Magnesium alloys have received an increasing interest in the past 12 years for potential applications in the automotive, aircraft, aerospace, and electronic industries. Many of these alloys are strong because of solid-state precipitates that are produced by an age-hardening process. Although some strength improvements of existing magnesium alloys have been made and some novel alloys with improved strength have been developed, the strength level that has been achieved so far is still substantially lower than that obtained in counterpart aluminum alloys. Further improvements in the alloy strength require a better understanding of the structure, morphology, orientation of precipitates, effects of precipitate morphology, and orientation on the strengthening and microstructural factors that are important in controlling the nucleation and growth of these precipitates. In this review, precipitation in most precipitation-hardenable magnesium alloys is reviewed, and its relationship with strengthening is examined. It is demonstrated that the precipitation phenomena in these alloys, especially in the very early stage of the precipitation process, are still far from being well understood, and many fundamental issues remain unsolved even after some extensive and concerted efforts made in the past 12 years. The challenges associated with precipitation hardening and age hardening are identified and discussed, and guidelines are outlined for the rational design and development of higher strength, and ultimately ultrahigh strength, magnesium alloys via precipitation hardening.

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Precipitation and Hardening in Magnesium Alloys

Dark optical solitons: physics and applications

In order to enable optical systems to operate with a high degree of compactness and reliability it is necessary to combine large number of optical functions in small monolithic structures. A development, somewhat reminiscent of that that took place in Integrated Electronics, is now beginning to take place in optics. The initial challenge in this emerging field, known appropriately as "Integrated Optics", is to demonstrate the possibility of performing basic optical functions such as light generation, coupling, modulation, and guiding in Integrated Optical configurations. The talk will review the main theoretical and experimental developments to date in Integrated Optics. Specific topics to be discussed include: Material considerations, guiding mechanisms, modulation, coupling and mode losses. The fabrication and applications of periodic thin film structures will be discussed.

Integrated optics

A prototype microscope built with self-reconstructing Bessel beams is shown to be able to reduce scattering artifacts as well as increase image quality and penetration depth in three-dimensional inhomogeneous opaque media.

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Microscopy with self-reconstructing beams

Non-Gaussian beam profiles such as Bessel or an- nular beams enable novel approaches to modifying materials through laser-based processing. In this review paper, proper- ties, generation methods and emerging applications for non- conventional beam shapes are discussed, including Bessel, an- nular, and vortex beams. These intensity profiles have important implications in a number of technologically relevant areas includ- ing deep-hole drilling, photopolymerization and nanopatterning, and introduce a new dimension for materials optimization and fundamental studies of laser-matter interactions.

Bessel and annular beams for materials processing

New optical combinations of axicons and axicons with spherical mirrors and lenses suitable for laser machining are presented. Linear and annular focusing, coaxially and radially to the laser beam, are possible. Most combinations allow continuous adjustment of exit beam parameters, focal line length, focal ring diameter, and magnification, by varying the relative position of one of the axicons. Potential new laser applications are also discussed in relation to these optical devices.

Linear, annular, and radial focusing with axicons and applications to laser machining

Magnesium-lithium base alloys containing aluminum, silicon and rare-earth additions have been prepared by melting and solidification in a low-carbon steel crucible, homogenized at 350°C and extruded at the same temperature. The distribution of alloying elements in homogenized specimens was determined and the microstructure of these alloys characterized. The mechanical properties were measured and compared with those of similar alloys.

Mechanical properties and microstructure of new magnesium-lithium base alloys

Pitting corrosion of AZ91D and AJ62x magnesium alloys in alkaline chloride medium using electrochemical techniques

In this paper, the microstructure of die-cast and slowly cooled specimens of two new experimental magnesium alloys (ZA104 + 0.3Ca and ZA104 + 0.6Ca) is examined. Microanalysis of specimens has revealed the presence of-Mg phase (matrix) and two intermetallic compounds containing calcium with different Zn/Al ratios. These compounds, which have a crystal structure close to that of phase [Mg32(Al,Zn)49], were also found in slowly cooled ZA104 + 0.3Ca specimens and identified as ( � and �). The microhardness of these intermetallic compounds has been obtained from specimens having the intermetallic composition and slowly cooled from the melt. The tensile and creep resistance of the two die-cast alloys (ZA104 + 0.3Ca and ZA104 + 0.6Ca) are also presented. Tensile properties are equivalent to those of the AZ91D reference alloy, but their creep deformation rate is significantly reduced by a factor 3.5–3.8 at 150 ◦ C and 4.0–7.2 at 175 ◦ C. Besides, it was found that the ultimate tensile strength and elongation of ZA104 + 0.3Ca alloy are superior to those of ZA104 + 0.6Ca alloy. It is then established that

http://library.nmlindia.org/FullText/MSEA385041286.pdf?origin=publication_detail

Microstructure and mechanical properties of ZA104 (0.3–0.6Ca) die-casting magnesium alloys

Thin films of Corning 7059, glass doped with CdS (2%–4% by weight) microcrystallites, with diameters presumably larger than 6 nm, were fabricated using rf sputtering technique. Sharp optical cutoff near 500 nm is visible on the absorption spectra of the films. Both Raman and absorption spectra presumably reveal the presence of size effects. At λ=632.8 nm the refractive index of the films varies from 1.55 to 1.69 depending on rf power. Propagation losses for TE0 guided mode are about 10 dB/cm.

Réal Tremblay

Papers

Linear, annular, and radial focusing with axicons and applications to laser machining

Mechanical properties and microstructure of new magnesium-lithium base alloys

Pitting corrosion of AZ91D and AJ62x magnesium alloys in alkaline chloride medium using electrochemical techniques

Microstructure and mechanical properties of ZA104 (0.3–0.6Ca) die-casting magnesium alloys

CdS microcrystallites‐doped thin‐film glass waveguides