RU2016112C1 - Method for modification of aluminium alloys - Google Patents

Abstract

FIELD: metallurgy. SUBSTANCE: modifying mixture is added into melted charge, its quantity being 0.02-0.20 mass % of charge mass. Said mixture contains carbide- and nitride- forming elements and oxides of aluminium and copper at ratio 30-70:0.1-0.5 together with alkali and alkali-earth elements and with their compounds; ratio of aluminium and copper oxides being 100: 0.01-0.98. EFFECT: improves airtightness of casting, increases its strength and plasticity. 3 cl, 2 tbl

Description

 The invention relates to metallurgy, more specifically to foundry, and can be used to produce castings from alloys based on aluminum of high quality, especially high tightness.

 To obtain castings from alloys based on aluminum of high quality, refining and modification using various gases and complex modifiers are used. This complicates and increases the cost of technology, does not allow to optimize the whole range of physical and mechanical characteristics and degrades manufacturability.

 The following methods for modifying aluminum alloys are known. A method for producing aluminum-titanium-boron system alloys involves the modification of alkali metal fluorides with titanium and boron, to which 2-10% by weight of fluorides of powdered aluminum oxide are added (Japanese Application No. 55-51499, class C 22C 1/02).

 This invention provides an increase in the strength characteristics of castings, however, the tightness of the castings is insufficient, the method is not economical.

 A known method of modifying an aluminum-titanium alloy, which includes introducing into the boron melt in the form of an ultrafine powder of lanthanum hexaboride (ed. St. N 1168622, class C 22 C 1/06, 1983).

 The method provides an improvement in the modifying effect while reducing the cost, but the tightness of the castings is unsatisfactory.

 A known method of processing hypereutectic silumins, which consists in modifying the mixture, which includes, wt.%: Phosphorus 7-13, copper 45-70, the amount of iron and chlorine 2.5-8, the rest is waste production of phosphorus containing sodium, potassium, calcium, silicon, oxygen (ed. St. N 687853, class C 22 C 1/06, 1977).

 The disadvantage of this method is the low ductility and tightness of castings due to the high content of copper and phosphorus.

 A known method for producing castings from aluminum alloys, including the use of ultrafine powders of sphen zircon (a mixture of oxides of zirconium, niobium and titanium) to modify the melt (see railway foundry, No. 4, 1991, p. 17).

 This method provides an increase in the strength and ductility of castings, however, their tightness remains at an unsatisfactory level, since the oxides and products of their interaction used in this technical solution are almost completely localized inside the grains (subgrains) and do not have a beneficial effect on the state of grain boundaries.

 The closest in technical essence and the problem to be solved is a method for refining and modifying aluminum alloys, which includes treating the melt with a mixture of potassium fluoride and potassium chloride salts together with sodium fluoride and / or sodium cryolite in an amount of 2-3% of the melt weight (ed. St. N 899698, CL C 22 C 1/06, 1982.

 This method simplifies the technology and reduces the cost of refining and modification, however, the tightness of the castings remains low, since there is no intensive grinding of grain, because the type II modification mechanism is implemented, i.e. due to inhibition of grain growth, and not an increase in the number of crystallization centers.

 The basis of the invention is the task: by using for the modification of aluminum-based alloys a new set of components in composition and concentration, to obtain castings with high tightness while maintaining increased strength and ductility.

 The problem is solved in such a way that in the proposed method for modifying aluminum alloys, including melting the mixture and introducing a modifying mixture, a mixture of carbide and nitride forming elements, the sum of aluminum and copper oxides in the ratio of elements and oxides 30-70: 0.1- are used as the modifying mixture. 0.5 and alkali and / or alkaline earth metals and their compounds in an amount of 0.02-0.20% by weight of the mixture. As carbide and nitride forming elements, oxides of zirconium, titanium, niobium, hafnium, and tantalum are used. Cryolite is used as alkali and / or alkaline earth metals and their compounds. The ratio of aluminum and copper oxides is 100: 0.01-0.98.

Comparative analysis with known technical solutions (analogues and prototype) allows us to conclude that the claimed method of modifying aluminum alloys is different in that:
carbide and nitride forming elements, aluminum and copper oxides, alkali and / or alkaline earth metals and their compounds are used as a modifying mixture;
components: carbide and nitride forming elements and the sum of aluminum and copper oxides are taken in a ratio of 30-70: 0.1-0.5, alkali and / or alkaline earth metals and their compounds - the rest;
the modifying mixture is introduced in an amount of 0.02-0.20% by weight of the mixture;
aluminum oxides and copper oxides are taken in a ratio of 100: 0.01-0.98.

 Some components - carbide and nitride forming elements, aluminum oxides, alkali and alkaline earth metals and their compounds - are known from the existing level of technology (analogues and prototype), however, in the proposed technical solution they are introduced as part of other components (new high-quality composition) and in other ratios (new quantitative ratio).

