Microstructure and Strengthening Mechanisms in an Ultrafine Grained Al-Mg-Sc Alloy Produced by Powder Metallurgy

• Published in: Metallurgical and materials transactions. A, Physical metallurgy and materials science Physical metallurgy and materials science, 2014-12, Vol.45 (13), p.6329-6343
• Main Authors: Harrell, Tammy J., Topping, Troy D., Wen, Haiming, Hu, Tao, Schoenung, Julie M., Lavernia, Enrique J.
• Format: Article
• Language: English
• Subjects: AL-MG-SC Alloy; Aluminum base alloys; Aluminum |c Binary systems; Applied sciences; Binary systems; Characterization and Evaluation of Materials; Chemistry and Materials Science; Exact sciences and technology; Intermetallic compounds; Magnesium |c Binary systems; MATERIALS SCIENCE; Metallic Materials; Metals. Metallurgy; Microstructrue; Microstructure; Nanotechnology; Powder metallurgy; Precipitates; Precipitation; Scandium; Strengthening; Structural Materials; Surfaces and Interfaces; Thin Films
• ISSN: 1073-5623; 1543-1940
• DOI: 10.1007/s11661-014-2569-6

Additions of Sc to an Al-Mg matrix were investigated, paying particular attention to the influence of Al 3 Sc precipitates and other dispersoids, as well as grain size, on mechanical behavior. Prior studies have shown that Sc significantly increases the strength of coarse-grained Al-Mg alloys. Prompted by these findings, we hypothesized that it would be of fundamental and technological interest to study the behavior of Sc additions to an ultrafine-grained (UFG) microstructure ( e.g. , 100’s nm). Accordingly, we investigated the microstructural evolution and mechanical behavior of a cryomilled ultrafine grained Al-5Mg-0.4Sc (wt pct) and compared the results to those of an equivalent fine-grained material (FG) produced by powder metallurgy. Experimental materials were consolidated by hot isostatic pressing (HIP’ing) followed by extrusion or dual mode dynamic forging. Under identical processing conditions, UFG materials generate large Al 3 Sc precipitates with an average diameter of 154 nm and spaced approximately 1 to 3  μ m apart, while precipitates in the FG materials have a diameter of 24 nm and are spaced 50 to 200 nm apart. The strengthening mechanisms are calculated for all materials and it is determined that the greatest strengthening contributions for the UFG and FG materials are Mg-O/N dispersion strengthening and precipitate strengthening, respectively.