Mechanical behavior and properties of mechanically alloyed aluminum alloys
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I.
INTRODUCTION
A. 9052 and 905XL MA Aluminum Alloys
THE mechanical alloying process has been described in detail by Benjamin and SchellengY] Mechanically alloyed (MA) powders are produced by controlling the repeated fracture and cold welding of the powder particles in a ball mill or an atrider. During this process, carbon and oxygen react in situ to form a fine dispersion of carbides and oxides within the particles. Once a stable particle size is achieved (normally 40 to 50/zm), the powder is collected and consolidated using conventional powder metallurgy methods. Mechanically alloyed aluminum alloys have exhibited good corrosion resistance with higher strength compared to ingot metallurgy alloysJ2-7J The United States Navy worked with Inco Light Alloys, Inco Alloys International, Inc. (INCO, Huntington, WV), during the development of commercial processes to produce MA A1-Mg and A1-Mg-Li alloys. Cylindrical forgings were made from different material lots of both the A1-Mg and the AI-Mg-Li alloys. The material lots are identified as iterations in this article. As the development of the MA process progressed at INCO, the MA A1-Mg alloy was designated IN-9052 and is now designated AL-9052. Similarly, the MA AI-Mg-Li alloy was first identified as IN-905XL, then as AL-905XL, and finally, it was assigned the Aluminum Association number AA5091. All iterations (material lots) of the MA A1-Mg alloy will be designated as 9052. The iterations of the MA A1-Mg-Li alloy will be designated 905XL. These alloys are strengthened by a combination of solid solution, dispersion, substructure, and fine grain size strengthening mechanisms.t2-8~It is recognized that there are lot-to-lot processing differences for both the powder and forgings that influence the material properties. The lot-tolot differences will determine the relative contribution of each of these strengthening mechanisms and will influence the ductility. Failure in MA alloys has been proposed to initiate at oxides and carbides present on grain boundaries391 The boundaries corresponding to the surface of the
H.R. LAST, Materials Research Engineer, and R.K. GARRETT, Jr., Materials Engineer, are with the Naval Surface Warfare Center, Indian Head Division, Silver Spring, MD 20903-5640. Manuscript submitted January 25, 1995.
METALLURGICAL AND MATERIALS TRANSACTIONS A
powder particles (prior particle bonndaries) have the greatest possibility of a higher concentration of dispersoids than other boundaries. The alloy 9052 has a nominal composition (in wt pct) of A1-4Mg-l.lC-0.50. The density of 9052 is 2.68 mg/m 3 (0.097 lb/in.3). This density is 5 pct lower than the density of age-hardenable ingot metallurgy alloys of comparable strengthY ~ Similar to other MA aluminum alloys, the typical microstructure for 9052 consists of a submicron grain size (0.2 to 0.5/xm) that is stabilized by a uniform dispersion of fine oxides and carbides, m The oxides, A1203 and MgO, t6J are approximately 0.01 ~m in size and are stable upon annealing. The carbides, A14C3, have been reported to b
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