The early view of superplasticity was that it was a phenomenon that could only be exhibited
by fine grained, two phase alloys. This effectively ruled out most alloys that possessed attractive
service properties. The first material to demonstrate good superplastic properties from a virtually
single phase microstructure was the Al-6%Cu-0.5%Zr, AA 2004 but this was followed by
superplastic versions of AA7475, AA8090 and AA5083. Superplasticity was also demonstrated in
magnesium based alloys at an early stage.
More recently different grain control additions, such as scandium or erbium have been investigated
and it has also been demonstrated that, in certain circumstances, aluminium simply with the addition
of a grain controlling element can exhibit good superplastic behaviour. While conventional wisdom
teaches that large fabricating strains are required to confer good superplastic properties in the sheet
product, recent results with both aluminium and magnesium alloys cast doubt on this belief.
Although, for many years, strip casting has appeared to provide an attractive semi-fabricating route
for superplastic sheet problems with centre line segregation in alloys with a wide freezing range have
precluded its use. It has been demonstrated that recent developments in strip casting enable
production of alloys with as wide a freezing range as AA5182 to be cast with a fine, equiaxed grain
structure across the strip thickness.
The paper will review the state of these various developments and their implications for the
manufacture of superplastic sheet materials.
Achieving superior superplastic properties in fine grained intermetallic alloys based on γ-TiAl + α2‑Ti3Al