EFFECT OF ANNEALING PROCESS ON THE CORROSION RESISTANCE OF ALUMINUM ALLOY Al-Qadisiya Journal For Engineering Sciences, Vol. 5, No. 2, 123-128, Year 2012 EFFECT OF ANNEALING PROCESS ON THE CORROSION RESISTANCE OF ALUMINUM ALLOY 2024-T3 Asst.Prof. Khairia Salman Hassan1 Asst. Prof. Dr. Hani Aziz Ameen2 Rahman Ali Hussain3 1 Institute of Technology – Baghdad, Mechanical Department. 2 Technical College / Baghdad - Dies and Tools Engineering Department. 3 Technical College / Baghdad - Dies and Tools Engineering Department ABSTRACT The effect of annealing process on corrosion resistance for aluminum (2024-T3) alloy is investigated. Samples of this alloy had been manufactured with dimensions (1.5*1.5*0.3) cm according to ASTM specifications. The annealing process applied by heating the metal in three deferent times; 270°C for two hours, 400°C for half hour and 350°C for one hour. After that the X- Ray Diffraction test has been done in order to know the phases resulted. The electrochemical corrosion test has been done by fixing the potential of the cell and changing it, the potential is chosen depending on open circle and comparing it with the standard metal potential of electrochemical series then adding 100 volt to show the cathode and anode behavior of metal, it had been found that the corrosion average resistance affected by temperature degree and time of the process, it had been noticed that increasing annealing temperature the corrosion resistance of alloy decreased, specially at 400°C, the heat treatment at the temperature 270°C was the best. KEYWORDS: Annealing, Corrosion, Aluminum Alloy. T3 -2024 تأثير عملية التلدين على مقاومة التاكل لسبيكة االلمنيوم 3 رحمن علي حسينم . م2هاني عزيز أمين. د.م. أ 1خيرية سلمان حسن . م.أ القسم الميكانيكي/ بغداد – معهد التكنولوجيا 1 القوالب والعدد قسم – بغداد/ الكلية التقنية 2 قسم القوالب والعدد–بغداد / الكلية التقنية 3 زــــــــــــــــلموجا اذ تـم تـصنيع T3 2024هدف الدراسة هو بيان تاثير عملية التلدين على مقاومة التاكل لسبيكة االلمنيـوم اجريت لها عملية تلـدين . ASTM وفق مواصفة الـ cm (0.3* 1.5* 1.5)ة بابعاد عينات من هذه السبيك من حيث تسخين المعدن الى درجة حرارة معينة ثم التبريد البطئ بالفرن حيث تم انتخـاب ثـالث درجـات لمدة ساعة واحـدة C°350 لمدة نصف ساعة، C°400 لمدة ساعتين، C°270حرارية وبثالث ازمان هي كـل آاجري اختبـار ت . لمعرفة االطوار الناتجة من العملية ) X-Ray ( االشعة السينية اختبار بعدها اجري تم اختيار الجهد اعتماداً على دائرة مفتوحة ومقارنتهـا ه ، كهروكيميائي من حيث تثبيت جهد الخلية وتغيير فولت لبيان الـسلوك الكثـودي (100)بالجهد القياسي للمعدن من السلسلة الكهروكيميائية ثم تم اضافة مقدار بارتفـاع درجـة لوحظ انـه واالنودي للمعدن وقد وجد ان معدل التاكل يتاثر بدرجة حرارة وزمن العملية Khairia Salman Hassan, Hani Aziz Ameen and Rahman Ali Hussain درجة مئوية وان المعاملة الحرارية 400حرارة التلدين تقل مقاومة السبيكة للتآكل خاصة المسخنة الى درجة .فضل اال درجة مئوية كانت 270عند درجة INTRODUCTION Annealing is a heat treatment used for changing the properties like rigidity and strength by heating the metal to a specified temperature degree and then cooling it slowly, the object of annealing is realizing the ductility and softness for metal and removing all internal stresses and making it homogeneous by fining the grains and improving cold forming properties. Annealing had been done by spreading atoms in solid case until stability reached, where the heat takes place in spreading by providing the required energy for breaking the bounds, the atoms movement has an effect on the redistribution and breaking the extract existed in metal caused by forming that makes the plastic forming process more easy where the annealing role is decreasing the energy required for forming and removing the internal stresses which could be removed in room temperature degree for several metal types or could be done quickly by heating to a high temperature degree. The annealing could be done in three stages the first called recovering by removing the linear crystal defects and internal stress which is caused by these defects, this stage cover most of annealing stages. The second stage is recrystalization where the new crystals created to take the place of deformed crystals by internal stresses resulted from forming process. Third stage is resulted from the higher temperature than recrystalizing temperature degree (RT) and run out time where the grains grows to course grains which affect the microscopic instruction of which decrease the mechanical properties. The (2024- T3) aluminum alloy considered one from the high strength alloys which is used in many engineering applications which needs high strength like gears, rotating shafts, pins, valves, bolts, nuts and other parts of aircrafts and computer structures, this alloy distinguished by good corrosion resistance and could be improved