Hypereutectic Silumins Research Articles

Inherited chemical inhomogeneity in oxide layers deposited by the method of microarc oxidizing on hypereutectic silumins

The effect of the size and of the kind of distribution of silicon in Al-Si alloys with hypereutectic composition on the characteristics of the oxide layer formed by microarc oxidizing (MAO) is studied. It is shown that the inhomogeneity of the distribution of silicon in the oxide layers is inherited from the initial structure of the alloys. The mechanism of the effect of silicon on the structure of oxide layers and the processes of their formation due to MAO of hypereutectic silumins are discussed. It is shown that it is principally possible to use the method of microarc oxidizing for obtaining hardened layers with controlled distribution of silicon.

Effect of the main parameters of helical rolling on the ductility properties of hypereutectic silumin alloys

The author examines how the number of cycles in which the work rolls of a rotary rolling mill load semifinished products made of hypereutectic silumin alloys depends mathematically on the degree of deformation e and feed angle in three-roll rotary rolling. Another mathematical model is proposed to describe the dependence of the dispersity (dimensions) of the silicon crystals (one of the two phases in the structure of hypereutectic silumins that adversely affects the ductility properties of these alloys) on the number of load cycles Nc, the feed angle α, and the deformation e. The proposed models adequately describe the experimental data, differing from the latter by no more than 5–7% and remaining within the permissible error.

Mathematical model of the movement of layers of metal during the rotary rolling of semifinished products made of hypereutectic silumins

A mathematical model has been constructed to describe the kinematics of the movement of metal on the surface of semifinished products made of hypereutectic silumin alloys as they undergo rotary rolling. The model is based on the dependence of the pitch of the helical lines of metal flow on the deformation e of the product and the feed angle α. The pitch is minimal when e = 50–55%, regardless of the feed angle α. The degree of deformation e = 50–55% is optimum for ensuring that the unit number of cycles in which the semifinished product is loaded by the work rolls is such as to produce a fine-grained structure and maximize the ductility characteristics of hypereutectic silumins.

Aspects of the piercing of shells made of hypereutectoid silumins on a universal 20–60 rotary rolling mill

The world’s first technology has been introduced for piecing hollows (tubes) of hard-to-deform hypereutectic silumin alloys (01390 and 01392). The tubes have the dimensions 80 mm diameter × 13.5 mm wall thickness and 74 mm diameter × 15 mm wall thickness. The are obtained on universal rotary rolling mill 20–60. The technology was developed by modeling the rotary rolling operation, studying the rheological properties of hypereutectic alloys, finding scientifically sound parameters (rolling scheme, feed angles, temperature-speed parameters) for an intermediate rotary-rolling operation performed to obtain bars with a crystalline structure and ductility properties 3–4 times better than those of the initial ingots, and the developing and introducing a piercing process that employs special spherical mandrels with a conical nose.

Effect of Helical Rolling on the Structure and Properties of Hypereutectic Silumin

Flow characteristics of ingots and bars form hard-to-deform hypereutectic silumin 01390 determined in tensile and torsion tests in the temperature range of helical rolling (HR) at actual rates of hot deformation are investigated. Special features of the structure and properties of ingots and rolled semiproducts from hypereutectic silumin rolled in a universal PVP 20-60 mill are discussed. The ultimate ductility and strain resistance of the hypereutectic silumin are compared at actual temperatures and deformation rates. The results of the study make it possible to optimize the processes of rolling of bars and piercing of pipes from hypereutectic silumins by the method of helical rolling.

Production of High-Quality Bars of Hypereutectic Silumins by Helical Rolling

A study is made of the possibility of improving the structure and properties of hard-to-deform hypereutectic silumins with the use of helical rolling (HRG) on the PVP 20-60 universal mill at the All-Union Scientific Research Institute of Light Alloys. The parameters of hot HRG are optimized by numerically modeling the deformation process in a three-high stand. The resulting data is confirmed experimentally by subjecting standard hypereutectic silumins 01390 and 01391 to HRG. The use of HRG makes it possible to refine the structure of hypereutectic silumins and improve their mechanical properties.

Peculiarities of structure formation during casting of hypereutectic silumin with inverted structure

Peculiarities of structure formation during casting of hypereutectic silumin with inverted structure

Morphology of dendritic bicrystals in hypereutectic aluminum-silicon alloys hardened in pressure casting

Hypereutectic silumins that possess a low coefficient of thermal expansion, high wear resistance and hightemperature strength, and excellent casting properties are an indispensable structural material for the production of cylinders, cylinder heads, pistons, and other parts of internal combustion engines. In pressure casting of hypereutectic alloys the structure formed is more complex than in hardening in metal or sand molds. In addition to excess silicon crystals and the eutectic such structures contain crystalline formations that are inadmissible in an equilibrium structure. The nonequilibrium components of the structure can transform during operational heatings due to redistribution of the alloying elements, which will inevitably affect the size precision of parts. However, the published data on the structure of hypereutectic silumins formed in pressure casting are quite scarce. The present paper is devoted to the special features of silumins manufactured by pressure casting.

Characteristic features of silumin alloys crystallization

The results differential thermal analysis (DTA) of crystallization of multicomponent silumin alloys with 8÷22 wt %Si and Mg, Cu, Ni and Fe minor admixtures are presented in the paper. It has been proved that to any one of the solid phases crystallizing from liquid (α, β, Mg2Si, Al6Cu3Ni, Al2Cu, AlgFe2Si) a particular thermal effect can be deduced and identified. A new hypothesis concerning hypereutectic silumin alloys crystallization has been proposed in the work.

Laser alloying of the surface of parts of silumins

1. The hardness and thermal stability of eutectic and hypereutectic silumins increase in laser remelting. 2. The proposed method of application of alloying powder makes it possible to increase the uniformity of distribution of the alloying elements in the zone of laser fusion. 3. As the result of laser alloying, intermetallides of varying compositions containing primarily aluminum and nickel are formed.

Viscosity of molten Al?21.5% Si

1. It is possible to detect structural transformations in molten metals with the use of highly accurate procedures followed by metrological evaluation of the measured results. 2. At certain temperatures in liquid hypereutectic silumin there are structural transformations connected with a change in close order prameters, and also with the occurrence and decomposition of different types of less clusters.

Modification of hypereutectic silumins with phosphorus and sodium

1. The nucleation theory of the refining of primary silicon crystals in hypereutectic Silumins microalloyed with phosphorus was verified by experiments. Particles were observed in silicon crystals (possible AIP) which served as additional centers of nucleation of primary silicon crystals. 2. Combined modification of high-silicon Silumins with phosphorus and sodium leads to refining of primary and eutectic silicon. 3. Modification with phosphorus is most expedient with phosphorus-containing salts, especially sodium phosphates.

Effect of phosphides on the structure and properties of hypereutectic silumins

1. All the phosphides investigated except gallium and indium phosphides have a considerable modifying effect on the structure and properties of hypereutectic Silumins. 2. Aluminum phosphide has the largest effect on these alloys. 3. Modification with AIIIBV phosphides increases the microhardness of the primary silicon grains. 4. If the operating characteristics of parts do not change with the addition of copper and zinc to hypereutectic Silumins at levels exceeding GOST or TU specifications then it can be recommended that these alloys be modified with copper phosphide (the most suitable technologically) or zinc phosphide (the cheapest).