On enhancing the mechanical properties of aluminum P/M alloys

Sintered aluminum alloys are an attractive material for the automobile industry, both because of the low specific gravity and high strength-to-weight ratio of aluminum itself, and the fabrication advantages associated with a powder metallurgy process. However, properties such as impact, stiffness, corrosion and wear resistance are often poor, thereby restricting the widespread use of these materials. Recent work by the authors has shown that hardness, wear resistance and tensile properties of a P/M Al–Cu–Mg ternary master alloy can be improved using a novel diffusion/supersolidus liquid phase sintering process. Improvements were due to in-situ microalloying during sintering, in particular, the influence of Ag and Sn. To complement this work, the present investigation addresses the response of a commercial alloy, AA2014, to the microalloying process. Results show that sintered densities for the commercial alloy were relatively unaffected by the presence of either Ag or Sn, and were superior to the ternary master alloy. Hardness and tensile properties were also improved relative to those obtained for the ternary, and were comparable to wrought 2014. Examination of final microstructure of Ag modified AA2014 using TEM showed the presence of Ω as the principal precipitate, but only after extended sintering times. This particular precipitate is believed to contribute to enhanced hardness. The apparent absence of Ω for short sintering times was due to the presence of silicon in the commercial product. However, the corrosion behavior of the P/M AA2014 was superior to the wrought product and thus the process is presented as a potential P/M alternative to using ingot metallurgy techniques for microalloying.