FORMING OF MICROSTRUCTURE OF THE AL-SI-FE-MN SYSTEM ALLOY BY EQUAL CHANNEL ANGULAR PRESSING WITH BACKPRESSURE

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1 FORMING OF MICROSTRUCTURE OF THE AL-SI-FE-MN SYSTEM ALLOY BY EQUAL CHANNEL ANGULAR PRESSING WITH BACKPRESSURE Abdrakman NAIZABEKOV (1), Violetta ANDREYACHSHENKO (1), Jiri KLIBER (2) (1)Karaganda State Industrial University, Republic avenue 30, , Temirtau, Republic Kazakstan, (2) VSB-Tecnical university of Ostrava, Czeck Republic, Abstract Recently more scientists are concerned wit te problem of te reception and studies of ultra fine materials. Also te alloys based on aluminium are raised by interest, in particular alloy of te system Al-Si-Fe-Mn. One of te ways of te creation of ultra fine structures in alloy is an equal cannel angular pressing (ECAP). Tis article is dedicated to study of te influence of equal cannel angular pressing wit backpressure (ECAPB) on microstructure formation of alloy based on aluminum. Te developed tool provides advantage compressing strains in all tree directions by deformation of specimens, tus te proper conditions for refined of te structure components are made. Besides, new tool allows obtain ig quality te products by smaller degree of te deformation. In tis work tere is a researc of microstructure formation by deformation of alloy of te system Al-Si-Fe-Mn in new tool for ECAPB wit step in exit cannel. As a result of studies it is discovered tat presence step in exit cannel allows increase te degree of deformation in one pass from 0,277 before 0,382. Suc increasing degree of deformation promotes essential grain refined already after several passes of deformation. Te experiments sowed tat developed tool allows to obtain ultra fine structure (0,8-1,2 µm) already after 2 passes of ECAPB wit total degree of deformation 0,764. ECAPB realization wit total degree of deformation of 1,146 (3 passes) promotes formation of microstructure wit grains size of 0,4-1 μm, at a time te accumulation of tangled dislocation can be observed. Keywords: ECAP, backpressure, alloy of te system Al-Si-Fe-Mn 1. INTRODUCTION At present essential interest for industry is use of non-ferrous material, in particular te materials based on aluminum. Suc materials are popular due to teir properties: ig mecanical features wit comparatively small weigt, stability in ig temperature, low factor of te termal expansion, sourness stability, corrosion stability and oters. Besides, alloys based on aluminum wit addition of suc elements, as Fe, Si, Mn allows to obtain te caracteristic, greatly exceeding pure metals, or double alloys. Recently te metods of several plastic deformation (SPD) ave been widly spread, in particular, equal cannel angular pressing (ECAP), allowing greatly refined te structure of te metal and providing te ig level of te mecanical features. Te most often ECAP in tool wit angle of te switcbox and rounding wit different angles is used. Tereat on exit from zone of te tool cannels joint tere are stretc strain developing in te billet tat influences negatively on te process. Te scientists of "KSIU" ave designed new way of te realization of equal cannel angular pressing wit backpressure, realized in tool wit step in exit cannel (fig.1) [1].

2 Te aim of tis researc is a study of microstructure formation of te Al-Si-Fe-Mn system alloy by deformation in new tool and determine its structured features. Fig. 1 Sceme of te tool for ECAPB 2. EXPERIMENTAL PROCEDURES Te material used in tis researc was Al-4Si-0.5Fe-1.12Mn commercial alloy. Te sample were subjected to annealing at 550 С by slow cooling inside te furnace before room temperature and te following RKUPP at room temperature [2]. Te sample subjected to RKUPP in tool wit te cannel angles 135, te angle of curvature 40 and angle conical part 45. Friction between te tool and billet was reduced by applying te palm oil as a lubricant. All samples were deformed from 1 to 4 passes wit te samples rotated at 180 round te longitudinal axis between eac pass, i.e. by route C. Following samples microstructure was researced using bot optical microscope Leica and transmission electron microscope JEOL JEM Te samples were prepared by standard metods. In tis researc samples from central zones of te deformed billet were used for exception periperal effect. Te total degree of sample deformation wit te usage of te new tool will differ from total degree of deformation for tool wit suc te cannel angles and te angles of curvature by usual ECAP. To calculate te total degree of deformation te following equation (1) [3] can be used: 2cot( ) csc( ) , (1) were φ is te cannel angle of te tool, ψ is te angle of curvature. Considering tat material of te billet will be a subject to deformation in step zone of exit cannel too, tis deformation is possible to be taken into account as follows (2): с ln, (2) v were is a widt of billet before step (te widt of te entrance cannel), v is a widt of specimen on exit from cannel. Tus, resulting degree of deformation after te 1-st pass of ECAPB will be (3):

