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Microstructural and Mechanical Characterization of Transition Elements-Containing Al-Si-Cu-Mg Alloys for Elevated-Temperature Applications
Başlık:
Microstructural and Mechanical Characterization of Transition Elements-Containing Al-Si-Cu-Mg Alloys for Elevated-Temperature Applications
Yazar:
Abdelaziz, Mohamed Hassan A., author.
ISBN:
9780438009066
Yazar Ek Girişi:
Fiziksel Tanımlama:
1 electronic resource (461 pages)
Genel Not:
Source: Dissertation Abstracts International, Volume: 79-10(E), Section: B.
Advisors: Fawzy Hosny Samuel.
Özet:
The main objective of this study was to understand how to enhance the mechanical performance of 354-type Al-Si-Cu-Mg cast alloys at both ambient and elevated temperatures through the addition of zirconium (Zr) as a base alloying element and subsequent additions of nickel (Ni) and manganese (Mn), to validate the use of such alloys in automotive engine applications. The motive behind these additions was to develop thermally stable microstructures capable of resisting coarsening instigated by prolonged exposure at elevated temperatures and hence preserve acceptable mechanical properties of these alloys when employed in high-temperature applications.
Examination of the data obtained from differential scanning calorimetric (DSC) and phase identification analyses shows that 354-type alloys developed complex as-cast microstructures containing the commonly existing phases, including alpha-Al, eutectic silicon, copper aluminide (Al2Cu) with different morphologies, Mg-rich phases such as magnesium silicide (Mg2Si), Q-phase (Al 5Cu2Mg8Si6), and Fe-based intermetallic phases including beta-Al5FeSi, alpha-Al15(Fe, Mn) 3Si2, and pi-Al8FeMg3Si6. The addition of transition elements Zr, Ni, and Mn produced other phases such as (Al,Si)3(Ti,Zr), (Al,Si)3Zr, Al9FeNi, Al3Ni, Al3CuNi, Al9FeSi3Ni 4Zr, and alpha-Al15(Fe,Mn)3Si2. Nickel proved to have a retarding effect on the kinetics of precipitation of the alpha-Al network and the eutectic Al-Si structure. Also, the presence of Ni consumed a considerable amount of Cu to form Al-Cu-Ni particles instead of Al 2Cu particles. Comparison between DSC thermograms obtained for as-cast and as-quenched alloys revealed that solution treatment at 495°C for 5 hours was sufficient to dissolve a large amount of Al2Cu particles in the alpha-Al matrix, which is mandatory for a successful aging treatment.
With respect to the strengthening precipitates, transmission electron microscopy (TEM) investigations confirmed that the investigated alloys were strengthened primarily by theta-Al2Cu and S-Al2CuMg precipitates and their precursors, in addition to a secondary strengthening effect by precipitates in the form of Alx(Zr,Ti)Si which formed following the addition of Zr. The data showed that the base alloy M1S, which is a Ni-free alloy, comprised higher fractions of theta-Al2Cu precipitates than the 4 wt.% Ni-containing alloy M4S.
Additions of Ni and Mn in different amounts and combinations increased the volume fraction of intermetallic compounds in the resulting alloys M2S through M5S, compared to the base alloy (cf. 12.21% for M4S with 2.5% for M1S), producing a significant effect on the mechanical performance. The proposed additions enhanced the mechanical performance of the alloys, namely, the ambient- and elevated-temperature tensile properties, hardness values, and impact properties. For the Mn-containing alloys, the improvement in properties was attributed to the formation of sludge particles in the form of blocky alpha-Al 15(Fe,Mn)3Si2 alongside the script-like alpha-iron phase which resisted crack propagation. The precipitation of Ni-bearing phases such as Al9FeNi, Al3CuNi, and Al3Ni in the Ni-containing alloys hindered the propagation of cracks and thus improved the mechanical properties.
The presence of asymmetric notches in the tensile test bars proved more deleterious than symmetric notches to the tensile properties obtained at ambient temperature and at 250°C, even if the reduced area was the same, owing to the complex state of stresses that develop at the notch root. The effects of various chemical additions on the tensile properties at ambient and high temperature were feeble in the case of notched bars compared to their obvious effects on the tensile properties of smooth (unnotched) bars. At ambient temperature, notch tensile strength (NTS) values were lower than the tensile strength values obtained for the corresponding smooth (unnotched) bars, attributed to the limited ductility of the Al-Si-Cu-Mg (354-type) cast alloys. The softening that took place during tensile testing at 250°C rendered the alloys some ductility, in particular, the M1S, M2S and M3S alloys. Consequently, the notched tensile bars with asymmetric holes for these alloys exhibited high NTS values compared to the tensile strength of unnotched bars subjected to similar treatment conditions, except for the M2S alloy in the T5-treated condition. (Abstract shortened by ProQuest.).
Notlar:
School code: 0862
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Yer Numarası | Demirbaş Numarası | Shelf Location | Lokasyon / Statüsü / İade Tarihi |
---|---|---|---|
XX(682591.1) | 682591-1001 | Proquest E-Tez Koleksiyonu | Arıyor... |
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