Effect of Ca addition on precipitation in the Pb-4 wt.% Sn alloy

The precipitation behaviour of Pb-4 wt.% Sn alloys containing 0.001 –0.088 wt.% Ca has been mainly studied by resistivity measurements and transmission electron microscopy. The addition of Ca to the Pb–Sn binary alloy suppresses the discontinuous precipitation and accelerates the formation of continuous precipitates with a high coherency. Therefore, the addition of Ca induces a higher age hardening. TEM observations reveal that the continuous precipitates in the Ca-doped alloys contain Pb, Ca, and Sn, and have an L1 -type ordered structure. The discontinuous precipitation reaction in the Pb-4 wt.% Sn–Ca alloys is suppressed by the formation of continuous precipitates and, furthermore, the segregation of the solute elements at the grain boundaries.