CORRELATION BETWEEN MICROSTRUCTURE AND MECHANICAL AND CORROSION RESISTANCES OF A LEAD-FREE Sn-0,7%Cu SOLDER ALLOY

Sn-Cu alloys are promising alternatives to the replacement of Pb-containing solder alloys. However, the effects of the cooling rate on the solidification microstructures of these alloys and the corresponding influence on the mechanical and corrosion resistances are not well known. In the present study, the transient directional solidification technique has been used to obtain a Sn-0,7wt.%Cu ingot. The experimental results include: solidification thermal parameters (cooling rate, Ṫ, growth rate, v, and metal/substrate heat transfer coefficient, hi ), cellular spacing, λc , and primary dendritic arm spacing, λ1 , corrosion rate, corrosion potential and polarization resistance and mechanical strength and ductility. The results show a cellular/dendritic transition with eutectic cells prevailing for Ṫ< 0,9°C/s. Lower corrosion resistances have been associated with dendritic regions compared with regions characterized by eutectic cells. In the interdendritic regions extremely fine and fibrous Cu6 Sn5 intermetallic particles can be observed.