ABSTRACT
A study of the effects of pressure on micro structure and mechanical properties of die cast aluminum alloys A1350 and A380 was carried out and subsequent analysis made. Pressure was regulated at various levels in the die cast machine. Both alloys were cast into samples
each under different applied pressures. The mechanical properties of both alloys were tested and micro structure analysis was done and the results for both tests were compared for both alloys. The results obtained show hardness, tensile strength, yield strength and
impact strength of both alloys varied with applied pressure in the casting process. The hardness values increased with applied pressure but not too significantly from 76 to 85 HRN for A380 alloy and 77 to 86 HRN for A1350 alloy as pressure rose from 350 to 1400kg/cm2. The yield strength of both alloys also increased with applied pressure. The impact strength and elongation both decreased with applied pressure in both alloys. Also the microstructure analysis carried out on both alloys showed structural changes in the morphologies of both alloys as some appeared granullar, lamellar, coarse e.t.c from pressure 350 to 1400kg/cm2. Also as the pressure increased, the grains became finer and porosity decreased. Models were developed and for all the models developed, a close relationship with the experimental results were underlying in view of the small errors generated by them and can be used to predict the experimental values of this research.
TABLE OF CONTENTS
Title Page i
Declaration ii
Certification iii
Dedication iv
Acknowledgements v
Abstract vi
Table of Contents vii
List of Figures x
List of Tables xii
List of Appendices xiii
CHAPTER 1 INTRODUCTION 1
1.1 Background of this study 1
1.2 Advantages of die casting 3
1.3 Aluminum A380 and A1450 alloys 4
1.4 Statement of problem 6
1.5 Present research 7
1.6 Justification of this research 7
1.7 Aims and objectives of this research 8
CHAPTER 2 LITERATURE REVIEW 9
2.1 Introduction 9
2.1.1 Hot chamber die casting process 10
2.1.2 Cold chamber die casting process 11
2.2 Mathematical modeling 15
2.3 Review of past work 17
CHAPTER 3 MATERIALS AND METHODS 22
3.1 Materials 22
3.1.1 Chemical composition of work piece materials 23
3.2 Equipment 25
3.2.1 Experimental procedure 26
3.3 Methodology 26
3.3.1 Pouring and melting 26
3.3.2 Pressure application 27
3.4 Description and specification of die cast machine 27
3.4.1 Operating mode 29
3.4.2 Display indication 29
3.5 Dies for experiment 29
3.5.1 Samples after casting 30
3.6 Mechanical test procedure 32
3.6.1 Tensile test 32
3.6.2 Hardness test 32
3.6.3 Impact test 33
3.7 Micro structure analysis 33
3.7.1 Etching and microscopy 33
3.7.2 Scanning electron microscope analysis 34
3.8 Regression models 34
3.8.1 Error analysis 37
CHAPTER 4 RESULTS AND DISCUSSION 38
4.1 Results 38
4.2 Discussions 45
4.2.1 Hardness 45
4.2.1.1 Regression model for hardness 45
4.2.2 Tensile strength 45
4.2.2.1 Regression model for tensile strength 46
4.2.3 Yield strength 46
4.2.3.1 Regression model for yield strength 47
4.2.4 Impact strength 47
4.2.4.1 Regression model for impact strength 48
4.3 Micro structure 48
4.3.1 Number of grains 48
4.3.1.1 Regression model for number of grains 48
4.3.2 Grain size 49
4.3.2.1 Regression model for grain size 49
4.3.3 Porosity measurement 50
4.4 Micro structure analysis 52
4.4.1 Micro structural characterization 52
4.4.2 Micro structure and micrograph of A380 samples 53
4.4.3 Micro structure and micrograph of A1350 samples 58
CHAPTER 5 CONCLUSIONS AND RECOMMENDATION 63
5.1 Conclusions 63
5.2 Recommendations for further work 65
5.3 Contribution to knowledge 65
REFERENCES 66
APPENDIXES 74
LIST OF FIGURES
Figure No Title Page
Figure 2.1 Hot chamber die casting cycle 10
Figure 2.2 Cold chamber die casting process 12
Figure 3.1 A1350 raw material 22
Figure 3.2 A380 raw material 22
Figure 3.3 X- ray generation schematics 24
Figure 3.4 High pressure cold chamber die casting machine 28
Figure 3.5 Samples of A1350 after casting 30
Figure 3.6 Samples of A380 after casting 31
Figure 4.1 Experimental and predicted plots of hardness vs pressure of A380 38
Figure 4.2 Experimental and predicted plots of hardness vs pressure of A1350 38
Figure 4.3 Experimental and predicted plots of tensile strength vs pressure of A380 39
Figure 4.4 Experimental and predicted plots of tensile strength vs pressure of A1350 39
Figure 4.5 Elongation vs pressure plots of A380 and A1350 40
Figure 4.6 Experimental and predicted plots of yield strength vs pressure of A380 40
Figure 4.7 Experimental and predicted plots of yield strength vs pressure of A1350 41
Figure 4.8 Experimental and predicted plots of impact strength vs pressure of A380 41
Figure 4.9 Experimental and Predicted Plots of Impact Strength vs Pressure of A1350 42
