Multi-component precipitates with nanoscale dimensions of elements with limited mutual solubilities can with advantage be made by sequential ion implantation. When the constituent elements of the precipitates are insoluble in the matrix, the precipitates can be considered as nanoscale ingots with the matrix acting as an array of nanoscale crucibles. Alloy precipitates of Pb-Sn embedded in an Al matrix made by sequential ion implantation have been investigated by transmission electron microscopy (TEM) and Rutherford backscattering analysis (RBS) in combination with channeling. In the as-implanted state the Pb-Sn precipitates have a cuboctahedral-like shape reminiscent of the shape of pure Pb precipitates, and they have a two-phase microstructure consisting of segments of Pb attached to Sn along planar interfaces close to {111}(fcc). In-situ heating and cooling experiments in the TEM show that the Sn segments in initially two-phase precipitates with off-eutectic compositions dissolve into the Pb segments below the eutectic temperature. The resulting single-phase precipitates can be heavily supersaturated with Sn in comparison with the equilibrium phase diagram, and thy melt in a single-stage size dependent process where the largest precipitates melt first. Solidification of the precipitates takes place with little undercooling and the smallest precipitates solidify first. During subsequent cooling the precipitates phase separate into Pb and Sn segments resulting in a two-phase microstructure similar to the original.