Magnesium Alloy AZ91E and its Usage in Bicycle Frame Design

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INTRODUCTION: A bicycle is a two wheeled vehicle driven by the riders feet pushing on cranks or pedals. A typical bicycle is comprised of several parts. The principal and essential being: the frame, front forks, wheels, pedals, saddle, handlebars, chain and brakes. The other important part in a bicycle is it’s wheels which are responsible for its motion. A bicycle stays upright while moving forward by being steered so as to keep its center of gravity over the wheels. This steering is usually provided by the rider, but under certain conditions may be provided by the bicycle itself. The bicycle is extraordinarily efficient in both biological and mechanical terms. The bicycle is the most efficient self-powered means of transportation in terms of energy a person must expend to travel a given distance. From a mechanical viewpoint, up to 99% of the energy delivered by the rider into the pedals is transmitted to the wheels, although the use of gearing mechanisms may reduce this by 10-15%. In terms of the ratio of cargo weight a bicycle can carry to total weight, it is also a most efficient means of cargo transportation and its wheels have a huge role to play for its efficiency. A bicycle frame is the main component of a bicycle, onto which wheels and other components are fitted. The modern and most common frame design for an upright bicycle is based on the safety bicycle, and consists of two triangles, a main triangle and a paired rear triangle. This is known as the diamond frame. In the diamond frame, the main triangle consists of the head tube, top tube, down tube and seat tube. The rear triangle consists of the seat tube, and paired chain stays and seat stays. The head tube contains the headset, the interface with the fork. The top tube connects the head tube to the seat tube at the top, and the down tube connects the head tube to the bottom bracket shell. The rear triangle connects to the rear dropouts, where the rear wheel is attached. It consists of the seat tube and paired chain stays and seat stays. The chain stays run parallel to the chain, connecting the bottom bracket to the rear dropouts. The seat stays connect the top of the seat tube (often at or near the same point as the top tube) to the rear dropouts. METHODS:
Magnesium, an alkaline earth metal, is the ninth most abundant element in the universe by mass. The commonness of magnesium is related to the fact that it is easily built up in supernova stars from a sequential addition of three helium nuclei to carbon (which in turn is made from a single reaction between three helium nuclei at once). Magnesium constitutes about 2% of the Earth's crust by mass, which makes it the eighth most abundant element in the crust. Magnesium ion's high solubility in water helps ensure that it is the third most abundant element dissolved in seawater. AZ91E alloy is a good substitute for the current materials that have been on use for the manufacturing of the Bicycle frame. Then AZ91E alloy is composed of Magnesium, Aluminum, Zinc and Manganese. AZ91E alloy is cheap but are also difficult to cast successfully. Sand castings are prone to outcropping, microporosity, and achieving pressure tight castings can be a problem unless extensive sealing treatments are carried out. AZ91E is used primarily in high pressure die cast form particularly by the automotive industry, as car makers worldwide aim to reduce vehicle weights in order to improve fuel economy. Sand cast Mg-Al-Zn alloys have reasonable properties in the T6 condition up to 120°C, although strength then decreases rapidly with increasing temperature and mechanical properties can vary substantially depending on section thickness. Despite these drawbacks, AZ91E castings are used in some aerospace applications, including complex aerospace sand castings such as the Westland Sea King helicopter gearbox. Introduction of high purity variants of these alloys with lower levels of heavy metal impurities (iron, copper, and nickel) has significantly improved corrosion performance. The sand casting alloy AZ91C has now been largely replaced by its high purity variant AZ91E which has a corrosion rate around 100 times better in salt fog tests. Temperature dependence:- The alloy has a liquidus and solidus temperature of 595C and 495C which makes it perfect for usage. Furthermore, the coefficient of linear thermal expansion, Specific Heat , latent heat of fusion and thermal conductivity of the alloy are also perfect for usage. Stiffness:- The material itself is stiff enough to handle a load from 0 to 200kg which is good enough to handle the weights of normal people.
Page 1: ME 250 Design Project. Magnesium al
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Magnesium Alloy AZ91E and its Usage in Bicycle Frame Design

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