Wyniki 1-8 spośród 8 dla zapytania: authorDesc:"Grażyna Mrówka-Nowotnik"

Analysis of precipitation strengthening process in 6xxx aluminium alloys

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In this paper differential scanning calorimetry (DSC), transmission electron microscopy (TEM), static tensile tests and hardness measurements have been utilized to study the effect of the precipitation strengthening on the microstructure, mechanical (Rm and Rp0.2) and plastic (A) properties in aluminium alloys 6005 and 6082. Therefore, the parameters (time and aging temperature) of precipita[...]

The degradation of mechanical properties of Al-Si5-Cu2-Mg and Al-Cu4-Ni2-Mg alloys after soaking at high temperature

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The application of aluminium alloys for aircraft industry is determined by their properties - low density and high relative mechanical strength (Rm/δ) in particular, good electrical and thermal conduction, and very good technological properties - castability and plastic deformability. The progress of engineering and science in all aspects of world aviation is inseparable connected to production and application of aluminium alloys characterized by lower density and better mechanical properties than other applied alloys. The casting aluminium- -silicon-copper alloys with magnesium addition are widely used in the aeronautical engineering. Silicon and copper (the main alloy additions) improve the technological properties (fluidity and lower solidification shrinkage), reduce the value of thermal linear expansion - important factor for pistons production, improve the wear resistance, tensile and fatigue strength. It is known that the addition of Mg and Cu facilitates the precipitation of fine Mg2Si and Al2Cu phases and therefore improves hardening [1÷12]. A great number of investigations have recently been devoted to the effect of Cu, Ag and Sn addition on mechanical properties of Al alloys. It was found that increasing of Cu contents causes increase in tensile strength and yield stress of alloys with no harmful effect on their plasticity. Due to technological problems occurring during processing (microcraks formation) the Al-Cu alloys are not used as a widely as Al-Si-Cu alloys. Nevertheless they are commonly used as a base material for multicomponents alloys. An example is quarternary Al-Cu-Ni-Mg alloys containing up to 4.5% Cu, 2% Mg and 2% Ni charcterized by very good thermal resistance to high temperatures. This is due to presence of intermetallic phases Al6Cu3Ni and Al2CuMg forming during primary crystallization and hardening process. The [...]

Influence of strain rate and deformation temperature on the microstructure of Inconel X750 superalloy

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A fundamental feature of plastic deformation is the homogeneity of strain distribution. It is commonly accepted that at low temperatures and high strains, flow localization may develop and affect the material ductility. On the other hand, hot-deformation at intermediate temperatures may also result in localized plastic flow and non- -homogenous deformation. Flow localization, as a result of substructure instability and collective motion of a large number of dislocations characterizes coarse slip or shear banding, Luders bands and the Portevin-LeChatelier effect. Kink bands and mechanical twins may also be considered as a individual form of flow localization. Coarse slip is usually used to describe the localized flow within individual grains, whereas shear bands traverse many grains very often without any significant relation to the position of easy glide systems plane. In pure metals and single phase alloys, shear bands have been found to be preferential sites for the nucleation of both static and dynamic recrystallization. It is widely believed that in age hardenable alloys, shear bands and dislocation substructure produce preferred sites for nucleation of precipitates, thus enhancing the nucleation. These same features also are believed to enhance the particle growth rate during hot deformation as a result of higher vacancy concentration produced by intensive straining as well as increased dislocation pipe diffusion. The study of processes which are associated with dynamic aging of supersaturated solid solution during hot deformation may turn out to be very complicated because of the mutual interaction between dynamic precipitation and the structure resulting from the deformation process. The contribution of flow localization to the strain hardening or flow softening and the flow stress-strain behaviour during hot deformation of precipitation hardenable alloys is still a subject of extensive research. The interaction between [...]

