Influence of heat treatment and cutting speed on chip segmentation of age hardenable aluminium alloy

Abstract

A change in chip shape has been observed as a function of age hardening and cutting speed during high speed milling of the aluminium alloy 7075. In order to study this effect systematically, the aluminium alloy was heat treated to produce different precipitation states and machined under carefully controlled conditions at cutting speeds between 1000 and 7000 m min^-1. The underaged state shows local shearing producing segmented chips. The degree of segmentation increases with cutting speed. In contrast, the overaged state shows continuous chips up to the highest cutting speeds. The chips obtained with the peak aged state show a fluctuation between segmented and continuous parts. These results can be understood in terms of the differing work softening/hardening behaviour of the under- and overaged states owing to the specific interactions between dislocations and precipitates during chip formation.