Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

Phd by thesis

Particle reinforced metal matrix composites are now being produced commerically, and in this paper the current status of these materials is reviewed. The different types of reinforcement being used, together with the alternative processing methods, are discussed. Depending on the initial processing method, different factors have to be taken into consideration to produce a high quality billet. With powder metallurgy processing, the composition of the matrix and the type of reinforcement are independent of one another. However, in molten metal processing they are intimately linked in terms of the different reactivities which occur between reinforcement and matrix in the molten state. The factors controlling the distribution of reinforcement are also dependent on the initial processing method. Secondary fabrication methods, such as extrusion and rolling, are essential in processing composites produced by powder metallurgy, since they are required to consolidate the composite fully. Other methods, suc...

Particle reinforced aluminium and magnesium matrix composites

Influence of grain size on the compressive deformation of wrought Mg-3Al-1Zn

Effect of long-period stacking ordered phase on mechanical properties of Mg97Zn1Y2 extruded alloy

In this paper, recent progress in magnesium matrix composite technologies is reviewed. The conventional and new processes for the fabrication of magnesium matrix composites are summarized. The composite microstructure is subsequently discussed with respect to grain refinement, reinforcement distribution, and interfacial characteristics. The mechanical properties of the magnesium matrix composites are also reported.

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Review of recent studies in magnesium matrix composites

Strengthening mechanisms in the rapidly solidified AZ 91 magnesium alloy

Magnesium alloy having a breaking load of at least 290 MPa, more particularly at least 330 MPa, having the following composition by weight: Al 2-11%, Zn 0-12%, Mn 0-0.6%, Ca 0-7%, but with the presence of at least Zn and/or Ca, having a mean particle size less than 3 μm, a homogeneous matrix reinforced with intermetallic compounds having a size less than 1 μm precipitated at the grain boundaries, this structure remaining unchanged after storage at 200° C. for 24 hours; and a process for producing it by rapid solidification and consolidation by extrusion at a temperature between 200° and 350° C.

High mechanical strength magnesium alloys and process for obtaining these alloys by rapid solidification

Molten magnesium oxidises rapidly during casting and handling unless it is protected by an atmosphere that stabilises the surface. In this article, results from the analysis of magnesium melt surfaces exposed to SO 2 and different fluorine-containing atmospheres are reported. The microstructure of the surface films, formed during controlled exposure in laboratory scale experiments, have been characterised using X-ray diffraction (XRD), electron probe microanalysis (EPMA) and transmission electron microscopy (TEM). Both SO 2 and the fluorine-containing gases were found to protect the melt from burning and vaporisation in oxidising atmospheres. The protected surfaces generally had a shiny metallic appearance, but turned dull grey after extended exposure to high concentrations of fluorine containing gases. All the surface films initially consisted of small crystallites of MgO forming a thin continuous film. This film was found to contain some sulphur when the melt was protected by SO 2 , while fluorine was the only element detected in the oxide when SF 6 or other fluorine-containing gases were used for protection. With increasing exposure time, the films gradually grew thicker and the fluorine/oxygen-ratio of the films formed in fluorine-containing atmospheres increased. Finally, after long term exposure to fluorine containing atmospheres, the thermodynamically stable MgF 2 -phase was formed. In a N 2 atmosphere, SO 2 and SF 6 -additions did not protect the magnesium, indicating that a rapid initial formation of MgO is necessary to obtain protective films.

Characterisation of the surface films formed on molten magnesium in different protective atmospheres

The superplastic properties of conventionally cast and rapidly solidified magnesium alloy AZ91 have been studied. The latter material had by far the best superplastic properties, and elongations of at least 1000% were obtained in the temperature range 275–300 °C. Formation of pores during superplastic deformation had an adverse effect on the room-temperature mechanical properties.

Superplasticity in magnesium alloy AZ91

Application of rapid solidification to magnesium alloys generally increases the mechanical properties by a factor of 2–2.5 compared with conventional wrought magnesium alloys. This is mainly due to a smaller grain size. What is the creep behaviour of these high strength magnesium alloys? Planar flow cast magnesium alloys have been cast and extruded. The mechanical properties in tension and compression, the stress-relaxation in compression and the tensile creep properties have been tested at temperatures from RT to 150 °C. Traditionally one would expect poor creep resistance in a small grained material. In some rapidly solidified aluminium alloys, however, the creep resistance is good, due to fine particles pinning grain boundaries and impeding dislocation movements. In the magnesium alloys tested there is a big difference in the creep resistance depending on the microstructure of the alloys. The on-going study focuses on the optimal microstructure for good mechanical properties and creep resistance.

Haavard T. Gjestland

Papers

Strengthening mechanisms in the rapidly solidified AZ 91 magnesium alloy

High mechanical strength magnesium alloys and process for obtaining these alloys by rapid solidification

Characterisation of the surface films formed on molten magnesium in different protective atmospheres

Superplasticity in magnesium alloy AZ91

Stress-relaxation and creep behaviour of some rapidly solidified magnesium alloys