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The research of forgeability of magnesium alloy at warm forming temperatures

Kapustova M., Sobota R., Bilik J.

Hutnik, Wiadomości Hutnicze

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2016

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Vol. 83, nr 9

410--412

EN

The presented contribution is aimed at research of temperature influence on workability of a selected magnesium alloy at temperature interval for warm forming. The magnesium alloy type AZ31 was selected for experimental purposes. The mentioned alloy is used for production of drop forgings. In order to consider forgeability, Židek´s pressure test at warm conditions was selected and used as technological test. The author of mentioned test recommends cylinder shaped test sample with four notches. For magnesium alloy AZ31 hot forming at temperature interval from 250°C to 425°C is recommended. The pressure tests were conducted within the temperature interval of 200−350°C, i. e. at temperatures belonging to lower limit of recommended temperature interval, in order to acquire as much information as possible on behaviour, plasticity and formability of magnesium alloy at lower forming temperatures.

PL

Zakres niniejszej pracy dotyczy wpływu temperatury na kowalność stopów magnezu. Wybrany do badań Stop AZ31 jest kształtowany w procesach kucia, czego efektem jest wytwarzanie odkuwek o zróżnicowanych kształtach. Biorąc pod uwagę kowalność do badań, wybrano metodę testu ciśnieniowego w podwyższonej temperaturze. Autorzy tej metody zalecają badania próbek w kształcie walca z czterema karbami. Dla badanego stopu zaleca się temperaturę obróbki plastycznej w przedziale 250°C do 425°C. Test ciśnieniowy przeprowadzono w zakresie temperatury od 200−350 °C, ze względu na analizę zachowania się stopu podczas kształtowania w temperaturze z dolnego zalecanego zakresu przeróbki plastycznej.

2

Warm stretch-formability of 0.2%C-1.5%Si-(1.5-5.0)%Mn TRIP-aided steels

Sugimoto K., Tanino H., Kobayashi J.

Archives of Materials Science and Engineering

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2016

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Vol. 80, nr 1

5--15

EN

Purpose: Warm stretch-formability of 0.2%C-1.5%Si-(1.5-5.0)%Mn transformation-induced plasticity (TRIP)-aided sheet steels with annealed martensite matrix was investigated for automotive applications. Additionally, the warm stretch-formability was related with the retained austenite characteristics. Design/methodology/approach: This study was aimed to enhance the stretchformability by warm forming which stabilizes mechanically a large amount of metastable retained austenite in the steels. Findings: The warm stretch-formability increased with an increase in Mn content. The stretch-formability of 5% Mn steel was improved by warm forming at peak temperatures of 150-300°C, which was the same level as that of 0.2%C-1.5%Si-1.5%Mn0.05%Nb TRIP-aided martensitic steel. The superior warm stretch-formability was caused by a large amount of mechanically stabilized retained austenite which suppresses considerably void initiation and growth at interface between matrix and transformed martensite. Higher peak temperatures for the stretch-formability than that for the total elongation was associated with high mean normal stress on stretch-forming. Research limitations/implications: The effect of warm forming on the stretchformability is smaller than that on the ductility. Practical implications: Investigation results can be easily applied to industrial technology. Originality/value: This paper presents an important result which the stretch-formability of 5% Mn TRIP-aided steel is mainly improved by stabilizing of retained austenite with low stacking fault energy. On the forming, only strain-induced α’-martensite transformation takes place and suppresses the void growth. The strain-induced bainite transformation never occurs during forming in 5% Mn steel, differing from conventional 1.5% Mn TRIP-aided steel.

3

Warm forming of stainless steel sheet

Stachowicz F., Trzepieciński T., Pieja T.

Archives of Civil and Mechanical Engineering

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2010

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Vol. 10, no 4

85-94

EN

The aim of warm sheet metal forming processes is to improve plastic flow of material, as well as to decrease the springback effect. This investigation deals with the effect of temperature in the range from 20 C to 700 C on basic material parameters of stainless steel sheet metal such as yield stress, ultimate strength, total and uniform elongation, strain hardening parameters and plastic anisotropy factor. The results of carried out investigations will be useful for deep drawing processes preparation and modification, especially considering proper forming temperature. It was determined that the most suitable temperature of warm forming of the AMS 5604 stainless steel sheet is 500 C. Examination of the influence of the temperature, sheet thickness and material heating method (only sheet heating, sheet and forming die heating, isothermal conditions) on springback quantity was performed in air bending test. The MSC Marc Mentat commercial computer code was used for numerical simulation of analyzed forming processes.

