<p> </p><p>TITLE PAGE<br>Declaration – – – – – – – – ii<br>Certification – – – – – – – – – iii<br>Dedication – – – – – – – – – iv<br>Acknowledgement – – – – – – – – v<br>Abstract – – – – – – – – vi<br>Table of Contents – – – – – – – – vii<br>List of Tables – – – – – – – – – x<br>List of Figures – – – – – – – – xii<br>List of Plates – – – – – – – – – xiii<br>

Chapter ONE

<br>1.0 Introduction – – – – – – – 1<br>1.1 Aims and Objectives – – – – – – 3<br>1.2 Background Information / Justification of the Research – 4<br>1.3 Scope of the Study – – – – – – 5<br>1.4 Statement of the Problem/Limitations of the Study – – 5<br>1.5 Contribution to Knowledge – – – – – 6<br>

Chapter TWO

<br>2.0 Literature Review – – – – – – – 7<br>2.1 Al – Si – Fe alloy – – – – – – – 7<br>2.2 Ternary and multi-component alloys – – – – 8<br>2.2.1 Alloy modification – – – – – – – 11<br>viii<br>2.3 Properties of Aluminium and its alloys – – – – 11<br>2.3.1 Physical Properties – – – – – – – 11<br>2.3.2 Mechanical properties – – – – – – 11<br>2.3.3 Corrosion Properties – – – – – – 12<br>2.4 Heat treatment of aluminium and its alloys – – – 14<br>2.4.1 Precipitation Hardening – – – – – – 16<br>2. 5 Application of aluminium and its alloys – – – – 19<br>

Chapter THREE

<br>3.0 Materials and Methods – – – – – – 20<br>3.1 Materials – – – – – – – – 20<br>3.2 Equipments – – – – – – – 20<br>3.3 Methods – – – – – – – – 20<br>3.3.1 Heat treatment – – – – – – – 21<br>3.3.2 Corrosion test – – – – – – – 21<br>3.3.2.1Corrosion rate determination – – – – – 22<br>3.4 Microstructural Examination – – – – – 22<br>

Chapter FOUR

<br>4.0 Results and Discussion – – – – – – 24<br>4.1 Results – – – – – – – – 24<br>4.2 Discussion – – – – – – – – 24<br>4.2.1 Tensile Strength hardness for as-cast and age-hardened<br>Al-Si-Fe alloy with Cr, Mn, and MnCr additions – – – 24<br>4.2.2 Impact energy of the as-cast and age-hardened<br>ix<br>Al-Si-Fe alloy with Cr, Mn, and MnCr additions – – – 26<br>4.2.3 Corrosion Resistance of the as-cast and age-hardened Al-Si-Fe<br>alloy with Cr, Mn, and MnCr additions over the exposure time 26<br>4.2.4 Microstructural Interpretation of tensile strength and hardness<br>for the as-cast and age-hardened Al-Si-Fe alloy with Cr, Mn,<br>and MnCr additions through grain boundary phenomenon – 27<br>

Chapter FIVE

<br>5.0 Summary – – – – – – – – 42<br>5.1 Conclusion – – – – – – – – 42<br>5.2 Recommendations – – – – – – – 43<br>References – – – – – – – 45<br>Appendix A; micrographs (Plates) – – – – – 50<br>Appendix B; Graphs (Figures)- – – – – – 58</p><p>&nbsp;</p><p>&nbsp;</p><h2>

