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78 Щицын Ю.Д., Кривоносова Е.А., Неулыбин С.Д. и др. / Физическая мезомеханика 24 6 (2021) 78-80
УДК 621.791.755
Особенности формирования структуры и свойств магниевых сплавов при плазменной аддитивной наплавке
Ю.Д. Щицын1, Е.А. Кривоносова1, С.Д. Неулыбин1, Р.Г. Никулин1, T. Hassel2, Д.Н. Трушников1
1 Пермский национальный исследовательский политехнический университет, Пермь, 614990, Россия 2 Ганноверский университет имени Лейбница, Ганновер, 30167, Германия
Работа посвящена аддитивному формированию изделий из магниевого сплава системы магний-алюминий-марганец-цинк путем плазменной наплавки током обратной полярности. Особое внимание было уделено следующим моментам: исследование влияния испарения легирующих элементов при плазменно-аддитивной наплавке на качество материала; изучение влияния режимов наплавки (непрерывное заполнение, послойное заполнение с охлаждением при различных термических циклах) на формирование структуры и свойств синтезированного материала; уточнение влияния термической обработки на структуру и свойства наплавленного металла. Правильный подбор параметров плазменной наплавки исключает пористость и трещины в наплавленных слоях. Установлено, что плазменная наплавка обеспечивает относительную стабильность структурно-фазового состава материала предыдущих слоев при термических циклах последующих по мере формирования заготовки. В целом дисперсность структуры наплавленного сплава МА5 значительно выше, чем у литых и термообработан-ных металлических конструкций по традиционным технологиям. Плазменная наплавка током обратной полярности обеспечивает наплавленному металлу высокие механические свойства, т.е. уникальное 5-9-кратное увеличение пластичности по сравнению с литым с повышенным пределом прочности на 7-10 % как с термообработкой, так и без нее.
Ключевые слова: магниевые сплавы, плазменная наплавка током обратной полярности, слоистые материалы, структура, свойства
DOI 10.24412/1683-805X-2021-6-78-80
Characteristics of structure and properties of magnesium alloys during plasma additive deposition
Yu.D. Shchitsyn1, E.A. Krivonosova1, S.D. Neulybin1, R.G. Nikulin1, T. Hassel2, and D.N. Trushnikov1
1 Perm National Research Polytechnic University, Perm, 614990, Russia 2 Gottfried Wilhelm Leibniz University Hanover, Hanover, 30167, Germany
This paper deals with the additive manufacture of magnesium alloy products of the magnesium-aluminum-manganese-zinc system by plasma surfacing with a reverse polarity current. Special attention was paid to the following points: studying the influence of evaporation of alloying elements during plasma additive surfacing on the material quality; studying the influence of surfacing modes (continuous filling and layer-by-layer filling with cooling at different thermal cycles) on the formation of structure and properties of the synthesized material; specifying the influence of the heat treatment on the structure and properties of the deposited metal. A correct selection of plasma surfacing parameters eliminates porosity and cracks in deposited layers. It is established that plasma surfacing provides a relative structural and phase stability of the previous layers under the influence of subsequent thermal cycles during the workpiece manufacture. In general, the dispersion of the structure of the deposited MA5 alloy is significantly higher than that of the cast and heat-treated metal structures produced by conventional technologies. Plasma surfacing with a reverse polarity current provides a deposited metal with high mechanical properties, i.e. a unique 5-9-fold increase in ductility compared to the cast material with an increase in ultimate strength by 7-10 %, both with and without heat treatment.
Keywords: magnesium alloys, plasma deposition with a reverse polarity current, layered materials, structure, properties
© Щицын Ю. Д., Кривоносова Е.А., Неулыбин С. Д., Никулин Р.Г., Hassel T., Трушников Д.Н., 2021
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1. Introduction
New manufacturing technologies of products from magnesium alloys, that have improved operating properties and can be produced economically, entail a challenge to industrial engineering. Casting, forming and welding technologies or their combinations are used to manufacture complex profiled dimensional products. Additive technologies (AT) or layer-by-layer additive technologies are the most dynamically progressing areas of digital production. The application of such technologies for production of metal structures makes it possible to speed up the problem solution of industrial technological preparation and release of products.
Deposition technologies with the use of concentrated energy sources [1-4], in particular, plasma arc [57], give multiple solutions of the mentioned problems.
