Wyniki 1-10 spośród 16 dla zapytania: authorDesc:"JAN DUTKIEWICZ"

Characterization of friction stir welds of 6013 and 6013/2017A aluminium alloy sheets

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The Friction Stir Welding (FSW) takes place due to rotation and movement of FSW tool. A tool moves the welded materials along its edges. As a result of the FSW process good quality of a weld is obtained below the melting point. The FSW weld consists of particular zones: the weld nugget (area in the centre), thermomechanically affected zone and heat affected zone. The weld nugget is frequently surrounded by rings known as an onion microstructure (rings) especially within the FSW welds of the aluminium alloys of 6XXX series. The microstructure and properties of the particular zones depend strongly on the welding parameters [1] and the type of the welding tool pin and shoulder. For example, a grain size within the weld nugget was found to depend strongly on the linear velocity of the tool [2]. The various studies of the aluminium alloys that underwent friction stir welding show various dislocation densities within welds’ nuggets [3]. The hardness in the region of the weld can change in many ways [4, 5]. The welds formed by FSW between the aluminium alloy sheets and especially between the 6XXX series alloys are much better than those formed by a high-temperature welding methods like Gas Metal Arc Welding especially due to lower temperature of welding [6]. The FSW technology is applied presently for welding of the aluminium and magnesium alloys as well as copper, steel, composites and dissimilar materials [7÷10]. The alloys of the 6XXX series are often applied in the constructions and transportation industry. The 6013 aluminium alloy has broad application in the production of many car parts like vehicle structure, wheels, panels and others [11]. The mentioned alloy can be welded by the means of the FSW method similarly as other alloys of the 6XXX series [11, 12]. Uzun et al. [13] signaled the possibility of welding the alloy with steel. Therefore, the aim of the paper was to analyze the microstructures and properties of the [...]

Modyfikacja mikrostruktury stopów magnezu Mg-7Al dodatkami metali ziem rzadkich oraz Mg-3Al metodą ECAP

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W ostatniej dekadzie zanotowano szersze zainteresowanie rozwojem nowych stopów magnezu. Obecnie stopy magnezu znajdują wiele zastosowań w przemyśle samochodowym oraz elektronicznym, przede wszystkim w urządzeniach przenośnych. Obserwuje się również rosnące zainteresowanie stopami magnezu przez przemysł obronny oraz w lotnictwie i kosmonautyce [1]. Jednym z ograniczeń szerokiego zastosowania stopów magnezu w podwyższonej temperaturze powyżej 120°C jest mała odporność na pełzanie. Aby zwiększyć wytrzymałość mechaniczną stopów magnezu w podwyższonej temperaturze wprowadza się nich dodatki metali ziem rzadkich. Do stopów Mg-Al dodaje się metali ziem rzadkich w postaci mischmetalu zawierającego głównie Ce, La i Nd [2, 3]. Przykładami takich stopów są AE41 czy AE42 o większej odporności na pełzanie dzięki stabilnym termicznie fazom międzymetalicznym utworzonym przez metale ziem rzadkich. Niemniej jednak nie ma dostatecznej wiedzy na temat wpływu poszczególnych pierwiastków metali ziem rzadkich na mikrostrukturę stopów Mg-Al. Drugim ograniczeniem stosowania stopów magnezu jest ich mała plastyczność i ograniczona ciągliwość w temperaturze pokojowej, co jest związane z budową krystaliczną magnezu, który ma strukturę heksagonalnie zwartą z dwoma podstawowymi systemami poślizgu. Jedną z metod poprawy właściwości mechanicznych stopów jest metoda przeciskania przez kanał kątowy ECAP (Equal Channel Angular Pressing), co powoduje znaczne rozdrobnienie ziarna, dzięki temu poślizg staje się możliwy przy udziale granic ziaren. Pozytywny efekt tej metody zanotowano dla wielu stopów: aluminium [4], miedzi [5] i magnezu [6, 8, 16÷18]. W artykule przedstawiono wpływ modyfikacji stopu Mg-7% Al polegającej na wprowadzeniu dodatku 3% Nd i 10% Ho na jego mikrostrukturę. Ponadto badano mikrostrukturę i właściwości mechaniczne stopu AZ31 po czterokrotnym przejściu przez kanał kątowy w temperaturze 150°C i 250°C. Materiały i metodyka badań Pierwsza czę[...]

