Effect of Cr, Ti, V, and Zr Micro-additions on Microstructure and Mechanical Properties of the Al-Si-Cu-Mg Cast Alloy
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THE recent growth in use of lightweight materials in automotive manufacturing is an answer to rising fuel costs as automakers try to provide consumers with greater fuel efficiency to meet stringent Corporate Average Fuel Efficiency (CAFE) regulations. The purpose of using light metals is to reduce the vehicle weight, increase fuel economy, improve vehicle performance, and enhance overall safety.[1–3] Due to low density, high specific strength and stiffness, and good recyclability, aluminum alloys are becoming attractive structural materials in the automotive and aerospace industries.[4,5] So far, applications of existing Al alloys are limited to about 453 K (180 C).[6] Beyond this temperature, the mechanical properties deteriorate quickly due to precipitates coarsening. To meet the requirements of automotive engine parts, the Al-Si alloys may be modified by changing their chemical composition and S.K. SHAHA, Ph.D. Candidate, and J. FRIEDMAN and D.L. CHEN, Professors, are with the Department of Mechanical and Industrial Engineering, Ryerson University, 350 Victoria Street, Toronto, ON M5B 2K3, Canada. F. CZERWINSKI, Group Leader, Research Scientist, is with CanmetMATERIALS, Natural Resources Canada, 183 Longwood Road South, Hamilton, ON L8P 0A1, Canada, and also Adjunct Professor with the Department of Mechanical and Industrial Engineering, Ryerson University. Contact e-mail: [email protected] W. KASPRZAK, Director of Operations, is with CanmetMATERIALS, Natural Resources Canada. Published with permission of the Crown in Right of Canada pertains to F. Czerwinski and W. Kasprzak. Manuscript submitted July 9, 2015. Article published online February 22, 2016 2396—VOLUME 47A, MAY 2016
post-casting heat treatment.[6,7] Thus, new demands of the automotive industry for aluminum alloys suitable for high-temperature power train applications require the development of cast Al-Si alloys with enhanced thermal stability. According to Knipling,[8] to develop cast Al alloys for high-temperature applications, alloying elements should fulfill several conditions. In particular, they should (i) be capable of forming thermally stable strengthening phases, (ii) have low solid solubility in the Al matrix, (iii) have low diffusivity in the Al matrix, and (iv) retain the ability for the alloy to be conventionally solidified. It is reported that among alloying elements, transition metals which form thermally stable and coarsening-resistant precipitates are promising in case of Al-Si alloys. A review of the published phase diagrams and crystallographic data[9–12] indicates that a number of alloying additions crystallize to form stable Al3M-trialuminides. The high-symmetry cubic L12 and related tetragonal D022 and D023 structures are prevalent among transition elements. To achieve this, different alloying elements such as Ni, Fe, Cr, Ti, V, and Zr were examined with cast Al-Si alloys as described in the literature.[13–30] Studies[31–33] showed that Al-Si alloys contain a certain amount of Fe impurities, which form b-AlSiFe (Al9Si2F
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