Thixoforging of 7075 Aluminium Alloys at High Solid Fraction

Abstract

Thixoforging is a type of semi-solid metal processing at high solid fraction (0.5<fs<1), which involves the processing of alloys in the semi-solid state. 7075 alloy has been used as a feedstock for thixoforming in order to investigate thixoformability of a high performance aluminium alloy at high solid fraction. The microstructure in semi-solid state consists of fine spheroidal solid grains surrounded by liquid. Thixo behaviour allows laminar flow that avoids macro-porosity and other casting defects and gives better mechanical properties; so we can reduce the weight of functional parts. Higher solid fraction of 7075 alloy is less sensitive to temperature, avoids metal splash at high speed, allows laminar flow at high speed and gives a good smooth surface without stick-slip phenomenon. The process is quicker with less energy and so the production rate increases and the tool has longer life. However, high solid fraction promotes freezing flow because of faster solidification and the lack of liquid phase. This freezing flow creates solid/liquid segregation and increases the forming force.