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The objective of the study was to determine the feasibility of plastic forming by hot rolling of the AA2519 aluminium alloy sheets and cladding these sheets with a layer of the EN AW-1050A alloy. Numerous hot-rolling tests were carried out on the slab ingots to define the parameters of the AA2519 alloy rolling process. It has been established that rolling of the AA2519 alloy should be carried out in the temperature range of 400-440°C. Depending on the required final thickness of the sheet metal, appropriate thickness of the EN AW-1050A alloy sheet, used as a cladding layer, was selected. As a next step, structure and mechanical properties of the resulting AA2519 alloy sheets clad with EN AW-1050A alloy was examined. The thickness of the coating layer was established at 0,3÷0,5mm. Studies covered alloy grain size and the core alloy-cladding material bond strength.

The aim of the study was to test and assess products extruded from the magnesium alloys type MgAlZn: AZ31, AZ61 and AZ80A alloys in the form of Ø35mm round bars and 80x15mm flat bars. The test material was extruded in a direct system with the ram feed speed of 1 mm/s and the extrusion ratio λ = 7 ÷ 9. The extruded bars were examined in as-extruded state and after heat treatment to the T5 temper and T6 temper. The strength properties were tested and microstructure was examined with calculation of the average grain size.

Contemporary materials engineering requires the use of materials characterised by high mechanical properties, as these precisely properties determine the choice of material for parts of machinery and equipment. Owing to these properties it is possible to reduce the weight and, consequently, the consumption of both material and energy. Trying to meet these expectations, the designers are increasingly looking for solutions in the application of magnesium alloys as materials offering a very beneficial strength-to-weight ratio. However, besides alloying elements, the properties are to a great extent shaped by the solidification conditions and related structure. The process of structure formation depends on the choice of casting method forced by the specific properties of casting or by the specific intended use of final product. The article presents a comparison of AZ91 magnesium alloys processed by different casting technologies. A short characteristic was offered for materials processed by the traditional semi-continuous casting process, which uses the solidification rates comprised in a range of 5 - 20°C/s, and for materials made in the process of Rapid Solidification, where the solidification rate can reach 106 °C/s. As a result of the casting process, a feedstock in the form of billets and thin strips was obtained and was subjected next to the process of plastic forming. The article presents the results of structural analysis of the final product. The mechanical properties of the ø7 mm extruded rods were also evaluated and compared.

This paper presents a new type of underactuated ground mobile robot called Caster Car. The platform consists of a front-driven and steered wheel and two uncontrolled rear caster wheels. The Caster Car model presented can be an interesting alternative for mobile robots that connects dynamic properties of hovercrafts and classical 4-wheeled cars. Underactuated properties of the Caster Car cause that classical proportional-derivative feedback control give the ability to affect only selected configuration variables. Three mathematical models of the Caster Car are proposed: a dynamic model with free-moving casters, a dynamic model with blocked casters, and a simplified hovercraft description. Models were tested during tracking tasks with demanding trajectory using selective and full-state control. This full state control was based on the computed torque technique with the pseudoinverse operation and proportional-derivative feedback. It gives the ability to suppress unstable behaviors of uncontrolled orientation but in cost of overall effect (higher position errors).

The effect of plastic deformation process on the dissolution rate of biocompatible Mg alloys was investigated. Two biocompatible MgLi1Ca0,2Zn1 and MgLi1Ca1Zn1 alloys were selected for the study. The alloys were deformed on a 100T press at a temperature of 350°C by conventional extrusion and by the equal channel angular extrusion process (ECAE). The grain size analysis showed a high degree of the grain refinement from approximately 110 mm in the initial state to 2.8 mm after the 3rd pass of the ECAE process. Compared to as-cast state, the degree of strengthening has increased after plastic forming. The results of biodegradation tests have shown a significant increase in corrosion rate after both conventional extrusion and ECAE, although after subsequent ECAE passes, this rate was observed to slightly decrease in the MgLi1Ca1Zn1 alloy. Based on the results of macro- and microstructure examinations, the corrosion progress in samples after the extrusion process was described. [ABSTRACT FROM AUTHOR]

The paper presents the results of the die forging tests of a modified EN AW-6101 alloy with the addition of Zr, using two types of the feedstock materials. The first feedstock materials were ingots cast in a vertical semi-continuous process, the second feedstock materials were extruded rods. The die forging process was carried with parameters enabling 'on line' heat treatment (T5 temper). For comparison, forgings were also heat treated to the T6 temper and to thermo-mechanical treated to the T8 and T9 temper. Then forgings made from both feedstock materials were characterised in terms of structure, mechanical properties and electrical conductivity. [ABSTRACT FROM AUTHOR]

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The effect of plastic deformation process on the dissolution rate of biocompatible Mg alloys was investigated. Two biocompatible MgLi1Ca0,2Zn1 and MgLi1Ca1Zn1 alloys were selected for the study. The alloys were deformed on a 100T press at a temperature of 350°C by conventional extrusion and by the equal channel angular extrusion process (ECAE). The grain size analysis showed a high degree of the grain refinement from approximately 110 mm in the initial state to 2.8 mm after the 3rd pass of the ECAE process. Compared to as-cast state, the degree of strengthening has increased after plastic forming. The results of biodegradation tests have shown a significant increase in corrosion rate after both conventional extrusion and ECAE, although after subsequent ECAE passes, this rate was observed to slightly decrease in the MgLi1Ca1Zn1 alloy. Based on the results of macro- and microstructure examinations, the corrosion progress in samples after the extrusion process was described.

The paper summarizes results of twenty years of seabird observations carried out between 1977 and 1996 on the western shore of Admiralty Bay (King George Island, South Shetlands, Antarctic). Changes in population size, distribution and phenology of the breeding species as well as the appearance of non-breeding species are reported. A total of 34 species of birds were observed, including 13 breeding species. Among the non-breeding species, four were observed to visit the site regularly, six rarely, and the remaining 11 were observed only occasionally. Among breeding populations, three Pygoscelis penguin species, the main krill consumers, were most numerous. The Adélie Penguin (P. adeliae) dominated among the penguins nesting in the investigated areas, reaching 23,661 breeding pairs in 1978. Two other penguin species were less abundant with population sizes of approximately 7,200 breeding pairs for the Chinstrap Penguin (P. antarcticus) and 3,100 breeding pairs for the Gentoo Penguin (P. papua) in the same year. During the following two decades, breeding populations of pygoscelid species experienced a declining trend and their numbers were reduced by 68.0% for Chinstrap, 67.1% for Gentoo, and 33.9% for Adélie Penguins. The data reported here represent a unique reference basis and provide valuable information about indicator species, suitable for comparison with contemporary observations of bird populations in the Antarctic Peninsula region, a place of rapidly occurring climate changes and intensive harvesting of marine living resources.

The order Passeriformes is the most successful group of birds on Earth, however, its representatives are rare visitors beyond the Polar Front zone. Here we report a photo-documented record of an Austral Negrito (Lessonia rufa), first known occurrence of this species in the South Shetland Islands and only the second such an observation in the Antarctic region. This record was made at Lions Rump, King George Island, part of the Antarctic Specially Protected Area No. 151 (ASPA 151). There is no direct evidence of how the individual arrived at Lions Rump, but ship assistance cannot be excluded.

This paper presents a set of basic problems concerning the control of an underactuated dynamic system. Exemplary system of a planar rigid body with a coupling input force is described. Lie brackets method is used to show accessibility of the system. A tracking problem is solved with computed torque algorithm. The coupling force makes the convergence to zero of all state variables errors impossible. After numerical simulation, stability of the system is mentioned