Dispersion strengthened aluminum-4 pct magnesium alloy made by mechanical alloying
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THE
application of the recently developed mechanical alloying process ~ to A1 provides a new avenue for A1 alloy development based on dispersion strengthening. SAP was the first oxide dispersion strengthened metal2 but its relatively coarse and unevenly distributed dispersion required a very high volume fraction of A1203 to obtain high strengths) Mechanical alloying, MA, developed for the manufacture of ODS Nibase alloys: has achieved high strength at far lower dispersoid contents than in SAP in a variety of alloy systems. The initial application of MA to pure A1 generated strengths of nearly 414 MPa (60 ksi): a strength level approaching that of conventional precipitation hardened A1 alloys such as the 2000 and 7000 series. The research to be reported here expands upon this initial work and describes the development of a magnesium-alloyed ODS A1 alloy.
ALLOY DESIGN Because dispersion strengthening contributes a large fraction of the strength of MA AI alloys, different strengthening methods from those usually employed become feasible. The high strength of MA pure aluminum, due predominantly to first and second order effects of the nonmetallic dispersoids present, offers the opportunity of avoiding use of precipitation hardening systems such as Zn-Mg or Cu-Mg for further strengthening and avoiding their negative effects on corrosion and stress corrosion cracking resistance. The study of dispersion strengthening of the solid solution aluminum-magnesium alloys was selected as the focus of the work. Conventional A1-Mg alloys have inherently good corrosion characteristics and dispersion strengthening of such alloys through MA was seen to be of technological value. It was upon this basis that the investigations described here were undertaken.
R. D. SCHELLENG is Senior Project Manager, Inco Research & Development Center, Inc., Sterling Forest, Suffern, NY 10901 and J. S. BENJAMIN is General Manager, IncoMAP (Inco Mechanically Alloyed Products), 1 New York Plaza, New York, NY 10004. Manuscript submitted November 24, 1980.
METALLURGICAL TRANSACTIONS A
MECHANICAL ALLOYING OF ALUMINUM-BASED SYSTEMS The MA process, a high energy, dry-milling technique which produces composite metal powders with submicron homogeneity, is normally carried out in high-energy stirred ball mills such as the Szegvari attritor. 6 A mixture of commercially available metal powders, such as aluminum and magnesium in the present case, is charged into a mill chamber filled with small steel grinding balls. These balls are agitated by a rotating impeller. Powder particles are trapped between colliding grinding balls and severe plastic deformation results. The surfaces of the starting aluminum and magnesium powder particles are covered by adsorbed gases, hydrated oxides, and other thin amorphous compounds such as carbonates. As shown in Fig. 1, flattening during processing increases the surface to volume ratio of these powder particles and ruptures the surface films, exposing atomically clean metal. As shown in Fig. 2(a), cold welds are formed between p
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