Physical properties of Sn affected Cu through lead-free solder and combined effect of severe cold deformation and thermal ageing

Abstract

The precipitation behavior of Cu, affected by lead free tin-based solder is investigated as a function of cold deformation and artificial ageing using microhardness measurements, electrical resistivity, differential scanning calorimetry, reflectance behavior as well as microstructural observation. To compare preciously the aforementioned properties commercially pure Cu and two amounts Cu-Sn alloys has been taken under consideration. When Sn doped to Cu, it has been found that changes in such parameters as cold rolling and ageing contribute significantly to the physio-electrical qualities of pure Cu. Cold rolling shows the superior hardness for Sn doped alloys because of the dissimilar crystal orientation BCC of Sn precipitated within the FCC Cu matrix. That is why increase then electrical resistivity. Two processes, namely precipitation strengthening through supersaturated solid solution and recovery as well as recrystallization softening are observed for the alloys. Fine precipitates hinder the dislocation movement as a result improves the recrystallization temperature. The DSC study also confirms the improvement by showing the peaks at higher temperatures. Spectral reflectance study reveals that Sn doping provides lower percent reflectance whereas improve under ageing treatment due to formation of fine precipitates. Micrographs studies confirm that cold rolling expands the grains in its rolling direction and relatively thick grain boundaries are observe as the presence of different particles at the grain boundaries for minor added alloys. All alloys under ageing treatment at 400ºC for one hour attain equiaxed grain by reaching more or less recrystallized state.