Low Temperature Mechanical Properties of Scandium-Modified Al-Zn-Mg-Cu Alloys

摘要

Tensile properties of three wrought alloys, (1) Al-10Zn-3Mg-1.2Cu-0. 15Zr, (2) Al-10Zn-3Mg-1.2Cu- 0.15Zr-0.39Mn-0.49Sc, and (3) Al-12Zn-3Mg-1.2Cu-0. 15Zr-0.39Mn-0.49Sc were studied in T6 and T7 conditions at 298K and 77K. The properties depended on the alloy compositions and heat treatment conditions. An increase in the concentration of Zn increased strength and decreased ductility. An addition of Sc increased both strength and ductility. The alloys showed very high strength both at room and cryogenic temperatures. In the T6 condition, the following properties were obtained at room temperature: YS = 760 to 805 MPa, UTS = 770 to 810 MPa, El = 3 to 9%. When the temperature was decreased to 77K, strength increased while elongation decreased, and their values were YS = 1005 to 1065 MPa, UTS = 1010 to 1065 MPa, El = 0.3 to 0.7%. Over-aging allowed an increase in elongation to a value as high as 8.5% at the values of YS = 805 MPa and UTS = 835 MPa at the cryogenic temperature. The deformed alloys showed mixed type of fracture. The fraction of the brittle component increased when the temperature decreased. Although they showed high elongation, the alloys in T7 condition fractured predominantly by intergranular mode at the cryogenic temperature.