Zhengrong PAN
金属学报(英文版)
The effects of 0.5 wt pct In on Al-3.3Cu-0.8Li alloy were studied. Instead of T1 (Al2CuLi) phase, there was an unknown cubic phase acting as the dominant precipitates in the In-added alloy in T6 temper, which disappeared in T8 temper. The orientation relationship between this phase and matrix was given by SAEDs: (001)p//(001)α, [010]p//[010]α. Both measuring directly from HREM images or calculating from it's FFTs gave an close lattice parameter about 0.83~nm. 3DAP composition analysis revealed the presence of Al, Cu and Li in the atomic percentages: 60%Al, 30%Cu and 10%Li. Thus, this cubic phase is considered to be Li-rich γ1 (Al4Cu9) phase or a new phase designated as χ (Al5Cu6Li2). Different from the traditional report providing heterogeneous nucleation sites for the precipitates, In was detected neither around nor in the cubic phase by EDX and 3DAP.
关键词:
Indium
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Precipitation
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Microstructure
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HRTEM
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3DAP
Majed M.R. Jaradeh
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Torbjorn Carlbergy
材料科学技术（英文）
The effects of Cu and Zr additions, on the microstructure formation, precipitation and ingot cracking, in commercial 3003 Al alloys have been studied. The investigation was carried out by characterizing the grain structure in DC-cast rolling ingots, and studying the solidification microstructure of Bridgman directionally solidified samples. To better understand the influence of the different Cu and Zr contents on the phase precipitations, differential thermal analysis (DTA) experiments were performed. Results from the ingot microstructure analysis show that in commercial alloys with relatively high contents of Cu and Zr, no significant differences in measured grain sizes compared to conventional 3003 Al alloys could be found. However, only Zr containing alloys exhibited significantly larger grain sizes. Increased grain refiner and/or titanium additions could compensate for the negative effects on nucleation normally following Zr alloying. Different types of precipitates were observed. Based on DTA experiments, increased Cu and Zr contents resulted in the formation of Al2Cu phase, and increased solidification range. It was also found that increased Mn content favors an early precipitation of Al6(Mn,Fe) giving relatively coarse precipitates. It was concluded that the Cu alloying has a detrimental effect on hot tearing.
关键词:
Aluminium 3003
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P. Fernandez G. Gonzalez I. Alfonso I.A. Figueroa
材料科学技术（英文）
Two ternary Al-2.2Zn-0.95Mg and Al-5.5Zn-2.1Mg (in wt pct) alloys, with Zn:Mg ratios close to 2.5 were produced by conventional ingot casting metallurgy. The ingots were solution heat treated at 500°C for 0.5 h and aged at 180°C for times between 0.5 and 80 h. The structural characterization was carried out by X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED) and Vickers microhardness measurements (HV). The study was focused on the investigation of the precipitates formation and the relationship between hardness and lattice parameter for α-Al. The results showed that there was an inverse correlation for all the experimental conditions, and the aged peaks coincided with lattice parameter minima. Significant precipitates formation only occurred for the alloy containing 5.5 wt pct Zn and 2.1 wt pct Mg, provoking an important strengthening and variations in the lattice parameter, however, this was not observed for the alloy containing 2.2 wt pct Zn and 0.95 wt pct Mg. A plausible explanation of the increment of hardness values could be the presence of a well distributed μ phase (MgZn2). At initial stages of the precipitation process, μ' was the most abundant precipitate while the phase τ was observed at overaged conditions. These results showed that the aging response of the conventionally cast Al-Zn-Mg alloys could be obtained using the lattice parameter of the α-Al matrix, even for alloy systems with low precipitates formation.
关键词:
Aluminum alloy
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X-ray diffraction
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Precipitation
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Lattice parameter
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Hardness
Muhammad Iqbal
材料科学技术（英文）
Minor alloying plays an important role in the synthesis and improvement of thermal stability of bulk metallic glasses (BMGs). The present study was conducted to investigate the effect of minor additions of Y, Ti and Nb on crystallization behavior and thermal properties of Zr64.5Ni15.5Al11.5Cu8.5 base alloy. Thermal parameters and the activation energies for crystallization were calculated for four [Zr0.645Ni0.155Al0.115Cu0.085]100-xMx (M = Y, Ti and Nb while x = 0, 2 at. %) alloys. Parameters describing thermal stability in these systems, including the activation energies for crystallization, were determined. The present alloys have wide supercooled liquid region of ≥87 K. Maximum activation energy was found to be greater than 300 kJ/mol for the base alloy. Four crystalline phases were identified in the samples annealed at 823 K. Reduced glass transition temperature (Trg) and other thermal parameters like γ, δ and β improved by Y and Ti addition. Niobium addition resists crystallization below annealing temperature 713 K however its effect on thermal properties is not very promising.
关键词:
Activation energy
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