PL

Celem procesów plastycznego kształtowania blach na półgorąco jest zwiększenie możliwości plastycznego płynięcia materiału, jak również zmniejszenie wartości powrotnych odkształceń sprężystych. Prezentowane wyniki badań dotyczą wpływu temperatury rozciągania próbek z zakresu 20 C do 700 C na wartość podstawowych parametrów mechanicznych blachy ze stali odpornej na korozję, takich jak: granica plastyczności, granica wytrzymałości, wydłużenie równomierne, wydłużenie całkowite, parametry krzywej umocnienia odkształceniowego, współczynnik anizotropii plastycznej. Uzyskane wyniki mogą być przydatne do opracowywania oraz modernizacji procesów plastycznego kształtowania blach, zwłaszcza w zakresie doboru temperatury kształtowania. Określono, że najbardziej odpowiednią temperaturą kształtowania na półgorąco blach ze stali odpornej na korozję AMS 5604 jest temperatura 500 C. Ocenę wpływu temperatury kształtowania, grubości blachy oraz sposobu nagrzewania (nagrzewana tylko blacha, nagrzewana blacha oraz podgrzewane narzędzia, nagrzewanie izotermiczne w przestrzeni zamkniętej) na wartość powrotnych odkształceń sprężystych przeprowadzono w próbie gięcia swobodnego. Przeprowadzone zostało modelowanie numeryczne analizowanego procesu gięcia przy wykorzystaniu oprogramowania MSC Marc Mentat.

4

Thermo-mechanical forming of sheet metal -- modelling of warm forming, heat treatments and transformations

Van Den Boogaard A. H., Kurukuri S., Ghosh M., Miroux A. G.

Computer Methods in Materials Science

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2009

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Vol. 9, No. 1

5-11

EN

Although basically all sheet forming processes are thermo-mechanical forming processes, the influence of temperature changes can most often safely be ignored. Two cases are considered, in which the interaction between thermal and mechanical behaviour cannot be neglected: 1. if the material is heated or cooled with the purpose to get different mechanical properties and 2. if the material properties vary considerably in the range between 20 and 100 °C, which is the range in industrial sheet forming processes without external heating or cooling. An example of the first one is temperature enhanced forming of aluminium sheet. In this process, parts of the tools are heated and other parts are cooled, in order to increase the formability. For simulations, this requires a material model that is suitable for the complete range of temperatures between 20 and 250 °C. Three models: a completely phenomenological model, the Bergström model and the Alflow model are evaluated with respect to temperature enhanced deep drawing of cylindrical cups of both Al-Mg and Al-Mg-Si alloys. A yet unexplained observation in experiments was that the earing profile changed between low temperature an elevated temperature deep drawing. Another type of temperature influence to enhance the formability of aluminium is an intermediate annealing step. Here, the thermal and mechanical loading is separated in time, but still they influence eachother, especially when aging materials are used. Experiments on, and models for an Al-Cu alloy are presented. The initial approach to completely reset the mechanical material properties after a heat treatment needed only very little correction. An example of the second type is the forming of austenitic stainless steels. Although the temperature dependence of austenite is not significant in ordinary industrial sheet forming situations, the material experiences a strain induced martensitic transformation which is highly sensitive to the temperature, exactly in the temperature range which is industrially the most common. Although progress is recently made in micro-scale modeling of the martensitic transformation, including transformation induced plasticity; these models are not feasible for full-scale forming simulations. Therefore, macroscopic models are developed that model the most relevant aspects in deep drawing: temperature, strain and stress dependent transformation and the influence on the macroscopic mechanical behaviour. The influence of stress is experimentally determined with a biaxial testing machine, in which several strain paths between simple shear and plane strain can be imposed.

PL

Temperatura oraz rozkład prędkości odkształcenia podczas formowania aluminium na ciepło charakteryzują się duża niejednorodnością. Wykorzystywane do analizy modele naprężenia uplastyczniającego powinny uwzględniać wpływ tych niejednorodności. Opracowany w niniejszej pracy fizyczny model Nes wykorzystano do symulacji tłoczenia aluminium AA6061-T4 w warunkach odkształcenia na ciepło. W trakcie analizy zaobserwowano znaczące różnice w kształcie wypływki uzyskanej podczas odkształcenia w temperaturze pokojowej oraz 250 °C. Analiza z wykorzystaniem modelu plastyczności kryształów wykazała aktywności dodatkowych systemów poślizgu w podwyższonych temperaturach. W pracy przedstawiono wyniki analizy numerycznej dla procesów rozciągania oraz tłoczenia.