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EN
Unconventional machining of magnesium alloys through die sinking and Wire Electrical Discharge Machining (WEDM) processes are preferred over conventional machining processes to overcome the rapid loss in strength and affinity that occurs with tool materials at high temperatures. in the present study, AZ91 magnesium alloy is machined in EDM using a prepared alloy tool (copper alloyed with titanium diboride). Based on Taguchi’s L27 orthogonal array, a total of 27 experiments have been conducted by varying the process parameters such as pulse on time (Ton), gap voltage (Vg) and current (Ip) with three different levels. Techniques for Order Preference by Similarity to Ideal Solution (TOPSIS) and Grey Relational Analysis (GRA) have been applied to optimize the response parameters of EDM to obtain maximum Material Removal Rate (MRR) and minimum Tool Wear Rate (TWR) and Surface Roughness (SR). Analysis of variance (ANOVA) is carried out based on F-test at a confidence interval of 95% to confirm the significant influence of individual parameters. From the above two optimization techniques, the obtained optimal values are current 15 A, gap voltage 55 V, pulse on time 30 μs and an error of less than 5% is observed from the confirmation experiments. Scanning Electron Microscope (SEM) images revealed that there is no formation of cracks but micro pits and holes are observed.
EN
In this study, AZ91 Magnesium alloy is produced by cold chamber high pressure die casting (HPDC) method. Different combinations of the cold chamber HPDC process parameters were selected as; in-mold pressure values of 1000 bar and 1200 bar, the gate speed of 30 m/s and 45 m/s, the casting temperatures of 640°C and 680°C. In addition, the test samples were produced by conventional casting method. Tensile test, hardness test, dry sliding wear test and microstructure analysis of samples were performed. The mechanical properties of the samples produced by the cold chamber HPDC and the conventional casting method were compared. Using these parameters; the casting temperature 680°C, in-mold pressure 1000 bar and the gate speed 30 m/s, the highest tensile strength and the hardness value were obtained. Since the cooling rate in the conventional casting method is slower than that of the cold chamber HPDC method, high mechanical properties are obtained by the formation of a fine-grained structure in the cold chamber HPDC method. In dry sliding wear tests, it was observed that there was a decrease in friction coefficient and less material loss with the increase of hardness values of the sample produced by the cold chamber HPDC method.
EN
In this study, surface remelting treatment of the AZ91 magnesium alloy by means of welding using a non-consumable electrode in an inert gas shield was carried out. Three variants of surface treatment were used, i.e. the single torch variant with a single heat source without cooling down the samples, the single torch variant with a single heat source and a cooling system with liquid nitrogen, and the double welding torch variant with a double heat source in the torches operating in a tandem configuration. Experimental verification of the applied apparatus solutions was based on both macro- and microstructural assessment of the obtained effects. Comparative analysis of the variants used and the obtained microstructural results allowed the authors to indicate the deficiencies and limitations of particular solutions and to single out the best solution that would be useful for modifying the surface layers of magnesium alloys, as well as other materials having a strong oxygen affinity.
PL
W pracy dokonano modyfikacji tarciowej z przemieszaniem materiału FSP (ang. friction stir processing) warstwy wierzchniej stopu magnezu AZ91 z wykorzystaniem cząstek ceramicznych Cr2O3. Zakres badań obejmował makro- i mikroskopową ocenę zmian mikrostrukturalnych wywołanych przeprowadzoną obróbką oraz pomiar twardości materiału. Stwierdzono korzystny wpływ modyfikacji tarciowej FSP na mikrostrukturę i właściwości stopu magnezu. Obróbce powierzchniowej towarzyszył wzrost twardości materiału oraz silne rozdrobnienie mikrostruktury w warstwie modyfikowanej. Stwierdzono intensywne rozproszenie cząstek fazy ceramicznej Cr2O3 w warstwie wierzchniej stopu, skutkujące powstaniem mikrostruktury kompozytowej typu metal-ceramika. Obecność cząstek Cr2O3 ujawniono zarówno w strefie wymieszania SZ (ang. stirred zone) jak i w strefie odkształcenia termomechanicznego TMAZ (ang. thermomechanically affected zone). Charakterystyczną cechą strefy wymieszania było silne rozdrobnienie mikrostruktury i obecność równoosiowych ziaren; w strefie TMAZ stwierdzono natomiast dominację ziaren o wydłużonym kształcie, rozmieszczonych wzdłuż linii przemieszczania się uplastycznionego materiału. Przeprowadzone badania wykazały, że wykorzystanie technologii FSP do modyfikowania warstwy wierzchniej stopów magnezu za pomocą cząstek ceramicznych jest rozwiązaniem obiecującym, o dużym potencjale aplikacyjnym.
