Superplastic behavior of friction-stir welded joints of an Al-Mg-Sc alloy with ultrafine-grained microstructure

摘要

The commercial Al-5.4Mg-0.2Sc-0.1Zr alloy was subjected to equal-channel angular pressing at 300℃ to a true strain ～12 followed by cold rolling to a total thickness reduction of 80%. The ultrafine-grained sheets were joined by friction stir welding (FSW). To evaluate superplastic properties of the weldments, the tensile samples including all of the characteristic FSW microstructural zones were machined perpendicular to the welding direction and pulled up to failure in the temperature range of 400 to 500℃ and at strain rates of 2.8×10~(-4) s~(-1) to 5.6×10~(-1)' s~(-1). The friction-stir welded material exhibited excellent superplastic properties. The highest elongation-to-failure of ～1370% was recorded at a temperature of ～450℃ and an initial strain rate of 5.6×10~(-2) s~(-1), where the strain rate sensitivity coefficient was about 0.64. The relationship between superplastic ductility and microstructure is discussed.