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Article
PITTING CORROSION STUDIES OF MG-BEARING HYPEREUTECTIC AL-17% SI ALLOY
دراسة التأكل النقري لسبيكة الالمنيوم- %17 سيليكون فوق اليوتكتيكية المحتوية على المغنيسيوم

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Abstract

In this study pitting corrosion is investigated in hypereutectic Al- 17wt% Si alloy bearing magnesium . Many alloys were prepared by die casting with adding different percentages of magnesium : 1 wt%, 4wt% & 9 wt% to the Al-17%Si alloy in order to study the influence of magnesium addition on the corrosion behavior and pitting properties in 3.5% NaCl solution. Results of microstructure examination show that primary silicon (Si) and eutectic silicon in base alloy was more susceptible to pitting corrosion compared to the other alloys containing magnesium . It was found that the corrosion rate of alloy Al-17%Si bearing Mg (in all percentages) was lower than that of base alloy. The corrosion potential shifts to less negative value ( to more noble direction) and Epit to more positive value with increasing Mg content to 9%wt. It means that the addition of Mg to Al-17% Si alloy improves resistance to pitting corrosion and that no pitting appears in passive region during the cyclic polarization test.

في هذا البحث تم دراسة التآكل النقري في سبائك الالمنيوم-%17 سيليكون المحتوية على نسب وزنية مختلفة من معدن المغنيسيوم ( 1, 4 ,9 )% والتي تم تحضيرها بطريقة السباكة في القوالب المعدنية وذلك لبيان تأثير اضافة المغنيسيوم على سلوك التآكل النقري في محلول ملحي من %3.5 كلوريد الصوديوم. وقد اظهرت نتائج الفحص المجهري ان السيليكون الاولي واليوتكتيك في السبيكة الاساس يكون اكثر ميلا للتأكل النقري مقارنة بالسبائك الحاوية على المغنيسيوم. وقد وجد ان معدل التآكل لسبيكة الالمنيوم% 17سيليكون المحتوية على المغنيسيوم ( لكل النسب المضافة) اقل مما هو عليه في حالة السبيكة الاساس . وقد لوحظ ان جهد التآكل ينتقل الى الى قيمة اقل سالبية ( الى الاتجاه الاكثر نبلا) وجهد التنقر الى قيمة اكثر موجبة مع زيادة نسبة المغنيسيوم الى 9% وهذا يعني ان اضافة المغنيسيوم عملت على تحسين مقاومة التآكل النقري. كذلك لوحظ اختفاء النقر وحلقة الهسترة من منطقة السلبية في منحني التفاعل الانودي خلال اجراء فحص الاستقطاب الدوري .


Article
Corrosion Resistance Enhancement in Acidic solution for Austenitic Stainless Steel by Gas-Phase Hybrid Deposition Process

Authors: A.D. Thamir --- F.Q. Mohammed --- A.S. Hasan --- A.L. Abid
Journal: Engineering and Technology Journal مجلة الهندسة والتكنولوجيا ISSN: 16816900 24120758 Year: 2017 Volume: 35 Issue: 8 Part (A) Engineering Pages: 788-794
Publisher: University of Technology الجامعة التكنولوجية

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Abstract

In acidic environments the corrosion rate of stainless steels is considered high, this is due to pitting occurrence in concentrated chloride environments. The Austenitic steels such as type 316 stainless steel generally not recommended for Hydrochloric acid storage in petroleum planets except when solutions are very dilute and at room temperature, otherwise pitting may occur. In this work, a multicomponent coating (Ti-B-N-C) was deposited on the austenitic stainless steels (AISI 316) that used in petroleum industry. The coating process has been achieved by mixed vapor deposition technique; this was done in attempt to improve the resistance to pitting corrosion for austenitic stainless steels surface. The structural characterization for the deposited Ti-Base coating was done by using XRD technique, and the Scanning Electron Microscopy (SEM). Electrochemical corrosion tests have been performed by using electrochemical test in 0.25M hydrochloric acid (HCl) as an aqueous solution at 22˚C to obtain the anodic polarization curves for the coated surfaces. Several interesting observations have been made During the test. As expected, the surface of the AISI 316 suffers from a sudden increase in the current density at the potential above 1500 mV due to the occurrence of pitting corrosion. In addition, the Ti-B-C-N coating surfaces show great future in reducing the current density of the steel surface in the anodic region, indicating improved pitting resistance for all Ti-based coating samples. No evidence for pitting corrosion was observed in the coated surfaces during electrochemical test even at potentials up to 2000 mV, instead, general corrosion was observed for the samples that was deposited at 750˚C since low potential values was observed for these samples .