EN
The study examined the effects of the friction stir processing (FSP) of the surface layer of AZ91 magnesium alloy with the application of Cr2O3 ceramic particles. The microstructural changes resulting from the treatment were assessed both macro- and microscopically, and hardness measurement was performed. FSP was found to have a positive impact on the microstructure and properties of the magnesium alloy. The surface treatment led to an increase in the hardness of the material and to a strong microstructure refinement of the processed layer. In the friction-processed samples, Cr2O3 ceramic particles were observed to be highly dispersed in the surface layer of the material, thus forming a metal-ceramic composite microstructure. Cr2O3 particles were present in both the stirred zone (SZ) and the thermo-mechanically affected zone (TMAZ). A characteristic attribute of the SZ was its high microstructure refinement and the presence of equiaxial grains, whereas in the TMAZ elongated grains distributed along the lines of displacement of the softened material were prevailing. The research has demonstrated that the use of the FSP technology for the processing of the surface layer of magnesium alloys with ceramic particles is a promising solution, which has a considerable application potential.
5
Content available remote Surface modification of the AZ91 magnesium alloy
EN
The main purpose of the study was to modify the surface layer of the AZ91 magnesium alloys with the use of the GTAW (Gas Tungsten Arc Welding) method. The remelting process was conducted with the use of an AC current with the concurrent cooling of the magnesium alloy in the liquid nitrogen bath. The assessment of the effectiveness of the treatment carried out with the use of the GTAW method was based on the analysis of the surface layer structure, and the investigation of hardness and the resistance to abrasion wear. Besides, the investigations of the corrosion resistance were carried out. The analysis of the treatment parameters combined with a macroscopic assessment and the structural changes in the surface layers allowed to distinguish some correlations attesting to the possibility of the remelting zone geometry shaping. The found structural effects of treatment such as significant refinement of the structure and its homogenization, as well as the positive results of corrosion investigations and mechanical tests proved that it is possible to achieve the intended research objectives and effectively modify magnesium alloys by the welding method.
EN
The results of structure investigations of an experimental magnesium matrix composite reinforced with Ti6Al4V particles in as-cast conditions and after heat treatment are presented. The commercial AZ91 magnesium alloy was used as the matrix alloy. The experimental composite was reinforced with 30 wt.% Ti6Al4V alloy spherical particles. The investigated material was obtained by the stir-casting method. The microstructure of the fabricated composites was characterized by uniform distribution of the titanium particles within the magnesium matrix. The phase composition of the composite was typical for the used component. New phases were not revealed by XRD techniques. Solution annealing at 693 K for 24 h and 48 h (with water quenching), followed by ageing at 423 K for 16 h was carried out. After ageing discontinuous precipitation process of the γphase (typical for AZ91 magnesium alloy) was observed. The applied heat treatment processes did not bring about changes in the chemical composition between the used components.
PL
Przedstawiono wyniki badań struktury kompozytów na osnowie magnezowej z cząstkami Ti6Al4V w stanie pierwotnym oraz po obróbce cieplej. Na osnowę kompozytu wytypowano komercyjny stop magnezu AZ91. Doświadczalny kompozyt umacniany był 30% wag. sferoidalnych cząstek Ti6Al4V. Badany materiał został wytworzony metodą odlewniczą. Mikrostruktura wytworzonego kompozytu charakteryzowała się jednorodnym rozmieszczeniem cząstek tytanowych wewnątrz magnezowej osnowy. Skład fazowy kompozytu był typowy dla użytych komponentów. Nie ujawniono metodami XRD występowania tych faz. Przeprowadzono ujednorodnianie w temperaturze 693 K przez 24 i 48 h (z chłodzeniem w wodzie) ze starzeniem w temperaturze 423 K przez 16 h. Po starzeniu obserwowano proces nieciągłego wydzielania fazy γ (typowego dla stopu magnezu AZ91). Użyte procesy obróbki cieplnej nie wywołały zmian w składzie chemicznym pomiędzy zastosowanymi komponentami.
EN
Magnesium alloys are widely applied in aircraft and automotive industry, due to their low density and high specific strength. Welding methods can be used to join Mg alloy elements and to repair or regenerate defective or worn-out castings. Therefore the influence of weld joint’s microstructure on mechanical properties needs to be studied. In present paper high temperature mechanical properties of AZ91 Mg alloy weld joint was investigated. Tensile tests were conducted in temperature range between 20 and 200°C. Ultimate tensile strength decreased as the temperature increased from 50°C. At temperature up to 150°C rapture occurred in the base metal, at 200°C rupture location switched to the weld fusion zone. Based on metallographic and fractographic observation, the fracture mechanism was described. Macro crack formed from the merger of micro cracks occurring at massive β phase precipitates.
EN
AZ91 magnesium alloy matrix composites with aluminosilicate glass cenospheres were fabricated successfully by the pressure infiltration method. Different parameters of the fabrication process, such as temperature of the mould and temperature of cenospheres were used. Influence of the temperature variation of particular parameters on the microstructure has been investigated. The microstructure of AZ91 magnesium alloy and fabricated composites have been investigated by light microscopy (LM) and scanning electron microscopy (SEM). The results revealed that AZ91 magnesium alloy consists of α-Mg matrix and eutectic α-Mg17Al12 and a small amount of discontinuous precipitates of γ phase. The microstructure of matrix AZ91 in fabricated composites is characterized also by the presence of α-Mg matrix and eutectic α-Mg17Al12. However, in the composite fabricated by using the mould heated to 500 °C more discontinuous precipitates of γ phase were observed.
