TY - JOUR
T1 - Effects of Mo and Mn microadditions on strengthening and over-aging resistance of nanoprecipitation-strengthened Al-Zr-Sc-Er-Si alloys
AU - De Luca, Anthony
AU - Seidman, David N.
AU - Dunand, David C.
N1 - Funding Information:
This research was sponsored by the Ford-Northwestern University Alliance . Atom-probe tomography was performed at the Northwestern University Center for Atom-Probe Tomography (NUCAPT). The LEAP tomograph at NUCAPT was purchased and upgraded with funding from NSF-MRI ( DMR-0420532 ) and ONRDURIP (N00014e0400798, N00014e0610539, N00014-0910781, N00014-1712870) programs. Instrumentation at NUCAPT was supported by the Initiative for Sustainability and Energy at Northwestern University (ISEN). This work made use of the MatCI Facility and the EPIC facility (NUANCE Center) at Northwestern University. NUCAPT, MatCI and NUANCE received support from the MRSEC program (NSF DMR-1720139) through Northwestern's Materials Research Center ; NUCAPT and NUANCE also from the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF NNCI-1542205). NUANCE received support from the International Institute for Nanotechnology (IIN); the Keck Foundation; and the State of Illinois, through the IIN. DNS and DCD disclose financial interests in Braidy Industries, which is active in the area of aluminum alloys. The authors kindly thank Drs. J. Boileau and B. Ghaffari (Ford Research Laboratory) for numerous useful discussions.
Publisher Copyright:
© 2018 Acta Materialia Inc.
PY - 2019/2/15
Y1 - 2019/2/15
N2 - Combined microadditions of 0.09 at.% Mo and 0.4 at.% Mn to a dilute Al-0.10Zr-0.01Sc-0.007Er-0.10Si (at.%) alloy lead to increases in strength upon peak-aging, and improved over-aging resistance at 400, 425 and 450 °C for at least 6 months. These improvements are related to four cumulative effects. Firstly, Mn and Mo provide, in the as-cast state, a solid-solution-strengthening contribution of ∼90 MPa. The solid-solution contribution from Mo (∼80 MPa) remains essentially unchanged during aging at 400–450 °C, due to its extremely small diffusivity and precipitation. Secondly, Mn and Mo partition to the cores and shells, respectively, of the nano-size coherent, L12 (Al,Si)3(Zr,Sc,Er) nanoprecipitates, which nucleate in <1 h at 400–450 °C. This is associated with an increase in their number density and a reduction in their growth and coarsening kinetics, thus delaying the loss of strength upon over-aging. Third, Mn and Mo provide precipitation strengthening via submicron α-Al(Mn,Mo)Si precipitates (which form between 1 and 11 days at 400 °C), which counterbalances the loss of Mn solid-solution strengthening. Finally, the α-Al(Mn,Mo)Si precipitates scavenge Si from the matrix, which is then not available to accelerate the coarsening of the L12 precipitates, thereby improving the over-aging resistance of the alloy. Iron additions (0.015 at.%), expected to replace some Mn in the α-phase Al(Fe,Mn,Mo)Si, does not affect the aging behavior.
AB - Combined microadditions of 0.09 at.% Mo and 0.4 at.% Mn to a dilute Al-0.10Zr-0.01Sc-0.007Er-0.10Si (at.%) alloy lead to increases in strength upon peak-aging, and improved over-aging resistance at 400, 425 and 450 °C for at least 6 months. These improvements are related to four cumulative effects. Firstly, Mn and Mo provide, in the as-cast state, a solid-solution-strengthening contribution of ∼90 MPa. The solid-solution contribution from Mo (∼80 MPa) remains essentially unchanged during aging at 400–450 °C, due to its extremely small diffusivity and precipitation. Secondly, Mn and Mo partition to the cores and shells, respectively, of the nano-size coherent, L12 (Al,Si)3(Zr,Sc,Er) nanoprecipitates, which nucleate in <1 h at 400–450 °C. This is associated with an increase in their number density and a reduction in their growth and coarsening kinetics, thus delaying the loss of strength upon over-aging. Third, Mn and Mo provide precipitation strengthening via submicron α-Al(Mn,Mo)Si precipitates (which form between 1 and 11 days at 400 °C), which counterbalances the loss of Mn solid-solution strengthening. Finally, the α-Al(Mn,Mo)Si precipitates scavenge Si from the matrix, which is then not available to accelerate the coarsening of the L12 precipitates, thereby improving the over-aging resistance of the alloy. Iron additions (0.015 at.%), expected to replace some Mn in the α-phase Al(Fe,Mn,Mo)Si, does not affect the aging behavior.
KW - Al-Zr-Sc-Er-Si-Mn-Mo alloy
KW - Atom-probe tomography
KW - High-temperature alloy
KW - Microhardness
KW - Precipitation strengthening
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U2 - 10.1016/j.actamat.2018.11.031
DO - 10.1016/j.actamat.2018.11.031
M3 - Article
AN - SCOPUS:85056961760
VL - 165
SP - 1
EP - 14
JO - Acta Materialia
JF - Acta Materialia
SN - 1359-6454
ER -