Microstructure evolution and its influence on martensitic transformation in Ni-Mn-Sn alloys

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Magnetic shape memory alloys (MSMA) have received considerable attention owing to their outstanding magnetoelastic and magnetocaloric properties [1?€3]. Among various MSMA the Heusler Ni-Mn-Sn alloy system has been identified as a promising alternative to the most widely studied Ni-Mn-Ga alloy, whose applications are limited by high Ga cost, poor ductility and low martensitic transformation temperature (Ms) [4, 5]. Ni-Mn-Sn is an off-stoichiometric intermetallic compound featuring L21 Heusler structure in the high temperature austenite phase. It may undergo temperature, stress or magnetic field induced martensitic transition to a lower temperature modulated martensite phase [6]. The magnetic field provoked behaviour is in this case similar to the usual shape memory effect occurring due to the heat induced reverse transformation, and therefore it is termed metamagnetic transition as opposed to Ni-Mn- Ga, which transforms from austenite to martensite in the presence of a sufficiently high magnetic field. The coupling between magnetism and structure observed in these alloys entails that the magnetic field can induce not only an entropy change of magnetic contribution (?˘SM) but also a supplementary fraction related to the latent heat associated with the structural transformation (?˘SS ). Entropy changes up to 10.4 J/kgK at 10 kOe has been reported for Ni-Mn- Sn alloy system [7]. Increased entropy changes may be utilized for magnetic refrigeration, which is of fundamental importance from the environmental point o view. The Ms and TC of the martensite phase are found to be strongly dependant on composition whereas TC of austenite is less sensitive to it [8]. The phase transition temperature dependence on composition is mainly attributed to the change in valence electron concentration (determined as the number of 3d and 4s electrons of Ni and Mn and the number of 5s and 5p electrons of Sn and expressed in terms of electron to [...]

Structure, thermal and magnetic properties of ferromagnetic Co-Ni-Al alloys

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Ferromagnetic shape memory alloys (FSMAs) are being intensively studied because of their potential applications as smart materials. Martensitic transformations and lattice reorientation processes in FSMAs can be triggered not only by changes in temperature and stress, as in conventional SMAs, but also by applying an external magnetic field. The martensitic phase transformation of the ferromagnetic Co-Ni-Al alloy systems has been studied in several papers [1÷5]. The Curie and the martensitic transition temperatures of the β phase increase and decrease with increasing the Co content, respectively. The shape memory effect proceeds due to the thermoelastic martensitic transformation from the B2 parent phase into the martensite phase with L10 structure. The unique properties of the Co-Ni-Al alloy system is an improved ductility allowing hot rolling and cold rolling of a presence of γ phase with fcc structure. The β single-phase polycrystalline alloys show a poor ductility [2]. It has been reported that the hot fabricability of NiAl-based alloys could be improved by the introduction of γ phase [6, 7]. Since the composition range of β phase exhibiting the FSM is located near the β + γ two-phase region, the β-based alloys are able to introduce the γ phase by suitable choice of composition and heat treatment temperature [1, 2]. Several percent of γ phase significantly improves the ductility of the Co-Ni-Al two-phase alloys, which is of great advantage for practical applications [8]. Compounds with a strong coupling between crystallographic structure and magnetism usually exhibit a magnetic field dependence of the structural transitions. A typical example is the Gd5(SixGe1-x)4 alloys (0.24 ≤ x ≤ 0.5), where a transformation from the paramagnetic monoclinic phase to the ferromagnetic orthorhombic phase can be induced either by cooling or by the application of a magnetic field [9[...]

