With AM/Ao = 1, the superplastic m- δ curves of Zn-Ni-Mg alloy have been studied. When T=220°C and έ (initial)=1.33×10−2 min−1, the curve was of the type. It was transformed into the mL =mmin =mo<mF,δL=δL<εF type of curve, when T=200°–230°C and έ (initial)=3.33×10−2 min−1 and further transformed the type at 240°–250°C with the same strain rate.

With AN/Ao<1 and >0.595, T=230°C and έ (initial)=3.33×10−2 min−1 the curves were all of the mL=mmax =mo <mF, δ.(=O)= δL < δF type. The δF values increased with increase in AN/Ao value. The effect mainly reflected on the CF value and the CL m-δ equation can be expressed to account for the notch effect as follows:

where and AN/Ao < 1 and > 0.595.

Symbols: Refer to the List of Symbols.