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8Journal of Siberian Federal University. Engineering & Technologies 2 (2014 7) 127-131
УДК 621.09
Metallographic Tests of Modifying Ability of Rods from Aluminum Alloys Obtained by Combined Casting and Rolling-Extruding
Ekaterina S. Lopatina*, Vitali S. Biront | and Sergey B. Sidelnikov
Siberian Federal University 79 Svobodny, Krasnoyarsk, 660041, Russia
Received 14.11.2013, received in revised form 27.02.2014, accepted 06.03.2014
Proposed new ways of obtaining rods-modifiers from aluminum and aluminum alloys. Were researched of their modifying ability and tested in industrial conditions modification technology in the production of aluminum alloy ingots.
Keywords: modifying, structure, combined casting and rolling-extruding, subgrain structure, rods-modifiers.
Structure and properties of deformed semi-finished products from aluminum and aluminum alloys largely depend on the quality of the ingot which is determined by the shape, size and internal structure of the grains. It is important to properly evaluate expediency of application the method of modification and find ways to overcome its negative aspects. Therefore, the search for new modifiers which have high ability of modifying along with the ability to maintain the chemical composition of the alloy after uploaded it and the study of the structure and properties of obtained semi-finished products is an actual task.
One of the leading causes of obtaining small grains as a result of the modifying effects on the melt is the process of homogeneous nucleation of the main substance as a result of the transformation of clusters into sTable nuclei. The number of nuclei in a supercooled liquid immeasurably more than the number of any foreign particles introduced into the melt with modifiers. Therefore it is necessary to study the modification mechanism of aluminum alloys based on the formation of a homogeneous nucleation, arising on the basis of advanced subtly differentiated sub grain structure of rod-modifier.
Most progressive trend in the manufacturing of non-ferrous metals and alloys is a combining in one process stream of casting and deformation. Complex of special properties of aluminum semifinished products can be obtained using the methods of the combined casting and rolling-extruding (CCRE).
To get modifying rods used molten aluminum grade A7 and also alloys AD31, 6082, V95pch, 2219. As a basic equipment to obtain rod-modifier used laboratory installment of combined casting
© Siberian Federal University. All rights reserved
* Corresponding author E-mail address: eslopatina@mail.ru
and rolling-extruding created on the basis of technical solution protected by patent RF №92200644. The metal is heated in an elecOric aurnace to a tempcratuae of 720 °C, obtained melt and pour it directly into the caliber of rolls (Fig. 1). After the capture by the rolls of crystallized in the form of a rectangular billat metal compeessed by roUs and reached tlie matrix under the influeact of the supplied by tolls trictioa stresses eatruded as eod of given diameter through calider hole ot the matrix. To prevent the penetration of the metal into the gap between the rolls and the matrix, the last with a special wedge device was tight compressed to the rolls and overlap caliber downstream of the rolls.
This technnlogy provides the most faoorable conditions of high speed cryseallization-dedoomatton od the metal and obtaining rod which has austained pettp subgrain stracrure. Stability of rod's sulgrain structure related to the onset of recrystallization temperature. The experimental results showed that temperature of the beginning and end of recrystallization for rods from aluminum grade A7 obtained with uting method CCRE a°e equal Tp11 = 290 °C, TPK = 350 "C. This is on 40-70 °C more than the recrystallization temperature of aluminum rod produced by traditional technology of bar rolling, that is indicating a more sTable subgrain structure of rod obtained with using method CCRE.
Were esrabllshed the opeimal technological parameters of modificadion aluminum alloys br aluminum rod obtained with using metdoa CCRE. The study op these parameders wae co^ucted using method Alkane-test. Maximum modification effect is achieved by introduction in liquid aluminum 3-4 % (Ta°le 1) rod-modifiar diameter 5a mm (Table 2), anal rhe temperature of molten aluminum at the moment of modification should be in the range 700-720 °C.
To obtain a homogeneous fine grained structure throughout section of the ingot necessary maintaining a minimum of 5 minutes and thorough mixing of the melt (Fig. 2) after the introduction of the modifying material.
Were carried out experiments on the modification of aluminum alloys AD31 and 6082 by rods from alloys of the same composition obtained with using method CCRE. Analysis of the macrostructure Alkane-test probe showeel tliet in the initial staoe rhe onmbea of grans ia an area oa r cm2 is 5-°5 pcs. After the introduceion of modifying; additive (2,5 % per 1 kg of melt) in the samples there is a significant grain refinement to 1200-2000 pcs/cm2 which proves the possibility of use as a modifying additive to grind grain in ingots of aluminum and its alloys rods of technical aluminum grade A7 and rods of alloys A^,31 and 6082 produced by method of casting and rolling-extruding.