by heat treatments (T8, T6) which could give more strength and stress and galvanic corrosion resistance. Ming Liu, 2008, studied the corrosion of commercial die-cast Mg–Al alloys was elucidated by a study, of the corrosion in 3% NaCl, of (i) high-pressure die-cast (HPDC) model Mg–Al alloys, (ii) low-purity Mg, (iii) high-purity (HP) Mg and (iv) HP Mg heat treated at 550 °C. In-Joon Son, 2009, studied the effect of equal-channel angular pressing (ECAP) on the pitting corrosion resistance of anodized Al-Cu alloy was investigated by electrochemical techniques in a solution containing 0.2 mol/l AlCl3 and also by surface analysis. The improvement of pitting corrosion resistance of anodized Al-Cu alloy processed by ECAP appears to be attributed to a decrease in the size of precipitates, which act as origins of pitting corrosion. Mohammad Tajally,2009, presented a research reports comparative analysis of effects of cold working (CW) and annealing on tensile and impact-toughness behavior of 7075 Al alloy. Rahman A. Hussain, 2002. Studied the effect of different quenching mediums on hardness of (Al –Cu) alloy, the results show that the hardness changed according to type and cooling rate and this is due to the types and amounts of solid solution resulting from cooling process. C. Scha¨fer, et. Al. Hence, prove that varying the heating rate the relative extent of various physical mechanisms (recrystallization, recovery, precipitation) can be strongly influenced. Srihari Kurukuri shows that on warm forming, three different aluminum alloys: Al–Mg alloy (AA5754) and Al–Mg–Si alloys (AA 6016 and AA 6061) used in the automotive industry are considered. In the stretch forming with intermediate heat treatments, aerospace Al–Cu alloy (AA 2024) is considered. In non-heat treatable Al–Mg alloys, hardening is mainly due to the presence of solute atoms in solid solution and in heat treatable Al–Mg–Si and Al- Cu alloys, strengthening is determined by precipitates formed during ageing treatment.. K. van der Walde et.al (2005) performed quantitative fractography on forty 2024-T3 sheet aluminum fatigue specimens. It was found that over half of the specimens analyzed had two or more crack-nucleating pits. The number of nucleating pits per specimen was found to be positively correlated with stress level and an interactive effect with corrosion exposure duration was observed. From the fatigue modeling efforts it is concluded that increased accuracy can be achieved by Al-Qadisiya Journal For Engineering Sciences, Vol. 5, No. 2, 123-128, Year 2012 124 EFFECT OF ANNEALING PROCESS ON THE CORROSION RESISTANCE OF ALUMINUM ALLOY 2024- T3 Al-Qadisiya Journal For Engineering Sciences, Vol. 5, No. 2, 123-128, Year 2012 125 incorporating multiple crack effects, particularly at higher stress levels where consistently un- conservative life predictions can be avoided. Al.Th. Kermanidis et.al (2005) prepared 2024 T351 Aluminum alloy in bare, sheet form of 1.6 mm nominal thickness. Machining of the specimens was made according to the specifications ASTM E 466-82 for the fatigue, ASTM E 647-93 for the fatigue crack growth and ASTM E 561-94 for the fracture toughness specimens. The effect of 36 h exposure to exfoliation corrosion solution of bare 2024 T351 aluminum specimens on the fatigue life of the specimens showed that the corrosion attack results in a significant drop of the materials fatigue life . Metallographic corrosion characterization of specimens exposed to 17 exfoliation corrosion solutions for 24 h showed that the presence of corrosion pitting and inter-granular corrosion facilitates essentially the onset of fatigue cracks and, hence, reduces the fatigue life of the corroded specimens appreciably. In this research an experimental test had been applied to explain the effect of annealing on corrosion resistance for aluminum (2024-T3) alloy. EXPERIMENTAL PART 1-Metal Selection Aluminum 2024-T3 alloy selected because it is used in many engineering applications like aircraft parts, the chemical analysis of it explained in Table 1. 2- Preparation of Test Specimens The specimens are prepared from alloy sheets with (1.5*1.5*0.3) cm according to ASTM standard specifications to apply the corrosion test experiment. 3- Specimens Classification After completing the preparation of specimens, it is classified as in Table 2. 