Thixotropic materials

Thixotropic materials

Keyword: Metals

Applicant: The University of Sheffield, Sheffield, GBPatent number:US5,037,489Publication date: 6 August 1991Title: Thixotropic materials

This invention relates to the manufacture of improved thixotropic materials and to an improved method and apparatus for casting and forging thixotropic material.

A method of producing a thixotropic material is provided which consists of deforming a fully solidified metal or metal alloy below its temperature of recrystallization by cold or warm working such as extrusion or rolling. The deformed material is then caused to recrystallize by heating and the temperature is either further raised or subsequently raised above the solidus of the material so that the re-crystallized structure partially melts. This provides discrete solid particles in the liquid matrix that will rapidly spheroidise under surface tension forces to produce a dispersion of near round solid particles. This results in a material which behaves thixotropically. The flow characteristics of the material are such that lower forming pressures are required. Therefore, the lower pressures involved in thixoforging are likely to reduce capital costs, the improved dimensional tolerances of the thixoforged product are likely to lead to reduced finishing costs, and weaker, non-metallic die materials may be used.