Figure 4.10 Experimental and predicted plots of number of grains vs pressure of A380 42
Figure 4.11 Experimental and predicted plots of number of grains vs pressure of A1350 43
Figure 4.12 Experimental and predicted plots of grain size vs pressure of A380 43
Figure 4.13 Experimental and predicted plots of grain size vs pressure of A1350 44
Figure 4.14 Predicted porosity vs pressure plots of A380 and A1350 44
Figure 4.15 Microstructure and micrograph of sample of A380 with injection pressure of 1400kg/cm2 53
Figure 4.16 Microstructure and micrograph of sample of A380 with injection pressure of 1050kg/cm2 54
Figure 4.17 Microstructure and micrograph of sample of A380 with injection pressure of 700kg/cm2 55
Figure 4.18 Microstructure and micrograph of sample of A380 with injection pressure of 350kg/cm2 56
Figure 4.19 Microstructure and micrograph of sample of A380 with injection pressure of 0kg/cm2 57
Figure 4.20 Microstructure and micrograph of sample of A1350 with injection pressure of 1400kg/cm2 58
Figure 4.21 Microstructure and micrograph of sample of A1350 with injection pressure of 1050kg/cm2 59
Figure 4.22 Microstructure and micrograph of sample of A1350 with injection pressure of 700kg/cm2 60
Figure 4.23 Microstructure and micrograph of sample of A1350 with injection pressure of 350kg/cm2 61
Figure 4.24 Microstructure and micrograph of sample of A1350 with injection pressure of 0kg/cm2 62
LIST OF TABLES
Table No Title Page
Table 3.1 Chemical composition of work piece materials 25
Table 3.2 Specification of die cast machine 27
Table 3.3 Input factors and their respective levels 31
Table 4.1 A380 predictor coefficient table for porosity level 50
Table 4.2 A1350 predictor coefficient table for porosity level 51
Table A1 Hardness number for A380 samples 74
Table A2 Hardness number for A1350 samples 74
Table A3 Tensile strength of A380 samples 75
Table A4 A380 predictor coefficient table for tensile strength 75
Table A5 Tensile strength of A1350 samples 76
Table A6 A1350 predictor coefficient table for tensile strength 76
Table A7 Yield strength of the A380 and A1350 samples 77
Table A8 A380 predictor coefficient table for yield strength 77
Table A9 A1350 Predictor coefficient table for yield strength 77
Table A10 Impact strength of A380 samples 78
Table A11 Impact strength of A1350 samples 78
Table A12 Number of grains for A380 samples 79
Table A13 Number of grains for A380 samples 79
Table A14 Grain sizes for A380 and A1350 samples 80
Table A15 A380 predictor coefficient table for grain size 80
Table A15 A1350 predictor coefficient table for grain size 80
LIST OF APPENDICES
Appendix Name Title Page
Appendix A Tables for various experiment and modeled parameter results 74
CHAPTER ONE
INTRODUCTION
1.1 BACKGROUND
According to Richard et al, (1967), metal casting may be defined as a metal object produced by pouring molten metal into a mould containing a cavity which has the desired shape of the end product, and allowing the molten metal to solidify in the cavity. Historical
data indicates that casting began around 4000 B.C. According to Taylor et al, (1959), copper was the first metal to be cast and it was used to produce bells for large cathedrals at the beginning of the 13th century. In the 14th through 16th centuries, metal casting evolved from
what was an art form to the casting of engineering shaped components (Mikelonis, 1986). However, the first authenticated casting in aluminium was produced in 1876 according to Anon (1978). In the present context, die casting involves all processes that are based on use of metallic moulds (Dahle, 2002). Casting or foundry is a process of forming objects through
pouring of molten metals into prepared moulds. Casting processes are among the oldest methods for manufacturing metal goods. In most early casting processes (many of which are still used today), the mold after use is commonly
collapsed in order to remove the product after solidification. The need for a permanent mold, which can be used to produce components in large quantities which are of high quality, is the obvious alternative. In the middle ages, craftsmen perfected the use of iron in the
manufacture of moulds (Doehler, 1951). Moreover, the first information revolution occurred when Johannes Gutenberg developed a method to manufacture components in large quantities using a permanent metal mold. Over the centuries, the permanent metal mold
processes continued to evolve. In the late 18th century, processes were developed in which metal was injected into metal dies under pressure to manufacture print type . These developments culminated in the creation of the linotype machine for printing by Ottmar