Also studied modifying possibility of rods under industrial conditions of production serial of ingots from different aluminum alloys such as B95nn, 2219 and AD31.
Table 1. The influence of modifier amount on grain refinement of aluminum ingots grade A7 based on the results macro-analysis
№ p/p modifier amount (% by mass) Number of grains per 1 cm2 after 1 min Number of grains per 1 cm2 after5 min The average grain size after 5 minutes, um
1 1 55 70 1450
2 2 650 750 425
3 3 1900 2000 225
4 4 1400 1600 255
5 5 700 800 360
Note: The original grain size is 4.0 microns
Table 2. Number and size of the grains of the modified aluminum grade A7 based on the results microanalysis
№ P/P Rod diameter, mm Temperature parameters, °C Number of grains in 1 cm2, pcs The average grain size, um
1 3 TH - 720; TK - 675 1700-1800 267
2 5 TH-700; TK - 690 11500-12500 98
3 7 TH - 700; TK - 690 11000-12000 109
4 7 TH -700; TK - 650 11200-12000 105
5 7 TH - 720; TK -650 11500-12500 100
6 9 TH -720; TK - 650 11200-12000 105
Note: TH - temperature of molten aluminum with the introduction of the modifying rod, TK - casting temperature of probe Alkane-test.
abc
Fig. 2 Macrostructure of Alkone-test probAs krom aluminum A7 (x 1,d)i modifiable by rod diameter 9 mm from A7: a - original aluminum A7; b - sampling in 1 minute adter injection of rod, without mixing; c - sampling in 5 minutes after injection of rod, with mixing
To estimate modifying ability of rods from aluminum A7 obtained with using method CCRE and compare their edfectiveness wieh tho applicable ao Veohnyaya Sadda Matalluogical Production Association (VSMPA) modifiere thera have been several versions of melts and obtained experimental ingots from alloys B95nn and 22199.
a b c d
Fig. 3 Macro structure of ingots diameter 52 mm from alloy B95nH (a, b) and alloy 2219) (c, d): a- mo difi ed by A7 and Al-Ti -B; b, d - modified by A7; c - modified by Al-Ti - B
Table 4. Quantitative parameters ofthe structure experimental ingots of alloy AD31
State of the sample Diameter of ingot, mm Grain size, um Number of grains in 1 cm 2
without addition of rod 110 192,9 2687,0
with addition of rod diameter 9 mm from alloy A7 110 147,8 4576,9
without addition of rod 192 212,1 222222,4
with addition of rod diameter 9 mm from alloy A7 192 197,2 2571,9
Macrostructure study showed that the introduction of into the alloy B95nn new modifying material in the form of rod from A7 jointly with ligature Al-Ti-B and without this ligature has provided reasonable; homogeneous, dense, fine grained equiaxed structure (Fig. 3 a, b). Macrostructure of the alloy 2219 modified by rod A7 (Fig. 3 d) has a similar fine grain structure; it can be concluded about perspective of the new modifier material during casting of industrial ingots from different aluminum alloys.
Hove been conducted studies of rod modifying ability obtained with using method CCRE during casting ingots diamener 110 mem and 192 mm fnom alloy AD31. Quantitative parameters of the storeture experimental ingots of alloys AD31 determined by the results of microstructural analysis (Table 4).
Thus, rhe study of the peoresses of a homogeneous modification and implementation of this process with the use of materials obtained by the method of high speed crystallization-deformation provide an opportunity to improve the quality of aluminum ingots by grinding their grain structure without contaminating the chemical composition by the substance of modifier. Technology of combined casting and rolling-extruding allow obtaining rods-modifiers with subgrain subtly differentiated structure required for effective modification of ingots. Established optimal ratio of technological parameters of production modifying rods and technology of modifying ingots with their use based on which provides methods for producing high-quality ingots.
Testing of modification technology in obtaining industrial ingots in Verhnyaya Salda Metallurgical Production Association showed that the modification by rod from aluminum obtained with using method CCRE results in the homogeneous grain structure of ingots from aluminum alloys. Consequently, these rods can be used as modifiers under industrial conditions.
Металлографические исследования модифицирующей способности прутков из алюминиевых сплавов, полученных методом совмещенного литья и прокатки-прессования
Е.С. Лопатина, В.С. Биронт , С.Б. Сидельников
Сибирский федеральный университет Россия, 660041, Красноярск, пр. Свободный, 79
Предложены новые способы получения прутков-модификаторов из алюминия и алюминиевых сплавов. Была изучена их модифицирующая способность и опробована в промышленных условиях технология модифицирования при производстве слитков из алюминиевых сплавов.
Ключевые слова: модифицирование, структура, совмещенное литье и прокатка-прессование, субзеренная структура, пруток-модификатор.
