Effect of Minor Sc Addition on Microstructure and Tensile Properties of Hot-Extruded 7055 Alloy

The microstructure and tensile properties of hot-extruded Al-8Zn-2Mg-2Cu-0.15Zr alloy (7055 alloy) with the minor addition of Sc were investigated. The 0.1 and 0.2 wt.% Sc were added into 7055 alloy during the preparation process by conventional casting. Attributing to the Sc additions, the grain sizes of as-cast ingots were remarkably refined and the irregular grain morphology changed to nearly spherical. Correspondingly, the distinctly refined microstructure of the 7055 alloy with Sc addition was achieved after hot extrusion. Unlike most reported extrusion cases of 7055 alloy, the extrusion temperature and ram speed were set to be 500 degrees C and 0.1 mm/s, respectively. As the added Sc increased from 0 to 0.1 and 0.2 wt.%, the yield strength (YS) of the T6 treated samples of extruded 7055 alloys were improved from 652 to 660 and 695 MPa, and the ultimate tensile strength (UTS) was 701, 706, and 744 MPa, respectively. The elongation of all the T6 samples remained to be about 11.5%. The good tensile properties of these experimental alloys are mainly attributed to grain refinement, extrusion texture, and the abundant precipitated particles, including Al-3(ScZr) and eta(MgZn2), which effectively pin the dislocation and hinder the migration of grain boundaries.