DEPENDENCE OF HARDNESS ON MICROSTRUCTURE OF A DIRECTIONALLY SOLIDIFIED Sn-40wt.Bi-0.7wt.Cu ALLOY

摘要

Continuous efforts in replacing Sn-Pb eutectic solder have been attempted. Sn-Bi alloys are candidates as lead-free solders for low temperature soldering due to its adequate cost and general consistency. Additions of Cu within these alloys can improve the ductility, mechanical strength and wettability. Nevertheless, a deeper study considering the characterization of the as-soldered ternary Sn-40wt%Bi-0.7wt%Cu microstructures remains still to be performed. Thus, the present experiments were carried out by directional solidification (DS) of the Sn-40Bi-0.7Cu with a view to establish experimental interrelations involving solidification thermal parameters (growth rate - V_L and cooling rate - T_L) with some microstructure features (λ_2). The experimental relations obtained for this alloy have been compared with those already determined for the binary Sn-0.7wt.%Cu and Sn-40wt.%Bi alloys. The microstructures from the bottom to the top along the Sn-Bi-Cu alloy were entirely dendritic. Further, a Hall-Petch equation is proposed relating HV to λ_2 for the Sn-40Bi-0.7Cu alloy.