PROSPECTS FOR IMPROVING THE PROPERTIES OF SECONDARY FOUNDRY ALLOYS OF THE AL-SI SYSTEM USING THE MODIFICATION PROCESS

The results of analytical studies of the use of modern modifiers for secondary aluminum alloys, which affect the structure of the metal of castings and allow to obtain the necessary physical and mechanical characteristics. It is shown that modifiers influencing the size of the primary grain and the shape of eutectic silicon inclusions are of the greatest interest for the production of castings from secondary silumins. It is shown that according to modern ideas the structure of the metal melt is not homogeneous. In some temperature range, complete mixing of atoms does not occur, and microregions with a short-range structure characteristic of the crystalline phase appear. These formations are called differently: atomic groups, clusters, clots, islands, complexes of atoms, clusters, etc. In the last decade, ultrafine powders of chemical compounds (nanopowders), which act as additional crystallization centers during primary crystallization, have become increasingly used as modifiers of cast alloys.

Preliminary Studies on HVOF Sprayed Coatings on Magnesium Alloys

In the field of the development of modern techniques, which improve and/or regenerate the component’s surface properties, High Velocity Oxygen Fuel (HVOF) spraying of carbides or metals and their alloys is a good alternative method to other conventional surface engineering ones, including magnesium foundry alloys. Coatings manufactured by thermal spraying are used to improve the durability and life time of machine parts, both the new and regenerated ones, by changing the surface layer properties. In this work the results of HVOF sprayed coatings deposited onto AZ31 magnesium alloy substrate are reported. The feeding material was composite powder Cr3C2–NiCr. The coatings were investigated in terms of their microstructure and selected mechanical properties. For structure examinations, microscopy studies (light and scanning ones) were used as well as phase composition analysis. In the case of mechanical properties, the wear resistance was determined also microhardness was measured.

The Assessment of the Possibility of Smelting a Cast Alloy for the Manufacture of Components and Parts of Arctic Technical Equipment Using Ore from the "Verkhnyaya Amga" Ore Occurrence

The research assesses the possibilities of using local minerals to create foundry alloys that are used in conditions of low temperature. The mineral-geochemical composition of iron ore from Verkhnyaya Amga ore occurrences in the Aldan region of the Sakha Republic (Yakutia) was studied in detail. The expedience of using iron ores from this ore occurrence to develop new cold-resistant and high-strength steels was analyzed. The chemical composition and microstructure of the cast alloys were studied. The ore contains oxides of alkaline earth metals: MgO; CaO; Sr0 and BaO, the total content of which is 4.2%, that contributes to the process of deoxidation of the melt during its cooling, and the deoxidation product in the form of oxides and other chemical compounds based on Ca, Sr and Ba floats into slag. During crystallization, the melt is cleaned of detrimental impurities, non-metallic inclusions, gases, pores, etc. Alloy is smelted from enriched ore, samples for static tension and toughness are made in order to study the physicomechanical properties. Microstructure of the obtained alloy and structural steel subjected to static tension at an external load of 0.8 yield strength (σ = 0,8 σт) was investigated. Mechanical properties and dynamic characteristics were measured. Analogues for comparing the strength and plastic properties were given.

The effect of the excess Titanium content on the microstructure of Al – Si foundry alloys

Grain refining is an important technological step for the nucleus growth of the melt, in order to increase the number of nuclei, to improve mechanical properties (tensile strength, yield strength, hardness, elongation), feeding conditions and to decrease the tendency of hot tearing and the degree of sintering. [1][2] The aim of the experiments was the determination of the grain refining effects of titanium (Ti) addition in the form of AlTi5B1 master alloy to the examined alloys (AlSi7MgCu0.5 – AC 42 000, AlSi9Cu3Fe0.5 – 46 500; AlSi9Cu1 – AC 46 400). The results prove that the addition of small amount of master alloy has a favourable effect on the foundry practice.

Solutions of the scientific problem of modifying of foundry alloys

For a solution of the problem of modification of a microstructure of cast alloys it is necessary to accept admission that crystallization centers of crystals of phases are the crystalline buildups consisting of nanocrystals of phases. The role of modifiers comes down to lower concentration in a metal melt of the dissolved surface-active elements and gases and (or) to formate of the moistened substrates on which process of gas generation and deleting gas bubbles will be most preferable.