Effect of Mg and Sr additions on the formation of intermetallics in Al-6 wt pct Si-3.5 wt pct Cu-(0.45) to (0.8) wt pct Fe 319-type alloys
- Univ. of Quebec, Chicoutimi, Quebec (Canada)
- General Motors Corp., Milford, NH (United States)
Al-Si alloys are materials that have been developed over the years to meet the increasing demands of the automotive industry for smaller, lighter-weight, high-performance components. An important alloy in this respect is the 319 alloy, wherein silicon and copper are the main alloying elements, and magnesium is often added in automotive versions of the alloy for strengthening purposes. the mechanical properties are also ameliorated by modifying the eutectic silicon structure (strontium being commonly employed) and by reducing the harmful effect of the {beta}-Al{sub 5}FeSi iron intermetallic present in the cast structure. Magnesium is also found to refine the silicon structure. The present study was undertaken to investigate the individual and combined roles of Mg and Sr on the morphologies of Si, Mg{sub 2}Si, and the iron and copper intermetallics likely to form during the solidification of 319-type alloys at very slow (close to equilibrium) cooling rates. The results show that magnesium leads to the precipitation of Al{sub 8}Mg{sub 3}FeSi{sub 6}, Mg{sub 2}Si, and Al{sub 5}Mg{sub 8}Cu{sub 2}Si{sub 6} intermetallics. With a strontium addition, dissolution of a large proportion of the needle-like {beta}-Al{sub 5}FeSi intermetallic in the aluminum matrix takes place; no transformation of this phase into any other intermetallics (including the Al{sub 15}(Fe,Mn){sub 3}Si{sub 2} phase) is observed. When both Mg and Sr are added, the diminution of the {beta}-Al{sub 5}FeSi phase is enhanced, through both its dissolution in the aluminum matrix as well as its transformation into Al{sub 8}Mg{sub 3}FeSi{sub 6}. The reactions and phases obtained have been analyzed using thermal analysis, optical microscopy, image analysis, and electron microprobe analysis (EMPA) coupled with energy-dispersive X-ray (EDX) analysis.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 316024
- Journal Information:
- Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science, Journal Name: Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science Journal Issue: 12 Vol. 29; ISSN 1073-5623; ISSN MMTAEB
- Country of Publication:
- United States
- Language:
- English
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