The high effect of modifying with a mixture of carbide and nitride forming elements, the sum of aluminum and copper oxides, alkali and / or alkaline earth metals and their compounds is explained by the fact that in the melt based on carbide and nitride forming elements after dissociation of oxides, Al _x colloidal dispersion intermetallides are formed Me _y , which during the crystallization process provide a refinement of the metal structure, a part of aluminum oxides similar in composition to stoichiometric acts similarly.

Copper compounds play an important role in the formation of the structure, submicrostructure, and, as a result, the physicomechanical, technological, and operational properties of castings and aluminum-based alloys: copper oxides and, in part, copper sulfides that are formed in the melt are responsible for a significant refinement of the structure, while the liquidus shifts toward higher temperatures, the crystallization dynamics increase - many undesirable inclusions in a very dispersed form are localized inside the ground grains. Secondly, copper compounds of the CuAl ₂ type and more complex in composition are separated from the solid solution along the grain boundaries. Due to a significant increase in the intergranular surface area due to grain refinement and uniform localization of these dispersed precipitates, a decrease in stress concentration is provided with a simultaneous increase in the density and tightness of the casting as a whole.

 The introduction of a modifying mixture of less than 0.02 wt.%. charge does not give the desired effect on the level of tightness and other characteristics, and going beyond the upper limit of 0.20 wt.% of the charge leads to a decrease in the ductility of castings.

 The limits of the ratio of the components of the modifying mixture are determined by the following considerations: when the ratio of carbide and nitride forming elements and the sum of aluminum and copper oxides is less than 30: 0.5, the number of crystallization centers is insufficient to ensure the proper level of casting properties; if the ratio exceeds 70: 0.1, the alloy becomes brittle due to an excessive amount of intergranular inclusions. Along with the loss of ductility, tightness also decreases, as the discontinuity in the near-boundary zones increases.

 When the ratio of aluminum oxides and copper oxides is greater than 100: 0.01, the effect of the secondary phases sharply decreases, since the oxides and other copper compounds are completely realized in the form of inclusions formed in the melt above liquidus and do not have a positive effect on the structure and properties of castings and, if this ratio is less than 100: 0.98, the number of secondary phases localized along grain boundaries increases so much that discontinuities appear in the places of precipitation and the tightness of such castings decreases.

PRI me R. In accordance with the calculation of the charge, the components were loaded into the ECT-250 250-kilogram and kilogram resistance furnace EST-250 to obtain the AK7ch (AL9) aluminum alloy. After melting of the charge and finishing on the chemical composition of the melt, the melt at a temperature of 650-780 ^{° C} was treated with a mixture of modifying, introducing it under the "bell" as close to the bottom of the crucible.

 Processing is carried out until the bubbling is over, after which the "bell is removed and slag is removed from the surface of the melt.

 In this way, a series of swimming trunks was smelted, in which the amount of the introduced modifying mixture and its composition were varied.

For comparison, one of the heats was modified with flux in an amount of 2.5 wt. % of the mixture prepared from a crushed dehydrated mixture of potassium fluoride with potassium chloride in a ratio of 2: 3 by weight, as well as sodium fluoride and sodium cryolite in equal proportions. Flux was applied on the surface of the melt at the last 720-740 ^C and stirred with a metal; after 10-15 minutes, the slag was removed.

 The resulting alloy had a chemical composition, wt.% .: manganese 0.46-0.52; copper 0.18-0.21; zinc 0.28-0.32; magnesium 0.2-0.4; iron 1.2-1.8, lead 0.03-0.05; tin 0.008-0.012; silicon 6.2-7.6; aluminum rest.

Testing of mechanical properties was carried out on samples made from ingots obtained in metal form, according to standard methods. Hydraulic tests were carried out at a pressure of 5 kG / cm ² on parts such as "pumping wheel" obtained by injection molding.

 The test results of samples and castings from AK7ch (AL9) alloy after various modification options are given in table. 1 and 2.

 An analysis of the results shows that the samples and castings of parts modified by the claimed method, with high strength and ductility, have a significantly higher density, and in parts - tightness.

 If compared with the prototype method, the claimed method increases the integrity of the casting by more than two times; compared with serial technology - four to six times.

 The proposed method can be used in foundries of engineering plants and specialized production of castings from aluminum alloys with increased requirements for tightness.

Claims (3)

 1. METHOD FOR MODIFICATION OF ALUMINUM ALLOYS, including melting the charge and introducing a modifier into the melt in the presence of cryolite, characterized in that a mixture of carbide-, nitride-forming elements and aluminum and copper oxides are used as a modifier with a ratio of elements and oxides of 30 - 70: 0.1 - 0.5 and alkali and / or alkaline earth metals and their compounds in an amount of 0.02-0.20% by weight of the alloy, the ratio of aluminum and copper oxides being 100: 0.01-0.98.  2. The method according to claim 1, characterized in that the oxides of zirconium, titanium, niobium, hafnium, tantalum are used individually or in any combination as carbide-, nitride-forming elements.  3. The method according to claim 1, characterized in that cryolite is used as alkali and / or alkaline earth metals and their compounds.

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