The deformation behaviour of an Fe -3Si (wt-%) steel was studied in the temperature range 400 -900°C over six orders of magnitude of strain rate. It was found that the Fe -3Si steel exhibits a threshold behaviour. A correlation between the deformation behaviour and the temperature dependence of the threshold stress was determined. An analysis in terms of the threshold stress showed that two modes of deformation behaviour exist in the power law creep regime. At normalised strain rate e . kT/(D 1 Eb) ranging from 2610 6 to 10 3 , the value of the true stress exponent n is equal to 7, and at lower values of e . kT/(D 1 Eb) the value of n is~5. The true activation energy for plastic deformation Q c increases from 250¡15 to 290¡30 kJ mol 1 with increasing temperature from 550 to 700°C, and remains virtually unchanged at high temperatures. The relationship between rate controlling mechanisms of plastic deformation and mechanisms of interaction between lattice dislocations and dispersoids is discussed.MST/5602
Superplasticity in 2219 aluminum alloy was achieved through thermomechanical processing. Tension tests showed that the alloy exhibits superplastic behavior in the temperature range of 450-540°C and strain rates ranging from 2.2x10 -5 to 1.1x10 -1 s -1 . A maximum elongationto-failure of 670% was recorded at 500°C and at the initial strain rate of 2.2x10 -4 s -1 . High cavitation level and intensive grain growth were observed. Sheet of the 2219 aluminum alloy was blow formed into conical shape using two different methods: simple negative and backpressure forming. A strain of 2.1 was obtained at 500°C under the backpressure blow forming condition. It was found that elongation to failure under blow forming with backpressure is about 1.5 times higher than that under a simple female forming. Microstructural evolution of blow formed parts was also examined.
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