Wpływ warunków umacniania wydzieleniowego na mikrostrukturę i właściwości mechaniczne stopu aluminium 2024

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Stopy aluminium grupy 2xxx (PN-EN 573-1:2006) charakteryzują się bardzo dobrą wytrzymałością na rozciąganie, dobrą odpornością na pękanie oraz zmęczenie [1÷3]. Ze względu na małą gęstość oraz bardzo dobre właściwości wytrzymałościowe są stosowane głównie w przemyśle lotniczym i samochodowym [4÷9]. Stopy te zawierają Cu jako główny dodatek stopowy oraz inne pierwiastki stopowe: Si, Mn, Mg, Ni i Ti. Jak większość technicznych stopów aluminium są wielofazowe, a objętość względna, skład chemiczny i morfologia składników fazowych mikrostruktury wywierają istotny wpływ na ich właściwości użytkowe. W zależności od zawartości Cu, Mg i Si w stopach tej grupy można wyróżnić fazy międzymetaliczne θ, S, Q [1÷4] oraz fazy zawierające żelazo: AlCuFeMn i AlCuFeMnSi [9]. Analiza wyników dotychczasowych badań [5÷7] stopów 2xxx wskazuje, że oprócz składu fazowego na właściwości wytrzymałościowe, plastyczne oraz odporność na pękanie decydujący wpływ ma obróbka cieplna, a w szczególności umacnianie wydzieleniowe. Mechanizm wydzielania faz międzymetalicznych z przesyconego roztworu α-Al jest podstawą do uzyskania dobrych właściwości mechanicznych. Pomimo wykonanych wielu prac badawczych [7, 8] zagadnienia wpływu składu chemicznego oraz kinetyki procesu wydzielania z przesyconych roztworów i rodzaju faz umacniających są nadal aktualne. Umacnianie stopów grupy 2xxx następuje wskutek wydzielania się metastabilnych faz przejściowych oraz tworzenia się stabilnych faz równowagowych [7, 8]. Przyjmuje się, że największy wzrost właściwości mechanicznych tych stopów jest wynikiem wydzielania z przesyconych stopów AlCuMg (2024) koherentnych z osnową stref Guiniera-Prestona-Bagaryatsky’ego (Cu, Mg) tworzących się z dużą prędkością poniżej temperatury 200°C i następnie częściowo koherentnych o dużej dyspersji przejściowych cząstek metastabilnych faz pośrednich S″, S′ i stabilnych S(Al2CuMg) [5, 6, 8]. Materiał do badań Materiał ba[...]

Procesy wydzielania cząstek faz umacniających z przesyconych stopów AlMgSi DOI:10.15199/28.2015.6.5

  Precipitation processes of strengthening phases' particles from supersaturated AlMgSi alloys The mechanical properties of aluminium alloy AlMgSi - a group 6xxx - allow them to be used in many areas of industries extensively. They are generally used for the production of medium-duty elements of aircraft structures, vehicles and rolling stock. Their highest strength properties are obtained when they were subjected to precipitation strengthening process. Despite of on-going projects carried out by many research's units, there is a strong need to examine the effect of chemical composition, kinetic of precipitation processes from supersaturated solutions and the influence of strengthening phases on aluminium alloys mechanical properties. This is due to both the development of new alloys, as well as the constantly increasing demands on their performance. Therefore, this paper is showing the results of study devoted to determination of the impact of the chemical composition and the precipitation strengthening process parameters on the precipitation sequence of the intermetallic phases (temperature and time) of the supersaturated AlMgSi alloys. The characteristics of the supersatureted solution decomposition sequence was performed based on calorymetry study of alloys group 6xxx. Thus, the temperature of phase precipitation for different heating rate was determined. Based on the calorimetric curves and the ln(Q/T2) of 1000/RT values the values of activation energy for precipitation and dissolution of phase components were established. Key words: stopy AlMgSi, procesy wydzielania, mikrostruktura, fazy umacniające, energia aktywacji. Właściwości mechaniczne stopów aluminium AlMgSi - grupa 6xxx - zapewniają szerokie ich stosowanie w wielu gałęziach przemysłu. Na ogół są używane do wyrobu średnio obciążonych elementów konstrukcji lotniczych, pojazdów samochodowych oraz taboru kolejowego. Swoje największe właściwości wyt[...]

