Tóm tắt
To produce useful strengthening, precipitation hardenable aluminium alloys rely on rapid
quenching from the solution heat treatment temperature to suppress the formation of coarse
equilibrium second phases. An unavoidable consequence of the rapid quenching of thick sections is
the severe thermal gradients that quickly develop in the material. The attendant inhomogeneous
plastic flow can then result in the establishment of residual stresses. The surface and through
thickness residual stress magnitudes present in heat treated high strength aluminium alloy
components are frequently reported to exceed the uniaxial yield stress of small specimens of the
same alloy measured immediately after quenching. In thick section plate and forgings it is proposed
that these high residual stress magnitudes are a consequence of hardening precipitation that occurs
during quenching which allows for a greater elastic stress to be supported. To investigate this
theory, thick sections of the quench sensitive alloy 7175 and the less quench sensitive alloy 7010
were heat treated in such a way as to allow the internal hardness to be measured immediately, after
quenching. The rate of cooling was also monitored during quenching and these data were used in
conjunction with time temperature property data to predict the degree of precipitation and
subsequent loss of hardening potential in the fully heat treated condition. The magnitudes of the
residual stresses induced during quenching were determined using standard x-ray diffraction
techniques.
