SAP-like ultrafine-grained Al composites dispersion strengthened with nanometric AlN

This paper reports the development of novel Sinter-Aluminum-Pulver (SAP)-like Al-AlN nanocomposites via replacing the native Al2O3 thin films on fine Al powder with a large volume fraction of in situ formed nanometric AlN dispersoids. Fine gas-atomized Al powder (d50=1.3µm) compacts were first partially nitrided at 590°C in flowing nitrogen, controlled by a small addition of Sn (0.3-0.4wt%), and subsequently consolidated by hot direct extrusion. The resulting Al-AlN composites consisted of submicrometric Al grains reinforced with nanometric AlN dispersoids together with some nanometric Al2O3 dispersoids. An Al-13vol% AlN nanocomposite fabricated this way achieved exceptional ultimate tensile strength of 227MPa, yield strength of 195MPa and Young's modulus of 66GPa at 300°C, superior to typical SAP materials and coarse grained Al-AlN composites. In addition, the Al-13vol% AlN nanocomposite exhibited good thermal stability up to 500°C. The strengthening mechanism is discussed.