This paper describes and compares the superplastic behaviour and microstructural evolution of twin roll cast AZ91 and WE43 rolled sheet alloys. Tests were carried out in uniaxial tension on both alloys across a range of temperatures (300 °C–525 °C) and strain rates (1⋅10‐4 s‐1–1⋅10‐1 s‐1). In the case of WE43 gas bulge testing was employed at 400 °C and 0.6 MPa to offer a better analogy to superplastic forming than uniaxial tensile testing. Elongations of over 400 % were observed within WE43 when tested at 450 °C and 1⋅10‐3 s‐1 strain rate, and over 200 % within AZ91 when tested at 350 °C and 1⋅10‐3 s‐1 strain rate. A peak cone height of 41 mm was achieved with WE43 at a temperature of 400 °C and pressure of 0.6 MPa. Electron back scattered detection technique was employed to analyse the microstructural evolution of the two alloys during the forming process. Both WE43 and AZ91 were observed to undergo dynamic recrystallization during elevated temperature tensile testing and failed at low strain rates mainly by means of coalescence of cavitation, in the case of AZ91 at high strain rates cracking of Al12Mg17 intermetallic particles was the dominating failure mechanism. Both alloys were seen to achieve good levels of superplastic ductility over 200 % elongation, which would be industrially useful in niche vehicle and aerospace manufacturing.