Aging impact on mechanical properties and microstructure of Al-6063

The impact of aging on the mechanical properties and microstructure of Al-6 063 alloys were studied, using scanning and transmission electron microscop y, as well as tensile measurements. It was found that the 0.5% yield stress and the ultimate tensile strength increase at the beginning of the aging p rocess, reach a maximum, and than decrease with increasing the aging durati on. On the other hand, the uniform elongation, the total elongation, and th e strain hardening factor decrease with increasing aging duration well afte r the material reaches the maximum strength (T6 conditions), reaches a mini mum and than increase again. The final fracture area reduction also decreas es to a minimum, which occurs simultaneously with the maximum of the ultima te tensile strength; then it increases with aging time. The final fracture area reduction is accompanied with morphology transition from transgranular shear rupture to a combination of transgranular shear rupture and intergra nular dimpled structure. The intergranular rupture area increases with agin g up to the minimum in the total elongation, and then decreases with aging duration. Aging is accompanied with the appearance of needle-like Mg2Si pre cipitates except in Precipitation Free Zones (PFZ) that are adjacent to the grain boundaries. The PFZ size depends on the annealing temperature, while the morphology and density of the precipitates depend on the annealing dur ation. A correlation has been established between the PFZ and the measured mechanical properties and fracture morphology. The impact of the Mg/Si rati o on the mechanical properties is discussed. (C) 2000 Kluwer Academic Publi shers.