The 7000 series aluminium alloys processed using elemental powder mixtures
are prone to distortion, which is manifest as hourglassing or waisting in c
ylindrical specimens. By characterising the density distribution using hard
ness measurements, it is shown that the green density is not evenly distrib
uted through a part, even though aluminium is relatively soft and readily c
ompacted. Because the density equilibrates during sintering, the non-unifor
m green density leads to distortion. The cause of this distortion is a resu
lt of differential shrinkage, which occurs during sintering as well as on s
olidification during cooling from sintering. Distortion can be controlled b
y increasing the compaction pressure, which homogenises the green density a
nd does not affect the tensile properties.