Thesis Abstract

<p> </p><p>A study of the effects of pressure on microstructure and mechanical properties of die cast<br>aluminum alloys A1350 and A380 was carried out and subsequent analysis made. Pressure<br>was regulated at various levels in the die cast machine. Both alloys were cast into samples<br>each under different applied pressures. The mechanical properties of both alloys were<br>tested and microstructure analysis was done and the results for both tests were compared<br>for both alloys. The results obtained show hardness, tensile strength, yield strength and<br>impact strength of both alloys varied with applied pressure in the casting process. The<br>hardness values increased with applied pressure but not too significantly from 76 to 85<br>HRN for A380 alloy and 77 to 86 HRN for A1350 alloy as pressure rose from 350 to<br>1400kg/cm2. The yield strength of both alloys also increased with applied pressure. The<br>impact strength and elongation both decreased with applied pressure in both alloys. Also<br>the microstructure analysis carried out on both alloys showed structural changes in the<br>morphologies of both alloys as some appeared granullar, lamellar, coarse e.t.c from<br>pressure 350 to 1400kg/cm2. Also as the pressure increased, the grains became finer and<br>porosity decreased.<br>Models were developed and for all the models developed, a close relationship with the<br>experimental results were underlying in view of the small errors generated by them and<br>can be used to predict the experimental values of this research.</p><p><strong>&nbsp;</strong></p> <br><p></p>

Thesis Overview

<p> INTRODUCTION<br>1.1 BACKGROUND<br>According to Richard et al, (1967), metal casting may be defined as a metal object<br>produced by pouring molten metal into a mould containing a cavity which has the desired<br>shape of the end product, and allowing the molten metal to solidify in the cavity. Historical<br>data indicates that casting began around 4000 B.C. According to Taylor et al, (1959), copper<br>was the first metal to be cast and it was used to produce bells for large cathedrals at the<br>beginning of the 13th century. In the 14th through 16th centuries, metal casting evolved from<br>what was an art form to the casting of engineering shaped components (Mikelonis, 1986).<br>However, the first authenticated casting in aluminium was produced in 1876 according to<br>Anon (1978). In the present context, die casting involves all processes that are based on use<br>of metallic moulds (Dahle, 2002). Casting or foundry is a process of forming objects through<br>pouring of molten metals into prepared moulds.<br>Casting processes are among the oldest methods for manufacturing metal goods. In most<br>early casting processes (many of which are still used today), the mold after use is commonly<br>collapsed in order to remove the product after solidification. The need for a permanent mold,<br>which can be used to produce components in large quantities which are of high quality, is the<br>obvious alternative. In the middle ages, craftsmen perfected the use of iron in the<br>manufacture of moulds (Doehler, 1951). Moreover, the first information revolution occurred<br>when Johannes Gutenberg developed a method to manufacture components in large<br>quantities using a permanent metal mold. Over the centuries, the permanent metal mold<br>processes continued to evolve. In the late 18th century, processes were developed in which<br>metal was injected into metal dies under pressure to manufacture print type . These<br>– 15 –<br>developments culminated in the creation of the linotype machine for printing by Ottmar<br>Mergenthaler in 1885 (<a target="_blank" rel="nofollow" href="http://www.en.wikipedia.org/wiki/die_casting">www.en.wikipedia.org/wiki/die_casting</a>), an automated type casting<br>device which became the prominent type of equipment in the publishing industry.<br>Doehler, (1910) is credited with developing die casting for the production of metal<br>components in large volumes. Initially, only zinc alloys were used in die casting. Demands<br>for other metals drove the development of new die materials and process variants.<br>By 1915, aluminum was being die cast in large quantities. Much progress had been made in<br>the development of die casting technologies over the last century. Developments continue to<br>be made driving the capabilities of the process to new levels and increasing the integrity of<br>die cast components. Cast aluminum products are in great use in various industrial sectors<br>and more so in the aerospace industry where precision and high quality products are of<br>utmost importance.