The Effect of Forming Temperature on the Microstructure and Stress Distribution for Lead Babbitt Alloy in Hot Backward Extrusion Process

Abstract

This study aims to modify the microstructure and mechanical properties of Babbitt alloy (ASTM B23 alloy 13). Two casting techniques were implemented to manufacture the alloy; Gravity Die Casting (GDC) and New Rheocasting (NRC) techniques. The microscope examination shows that the structures contained two phases, α-Pb and cubic shaped intermetallic compound (β-SbSn) in a matrix of ternary phases. GDC structure was a dendrite α-Pb phase, while the equiaxed structure was observed via NRC, with remaining β-SbSn phase as a cubic shape. The manufactured Babbitt alloy by NRC has the best compression and yield strength, while the castings produced by GDC recorded lower properties. Backward extrusion was used to improve the properties of alloy 13 produced by two casting techniques. The backward extrusion were carried in the temperature range of 20-100°C.NRC samples showed the highest mechanical properties under all extruded conditions. The enhanced mechanical properties were mainly attributed to the grain refinement. FEM-simulation code DEFORM 3D was used to investigate the stress distribution in backward extrusion process of billet. Highest effective stress exists in the transition area between bottom and wall of the workpiece (punch corner). At the inner side of the wall, stress is higher than at the outer side of wall.

Keywords: lead Babbitt alloy, gravity die casting, new rheocasting, backward extrusion, microstructure, mechanical properties, FEM-simulation.