Chapter ONE

</h2><p>INTRODUCTION<br>Aluminium and its alloys are characterized by a relatively low<br>density (2.7g/cm3 as compared to 7.9g/cm3 for steel and 8.86g/cm3 for<br>copper), high electrical and thermal conductivities and resistance to<br>corrosion in some common environments such as atmosphere, water: and<br>salt water (William, 1997, Fontana and Greene, 1987, Micheal and James,<br>1993). These qualities makes aluminum alloys one of the most used non<br>ferrous alloys used in the production of automotives components,<br>construction materials, containers and packaging, marine, aviation,<br>aerospace and electrical industries (Allen, 1979). The good properties and<br>low cost of aluminium alloys have resulted in such increased use that in<br>1990 aluminium was the second most widely used metal i.e (Second only<br>to steel)(International Aluminium Institute, 2000, Kenneth, 1999) .<br>Based on these good mechanical properties, the alloys can be<br>forged, stamped, extruded and sand cast (Rajan et al, 1988). Based on<br>the fact that they can be forged to desired shapes at elevated<br>temperatures the can equally be solution treated and aged hardened to<br>obtain desired microstructures and mechanical properties (Nwajagu, 1994<br>and Rollason, 1964). However, the mechanical properties especially<br>strength of aluminum and its alloy can be enhanced by cold working and<br>alloying, although both processes tend to diminish resistance to corrosion<br>in some alloys (Micheal and James, 1993). Due to the numerous<br>2<br>applications of aluminium in a variety of corrosive environments, different<br>methods/processes have been investigated with the aim of increasing the<br>corrosion resistance of aluminium alloys (William, 1997).<br>The mechanical properties of aluminium alloys are improved by<br>heat treatment processes such as age-hardening and solution treatment<br>(Michael and James, 1993). Aluminum–silicon-iron alloy provides good<br>combination of cost, strength, and corrosion resistance, high fluidity and is<br>always free from hot shortness (Metals Hand Book, 1975). The<br>compositional specifications of the alloys rest mainly on the amount of<br>iron, silicon, chromium, manganese added as alloying elements in various<br>compositions. Chromium is generally noted for its improvement on<br>strength and resistance to corrosion (Metal Hand Book, 1979A).<br>Manganese is believed to increase toughness, hardenability and<br>counteraction of embrittlement and hot shortness. While iron increases the<br>strength, hardness and reduce tendency to hot cracking and silicon<br>improves the fluidity as well as the castability and some mechanical<br>properties of the cast alloys (Datsko, 1966).<br>Because of the combined excellent mechanical properties and<br>corrosion resistance, aluminium alloys have found wide applications in<br>aviation, automotive, marine Industries, etc. (Avner, 1974). Although the<br>effects of copper addition on the corrosion behavior of as-cast Al-Si-Fe<br>alloy in acidic media, have been studied by Yaro and Aigbodion, 2006, the<br>authors observed that the addition of Cu to Al-Si-Fe alloy increases its<br>3<br>susceptibility to corrosion attack in the two acidic media used (HCl and<br>HN03 ) up to 4% Cu addition. The rate of corrosion is higher in HCl than in<br>HN03 and the rate of corrosion of coupon in HCl decreased with time<br>(Yaro and Aigbodion, 2006). The Researchers also studied the effect of<br>Cu addition on the mechanical properties of Al-Si-Fe and observed that<br>addition of Cu increased the tensile strength and hardness up to 6% Cu<br>addition (Yaro et al, 2006).<br>1.1 AIMS AND OBJECTIVES<br>The aim of the research is to investigate the mechanical properties and<br>corrosion resistance of Al-Si-Fe alloy in 0.5M HCl solution in as-cast<br>condition at room temperature and compare the result with those obtained<br>when the alloys were age-hardened.<br>The specific aims and objectives of this research was to understand,<br>1. The individual and simultaneous effects of Cr and Mn addition with Al-<br>Si-Fe alloy on the mechanical properties (tensile properties, hardness<br>and impact strength) in the as-cast condition.<br>2. The individual and simultaneous effects of Cr and Mn with Al-Si-Fe<br>alloy and age-hardening treatment on the mechanical properties of Al-<br>Si-Fe alloy.