Development and Application of Aluminium-Lithium Alloy

The history of aluminium-lithium alloys development has been reviewed in this paper. According to the strength, weld ability and corrosion resistance, thermal stability and plasticity, aluminium-lithium alloy has been categorized and the defects of aluminium-lithium alloys in early stage have been analyzed. As compared the third generation of aluminium-lithium alloy with normal aluminum alloy and composite materials, it indicates aluminium-lithium alloy has better performance, lower cost and reduced weight. After analyzing the advantages and disadvantages of the rapid solidification, ingot casting metallurgy and electromagnetic simulated microgravity methods in synthesis of aluminium-lithium alloy, it has been found microgravity method has prominent effect on reducing the alloy segregation and lithium losses. Finally, the future development of aluminium-lithium alloys has been discussed.

Optimal Filling of Test Dies for Evaluating Properties of Semi-Solid Alloys

An investigative study was conducted on how two different dies designed to produce sound specimens for evaluating mechanical properties of semi-solid alloys could be filled optimally. The first die contains one cavity that produces a wedge with a sectional thickness varying from 19.05 mm (0.75 in) to 9.52 mm (0.375 in). The second die contains four cavities fed by a single runner, producing ASTM-type round bars with a diameter of 9.52 mm (0.375 in). Experiments were undertaken to cast partial and complete shots of A356 alloy test specimens under controlled injection conditions. Flow patterns developed from the moment the alloy entered the cavity were noted, including difficulties experienced in balancing flow in the four-cavity die. Microstructural abnormalities were observed in the bar specimens examined using optical and electron microscopy. It was found that control of filling and solidification in the wedge die was much easier and specimens produced did not result in any significant alloy segregation.

Composition modulation and local structure in strained diluted GaInNAs nitride alloy thin layers on GaAs substrates

ABSTRACTThe theoretical study reported here is devoted to diluted GaInNAs nitride alloys, and focuses on correlation between local chemical atomic neighborhood and atomic distances. The model used is Valence Force Field approximation, and we model a periodic Ga1−xInxNyAs1−y alloy film deposited on a GaAs substrate. The surface is dimerised (for simplicity we consider 2×1 anion rich surfaces). First starting from a random film, first and second nearest neighbor distances are calculated, and the corresponding histogram drawn. Then a pseudo-annealing process is simulated by allowing the N atoms to choose their optimal location. This pseudo-annealing strongly enhances the number of In-N bonds, in agreement to experimental studies. From this statistical study, fine structure of each peak of the histograms is shown to be not directly related to a given surrounding chemical distribution up to 3rd nearest neighbors. The positions (in distance) of the peaks appear not to be modified by alloy composition nor alloy segregation, which only alter relative intensities and peak shapes. Last, we consider stripes of In-rich and In-poor zones: calculated energy variations show a strong tendency for N atoms to completely desert In-poor zones.

Optical and Electrical Properties of Al1−xInxN Films Grown on Sapphire (0001) by Plasma Source Molecular Beam Epitaxy

ABSTRACTA series of epitaxial InxAl1−xN alloy films (thickness ~ 150 nm) with 0 ≤ × ≤ 1.0 were grown by Plasma Source Molecular Beam Epitaxy (PSMBE) on sapphire (0001) at a low substrate temperature of 375 °C. X-ray diffraction (XRD) measurements confirm a c-axis oriented epitaxial growth of alloy films without any alloy segregation. However, the degree of crystalline mosaicity, compositional fluctuation and surface roughness, all increase with increasing x. The direct energy band gap of alloy films were determined using optical (UV-VIS) transmission and reflection measurements. The observed bowing of the direct gap versus x plot, when compared to the theoretical prediction, is less pronounced than seen in earlier studies reported in literature. Electrical resistivity and Hall effect measurements show n-type electrical conductivity in these alloys with carrier concentrations ~1019-1020 cm−3 for x > 0.5.