STUDIES ON THE EFFECT OF MAGNESIUM ON TENSILE STRENGTH, HARDNESS AND MICRO-STRUCTURE OF ALUMINUM,USING-CASTING METHOD

TABLE OF CONTENTS

LIST OF TABLES
Table 2.1 Alloying Elements 7
Table 2.2 Alloys Used in Shipping 9
Table 2.3 The AA alloy specification for wrought and cast aluminium alloys is as follows Cast Aluminium alloys 15
Table 3.1 Tensile strength and hardness data and their different percentage 38
composition of silicon and magnesium
Table 4.1 Tensile Stress Test Results of Al-Mg Allow 39
Table 4.2 Brinell Hardness Test Result of Al-Mg Alloy.. 40
Table 4.3 ANOVA Results for Tensile Strength and Hardness 44
Table 4.4 ANOVA summary table for tensile strength 45
Table 4.5 ANOVA summary table for hardness test 45


LIST OF FIGURES
Fig 3.1 Aluminium scraps in a measuring scale 25
Fig 3.2 (a) Ohaus sensitive measuring scale (b) Samples of powdered magnesium 26
Fig 3.3 patterns for hardness and tensile test respectively, with their different dimensions 27
Fig 3.4 (a) Mold preparation (b) Finished mold 28
Fig 3.5 The stir casting machine 29
Fig 3.6 Tensile test specimen 32
Fig 3.7 Avery-Dimension Universal Testing Machine 32
Fig 3.8 Hardness test specimen with dimensions in mm 34
Fig 3.9 Brinell hardness Testing Machine 34
Fig 3.10 Light Optical Microstructural Testing machine 36
Fig 4.1 Al-Mg cast parts 38
Fig 4.2 Varying composition of Al-Mg alloy machined to sizes prior to test 39
Fig 4.3 Increasing Tensile Stress with Increase in Magnesium Composition 40
Fig 4.4 Increasing Hardness with Increase in Magnesium Concentration 41
Fig 4.5(a) Micrograph of Al-Mg alloy with 4% weight composition of magnesium with 100x magnification 44
Fig 4.5(b) Micrograph of Al-Mg alloy with 8% weight composition of magnesium with 100x magnification 44
Fig 4.5(c) Micrograph of Al-Mg alloy with 14% weight composition of magnesium with 100x magnification 45

ABSTRACT
Aluminium on its own is soft, brittle and has low tensile strength, so it is not readily used engineering construction work. To improve on this, draw back this study was carried out and aimed at improving the mechanical properties looking out tensile strength, hardness and microstructure of the aluminium by alloying it with magnesium. The casting of aluminium and magnesium alloy was carried out using sand mold because of cost effectiveness and availability.
In cause of this study 20kg of aluminium scrap were purchased at Uwelu Motor Spare Parts and were degreased with premium motor spirit (PMS), while the magnesium alloy were purchased at Owode-oniran market Lagos State, and were grinded to powder form. The sand mold was prepared with green sand with the gate located at the bottom of the mold to allow easy flowability of the molten metal. The patterns for the different test were made, tensile strength pattern 250mm by 25mm and hardness 200mm by 14mm. These patterns were placed in the mold and covered with the molding sand and rammed. Aluminium scrap of 2kg was placed in the crucible furnance and heated to a temperature of 7500c and impurities were removed with the aid of a skimmer. The powdered magnesium alloy of 4% composition was added to the molten aluminium and mixed together with the stir casting machine and poured into the mold cavity at a temperature of 7300c which was allowed to solidify. This process was repeated for 6,8,10,12 and 14% composition of magnesium alloy. The solidified Al-Mg cast parts were further machined to the various test specification to enable the tensile strength and hardness test to be carried out. The tensile strength test specimen of dimension 100mm by 13mm was carried out using Avery-Dimensional Universal Testing Machine, while the hardness test specimen dimension of 20mm by 20mm was carried out using Brinell Hardness Testing Machine. The microstructural test specimen of 10mm by 10mm was carried out using the Light Optical Microstructural Testing Machine and a micrograph of 100x magnification were taken. The analysis of variance (ANOVA) was carried out on tensile strength and hardness test results for magnesium alloy, comparing with results from silicon alloy by Ezewanka and Ekpo 2020.
It is inferred from the results of this study that as the percentage by weight composition of magnesium increases, the tensile strength and hardness also increases. Comparing this with other literature shows same trend that increase in percentage composition of magnesium in Al-Mg alloy also increases tensile strength and hardness of the cast parts. The microstructure of Al-Mg alloy with 4% composition of magnesium shows a well-defined grain sizes, for Al-Mg alloy with 8% composition of magnesium shows the presence of eutectic magnesium in the inter-dendritic region, which is an arrangement of primary and secondary dendrites, this improves the tensile strength and hardness properties of the cast parts. Al-Mg alloy with 14% weight composition of magnesium shows a uniform distribution of Mg in Al-matrix, which causes complete fusion with the primary aluminium grains changing its original coarse grain form, thereby increasing the strengthen effect of the cast parts. The analysis of variance for both tensile strength and hardness shows that there is sufficient evidence to accept the null hypothesis which indicates that both alloying element (silicon and magnesium) have the same effect on tensile strength and hardness of the cast parts.

CHAPTER ONE

INTRODUCTION

1.1 Background of the study
An alloy is a combination of metals or metals combined with one or more other elements to improve the mechanical properties of the metal. An alloy is distinct from an impure metal in that, with an alloy, the added elements are well controlled to produce desirable properties, while impure metals such as wrought iron are less controlled, but are often considered useful. Alloys are made by mixing two or more elements, at least one of which is a metal. This is usually called the primary metal or the base metal, and the name of this metal may also be the name of the alloy. The other constituents may or may not be metals but, when mixed with the molten base, they will be soluble and dissolve into the mixture.
Helmenstine (2019) defined alloy as a substance made by melting two or more elements together, at least one of them a metal. An alloy crystallizes upon cooling into a solid solution, mixture, or intermetallic compound.
The mechanical properties of alloys will often be quite different from those of its individual constituents. A metal that is normally very soft (malleable), such as aluminium, can be altered by alloying it with another soft metal, such as copper. Although both metals are very soft and ductile, the resulting aluminium alloy will have much greater strength. Adding a small amount of non-metallic carbon to iron trades its great ductility for the greater strength of an alloy called steel. Due to its very-high strength, but still substantial toughness, and its ability to be greatly altered by heat treatment, steel is one of the most useful and common alloys in modern use. By adding chromium to steel, its resistance to corrosion can be enhanced, creating stainless steel, while adding silicon will alter its electrical characteristics, producing silicon steel.

1.2 Problem Statement
Aluminium is a relatively weak material, due to its weak nature it cannot be readily used in its single state. It is therefore alloyed with magnesium to increase its mechanical properties using sand casting method under controlled temperature.