Evolution of Intermetallics, Dispersoids, and Elevated Temperature Properties at Various Fe Contents in Al-Mn-Mg 3004 Al
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TRODUCTION
WITH the rapid development of automotive and aerospace industries, the demand for aluminum alloys working at elevated temperatures [~573 K (~300 C)] is greatly increasing due to the lighter weight and lower cost. However, traditional precipitation-hardened aluminum alloys, such as 2xxx, 6xxx, and 7xxx, are hard to meet the strength requirement at elevated temperature due to the rapid coarsening of precipitates (overaging effect).[1,2] For instance, the instant yield strength (YS) of 6061 alloys at 588 K (315 C) can reach at 75 MPa, but it rapidly decreased to 31 MPa after 100 hours holding.[1] On the other hand, dispersoid strengthening is reported to be promising at elevated temperature. Hence, the addition of transition and rare earth elements either individual or combination of Sc with Zr, Ti, Gd, Sm, Er, and Yb to wrought aluminum alloy has been explored, especially in 1xxx alloys to form coherent or semi-coherent Al3M dispersoids, which are thermally stable up to 573 K (300 C).[3–7] However, the high cost of these elements limits their wide applications. Therefore, developing lower cost but thermally
K. LIU, Research Professor, and X.-G. CHEN, Professor, are with the NSERC/Rio Tinto Alcan Industrial Research Chair in Metallurgy of Aluminum Transformation and REGAL Aluminum Research Center, University of Quebec at Chicoutimi, 555, Boul. de l’Universite´, Saguenay, QC, G7H 2B1, Canada. Contact e-mail: [email protected] Manuscript submitted September 16, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS B
stable aluminum alloys at elevated temperature has been always an attractive industrial target. The work-hardening Al-Mn 3xxx alloys have been widely used in architecture and packaging industry because of the excellent formability and corrosion resistance.[8,9] In 3xxx alloys, Mn is the major element and most of it will be dissolved into the aluminum matrix to form a supersaturated solid solution during the casting process. Therefore, dispersoids are likely to precipitate during the heat treatment due to the decomposition of supersaturated solid solution.[10–14] In the research works of Li et al.,[12,14] the partially coherent a-Al(MnFe)Si dispersoids were reported to form during the annealing process in AA3003 alloy, leading to an increase of mechanical properties at room temperature (RT). However, the improvement on mechanical properties was limited due to low volume fraction of dispersoids, which was reported to be 0.77 vol pct at peak condition.[12] Therefore, optimizing the dispersoid precipitation, such as the volume fraction and size to further improve the properties at both RT and elevated temperature, is the key solution in developing aluminum alloys for elevated temperature applications. To date, limited work has been performed about the influence of heat treatment and alloying elements on the characters of dispersoids in 3xxx alloys. In the study of Huang et al.,[13] it was found that the volume fraction of dispersoids decreased with increases of homogenization temperature in 3003 alloys. The
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