<br>Most recently, pressure die cast (PDC) aluminum products have played a significant role<br>in the renovation of historic buildings (<a target="_blank" rel="nofollow" href="http://www.webcitaion.org)">www.webcitaion.org)</a>. The characteristics and<br>properties of PDC aluminum as a material have led to revolutionary and innovative changes<br>in building techniques, architectural and engineering projects. Re-melting used aluminum<br>requires only 5 per cent of the energy needed to produce the primary metal. Thus, rather than<br>contributing to society’s growing waste problem, aluminum can be re-melted and reformed to<br>produce a new generation of parts. Aluminum in general has always been recycled at a<br>higher rate than most other raw materials. Given the necessary infrastructure, it is possible to<br>recycle all aluminum in construction industry applications, for several reasons. First, there is<br>a relatively high level of scrap aluminum available. Second, aluminum has a high scrap<br>value, which can contribute significantly towards covering demolition costs. Finally, the<br>infrastructure required for the collection of scrap metals is already well established and will<br>– 16 –<br>continue to grow on its own economic merit as it has done in the past to provide an<br>increasingly efficient recycling system.<br>Nearly 40 per cent of all aluminum used today is recycled, (<a target="_blank" rel="nofollow" href="http://www.webcitaion.org">www.webcitaion.org</a>), In<br>addition all the standards that have been set for using of metal components, die cast<br>aluminum alloys satisfy the need to the utmost. Hence, they are certified safe for use (ISO<br>9001). Today there is an increasing trend in the industry towards alloys that provide increased<br>strength over traditional alloys. In order to determine whether the casting process produces a<br>part with proper as-cast mechanical properties, microstructure prediction is required.<br>Microstructure of metals is a useful tool in the sense that it indicates casting defects<br>(<a target="_blank" rel="nofollow" href="http://business.ezinemark.com/die-casting)">http://business.ezinemark.com/die-casting)</a>.<br>1.2 ADVANTAGES OF DIE CASTING<br>Die casting is an efficient, economical process offering a wide range of shapes and<br>components than any other manufacturing technique. Parts have long service life and may be<br>designed to compliment visual appeal of the surrounding parts. The designer can gain a<br>number of advantages and benefits by specifying die casting parts. The other advantages of<br>die casting include:-<br>1.2.1 High Speed Production<br>Die casting provides complex shapes with close tolerances more than any other mass<br>production process. Little or no machining is required and thousands of identical parts can be<br>produced before additional tooling is required.<br>– 17 –<br>1.2.2 Dimensional Accuracy and Stability<br>Die casting produces parts that are durable and dimensionally stable, while maintaining close<br>tolerances. They are also heat resistant.<br>1.2.3 Strength and Weight<br>Die cast parts are stronger than plastic injection molded parts having the same dimensions<br>.Thin walled castings are stronger and lighter than those possible with other casting methods.<br>Die cast products do not require separate parts to be welded or fastened together and the<br>strength is that of the alloy which is greater than that of the joint in a joining process.<br>1.2.4 Multiple Finishing Techniques<br>Die cast parts can be produced with smooth or textured surfaces and they are easily plated or<br>finished with a minimum of surface preparation.<br>1.2.5 Simplified Assembly<br>Die casting provides integrated fastening elements such as bosses and studs. Holes can be<br>cored and made to tap drill size or external threads can be cast. (<a target="_blank" rel="nofollow" href="http://www.webcitaion.org)">www.webcitaion.org)</a>.<br>1.3 ALUMINUM A380 AND A1350 ALLOYS<br>Certain general importance related to the use of aluminum A1350, as distinct from other<br>aluminum alloys, is their application as electrical conductors which principally are:<br>1.3.1 Conductivity: More than twice that of copper<br>1.3.2 Light weight: Ease of handling, low installation costs, longer spans, and more<br>distance between pull-ins.<br>– 18 –<br>1.3.3 Strength: A range of strengths from dead soft to that of mild steel, depending on the<br>electrical conductor.<br>1.3.4 Workability: Permitting a wide range of processing from wire drawing to extrusion<br>or rolling and excellent bend quality.<br>1.3.5 Corrosion resistance: A tough, protective oxide coating quickly forms on freshly<br>exposed aluminum A1350 and it does not thicken significantly from continued<br>exposure to air. The inherent corrosion resistance of aluminum A1350 is due to the<br>thin, tough oxide coating that forms directly after a fresh surface is exposed to air<br>and is well suited for ocean shore applications as well as for usual industrial and<br>chemical atmospheres.<br>1.3.6 Creep: Like all metals under sustained stress, there is a gradual deformation over a<br>term of years but the extent of creep is determined by the properties of the metal<br>involved, applied stress, temperature and time under load. For example, hard-drawn<br>1350-H19 aluminum wire in stranded cables under a steadily applied load of about<br>70 percent of its minimum yield strength will creep approximately 0.4 to 0.6<br>percent of initial length in 10 years.