Mergenthaler in 1885 (www.en.wikipedia.org/wiki/die_casting), an automated type casting device which became the prominent type of equipment in the publishing industry. Doehler, (1910) is credited with developing die casting for the production of metal components in large volumes. Initially, only zinc alloys were used in die casting. Demands for other metals drove the development of new die materials and process variants. By 1915, aluminum was being die cast in large quantities. Much progress had been made in
the development of die casting technologies over the last century. Developments continue tobe made driving the capabilities of the process to new levels and increasing the integrity of die cast components. Cast aluminum products are in great use in various industrial sectors and more so in the aerospace industry where precision and high quality products are of
utmost importance. Most recently, pressure die cast (PDC) aluminum products have played a significant role
in the renovation of historic buildings (www.webcitaion.org). The characteristics and properties of PDC aluminum as a material have led to revolutionary and innovative changes in building techniques, architectural and engineering projects. Re-melting used aluminum requires only 5 per cent of the energy needed to produce the primary metal. Thus, rather than contributing to society’s growing waste problem, aluminum can be re-melted and reformed to produce a new generation of parts. Aluminum in general has always been recycled at a
higher rate than most other raw materials. Given the necessary infrastructure, it is possible to recycle all aluminum in construction industry applications, for several reasons. First, there is a relatively high level of scrap aluminum available. Second, aluminum has a high scrap
value, which can contribute significantly towards covering demolition costs. Finally, the infrastructure required for the collection of scrap metals is already well established and will continue to grow on its own economic merit as it has done in the past to provide an
increasingly efficient recycling system. Nearly 40 per cent of all aluminum used today is recycled, (www.webcitaion.org), In
addition all the standards that have been set for using of metal components, die cast aluminum alloys satisfy the need to the utmost. Hence, they are certified safe for use (ISO9001). Today there is an increasing trend in the industry towards alloys that provide increased
strength over traditional alloys. In order to determine whether the casting process produces a part with proper as-cast mechanical properties, microstructure prediction is required. Micro structure of metals is a useful tool in the sense that it indicates casting defects
(http://business.ezinemark.com/die-casting).
1.2 ADVANTAGES OF DIE CASTING
Die casting is an efficient, economical process offering a wide range of shapes and components than any other manufacturing technique. Parts have long service life and may be designed to compliment visual appeal of the surrounding parts. The designer can gain a number of advantages and benefits by specifying die casting parts. The other advantages of die casting include:-
1.2.1 High Speed Production
Die casting provides complex shapes with close tolerances more than any other mass production process. Little or no machining is required and thousands of identical parts can be produced before additional tooling is required.
1.2.2 Dimensional Accuracy and Stability
Die casting produces parts that are durable and dimensionally stable, while maintaining close tolerances. They are also heat resistant.
1.2.3 Strength and Weight
Die cast parts are stronger than plastic injection molded parts having the same dimensions.Thin walled castings are stronger and lighter than those possible with other casting methods. Die cast products do not require separate parts to be welded or fastened together and the strength is that of the alloy which is greater than that of the joint in a joining process.
1.2.4 Multiple Finishing Techniques
Die cast parts can be produced with smooth or textured surfaces and they are easily plated or finished with a minimum of surface preparation.
1.2.5 Simplified Assembly
Die casting provides integrated fastening elements such as bosses and studs. Holes can be cored and made to tap drill size or external threads can be cast. (www.webcitaion.org).
1.3 ALUMINUM A380 AND A1350 ALLOYS
Certain general importance related to the use of aluminum A1350, as distinct from other aluminum alloys, is their application as electrical conductors which principally are:
1.3.1 Conductivity: More than twice that of copper
1.3.2 Light weight: Ease of handling, low installation costs, longer spans, and more distance between pull-ins.-
1.3.3 Strength: A range of strengths from dead soft to that of mild steel, depending on the electrical conductor.
1.3.4 Workability: Permitting a wide range of processing from wire drawing to extrusion or rolling and excellent bend quality.
