On development of sintered 7xxx series aluminium alloys

The sintering characteristics and the tensile properties of the 7000 series Al-Zn-Mg-Cu alloys, fabricated using elemental powders in a conventional press and sinter powder metallurgy process, are examined. Microalloying with 100 ppm of lead or tin enhances the sintering response of these alloys significantly, with a corresponding increase in the tensile strength. The system has aspects of both transient and supersolidus liquid phase sintering. Zinc melts and eutectic liquids form during heating to the sintering temperature but these liquid phases are absorbed by the aluminium on further heating. Sintering above the solidus induces the formation of additional liquid. Because it has aspects of both transient and supersolidus liquid phase sintering, the system is extremely sensitive to process variables, including particle size, sintering temperature, and heating rate, but insensitive to green density. When the alloy composition and the process variables are optimised, tensile strengths in excess of 400 MPa are possible.