Brazing is applied to the merge of the pieces which are most required, tensile strength of the solder can reach high values. By brazing there can be assembled pieces of most metals and ferrous and nonferrous alloys, with high melting temperature. This paper presents an analysis of the microstructure of materials from a brazed merge of aluminum alloy L103 which is often used to produce pieces of aeronautical industry. Brazing material was performed using several technologies, and after examination of the microstructure of materials from the merge area it was established as optimal technology the technology which consist of pickling in Aloclene 100 solution with the deposition of filler material on both sides of the base material and the use of spectral acetylene and neutral flame.
Key words

A. Dimitrescu

D. Dobrotă

D. F. Niţoi

Z. Apostolescu

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383METALURGIJA 54 (2015) 2, 383-386A. DIMITRESCU, D. F. NIŢOI, D. DOBROTĂ, Z. APOSTOLESCURESEARCHES AND STUDIES REGARDING BRAZED ALUMINIUM ALLOYS MICROSTRUCTURE USED IN AERONAUTIC INDUSTRYReceived – Prispjelo: 2014-06-13Accepted – Prihvaćeno: 2014-10-15Preliminary Note – Prethodno priopćenjeISSN 0543-5846METABK 54(2) 383-386 (2015)UDC – UDK 669.715:621.791.3:620.18=111A Dimitrescu, D. F. Niţoi, Z. Apostolescu, Engineering and Tehnologi-cal Systems Management Faculty, Polytehnic University of Bucharest, Romania, D. Dobrotă, Engineering Faculty, University “Constantin Brâncuşi” of Târgu-Jiu, RomaniaBrazing is applied to the merge of the pieces which are most required, tensile strength of the solder can reach high values. By brazing there can be assembled pieces of most metals and ferrous and nonferrous alloys, with high melt-ing temperature. This paper presents an analysis of the microstructure of materials from a brazed merge of alu-minum alloy L103 which is often used to produce pieces of aeronautical industry. Brazing material was performed using several technologies, and after examination of the microstructure of materials from the merge area it was established as optimal technology the technology which consist of pickling in Aloclene 100 solution with the depo-sition of filler material on both sides of the base material and the use of spectral acetylene and neutral flame.Key words: aluminium allloys, microstructure, braze technology, structural homogenizationINTRODUCTIONStructural imperfections may be realived by distruc-tive testings followed by metal examinations. Distruc-tive testings are very usefull to determine the hard glue process tendency or any influences to base or addition material [1, 2]. Distructive testing methods may be con-sidered a real guide to metal junction quality determina-tion but are not able to determine the imperfections causes. The imperfection concequences depends, on a hand, by the proceses that shortage the junction life time, and on the other hand by the life time request spe-cific to hard glue [3, 4]. The brazing frequent junction are design considering the stacked metal pieces. Most frequently discontinuities placements are situated in the junction zone because of the capilarity phenomenon. The discontinuities axis are paralel to joining plane [5, 6]. Any other imperfections (inhomogeneity, other ma-terial inclusions, surface of interior defects ) are the re-sult of base material or added material stress before the hard joining process.In the case of standard sample, the proper distructive testing is the metallografic examination because the achieved informations are relevant for the brazing qual-ification [7].MATERIALS AND METHODSConcerning SR EN 12797 [8] “Hard glue joint qual-ity and fundamental informations about chemical reac-tion between base material and addition material, diffu-sion characterstics and other aspects can be investigated by macro and microscopic investigations”. Informa-tions about section surfaces are offered by this distruc-tive method. Bigger surfaces sets of probes are needed cutted from the same material in the same technological condtions.For the examination of metallographic microstruc-ture there were comprised the following stages:-  debiting which was done on automatic debiting machine ISOMET 4000;-  recording and noting the samples which were taken from the brazed cord. It should be noted that they were debited inside the cord from a minimum dis-tance of 5 / mm from the edge;-  embedding samples was used on a embedding ma-chine with interchangeable resin IPA 40;-  polishing which was performed on an automatic polishing machine Vector;-  chemical attack which was carried out with rea-gents 3, 2, 6, whose chemical composition is shown in Table 2.The experiments consists in sixteen probe, four pro-bes for each glue technology as presented in the Table 1.The forth preparing technologies of the alluminium alloy probes are according to the following. Because exact references about aluminium 3L59 brazing using L103 aluminium alloy are not offered by specialized lit-erature, qualitative and cantitative interpretations are needed. Considering this, comparative interpretation between experimental results and ideal model is very difficult to be done. Because constant and