The effect of chromium and manganese on the mechanical properties and corrosion resistance of al-si-fe alloy in 0.5m hcl solution

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

Chapter ONE

INTRODUCTION

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

Chapter TWO

LITERATURE REVIEW

• 2.0Literature Review – – – – – – – 7
• 2.1Al – Si – Fe alloy – – – – – – – 7
• 2.2Ternary and multi-component alloys – – – – 8 2.
• 2.1Alloy modification – – – – – – – 11 viii
• 2.3Properties of Aluminium and its alloys – – – – 11 2.
• 3.1Physical Properties – – – – – – – 11 2.
• 3.2Mechanical properties – – – – – – 11 2.
• 3.3Corrosion Properties – – – – – – 12
• 2.4Heat treatment of aluminium and its alloys – – – 14 2.
• 4.1Precipitation Hardening – – – – – – 16
• 2.5 Application of aluminium and its alloys – – – – 19

Chapter THREE

SYSTEM DESIGN AND IMPLEMENTATION

• 3.0Materials and Methods – – – – – – 20
• 3.1Materials – – – – – – – – 20
• 3.2Equipments – – – – – – – 20
• 3.3Methods – – – – – – – – 20 3.
• 3.1Heat treatment – – – – – – – 21 3.
• 3.2Corrosion test – – – – – – – 21 3.3.2.1Corrosion rate determination – – – – – 22
• 3.4Microstructural Examination – – – – – 22

Chapter FOUR

SYSTEM TESTING AND EVALUATION

• 4.0Results and Discussion – – – – – – 24
• 4.1Results – – – – – – – – 24
• 4.2Discussion – – – – – – – – 24 4.
• 2.1Tensile Strength hardness for as-cast and age-hardened Al-Si-Fe alloy with Cr, Mn, and MnCr additions – – – 24 4.
• 2.2Impact energy of the as-cast and age-hardened ix Al-Si-Fe alloy with Cr, Mn, and MnCr additions – – – 26 4.
• 2.3Corrosion Resistance of the as-cast and age-hardened Al-Si-Fe alloy with Cr, Mn, and MnCr additions over the exposure time 26 4.
• 2.4Microstructural Interpretation of tensile strength and hardness for the as-cast and age-hardened Al-Si-Fe alloy with Cr, Mn, and MnCr additions through grain boundary phenomenon – 27

