Microstructural and Mechanical Response of Pb-Sn Eutectic Alloy to Cyclic Expansion Extrusion Processing

Abstract

This study evaluates the effectiveness of the Cyclic Expansion Extrusion (CEE), a novel severe plastic deformation (SPD) technique, in refining the microstructure and enhancing the mechanical properties of a Pb-Sn eutectic alloy, known for its superplastic characteristics. Pb-Sn samples were initially cast and annealed, followed by CEE processing through 1, 2, 4, 6, and 8 passes at room temperature using a custom-designed die and reciprocating press setup. Microstructural analysis revealed significant grain refinement from 25.48 μm in the annealed state to approximately 300 nm after 8 passes. Tensile testing showed an increase in yield strength from 28.5 MPa to 38.7 MPa after 8 passes, with tensile strength increasing from 33.38 MPa to 44.85 MPa and elongation from 12.96% to 46.55%. Interestingly, the hardness decreased from 14.66 ± 0.5 HB to 10.44 ± 0.8 HB with further passes. The findings reveal that CEE effectively enhances tensile properties of Pb-Sn alloy through ultrafine microstructure development. The observed decrease in hardness coupled with increased elongation after grain refinement contradicts typical SPD behavior in most alloys, highlighting unique characteristics of the CEE process and specific material response of the Pb-Sn eutectic system. CEE proves to be an effective method for producing superplastic materials with enhanced mechanical properties.