeiting. Companies involved in the late 90's in the production of the large quantities of Nordic Gold met indeed with great difficulties to produce it economically, that is starting with vertical semi continuous casting.
The presentation will first address the continuous casting of tin containing alloys. A succession of peritectic transformations involving fragile intermetallics and an unusually large solidification temperature interval in the Cu-Sn phase diagram explains the microsegregation related difficulties. Differential thermal analysis of solidification and EPMA microanalysis of solidified products led to a modified Scheil type modelling of microsegregation ending with the formation of interdendritic tin rich phases. The large tin contents of the last liquid and the stresses on the first solidified skin leads in turn to the "inverse" macro-segregation of tin and eventually to the blocking of the vertical continuous casting which inclines the industry to select the horizontal continuous casting of thin (2 cm) slabs associated with a lower productivity and material yield.
The presentation will then deal with the processing steps following casting during which tin (and to a lesser the other solutes) creates a risk of "burning" during reheating and a risk of crack initiation on fragile intermetallic phases during hot rolling. This is especially true for the monetary Nordic Gold alloys owing to a composition and to an electron per atom ratio which places it at the limit of alpha phase stability especially when microsegregation is active. Ternary phase diagram information and a laboratory study guides processing optimisation.

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