Wpływ długotrwałego wyżarzania ujednorodniającego na mikrostrukturę i właściwości stopu aluminium 6066 DOI:10.15199/28.2015.6.6

  Influence of long-lasting solution annealing on the microstructure and properties of aluminum alloy 6066 The microstructure evolution and changes on the mechanical properties of aluminium alloy 6066 and its homogenization process were investigated. Therefore, the alloy was heat treated at temperature of 565°C for 3, 5, 10, 24, 48 and 72 h and this allowed to determine the influence of holding time on the morphology of microstructure constituents and mechanical properties of the examined 6066 alloy. The microstructure evolution were investigated by light microscope and scanning electron microscope. The results show that the main constituent phase in the alloy - plate-like and needle-like dispersoid of Al5FeSi transformed during homogenization process into spheroidal in shape Al(FeMn)Si phase. Additionally, the following primary phases formed during crystallization: precipitates of silicon and eutectic phases with addition of copper - Q-Al5Cu2Mg8Si6 and θ-Al2Cu were not visible, meaning they completely dissolved in the matrix of α-Al. However, primary precipitates of Mg2Si were being dissolved partially and the remnants of these precipitates with the shape of “chinese script" turn their shape into spheroidal after being heat treated for 48 hours. Key words: 6066 aluminium alloy, homogenizing, microstructure, mechanical properties. W pracy przeprowadzono długotrwałe wyżarzanie ujednorodniające w temperaturze 565°C przez 3, 5, 10, 24, 48 i 72 h i określono wpływ temperatury i czasu wyżarzania na zmiany morfologii mikrostruktury i właściwości mechanicznych stopu aluminium 6066. Ewolucję morfologii składników fazowych mikrostruktury obserwowano za pomocą mikroskopu świetlnego oraz skaningowego mikroskopu elektronowego. Stwierdzono, że podczas wyżarzania ujednorodniającego płytkowe i iglaste cząstki fazy Al5FeSi uległy przemianie w sferoidalne cząstki fazy Al(FeMn)Si. Powstałe podczas procesu krystalizacji stopów pierwotn[...]

Analysis of precipitation strengthening process in 2xxx aluminium alloys DOI:10.15199/28.2016.3.2

  This paper is showing the results of study devoted to determination of the chemical composition and strengthening process parameters effect on the precipitation sequence of intermetallic phases in the supersaturated 2xxx aluminium alloys. This study was based on a calorimetric study where temperature’s effects were determined when precipitation process occurred during heating with different heating rate of the supersaturated alloys group of 2xxx. Based on the calorimetric curves and estimated values of ln(Q/T2) and 1000/RT an activation energy for precipitation and dissolution of phase components were evaluated. Key words: aluminium alloys, precipitation strengthening, calorimetry, activation energy. Inżynieria Materiałowa 3 (211) (2016) 104÷108 DOI 10.15199/28.2016.3.2 © Copyright SIGMA-NOT MATERIALS ENGINEERING 1. INTRODUCTION The 2xxx series of aluminium alloys generally contain 2 up to 10% copper, with smaller additions of other elements. The copper provides substantial increases in strength and facilitates precipitation hardening. The introduction of copper to aluminum can also reduce ductility and corrosion resistance [1, 2]. Thus, the most common applications for these type of alloys are aerospace and automotive industries. Due to both the development of new alloys, as well as the constantly increasing demands on their performance, there was a still need to examine the effect of chemical composition, kinetic of precipitation processes from supersaturated solutions and the influence of strengthening phases on the final mechanical properties of newly developed aluminium alloys. The mechanism of age hardening responsible for strengthening is based on the formation of intermetallic products through the decomposition of a metastable supersaturated solid solution SSS obtained by solution treatment and quenching. Since the interactions between the decomposition products and the dislocations are mainly responsible for the[...]

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