<br>3. To determine the individual and simultaneous effects of concentration<br>of Cr, Mn, MnCr and time of exposure on the corrosion resistance of<br>Al-Si-Fe alloys in 0.5M HCl solution at 280C for 480 hrs in the as-cast<br>and age-hardened conditions.<br>4<br>4. To study the microstructural changes that occur as a result of Cr and<br>Mn additions to Al-Si-Fe alloy in as-cast and age-hardened condition<br>5. The correlation between the studied mechanical properties and<br>microstructures of all the alloys produced.<br>1.2 BACKGROUND INFORMATION / JUSTIFICATION OF THE RESEARCH<br>The successful development of aluminium castings in parts and<br>components applications requires, that the casting display a combination<br>of high strength and toughness in thin and thick sections. These properties<br>are determine by the strength and integrity of the microstructures. Though<br>years of research, development and experience, the microstructure<br>characteristics required to achieve these properties in casting have been<br>determined and expressed in a variety of ways. Ultimately, the quality of<br>the microstructures of an alloy determines the performances that can be<br>obtained. However, as reported by Odutola (2005), that all engineering<br>materials are chemically reactive. Hence, the corrosion characteristics of<br>as-cast and age-hardened alloys with individual and simultaneous<br>additions of Cr and Mn in 0.5M HCl solution at 280C over a period of 480<br>hrs. Based on the mechanical properties requirement and corrosion<br>resistance of Al-Si-Fe alloy in automobile industry as oil pan, flywheel and<br>rear-axle housing, crank cases, etc. In aerospace industry as tankages for<br>storage of liquid fuels and oxidizers, engines, airframes, propellers,<br>accessories, etc. This research work improved these properties<br>significantly through alloying and age-hardening treatment.<br>5<br>1.3 SCOPE OF THE STUDY<br>The study involves determination of the mechanical properties (tensile<br>properties, hardness, and impact strength) of Al-Si-Fe alloy with addition<br>of Cr and Mn in as-cast and age-hardened conditions using standard test<br>procedures. The corrosion test was also carried out on the as-cast and<br>age-hardened samples at room temperature (280C) using weight loss<br>method over a period of 480 hrs of exposure time.<br>1.4 STATEMENT OF THE PROBLEM / LIMITATIONS OF STUDY<br>There are other important mechanical properties of aluminium and its<br>alloys, but since the service condition is a major factor in selection of the<br>mechanical property to be tested for, other properties have to be<br>investigated. Based on this, the tensile strength, hardness and impact<br>properties were investigated. Despite various ways of evaluating corrosion<br>resistance of metal/alloys, the weight loss method of investigating<br>corrosion was used due to its simplicity and method of result<br>computations.<br>The HCl acid concentration used for the corrosion test was fixed at 0.5M<br>because it is the optimum concentration of most acids (Yawas, 2005).<br>While the use of the acid as an environment for the samples was as a<br>result of the fact that the alloys found area of applications most in<br>automobiles and aerospace industry. Corrosion due to HCl acid in<br>crude/oil represent a significant portion of the refining cost. In this unit,<br>corrosion comes primarily from chlorides. Chloride corrosion is caused by<br>6<br>hydrogen chloride, which is formed from hydrolysis of the chloride salt<br>contained in the crude. The released hydrogen chloride is relatively noncorrosive<br>in the vapor phase. However, below the dew point of water,<br>hydrogen chloride forms an acidic solution and becomes very corrosive to<br>many structural materials (Quraishi, 2000, 2003) in Yawas (2005).<br>However, some aircraft may be operated in an environment containing<br>ions chloride, sulphate and polluting dust (Odutola, 2005). These chlorides<br>combine with hydrogen gas in the atmosphere forming acid rain which<br>subsequently affects the aircraft components over a period of time. Hence,<br>the use of the HCl solution as the corrosion medium.<br>1.5 CONTRIBUTION TO KNOWLEDGE<br>So far, to the best of my knowledge, no previous work has been carried<br>out on the individual and simultaneous addition of Cr and Mn with Al-Si-Fe<br>alloy. Therefore, this research has been able to improve significantly and<br>simultaneously the mechanical properties and corrosion resistance of Al-<br>Si-Fe alloy by alloying and age-hardening treatment.</p><p>&nbsp;</p> <br><p></p>