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The effect of micro alloying on the structure and mechanical properties of aluminium-4% copper alloy was studied using standard techniques. The dopants were added in concentrations of 0.25%, 0.5%, 0.75%, and 1% by weight by mixing with stirrer and cast by gravity die casting. Subsequently the specimens were subjected to machining. The mechanical properties such as ultimate tensile strength, hardness and impact strength were determined for each specimen using universal testing machine (SRNO0723), Brinel hardness tester and universal impact testing machine (U1820) respectively.

The microstructure of the samples was also studied using metallurgical microscope (L2003A) with image analysis software for measuring grain size and dendrite arm spacing and the photographs taken. The results showed that the ultimate tensile strength and hardness value of the alloy increased with increase in the concentration of magnesium and zinc. An increased ultimate tensile strength was also observed as the concentration of calcium increased. Manganese reduced all the mechanical properties in the order of its increasing concentration. The micro-structural analysis result showed that addition of magnesium reduced the grain size. Manganese retarded the precipitation of the strengthening phases in the alloy in the order of its increasing concentration. Results obtained showed a striking dependence of the mechanical properties on the atomic sub-structure of the dopants, such as atomic size and valence electrons concentration.





1.1 Background

Aluminium is the third most abundant element. It forms some 80% of the earth’s crust. It does not exist as free element in the earth’s crust. It exists in the form of an impure aluminosilicate oraluminium oxide called bauxite as a result of its high affinity for oxides and silicates. Aluminium is high in the electrochemical series, therefore involves high temperature, too high to be economic when it is extracted from its ore (bauxite) using carbon reduction.

Aluminium is made up of grains or crystals which interlock when the metal is cooled from molten state. Each grain comprises rows of atoms in an ordered lattice arrangement, giving each grain an isotropic structure (Dieter, 1988). Although, the different grains are somewhat randomly arranged with grain boundaries forming during the cooling process; the atoms within each crystal are normally aligned, which makes the whole metal isotropic, like the individual grains (Polmear, 1995). Aluminium is a metallic element, and its structure is mostly similar to most other elements or metals. It is malleable and ductile due to its polycrystalline structure (Kissell and Ferry; 1995).

Aluminium atoms are arranged in a face centered cubic (FCC) structure with stacking fault energy of approximately 200mJ/m2 (Dieter, 1988). Aluminium is capable of being a superconductor with a superconducting critical temperature of 1.2 kelvin and a critical magnetic field of about 100 gauss ...Get Complete Material.

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