Effect of friction stir processing on the kinetics of superplastic deformation in an Al-Mg-Zr alloy

Abstract

The effect of friction stir processing on the superplastic behavior of extruded Al-4Mg-1Zr was examined at 350°C to 600°C and at initial strain rates of 1 ϫ 10 Ϫ3 to 1 s Ϫ1 . A combination of a fine grain size of 1.5 m and high-angle grain boundaries in the friction stir-processed (FSP) alloy led to considerably enhanced superplastic ductility, much-reduced flow stress, and a shift to a higher optimum strain rate and lower optimum temperature. The as-extruded alloy exhibited the highest superplastic ductility of 1015 pct at 580°C and an initial strain rate of 1 ϫ 10 Ϫ2 s Ϫ1 , whereas a maximum elongation of 1280 pct was obtained at 525°C and an initial strain rate of 1 ϫ 10 Ϫ1 s Ϫ1 for the FSP alloy. The FSP alloy exhibited enhanced superplastic deformation kinetics compared to that predicted by the constitutive relationship for superplasticity in fine-grained aluminum alloys. A possible origin for enhanced superplastic deformation kinetics in the FSP condition is proposed.

Friction Stir Processing Technology: A Review

“…The use of the FSP technique resulted in the generation of significant superplasticity in a number of aluminum and magnesium alloys, in particular, at high strain rates or low temperatures. Although most superplastic data were obtained by using minitension specimens taken from the traverse section of the FSP samples, [19,36,41,[46][47][48][49][50] significant superplasticity was illustrated by using full-sized specimens along the FSP direction. [51][52][53][54] In the past few years, various processing techniques such as thermomechanical treatment (TMT), [55,56] equal channel angular pressing (ECAP), [57,58] torsion under compression, [59] multiaxial alternative forging (MAF), [60] and accumulative roll bonding (ARB) [61] have been used to produce the fine-grained materials for superplasticity.…”

Effect of Heat Input Conditions on Microstructure and Mechanical Properties of Friction-Stir-Welded Pure Copper

“…Grain boundary characteristics have significant meaning for investigating the recrystallization and superplasticity mechanisms. [18][19][20][21][22] It was reported that the percentage of the HAGBs in the SZ of FSW aluminum alloys was higher than in that processed by conventional thermal working techniques. [18] Liu et al [19] indicated that for FSW cold-rolled 1050 aluminum alloy, the percentages of the HAGBs of the PM and the SZ were 32 and 70 pct, respectively.…”

“…[18][19][20][21][22] It was reported that the percentage of the HAGBs in the SZ of FSW aluminum alloys was higher than in that processed by conventional thermal working techniques. [18] Liu et al [19] indicated that for FSW cold-rolled 1050 aluminum alloy, the percentages of the HAGBs of the PM and the SZ were 32 and 70 pct, respectively. Mishra and Mahoney, [20] Norman et al, [21] and Liu et al [22] reported that in the SZ of FSW aluminum alloys, the percentage of the HAGBs is 85 to 97 pct.…”

Friction stir processing (FSP) and superplasticity

“…After FSP of such alloys as well as AA7050 and the cast alloy AA356 superplastic ductilities exceeding 500 pct. at strain rates >10 -2 s -1 have been attained [17][18][19][20][21][22][23][24][25][26][27][28]. Grain sizes are typically <5 μm and thus finer than in conventionally processed material although the grain size depends strongly on FSP conditions.…”