The main problems in the arc deposition of magnesium alloys are associated with a number of factors [8, 9]:
- The refractory and insolating film of magnesium oxide MgO formed during welding (Tm = 2500 °C) complicates the building process. It is necessary to use the effect of cathode cleaning during the deposition with a reverse polarity current to destroy this film.
- Susceptibility to crystallization cracking associated with the low-melting eutectics formation: MgCu (Tm = 485 °C), MgAl (Tm = 436 °C), and MgNi (Tm = 508 °C).
- Susceptibility of alloys, especially manganese-containing ones, to grain coarsening in the heat-affected zone.
- An increased absorption of active gases by the liquid metal gives rise to void formation, which requires reliable protection of the high-temperature building zone from the surrounding air.
- The high linear expansion coefficient of magnesium alloys leads to a significant distortion of structures.
Methods for preventing these limitations in the conventional technologies of casting, forming, welding, and pressure treatment are partially considered in the literature [10-14]. However, highly recommended Mg-Al-Mn-Zn alloys have not been recently used for additive processes, partly because structure formation during layer-by-layer synthesis and the possibility of obtaining defect-free products with a number of mechanical properties at the monolithic level have not been investigated. The most interesting problem is the structural and phase stability of the
previous layers under the influence of subsequent thermal cycles during the workpiece formation in the layer-by-layer process [15-17].
This work uses one of the most effective additive manufacturing technologies, i.e. plasma deposition with a reverse polarity current. Plasma deposition provides a number of technological and economic advantages [1, 6]. They include high productivity, wide-range regulations of heat transfer to the base and bonded material and the associated control of the penetration depth and width, structure, composition, and properties of the formed material. Plasma deposition with a reverse polarity direct current [17] makes it possible to solve many problems of cladding magnesium alloys and increasing the productivity while maintaining high quality. Plasma deposition with a reverse polarity current provides cleaning of the previous layer surface from contaminations due to the cathode cleaning effect, good wetting, and flow of the liquid metal with the minimum surface heating. This ensures the production of layered materials with a required structure without internal defects.
We investigated wrought magnesium alloy (Mg-Al8Zn), with the alloying system providing structure refinement due to modification, the maximum strengthening effect, and a number of advanced special properties, e.g. corrosion resistance.
It is specific for magnesium alloys that heat treatment can be applied to them. It was found that the hardening and aging treatments do not increase the strength of magnesium alloys [10, 18]. Optimum strengthening is usually achieved due to a high density of uniformly distributed, partly coherent and very closely located dispersed precipitates. The movement of gliding dislocations is impeded by these precipitations (hardening + aging is the heat treatment mode T6 according to DIN EN 1753).
Funding
The work was performed at the support of the Ministry of Education and Science of the Perm Region (Agreement No. C-26/511 of March 9, 2021), the Ministry of Science and Higher Education of the Russian Federation (State Assignment of Work No. FSNM-2020-0028), within the national project "Science and Universities" and the State Assignment of Work "Development of Scientific and Technological Foundations for the Formation of a Material-Structure System with Special Properties Based on Hybrid Additive Technologies".
S0 Щицын Ю.Д., Кривоносова Е.А., Неулыбин С.Д. и др. / Физическая мезомеханика 24 б (2021) 78-80
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Received 17.09.2021, revised 15.11.2021, accepted 15.11.2021
This is an excerpt of the article "Characteristics of Structure and Properties of Magnesium Alloys during Plasma Additive Deposition". Full text of the paper is published in Physical Mesomechanics Journal. DOI: 10.1134/S1029959921060102
Сведения об авторах
Щицын Юрий Дмитриевич, д.т.н., проф., зав. каф. ПНИПУ, schicin@pstu.ru Кривоносова Екатерина Александровна, д.т.н., проф., проф. ПНИПУ, katerinakkkkk@mail.ru Неулыбин Сергей Дмитриевич, к.т.н., нс ПНИПУ, sn-1991@mail.ru Никулин Роман Германович, асп. ПНИПУ, nikromonger.ro@gmail.com
Hassel Tomas, Prof., Gottfried Wilhelm Leibniz University Hanover, Germany, hassel@iw.uni-hannover.de Трутников Дмитрий Николаевич, д.т.н., проф. ПНИПУ, trdimitr@yandex.ru
