Effects of extrusion ratio and extrusion temperature on the microstructure and mechanical properties of 6063 aluminum alloy prepared by hot extrusion consolidation of chips

6063 aluminum alloy samples were prepared by thermomechanical consolidation of alloy chips which involves hot extrusion of chip compacts with extrusion ratios of 9:1 and 25:1 and extrusion temperatures of 450 ℃ and 500 ℃, respectively, followed by a T6 heat treatment. The microstructure , tensile properties and fracture behavior of the samples were studied. The results show that with an extrusion temperature of 500 ℃, dynamic recrystallization occurs in the consolidated samples, and the recrystallized grains are confined within the chips and become elongated. With the increase of extrusion ratio, the grains become finer, the yield strength (YS) and ultimate tensile strength (UTS) increase from 198 and 242 MPa to 252 and 275 MPa, respectively, and the elongation to fracture decreases clearly from 19.5%-15.2%. With an extrusion ratio of 25:1, an decrease of the extrusion (EL) from 500 ℃ to 450 ℃ caused a slight increase of the average grain size, the YS and UTS remain almost unchanged, and the elongation to fracture decreases clearly from 15.2% to 12.1%. For comparison, 6063 aluminum alloy samples were also prepared by hot extrusion of ingots under the same conditions followed by the same T6 heat treatment. It was found that the average grain size changes little with the increase of extrusion ratio, but decreases slightly with the decrease of extrusion temperature. The tensile properties remain almost unchanged in these two cases (YS: 192-202 MPa, UTS: 228-237 MPa, EL: 18.4-19.1%). Both types of materials exhibit ductile tensile fracture, but the mode of fracture is different, with the material prepared by consolidation of chips shows interchip decohesion. Correlations among processing conditions, microstructure and mechanical properties are discussed.