No abstract

The aim of the present investigation was to determine and to compare the superplastic behaviour of the AA5083 (Al-Mg-Mn) alloy with Sc and Zr additions. The investigated alloys were processed to form sheets by conventional hot and cold rolling. The superplastic properties were determined with strain rates in the range of 1x10-4to 5x10-2s-1and forming temperatures of 350 to 550°C. The results showed that the alloy with about 0.4% Sc exhibited a high superplastic ductility across a wide temperature range and strain rates up to 1x10-2s-1. The highest elongations to failure of about 2000% were attained at 550°C and at an initial strain rate of 5x10-3s-1. However, the alloy with about 0.15% Zr exhibited elongations up to 600%. The FSP processed Al-4.5Mg alloy with combined addition of about 0.2% Sc and 0.15% Zr exhibited good superplastic properties at higher strain rates (> 1x10-2s-1) with elongations up to 1500%.

This article describes the superplastic behavior of the Al-4.5Mg-0.46Mn-0.44Sc alloy. The investigated alloy was produced by casting and was conventionally processed to form a sheet with a thickness of 1.9 mm and an average grain size of 11 lm. The superplastic properties of the alloy were investigated using a uniaxial tensile testing with a constant cross-head speed and with a constant strain rate in the range 1 3 10 24 to 5 3 10 22 s 21 at temperatures from 390 to 550°C. The investigations included determinations of the truestress, true-strain characteristics, the maximum elongations to failure, the strain-rate sensitivity index m, and the microstructure of the alloy. The m-values determined with the strain-rate jump test varied from 0.35 to 0.70 in the temperature interval from 390 to 550°C and strain rates up to 2 3 10 22 s 21 . The m-values decreased with increased strain during pulling. The elongations to failure were in accordance with the m-values. They increased with the temperature and were over 1000%, up to 1 3 10 23 s 21 at 480°C and up to 1 3 10 22 s 21 at 550°C. A maximum elongation of 1969% was achieved at an initial strain rate of 5 3 10 23 s 21 and 550°C. The results show that the addition of about 0.4 wt.% of Sc to the standard Al-Mg-Mn alloy, fabricated by a conventional manufacturing route, including hot and cold rolling with subsequent recrystallization annealing, results in good superplastic ductility.

The paper describes the effect of minor additions of scandium and zirconium on the superplastic behaviour of friction stir processed Al-5Mg based alloy. The measurements included the flow curves and tensile elongations of (in wt.%) Al-5Mg-0.1Zr, Al-5Mg-0.2Sc, and Al-5Mg-0.2Sc-0.15Zr alloys at initial strain rates ranging from 1 × 10−3 to 1 × 10−1 s−1, and at forming temperatures from 350 to 500°C. The inclusion of friction stir processing at tool rotation rates of 95 and 475 rpm considerably enhanced the superplastic behaviour of the Al-5Mg-0.2Sc-0.15Zr alloy, which was reflected in elongations without failure of over 1900%. Other friction stir processed alloys, treated at lower tool rotation rates, did not achieve superplasticity due to abnormal grain growth. The results yielded by the friction stir processed alloys are compared with the superplastic behaviour of the same alloys produced conventionally by cold rolling.