uniform tem-perature environment was used for whole surface joint brazing, the probes are considered closed to ideal situa-tion. To be sure that the structure is not modified, high 384  METALURGIJA 54 (2015) 2, 383-386A. DIMITRESCU et al.: RESEARCHES AND STUDIES REGARDING BRAZED ALUMINIUM ALLOYS MICROSTRUCTUREattention has to be given to probe cutting. Cut position has to be marked and registered to avoid any confusion and done not closer than 5 / mm of probe extremity. Cutted surfaces has to be polished to get a correspond-ing surface quality. A plate section, without scratches, pinches and specially oxides in the case of alluminium alloy has to be prepared for microscopic axamination. To get all, short time between probe preparation and ex-amination is allowed. Table 2 presents reagents chemi-cal composition.structure, without elongate composite elements as pre-sented in Figure 1.A slight grain dimension increasing is observed after maintenance in baking oven at brazing temperature. In volume, base material structural characteristics are not changed, that means the 570 / 0C is corectly set. Figure 2 presents the base material probe after baking oven maintenance at 570 / 0 C.Absence of continuum difusion layer between the two materials revealed in the microstructure analisys of the brazed layer showed a sufficient time maintenance for chemical and structural homogenization of the ma-terials in the contact zone. Figure 3 presents a typical brazing structure of the T4 probe.Figure 3 Typical brazing structure of the T4 probeTable 1 Preparing technology for brazing technologyNo. Preparing technologyHeating timeSimbol Glue area /mm2t1 – 30 / mint2 – 20 / min1 TP I AL X T1 30 x 10,3 = 3092 TP I AL X T2 30 x 6,8 = 2043 TP I AL X T3 30 x 7,6 = 2284 TP I AL X T4 30 x 7,5 = 2255 TP II AL X A1 30 x 7,4 = 2226 TP II AL X A2 30 x 6,9 = 2077 TP II AL X A3 30 x 7,1 = 2138 TP II AL X A4 30 x 7,4 = 2229 TP III AL X V1 30 x 7,4 = 22210 TP III AL X V2 30 x 7,2 = 21611 TP III AL X V3 30 x 8,1 = 24312 TP III AL X V4 30 x 7,9 = 23713 TP IV AL X M1 30 x 6,3 = 18914 TP IV AL X M2 30 x 7,8 = 23415 TP IV AL X M3 30 x 7,2 = 21616 TP IV AL X M4 30 x 8,6 = 258Table 2 Reagents chemical compositionReactive Composition Utilization instructions2 1 / g NaOH100 / ml water-  10 seconds dabbering for general structure making evidence;-  10 - 20 / sec. imersion;-  10 / min. washing in water for fi lm formation that varies with grain orientation; 3 2 / ml HF3 / ml HCl5 / ml HNO3150 / ml water-  Immersion for 10 - 20 / sec. Washing in current of hot water current. Gene-ral structure evidentiation;-  dillution with Diluarea cu 4 water portions. Constituents colouring. 6 25 / ml HNO375 / ml water-  Immersion for 40 secunde 70 / 0C temperature. Cold water rinsing. Surface preparation was done by the following tech-nological process: polishnig with water at 300 / rpm during 3 / min, using 00/600/800/1000/1200/2500 abra-sive disc; emery cloth polishing using TOPOL 2, 0,7 / μm alumina water suspension at 50 rpm with 20 / N force during 6 / min; emery cloth polishing using TOPOL 3, 0,25 / μm alumina water suspension at 50 / rpm with 20 / N force during 6 / min;.EXPERIMENTAL RESEARCHESMetallic plates used for standard probes manufac-turing, before preparation process has a homogenous Fi gure 1  Drawn probe from the base material without thermal influenceFigure 2  Base material probe after baking oven maintenance at 570 / 0 C.385METALURGIJA 54 (2015) 2, 383-386A. DIMITRESCU et al.: RESEARCHES AND STUDIES REGARDING BRAZED ALUMINIUM ALLOYS MICROSTRUCTUREThe image study shows (Figure 4):-  structural modification only in the brazing zone;-  continuous difusion layer appearance on the whole brazing bead;-  the two materials chemical and microstructural ho-mogenization is not possible in the contact zoneBecause of temperature rapid increasing on the braz-ing bead free zone, the intercristaline oxidation and cor-rosion appeared as a result of supratemperature.In the normal situation, of a well done base material capping process, on the first brazing process, detached damages appeared on the base material-allowance ma-terial interface. At the second brazing process, local damages appeared because of sinterized layer bad cap-ping process as presented in the Figure 6.In the case of initial sinterizing process, lack of dam-ages are encountered between base and allowance ma-terial. At the second brazing, the izolate defects reproted on the same interface shows that superficial oxides on the sinterized layer were not removed using this tech-nology (Figure 8).Figure 4 Typical image of the brazed layer for the A1 probeIn the case of defective capping, on the first brazing, minor damages appeared on the base material-allow-ance material interface and continuous damages at the second brazing (Figure 5).Figure 5  Technology No. 49: Technological process TP II AL for surfaces preparation, allowance material bed on a base material surface; M1 probeFigure 6  Technology No. 50: technological process TP IV AL for surfaces preparation, allowance material bed on a surface base material, M 3 probeFigure 8  Technology No. 52: Technological process TP III ALfor surfaces preparation, allowance