Effect of equal-channel angular pressing on superplastic behavior of eutectic Pb–Sn alloy

An eutectic lead – tin alloy was casted in the form of cylindrical billets that were machined down, and then processed in a 90° equal channel angular pressing (ECAP) die, via route C to four passes. Evaluation of the microstructure was done via optical and scanning electron microscopy. This process resulted in dynamically recrystallized α + β structure of interphase boundary size of ∼6 μm. Tensile testing was performed at different initial strain rates at three temperatures of 25 (room temperature), 50 and 75 °C. The steady state true stresses were depicted and plotted against the respective strain rates. A constant strain rate sensitivity parameter m of 0.44 was observed at the three testing temperatures. The high value of m, the activation energy along with large elongation percent suggest the operation of grain boundary sliding as rate controlling process. The value of elongation percent (ductility) was also depicted and plotted as a function of strain rate at various temperatures. It was noticed that, the ductility values at each temperature attain a maximum value and this maximum value increases and shifts to high strain rates with increasing temperature.

► ECAP route C 4 passes resulted in dynamic recrystallized structure of 6 μm in size.
► Constant m of 0.44 was observed at the three testing temperatures.
► High value of, m, Qa and % el suggest grain boundary sliding.
► Ductility at each temperature has a maximum value.
► Max ductility at each temperature shifts to high strain rates with increasing temp.