Article
STUDY OF THE PITTING CORROSION FOR SHOT PEENING 6061-T6ALUMINUM ALLOY IN SEA WATER
دراسة تاثير قذف سبيكة الالمنيوم 6061-T6 بكرات معدنية على التأكل النقري في ماء البحر

Author: Mohammad Salih Faris محمد صالح فارس
Journal: Iraqi journal of mechanical and material engineering المجلة العراقية للهندسة الميكانيكية وهندسة المواد ISSN: 20761819 Year: 2017 Volume: 17 Issue: 4 Pages: 724-733
Publisher: Babylon University جامعة بابل

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Abstract

This paper aims to clear some influential parameters, like shape and size of shot-peening on pitting corrosion for aluminum alloy 6061-T6. Many specimens" were "prepared for corrosion test" with dimensions of (15*15*3) mm according to ASTM G71-31 and these specimens were categorized into four group having symbols (A,B,C,D). Three of these groups were shot peened using different ball sizes. Group B shot by steel ball having diameter 1.25 mm while group C shot by steel ball with diameter 2.75 mm. Steel cylinder with diameter of 2.75 mm" and length 3mm was to shot" another "specimens. Shot "time" was fixed of (10) min. Many tests have been carried out to measure the surface roughness, Vickers hardness ,residual stresses. SEM micrograph for all specimens . Corrosion test was done by cyclic electrochemical methods for all specimens in environments of "3.5% NaCl solution". The Corrosion value has calculated by using Tafel equation. Results obtained show that shot peening contribute in decreasing corrosion rate comparing with base metal and shot peening using steel ball give low corrosion rate than cylinder steel due to plastic deformation causes by cylinder steel and steel ball having diameter 2.75 give the best result due to residual stress .

تناولت الدراسة تأثير بعض متغيرات القذف بكرات فولاذية من القطر والشكل على سلوك التآكل لسبيكة ألمنيوم ذات المتانة المتوسطة6061-T6. صنعت عدد من عينات اختبارالتآكل بابعاد(15*15*3) ملم وفق المواصفة القياسية ASTM-G71-31 .صنفت هذه العينات الى اربعة مجاميع باحرف (A,B,C,D) تعرضت ثلاثة مجاميع وهي عينات المجموعة B الى القذف بكرات فولاذية قطرها 1.25 ملم وعينات المجموعة Cقذفت بكرات فولاذية قطرها .2.75ملم لبيان تأثير قطر الكرة على سلوك التآكل اما عينات المجموعة D فقد قذفت بأسطوانات فولاذية طولها 3 ملم وقطرها 2.75ملم لبيان تأثير شكل أداة القذف على سلوك التآكل مع تثبيت الزمن10د قيقة لكافة عمليات القذف . تم قياس الخشونة السطحية ، الصلادة ، الاجهادات الضغطية المتولدة كما اجري اختبار التآكل الكهروكيماوي على مجاميع العينات في محلول ماء البحر3.5% NaCL وتم تسجيل النتائج القرائية من جهد وتيار بطريقة تافل. واستخدمت معادلة تافل لحساب معدل التآكل. أظهرت النتائج إن زيادة قطر الكرة ساهم في تقليل معدل التاكل نتيجة زيادة في الاجهادات الضغطية المتولدة جراء القذف .


Article
Prediction the Initiation of Pitting Corrosion Depending on Carbides in the Microstructure of 304 Stainless Steel

Authors: S. I.Alrubaiey --- Sh. F.Hasan
Journal: Engineering and Technology Journal مجلة الهندسة والتكنولوجيا ISSN: 16816900 24120758 Year: 2017 Volume: 35 Issue: 10 Part (A) Engineering Pages: 975-980
Publisher: University of Technology الجامعة التكنولوجية

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Abstract

Stainless steel has excellent corrosion resistance due to formation oxides protective films in many environments. When steel exposed to temperature in the range of (500-900) ºC, the carbon in the structure will be effective to react with chromium in the structure , which is no less than 18.6% in the present used steel, to form chromium carbides in different types (M23C6, M7C3, M2.9C) in which M represent chromium. Therefore pitting corrosion will be initiated due to two reasi, the first was depleted zone and the second is galvanic effects between carbides and matrix. The present work was aimed to find relationships to predict the initiation of pitting corrosion depending on carbides in the microstructure of 304 stainless steel, which formed in heated specimens at (500 - 900) ºC. The potentiodynamic cyclic polarization (PCP) measurement was performed to investigate and analyze pitting corrosion resistance properties.

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