1.3.5 Corrosion resistance: A tough, protective oxide coating quickly forms on freshly exposed aluminum A1350 and it does not thicken significantly from continued exposure to air. The inherent corrosion resistance of aluminum A1350 is due to the thin, tough oxide coating that forms directly after a fresh surface is exposed to air and is well suited for ocean shore applications as well as for usual industrial and
chemical atmospheres.
1.3.6 Creep: Like all metals under sustained stress, there is a gradual deformation over a term of years but the extent of creep is determined by the properties of the metal involved, applied stress, temperature and time under load. For example, hard-drawn 1350-H19 aluminum wire in stranded cables under a steadily applied load of about 70 percent of its minimum yield strength will creep approximately 0.4 to 0.6 percent of initial length in 10 years.
1.3.7 Compatibility with insulation: Does not adhere to or combine with usual insulating materials. No tin-coating required and clean stripping. Also typically using an aluminum A380 casting to replace an iron casting will result in cutting the component and overall weight by half which means that automobile manufacturers are investigating potential applications in areas including engine, drive train
and suspension components which made most applications make use of the A 300 series, aluminum – silicon series alloys, particularly the hypoeutectic alloys. The silicon gives good fluidity when casting, enabling thin sections to be successfully cast. The magnesium provides strength (through heat treatment) while maintaining reasonable ductility. Also the lowest cost general purpose alloy is A380 and is frequently used in the aerospace industry and the ductility is better than that of many wrought alloys. The cast alloys incorporating copper generally have the highest strengths at elevated temperatures. An important feature of aluminum and its alloys (and other non – ferrous alloys) is that unlike ferrous alloys that exhibit finite fatigue endurance strength, the fatigue strength of aluminum alloys continues to fall with increasing stress cycles and this must be accounted for in the design process. Experience may however permit the requirements to be more accurately defined. Porosity of cast components can have a significantly deleterious effect on the fatigue strength of aluminum castings and care must be taken to minimize the entrapment of gas during casting hence a need to evolve other procedures that can limit or minimize this defect in the die casting process. (www.tech/info/al-alloys/imptce.com). uploaded dec- 6- 2012
1.4 STATEMENT OF PROBLEM
Die casting is utilized to produce many products in the current global market. Unfortunately, conventional die casting has a major limitation that is preventing its use on a broader scale. A potential defect, commonly found in die cast components, is porosity.
Porosity often limits the use of the conventional die casting process in favor of products fabricated by other means because it results in leakages of fluids. Leakages tend to occur in die cast products like pumps, valves, gaskets, e.t.c over some time,
compromising the integrity of the product. Durability of die cast products is reduced as porosity affects the mechanical properties of die
cast components. In structural applications, porosity can act as a stress concentrator creating initiation sites for cracks.
1.5 PRESENT RESEARCH
Although much work has been done on various casting processes including die casting, especially on regulation of certain variables like speed, pressure, temperature e.t.c, no work has been reported in the literature which explains effects of pressure on the microstructure
and mechanical properties of die cast aluminum alloys A380 and A1350. Moreover, no work has been reported in the literature which optimizes a cold chamber die casting process parameter using A380 and A1350 aluminum alloy. These alloys have a very wide number of
applications in aeronautic, automotive, electrical industries and domestic use but still not much work has been done on their properties with different input process parameters.
1.6 RESEARCH JUSTIFICATION
The effects of casting pressure on the properties of aluminum die castings would hopefully reduce porosity and improve the micro structure and mechanical properties. These improved properties of products should meet the requirements needed for many applications.
Furthermore industries could easily relate the parameters used and further improve on their product qualities and standards.The results of this research can be applied to practical foundry problems for manufacturing castings of better properties, and also contribute in many ways to further improving the quality standards for aluminum die casting by:
1. Provision of good quality and durable castings by reduction of defects such as porosity and shrinkage.
2. Provisions of a cleaner atmosphere since most aluminum die casting processes are environmentally friendly.
3. Enhance more usage of die castings.
4. Increase optimization in die casting production lines.
5. Ensure that castings are less prone to rejection and functions maximally in its operation.
1.7 AIM AND OBJECTIVES
The aim of this research is to study the effects of pressure on the microstructure and mechanical properties of aluminum die castings which will be of better qualities and free from defects. The specific objectives are to:
1. Evaluate the influence of different applied pressures on the mechanical properties and microstructures of die cast aluminum A380 and A1350.
2. Compare the mechanical properties of both alloys.
3. Study the grain size and numbers of both alloys.
4. Establish the level of porosity in both alloys.
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