Coarsening rate of microstructure in semi-solid aluminium alloys

H.V Atkinson,D Liu

doi:10.1016/s1003-6326(09)60356-3

Abstract

The rate of microstructural coarsening of recrystallisation and partial melting (RAP) and cooling slope (CS) processed materials in the semi-solid state is compared with rates found in the literature. The rate of coarsening depended on the liquid fraction but RAP route 2014 alloy with 37% liquid coarsened slightly more slowly than the CS route 2014 alloy with a lower liquid fraction of 17%, contrary to expectations. For the CS route, an increase in liquid fraction resulted in faster coarsening. A modified 2014 alloy with Fe, Mn and Zn stripped out of the composition gave a relatively high coarsening rate. The coarsening rate was also relatively high for CS 201 alloy in comparison with either RAP 2014 or CS 2014. Low coarsening rates are thought to be associated with the presence of particles which inhibit the migration of liquid film grain boundaries. This could be the result of pinning or of the liquid film impeding diffusion at the boundary.

Highlights

Semi-solid processing takes place between the liquidus and solidus temperatures and requires the microstructure in the semi-solid state to consist of spheroids of solid in a liquid matrix [1]
We focus here on results for the coarsening constants
It is clear that the alloy 2014, made by either the cooling slope (CS) or the Recrystallisation and Partial melting (RAP)

Summary

Introduction

Semi-solid processing takes place between the liquidus and solidus temperatures and requires the microstructure in the semi-solid state to consist of spheroids of solid in a liquid matrix [1]. This paper compares the rates of coarsening in material produced by two different routes: recrystallisation and partial melting (RAP) [2] and cooling slope casting (CS) [3]. When this material is reheated into the semi-solid state it recrystallises and the first liquid to form tends to be on the recrystallised boundaries.

Results

Conclusion