NANO-OXIDE STRENGTHENED ALUMINUM MATRIX COMPOSITES

摘要

The development of fine microstructures in wrought aluminum has resulted in increased strength levels as well as other unique properties of these alloys. Payton et al reported on superplastic forming of high strength 7000 series aluminum alloys that also maintained high strength after the forming operation [Ref. 1]. This alloy was heavily hot and cold worked with strict controls on the annealing cycles in order to develop the required microstructure for strength retention. More recently, researchers have experimented with cryogenic milling of aluminum powders in liquid nitrogen creating nano-scale grains resulting in aluminum alloys with strength levels greater than 827 MPa at room temperature. Additionally, he low temperature milling operation creates oxy-nitride particles that have sizes in the 10{sup}(-7) to 10{sup}(-9) m range that are compatible with the definition of nano-scale particles. This process is a very time consuming, expensive and not easily scale for commercial production. The present research centers on the development of insitu nano-scale aluminum oxide particles within the aluminum alloy. The nano-oxide particles impart dispersion strengthening to the alloy system. This process is designed to be low cost, utilizing commercially available gas-atomized powder without any special milling or handling required. The alloy in bulk form differs from "Sintered Aluminum Powder" (SAP) in several ways; the current product uses aluminum alloys rather than pure aluminum, the oxide particles are discreet nano-scale particles rather than a continuous network, and the present material is designed for use in structural applications [Ref. 2]. The nano-oxide content and chemistry is tailorable during all phases of processing into bulk forms. This paper describes the work conducted with 2000 and 7000 series alloys. These alloys were produced from prealloyed powders as well as blended elemental powders in order to define manufacturing limits. The nano-oxide containing alloys were also used as matrix alloys for macro-scale particle reinforced composites. This part of the study shows that the hybrid composites exhibit both high strength and high elastic modulus.