3 2cot( ) csc( ) ln 3. (3) v Finally, in one pass of ECAPB degree of deformation equal to 0,382 will accumulate in billet, erewit, by ECAP in tool wit cannel angle of 135 and te same angle of curvature, degree to deformation will be 0, THE RESULTS OF THE RESEARCH Te results of microstructure researc after annealing are sown on fig. 2. Annealed alloy as grains of size µm in one direction and µm in any direction. Besides, tere are large inclusion wit size from 2 to 10 µm (2а) and small inclusion wit size of 0,05-0, in structure of te metal. Fig. 2 Microstructure of sample after annealing a - OM, X1000, b - TEM, brigtfield image Potograpies of sample after te first passes ECAPB in brigtfield and darkfield are brougt on fig. 3. Fig. 3 Microstructure sample after 1 pass ECAPB, TEM, a- brigtfield, b- darkfield

4 Extended grain wit size of 1-2 µm widt and 3-5 µm lengt are formed after 1 pass of ECAPB. Inclusions are portioned non-uniform on sample and do not form some concourses. Sample microstructure after 2 passes of ECAPB in brigt and dark field is brougt on fig. 4. After 2 passes of ECAPB enoug equalaxis grains wit size 0,8-1,2 µm are formed. 3 passes of ECAPB realization promotes formation of tangle dislocations in pre-formed grains, promoting fragmentations of te lasts (fig. 5). Tere by some elongation of grains exists, teir sizes are from 0,4 to. Fig. 4 Microstructure sample after 2 passes of ECAPB, TEM, a- brigtfield, b- darkfield Fig. 5 Microstructure sample after 3 passes of ECAPB, TEM, a- brigtfield, b- darkfield 4. DISCUSSION In tis work analysis of te microstructure cange of te system Al-Si-Fe-Mn alloy is conducted as a result of ECAPB realization in new tool wit step in exit cannel. Te total degree of deformation in one pass exceeds te degree of deformation accumulated by metal deforming in similar tool wit same cannel angle, but witout step in exit cannel by use te new tool. Increase of total degree of deformation is connected wit backpressure, influencing on billet from step. Wile deforming te billet is acted upon compressing strains during all cycle of deformation in all 3 directions, tus te proper conditions for refined of te structure components are made. As a result of conducting annealing at 550 С for 1 our coarse-grain structure is formed in alloy, as it is sown on fig. 2а. Tereby inclusions falling out by annealing cause curve boundaries of grain by its

5 migration (fig. 2, preventing, tereby, growing of grains. Besides, exists straigtening te particles in one line is observed. One pass of ECAPB realization promotes refined grain, as it is sown on fig. 3. However first grains ave not an equal axis form. Also elongation of grains along one direction exists. Te large amount of te small inclusions promotes refined grains, often executing function of nucleation or centre of te forming of small grains. As a result of 2 passes of ECAPB realization uniform microstructure is formed on te wole section of billet. Tereby crusing of elongated grains occurs after te first pass ECAPB as well as some teir turn comparatively eac oter (fig. 4). On fig. 4 particle is specified circumferences, situated on joint nearby grains, probably, acting role of te nucleation centre by crusing of te structured components. As a result already after 2 passes of ECAPB uniform ultra fine structure is formed wit some grain less tan 0,5 µm. After 3 passes of ECAPB same grain elongation can be seen, teir size is from 0,4 to. Increase degree of deformation up to 1,146 after 3 passes of deformation causes formation of tangled dislocation in earlier formed grains, promoting fragmentations of te lasts. Tereby, te refine grains become less intensive in contrast wit 1 and 2 passes of deformation. But, owever, large amount of small less-angled fragments exist in grains. Tereby some grains are practically free of dislocations. Besides, te damage of te inclusions is observed, being presented in structure of te metal tat can be te reason of te formation microcracks. As a result of realization of 4 passes of deformation te damage of te billet is observed by ECAPB directly. Wit tis connection, microstructure researc of samples after 4 passes were not conducted. 5. CONCLUSIONS In tis work tere is a researc of microstructure formation by deformation of alloy of te system Al-Si-Fe-Mn in new tool for ECAPB wit step in exit cannel. As a result of studies it is discovered tat presence of step in exit cannel allows to increase te degree of deformation in one pass from 0,277 to 0,382. Suc increasing degree of deformation promotes essential refined grain already after first pass of deformation. So after te first pass of deformation grains as elongate form wit size of 1-2 µm widt and 3-5 µm lengt. Already after two passes of deformation grain sizes are 0,8-1,2 µm, wit some grains less tan 0,5 µm. Tereby structure is formed even and equalaxis. Inclusions execute te function of a forming ultra fine grains centre. Tereby, as a result of conducting of deformation in new tool after 2 passes of ECAPB total degree of deformation is up to 0,764 tat provides forming even ultra fine structures. ECAPB realization wit total degree of deformation of 1,146 (3 passes) promotes formation of microstructure wit grains size of 0,4-1 μm, at a time te accumulation of tangled dislocation can be observed. Realization of 4 passes of ECAPB causes te damage of te billet by deformation directly. LITERATURE [1] NAYZABEKOV A.B., LEZHNEV S.N., ANDREYACHSHENKO V.A. Innovation patent RK "Device for angular pressing" publised [2] NAYZABEKOV A.B., ANDREYACHSHENKO Cange of microstructure aluminum alloy by te action of plastic deformation. Tecnology production metals and secondary, 1 (19) February, 2011 year. s [3] Gader Faraji, Mamoud Mosavi Masadi, Hyoung Seop Kim. Materials Letters 65 (2011)