The role of ECAP in densification behaviour of PM aluminium alloy

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Powder metallurgy (PM) of aluminium alloys are used in a variety of industrial applications, such as the transportation (automotive and aerospace), and commercial areas. Light weight aluminium alloys, showing excellent workability, high thermal and electrical conductivity, represent a good choice for the PM industry to produce new materials with unique capabilities, not currently available in any other powder metal parts. Moreover, the requirement on mechanical properties (i.e. high tensile strength with adequate plasticity) should assure an increasing role for aluminium alloys in the expanding PM market. Due to their unique mechanical and physical properties, aluminium PM alloy parts are advantageous in engineering applications because of higher possibilities in material selection and design. Therefore, application of PM products is possible only if the designer understands the deformation characteristics of the virgin material. On the other hand, due to the presence of porosity in the aluminium PM parts, the deformation behaviour of the PM parts is considerably different from the conventional cast and wrought materials. It has already been extensively demonstrated that the mechanical and tribological properties of PM materials are directly controlled by their density and microstructure [1÷3]. Therefore a boost up in the application of PM materials could be derived from a complete knowledge of the mutual relationship between density (and/or porosity), composition and microstructure. Conventional PM method (press-and-sinter) is still most used process in PM production, mainly due to its cost effective properties. The process of powder pressing depends on a number of factors, such as the rheology (flow properties of powders during process), stress distribution within compacts and across particle-toparticle, hardness of particles (with respect the work hardening), strength distribution of particles, lubricant type and place of d[...]

Ball milling of Al-based alloys to obtain amorphous-nanocrystalline structure

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Considering a high strength to weight ratio of Al-based alloys as well as outstanding properties of metallic materials in a glassy state, amorphous aluminum alloys have attracted considerable attention due to their potential in structural applications for transportation and aviation industry[1÷8]. Metastable phases in amorphous or quasicrystalline state can induce two to three times higher strength as compared with those processed through precipitation/age-hardening in crystalline Al‑alloys [1, 2]. The first formation of amorphous single phase in Al‑based alloys containing more than 50 at. % Al was found in 1981 for Al-Fe-B and Al-Co-B ternary alloys [1], but they were very brittle and hence have not attracted much attention. Since then, glass forming ability has been determined in a number of Al-based alloys consisting of Al + transition metal + rare-earth elements, processed mainly by rapid solidification or gas atomization methods [8]. It has been also found that ductility in aluminum alloys can be improved when a few nanometer size crystals are embedded in the amorphous matrix [7]. Choi et al. [9] reported tensile fracture strength as large as 1980 MPa for an amorphous alloy containing about 18% Al nanocrystals - this strength was nearly 1.6 times higher than for the fully amorphous alloy. Later, Kawamura et al. [3] attained a bulk compressive strength of 1420 MPa by hot compaction of gas-atomized amorphous Al85Ni5Y8Co2 powder with nanocrystalline dispersed amorphous matrix. Among many techniques of synthesizing novel materials including nanocrystalline or amorphous products there are melt spinning, gas atomization and similar rapid quenching methods [2] but mechanical alloying (MA) by high-energy ball milling is a convenient solid state synthesis alternative for them. It gives the opportunity of obtaining various phases in the material without need to melt pure elements of the alloy. Furthermore, in the one pro[...]

Structural analysis of composite powders obtained from recycled material

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Aluminium chips obtained from machining are very difficult to be recycled. Most of them are used in industry, mainly in foundry operations, due to the relatively high tolerances in the chemical composition of molten wrought alloys. However, melting and casting techniques cause high environmental pollution and form other scraps in the final stage of processing generated elements [1, 2]. Therefore scientist try to find some alternative processes for the use of chips. In several publications aluminium chips have been used in powder metallurgy (PM), starting from recycled material, milled or cut, adding reinforcement particles then followed by either cold pressing, hot extrusion, as well as hot pressing [2÷5]. Some works consider also recycled material directly in the form of chips, without any other addition, shaped by cold or hot extrusion and plastic consolidation as additional operations [6, 7]. The most promising solution seems to be the mechanical alloying (MA) process. The method allows to obtain uniformity of components, good adhesion between the reinforcement particles and metal matrix, as well as a significant fragmentation of the microstructure [8]. In this work the microstructural changes in powder particles and the influence of MA processing on the distribution of SiC reinforcement and their corresponding properties are investigated. Experimental procedure AlSi5Cu2 aluminium alloy chips obtained from recycled materials were reinforced 10 wt % of silicon carbide (α-SiC) particles having an average initial size of about 2 μm. The chemical composition of[...]

Massive amorphous CuZrTiAg alloy processed by ball milling and hot pressing

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Cu50Ag10Zr30Ti10 alloy well known as a good glass former has been ball milled for 40 hours starting from pure elements. Changes of particle’s size and crystallographic structure during milling has been determined. The particles first grow, then decrease after 40 hours of milling, when powders possess amorphous structure. The transmission electron microscopy TEM studies of powders allowe[...]

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