material bed on a base material surface, A3 probeFigure 7  Technology No. 51: Technological process TP III AL for surfaces preparation, allowance material bed on a base material surface; V1 probeFigure 9  Technology No. 53: Technological process TP IV AL for surfaces preparation, allowance material bed on a base material surface; M4 probe386  METALURGIJA 54 (2015) 2, 383-386A. DIMITRESCU et al.: RESEARCHES AND STUDIES REGARDING BRAZED ALUMINIUM ALLOYS MICROSTRUCTUREFigure 10  Technology No. 54: Technological process TP III AL for surfaces preparation, allowance material bed on a base material surface; V4 probeAs presented in Figure 8, because of material bad capping process, inclusions remained on its surface di-fused on brazing material that causes a defected struc-ture and an uncoresponding difuzion zone (inclusions, cavity, able to affect brazed joining strenght)Because the both material partial capping process, izolate inclusions apeared between base and allowance material (Figure 9).For a good capping process and in the situation of simultaneous both materials brazing, no defects were reported at both base material - allowance material in-terfaces as presented in Figure 10.CONCLUSIONSTo obtain a homogeneous microstructure at the re-conditioning of aluminum alloys by brazing is recom-mended:-  use the brazing method by flame;-  the brazing of aluminum alloys is recommended to be done with the use of oxyacetylene flame by fuel type;-  the brazing of aluminum alloys is recommended to use high purity acetylene known as spectrum acet-ylene;-  the brazing of aluminum alloys is recommended to be done with the deposition of the filler material on the both surfaces of the base material and then con-tacting the pieces and heating them;-  deposition of filler on both surfaces of the base ma-terial has superior results to other deposition meth-ods by lack of isolated defects between the initial sintered layer and the last one brazed;-  holding time of the sample in the oven (30 to 20 / min.) at the brazing temperature (570 / 0 C) does not significantly affect the microstructure of the base material, the filler material or the diffusion zone between the base material and the filler one;-  in case of using the preparation technology of TP III AL surfaces (pickling in Aloclene 100 solution), diffusion zones between the base material and the filler material have larger widths and predominate structural constituents specific to base material and filler material;-  using surface preparing technology, named here TP III AL, a total oxides removal from base material surface is obtained. As a direct result, allowance material deposition on both material surfaces has better results compared with other techniques. No izolate defects are reported between initial sinter-ized layer and brazed layer in final;-  in the case of experimental samples realised  using oxidizing flame type occurs defects by type of lack of penetration and burnt surface;-  technology which consist of pickling in Aloclene 100 solution, with the deposition of filler material on both sides of the base material, the use of spec-tral acetylene and neutral flame may be considered optimal because, after the examination of metallo-graphic microstructure there are not revealed sig-nificant defects in brazed materials of merge.REFERENCES[1]  D. Klobčar, J. Tušek, A. Skumavc, A. Smolej, Metalurgija 53 (2014) 1, 21-24[2]  P. de Greiff, Handbook of Reparations, Oxford University Press, USA, 2006.[3]  Minford, Handbook of Aluminium Bonding Technology and Data, Ed. Marcel Dekker Inc., New York, 1993.[4]  L. Blacha, G. Siwiec, B. Oleksiak, Metalurgija 52 (2013) 3, 301-304.[5]  American Welding Society, Brazing Handbook 5th Edition, 2007.[6]  A. Dimitrescu, Fiability & Durability Supplement (2013) 1, 273-277.[7]  A. Dimitrescu, Fiability & Durability Supplement (2013) 1, 278-282.[8]  SR EN 12797:2002, Încercări distructive ale îmbinărilor lipite tare, ASRO, 2002.Note:  The responsible translator for English language is S.C. PUR-TRAD S.R.L., Targu Jiu, Romania

Researches and studies regarding brazed aluminium alloys microstructure used in aeronautic industry

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Brazing is applied to the merge of the pieces which are most required, tensile strength of the solder can reach high values. By brazing there can be assembled pieces of most metals and ferrous and nonferrous alloys, with high melting temperature. This paper presents an analysis of the microstructure of materials from a brazed merge of aluminum alloy L103 which is often used to produce pieces of aeronautical industry. Brazing material was performed using several technologies, and after examination of the microstructure of materials from the merge area it was established as optimal technology the technology which consist of pickling in Aloclene 100 solution with the deposition of filler material on both sides of the base material and the use of spectral acetylene and neutral flame

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Researches and studies regarding brazed aluminium alloys microstructure used in aeronautic industry

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