<br>1.3.7 Compatibility with insulation: Does not adhere to or combine with usual insulating<br>materials. No tin-coating required and clean stripping.<br>Also typically using an aluminum A380 casting to replace an iron casting will result in<br>cutting the component and overall weight by half which means that automobile<br>manufacturers are investigating potential applications in areas including engine, drive train<br>and suspension components which made most applications make use of the A 300 series,<br>aluminum – silicon series alloys, particularly the hypoeutectic alloys.<br>– 19 –<br>The silicon gives good fluidity when casting, enabling thin sections to be successfully cast.<br>The magnesium provides strength (through heat treatment) while maintaining reasonable<br>ductility. Also the lowest cost general purpose alloy is A380 and is frequently used in the<br>aerospace industry and the ductility is better than that of many wrought alloys. The cast<br>alloys incorporating copper generally have the highest strengths at elevated temperatures.<br>An important feature of aluminum and its alloys (and other non – ferrous alloys) is that unlike<br>ferrous alloys that exhibit finite fatigue endurance strength, the fatigue strength of aluminum<br>alloys continues to fall with increasing stress cycles and this must be accounted for in the<br>design process. Experience may however permit the requirements to be more accurately<br>defined. Porosity of cast components can have a significantly deleterious effect on the fatigue<br>strength of aluminum castings and care must be taken to minimize the entrapment of gas<br>during casting hence a need to evolve other procedures that can limit or minimize this defect<br>in the die casting process. (<a target="_blank" rel="nofollow" href="http://www.tech/info/al-alloys/imptce.com)">www.tech/info/al-alloys/imptce.com)</a>. uploaded dec- 6- 2012<br>1.4 STATEMENT OF PROBLEM<br>Die casting is utilized to produce many products in the current global market. Unfortunately,<br>conventional die casting has a major limitation that is preventing its use on a broader scale. A<br>potential defect, commonly found in die cast components, is porosity.<br>Porosity often limits the use of the conventional die casting process in favor of products<br>fabricated by other means because it results in leakages of fluids.<br>Leakages tend to occur in die cast products like pumps, valves, gaskets, e.t.c over some time,<br>compromising the integrity of the product.<br>Durability of die cast products is reduced as porosity affects the mechanical properties of die<br>cast components. In structural applications, porosity can act as a stress concentrator creating<br>initiation sites for cracks.<br>– 20 –<br>1.5 PRESENT RESEARCH<br>Although much work has been done on various casting processes including die casting,<br>especially on regulation of certain variables like speed, pressure, temperature e.t.c, no work<br>has been reported in the literature which explains effects of pressure on the microstructure<br>and mechanical properties of die cast aluminum alloys A380 and A1350. Moreover, no work<br>has been reported in the literature which optimizes a cold chamber die casting process<br>parameter using A380 and A1350 aluminum alloy. These alloys have a very wide number of<br>applications in aeronautic, automotive, electrical industries and domestic use but still not<br>much work has been done on their properties with different input process parameters.<br>1.6 RESEARCH JUSTIFICATION<br>The effects of casting pressure on the properties of aluminum die castings would hopefully<br>reduce porosity and improve the microstructure and mechanical properties. These improved<br>properties of products should meet the requirements needed for many applications.<br>Furthermore industries could easily relate the parameters used and further improve on their<br>product qualities and standards.<br>The results of this research can be applied to practical foundry problems for manufacturing<br>castings of better properties, and also contribute in many ways to further improving the<br>quality standards for aluminum die casting by:<br>1. Provision of good quality and durable castings by reduction of defects such as<br>porosity and shrinkage.<br>– 21 –<br>2. Provisions of a cleaner atmosphere since most aluminum die casting processes are<br>environmentally friendly.<br>3. Enhance more usage of die castings.<br>4. Increase optimization in die casting production lines.<br>5. Ensure that castings are less prone to rejection and functions maximally in its<br>operation.<br>1.7 AIM AND OBJECTIVES<br>The aim of this research is to study the effects of pressure on the microstructure and<br>mechanical properties of aluminum die castings which will be of better qualities and free<br>from defects. The specific objectives are to:<br>1. Evaluate the influence of different applied pressures on the mechanical properties and<br>microstructures of die cast aluminum A380 and A1350.<br>2. Compare the mechanical properties of both alloys.<br>3. Study the grain size and numbers of both alloys.<br>4. Establish the level of porosity in both alloys. <br></p>