Chapter FIVE

SUMMARY, CONCLUSION AND RECOMMENDATIONS

• 5.0Summary – – – – – – – – 42
• 5.1Conclusion – – – – – – – – 42
• 5.2Recommendations – – – – – – – 43 References – – – – – – – 45 Appendix A; micrographs (Plates) – – – – – 50 Appendix B; Graphs (Figures)- – – – – – 58  CHAPTER ONEINTRODUCTION Aluminium and its alloys are characterized by a relatively low density (2.7g/cm3 as compared to 7.9g/cm3 for steel and 8.86g/cm3 for copper), high electrical and thermal conductivities and resistance to corrosion in some common environments such as atmosphere, water: and salt water (William, 1997, Fontana and Greene, 1987, Micheal and James, 1993). These qualities makes aluminum alloys one of the most used non ferrous alloys used in the production of automotives components, construction materials, containers and packaging, marine, aviation, aerospace and electrical industries (Allen, 1979). The good properties and low cost of aluminium alloys have resulted in such increased use that in 1990 aluminium was the second most widely used metal i.e (Second only to steel)(International Aluminium Institute, 2000, Kenneth, 1999) . Based on these good mechanical properties, the alloys can be forged, stamped, extruded and sand cast (Rajan et al, 1988). Based on the fact that they can be forged to desired shapes at elevated temperatures the can equally be solution treated and aged hardened to obtain desired microstructures and mechanical properties (Nwajagu, 1994 and Rollason, 1964). However, the mechanical properties especially strength of aluminum and its alloy can be enhanced by cold working and alloying, although both processes tend to diminish resistance to corrosion in some alloys (Micheal and James, 1993). Due to the numerous 2 applications of aluminium in a variety of corrosive environments, different methods/processes have been investigated with the aim of increasing the corrosion resistance of aluminium alloys (William, 1997). The mechanical properties of aluminium alloys are improved by heat treatment processes such as age-hardening and solution treatment (Michael and James, 1993). Aluminum–silicon-iron alloy provides good combination of cost, strength, and corrosion resistance, high fluidity and is always free from hot shortness (Metals Hand Book, 1975). The compositional specifications of the alloys rest mainly on the amount of iron, silicon, chromium, manganese added as alloying elements in various compositions. Chromium is generally noted for its improvement on strength and resistance to corrosion (Metal Hand Book, 1979A). Manganese is believed to increase toughness, hardenability and counteraction of embrittlement and hot shortness. While iron increases the strength, hardness and reduce tendency to hot cracking and silicon improves the fluidity as well as the castability and some mechanical properties of the cast alloys (Datsko, 1966). Because of the combined excellent mechanical properties and corrosion resistance, aluminium alloys have found wide applications in aviation, automotive, marine Industries, etc. (Avner, 1974). Although the effects of copper addition on the corrosion behavior of as-cast Al-Si-Fe alloy in acidic media, have been studied by Yaro and Aigbodion, 2006, the authors observed that the addition of Cu to Al-Si-Fe alloy increases its 3 susceptibility to corrosion attack in the two acidic media used (HCl and HN03 ) up to 4% Cu addition. The rate of corrosion is higher in HCl than in HN03 and the rate of corrosion of coupon in HCl decreased with time (Yaro and Aigbodion, 2006). The Researchers also studied the effect of Cu addition on the mechanical properties of Al-Si-Fe and observed that addition of Cu increased the tensile strength and hardness up to 6% Cu addition (Yaro et al, 2006).
• 1.1AIMS AND OBJECTIVES The aim of the research is to investigate the mechanical properties and corrosion resistance of Al-Si-Fe alloy in 0.5M HCl solution in as-cast condition at room temperature and compare the result with those obtained when the alloys were age-hardened. The specific aims and objectives of this research was to understand,
• 1.The individual and simultaneous effects of Cr and Mn addition with Al- Si-Fe alloy on the mechanical properties (tensile properties, hardness and impact strength) in the as-cast condition.
• 2.The individual and simultaneous effects of Cr and Mn with Al-Si-Fe alloy and age-hardening treatment on the mechanical properties of Al- Si-Fe alloy.
• 3.To determine the individual and simultaneous effects of concentration of Cr, Mn, MnCr and time of exposure on the corrosion resistance of Al-Si-Fe alloys in 0.5M HCl solution at 280C for 480 hrs in the as-cast and age-hardened conditions. 4
• 4.To study the microstructural changes that occur as a result of Cr and Mn additions to Al-Si-Fe alloy in as-cast and age-hardened condition
• 5.The correlation between the studied mechanical properties and microstructures of all the alloys produced.
• 1.2BACKGROUND INFORMATION / JUSTIFICATION OF THE RESEARCH The successful development of aluminium castings in parts and components applications requires, that the casting display a combination of high strength and toughness in thin and thick sections. These properties are determine by the strength and integrity of the microstructures. Though years of research, development and experience, the microstructure characteristics required to achieve these properties in casting have been determined and expressed in a variety of ways. Ultimately, the quality of the microstructures of an alloy determines the performances that can be obtained. However, as reported by Odutola (2005), that all engineering materials are chemically reactive. Hence, the corrosion characteristics of as-cast and age-hardened alloys with individual and simultaneous additions of Cr and Mn in 0.5M HCl solution at 280C over a period of 480 hrs. Based on the mechanical properties requirement and corrosion resistance of Al-Si-Fe alloy in automobile industry as oil pan, flywheel and rear-axle housing, crank cases, etc. In aerospace industry as tankages for storage of liquid fuels and oxidizers, engines, airframes, propellers, accessories, etc. This research work improved these properties significantly through alloying and age-hardening treatment. 5
• 1.3SCOPE OF THE STUDY The study involves determination of the mechanical properties (tensile properties, hardness, and impact strength) of Al-Si-Fe alloy with addition of Cr and Mn in as-cast and age-hardened conditions using standard test procedures. The corrosion test was also carried out on the as-cast and age-hardened samples at room temperature (280C) using weight loss method over a period of 480 hrs of exposure time.
• 1.4STATEMENT OF THE PROBLEM / LIMITATIONS OF STUDY There are other important mechanical properties of aluminium and its alloys, but since the service condition is a major factor in selection of the mechanical property to be tested for, other properties have to be investigated. Based on this, the tensile strength, hardness and impact properties were investigated. Despite various ways of evaluating corrosion resistance of metal/alloys, the weight loss method of investigating corrosion was used due to its simplicity and method of result computations. The HCl acid concentration used for the corrosion test was fixed at 0.5M because it is the optimum concentration of most acids (Yawas, 2005). While the use of the acid as an environment for the samples was as a result of the fact that the alloys found area of applications most in automobiles and aerospace industry. Corrosion due to HCl acid in crude/oil represent a significant portion of the refining cost. In this unit, corrosion comes primarily from chlorides. Chloride corrosion is caused by 6 hydrogen chloride, which is formed from hydrolysis of the chloride salt contained in the crude. The released hydrogen chloride is relatively noncorrosive in the vapor phase. However, below the dew point of water, hydrogen chloride forms an acidic solution and becomes very corrosive to many structural materials (Quraishi, 2000, 2003) in Yawas (2005). However, some aircraft may be operated in an environment containing ions chloride, sulphate and polluting dust (Odutola, 2005). These chlorides combine with hydrogen gas in the atmosphere forming acid rain which subsequently affects the aircraft components over a period of time. Hence, the use of the HCl solution as the corrosion medium.
• 1.5CONTRIBUTION TO KNOWLEDGE So far, to the best of my knowledge, no previous work has been carried out on the individual and simultaneous addition of Cr and Mn with Al-Si-Fe alloy. Therefore, this research has been able to improve significantly and simultaneously the mechanical properties and corrosion resistance of Al- Si-Fe alloy by alloying and age-hardening treatment.