EN
The main characteristic of aluminosilicate glass cenospheres and their possible use as a component of magnesium matrix composites were presented. The results revealed that particular parts of cenospheres differ insignificantly from each other and it depends on which power plant cenospheres come from. The characteristic of cenospheres concerned their structure and phase composition and dimensions such as: wall thickness and size of pores occurring in walls, depending on cenospheres origin. Thickness of cenospheres walls and pore size were measured by using ImageJ computer software. The structure of aluminosilicate glass cenospheres and their phase composition have been investigated by scanning electron microscopy and X-ray diffraction (XRD). The possibility of cenospheres utilization in the fabrication of magnesium matrix composites was presented on the example of AZ91 magnesium alloy composite with fly ash cenospheres. Composite was fabricated by pressure infiltration method.
EN
Derivative thermal (ATD) and microstructure analyses of gravity cast AZ91 magnesium alloy are presented. The alloy was cast into cold steel and sand moulds with the same dimensions. ATD curves - solidification curves and their first derivative - are presented. The investigated alloy exhibited a strong alloying elements segregation and the presence of [alpha] solid solution and [alpha+gamma] (Mg17Al12) eutectic mixture. Discontinuous precipitates of [gamma] phase were also observed in the microstructure of AZ91 cast into sand mould.
EN
The paper presents the results of studies on the effect of heat treatment and cyclic deformation on the properties of the magnesium alloy AZ91. The alloy was subjected to heat treatment by solutioning and ageing (420 °C/24 h/powietrze+210 °C/4 h/powietrze) and then to cyclic uniaxial zero-start pulsating loads. The maximal amplitudes of cyclic loads 54 and 74 MPa were lower than the offset yield strength of the alloy. The microstructure of the alloy is presented, while the properties of the alloy before and after cycling loading (up to 50 and 70 cycles) are determined by measurements of residual stress made by the X-ray method of sin2fi. It has been found that cyclic deformation causes the strengthening of the alloy AZ91. The strengthening of the alloy is found to increase with increasing loading amplitude and number of cycles, with the greatest strengthening effect occurs in the first three loading cycles.
PL
W pracy przedstawiono wyniki badań wpływu obróbki cieplnej i cyklicznego odkształcania na własności stopu magnezu AZ91. Stop poddano obróbce cieplnej przesycania i starzenia (420 stopni C/24 h/powietrze+210 stopni C/4 h/powietrze) a następnie cyklicznym jednoosiowym obciążeniom odzerowo tętniącym. Maksymalne amplitudy cyklicznych obciążeń 54 i 74 MPa były niższe od umownej granicy plastyczności stopu. Przedstawiono mikrostrukturę stopu, a własności stopu przed i po cyklicznym obciążaniu (po 50 i 70 cyklach) określono przez pomiary naprężeń szczątkowych metodą rentgenowską sin2 fi. Stwierdzono, że cykliczne odkształcanie powoduje umocnienie stopu AZ91. Wykazano, że umocnienie stopu zwiększa się wraz ze wzrostem amplitudy obciążania oraz z liczbą cykli, a największy efekt umocnienia występuje w pierwszych trzech cyklach obciążania.
PL
Celem publikacji jest ocena wpływu różnych sposobów klasycznej obróbki cieplnej na zmiany właściwości mechanicznych - w temperaturze pokojowej - stopu magnezowego typu AZ91, w odniesieniu do analogicznych charakterystyk dla stanu wyjściowego (lanego). Materiał badawczy odlewano grawitacyjnie do form piaskowych oraz kokil. Odpowiednio przygotowane mechanicznie próbki poddano obróbce cieplnej, podczas której doprowadzone zostały ze stanu wyjściowego (F - as-fabricated) do stanów: T4, T5 oraz T6. Badanie właściwości mechanicznych obejmowało wyznaczenie Rm, Rp02 i A5 w statycznych próbach rozciągania oraz pomiary twardości (HB) metodą Brinella. Wyniki badań wskazują, iż właściwości mechaniczne odlewniczego stopu AZ91 można w istotny sposób kształtować, poprzez zastosowanie odpowiedniej obróbki cieplnej.
EN
The aim of this publication is to assess the effect of different types of the standard heat treatment on changes in mechanical properties at room temperature of magnesium alloy from AZ91 family referred to the same properties in as-fabricated state. The investigated alloy was gravity cast into sand and metal moulds. The mechanically prepared specimens were subjected to a heat treatment during which they were transformed from the as-fabricated state to conditions: T4, T5 and T6. Testing of mechanical properties included determination of Rm, Rp02 and A5 during static tensile test and Brinell hardness measurements (HB). The results of the investigations indicate that the mechanical properties of cast AZ91 alloy can be successfully shaped through the application of proper heat treatment.
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