4- Heat Treatments The annealing had been done for all specimen groups in Table 2 where it is included heating to the mentioned temperatures and period of time. 5- Tests A- X-Ray Diffraction Test; applied on specimens mentioned in Table 2 by using spectrometer, the results shown in Table 3. B- Corrosion Test: Electrochemical corrosion test had been done on all specimen in Table 2 where the specimens represent the positive pole from a platinum in seawater solution as an electrolyte solution where the potential of cell fixed by open circuit (Sami et al, 2005). The result’s value compared with the potential standard of the metal in electrochemical series, the potential hand been increased 100 volt to show the cathode and anode behavior for metal after current passing through it, Figure 1 shows a picture of electrochemical cell. RESULTS AND DISCUSSION 1- Results of electrochemical corrosion The microstructure of the alloy specimens is shown in Figure 2. Results of corrosion of alloy in different annealing temperatures are shown in Table 4 and Figure 3 shows the relation between current intensity and potential of electrochemical cell. Khairia Salman Hassan, Hani Aziz Ameen and Rahman Ali Hussain The aluminum (2024-T3) alloy considered one from high strength alloys therefore it is used in many engineering applications like aircraft structures, so the applications of this alloy make it specified with specific properties such as hardness and strength in addition to corrosion resistance so this alloy has to be treated to improve its properties. The improvement may be by cold working or treated by isothermal processing. In this research annealing was the heat treating process applied to develop the corrosion resistance of this alloy. The results of electrochemical corrosion test show that the heating to (270°C) for two hours gave high corrosion resistance compared with the other tests, and this is because of the long period of time for heating which allows the alloy to take sufficient time for all phases to precipitate then gave the alloy a good mechanical and physical properties and this means a good corrosion resistance. CONCLUSIONS 1- By increasing annealing temperature, the corrosion resistance of alloy decreased specially at the 400°C. 2- The original alloy without heat treatment gave good corrosion resistance. 3- Heat treatment at 270°C was the best temperature. REFERENCES [1] Ming Liu " Calculated phase diagrams and the corrosion of die-cast Mg–Al alloys ", 2008. [2] In-Joon Son " Effect of equal-channel angular pressing on pitting corrosion resistance of anodized aluminum-copper alloy", 2009. [3] Mohammad Tajally " A comparative analysis of tensile and impact-toughness behavior of cold- worked and annealed 7075 aluminum alloy",2009. [4] Sami A. Ajeel, Jamal Ibrahim Hussein & Talib Mohamed “Improvement of corrosion resistance for carbon steel alloy (st-52) used in marine environment”, Eng. & technology, Vol. 24, No.3, 2005. [5] Rahman A. Hussain, “The effect of cooling mediums on the brinel hardness of (Al – Cu) alloy, 1st. international congress of mechanics - constantine faculty of engineering department of mechanical engineering, university of Constantine , Algeria 14-16 december 2002. [6] C. Scha¨fer , V. Mohles, G. Gottstein ,”Modeling of non-isothermal annealing: Interaction of recrystallization, recovery, and precipitation”,Acta Materialia 59 (2011) 6574–6587, Published by Elsevier Ltd [7] Srihari Kurukuri,”Simulation of Thermally Assisted Forming ofAluminum Sheet”, Ipskamp Drukkers, 2010, India. [8] K. van der Walde et.al, localized corrosion of 7xxx-t7 aluminum alloys in chloride media, ,Technical Contribution to the xxst International Congress of the ABM, January 24-27th 2007, Rio de Janeiro – RJ – Brazil. [9] Al.Th. Kermanidis et.al ,”Fatigue and damage tolerance behaviour of corroded 2024 T351 aircraft aluminum alloy”, Journal of Theoretical and Applied Fracture Mechanics 43 (2005) 121– 132), 2005. Al-Qadisiya Journal For Engineering Sciences, Vol. 5, No. 2, 123-128, Year 2012 126 EFFECT OF ANNEALING PROCESS ON THE CORROSION RESISTANCE OF ALUMINUM ALLOY 2024- T3 Al-Qadisiya Journal For Engineering Sciences, Vol. 5, No. 2, 123-128, Year 2012 127 Table 1 Chemical analysis of used alloy Elements Cu Mg Mn Fe Si Zn Cr Ti Al Rem Actual 4.4 1.5 0.6 0.3 0.4 0.1 0.05 0 92.6 Standard 3.8-4.9 1.2- 1.8 0.30- 0.9 0- 0.50 0- 0.50 0- 0.25 0-0.1 0- 0.15 Table 2 classification test specimens Specimen symbol The case A metal without heat treatment B metal treated to 400°C for one hour C metal treated to 350°C for half an hour D metal treated to 270°C for two hours Table 3 Phases resulted from annealing process The phase Specimen symbol AlCu+Al4Cu9B AlCu4+AlCu3 C AlCu+AlCu4 D Table 4 Results of corrosion alloy in different annealing temperature. Figure 1 The electrochemical cell. Khairia Salman Hassan, Hani Aziz Ameen and Rahman Ali Hussain (B-group) (C-group) (D-group) Figure 2 Pictures of electrochemical corrosion for different annealing temperatures. Figure 3 Relation between current intensity and potential cell. Al-Qadisiya Journal For Engineering Sciences, Vol. 5, No. 2, 123-128, Year 2012 128