EFFECT OF AGEING TIME AND TEMPERATURE ON THE MICROSTRUCTURE AND MECHANICAL PROPERTIES OF ALUMINUM BRONZE ALLOY

Author: Anene Franklin Amaechi
Department: Metallurgical and Materials Engineering
Affiliation: Nnamdi Azikiwe University Awka

This research studied the feasibility of producing a dual-phase aluminum bronze alloy as a potential replacement for conventional structural materials, particularly steels, by the use of selected heat treatments to improve on the
mechanical properties of the produced alloy. Sand casting was used due to its advantages of low cost, ease of use and flexibility in the production of a dual phase aluminum bronze alloy with 10% aluminum content. The selected heat
treatments were solution heat treatment, quenching and ageing. The cast specimens were solutionized at 900oC for 1hr, quenched in water and then aged at temperatures of 150oC, 250oC, 350oC and 450oC and soaked for 0hr, 1hr, 2hrs and 3hrs respectively at each ageing temperature. The standard heat treated specimens were subjected to various mechanical tests (UTS, yield strength, %E, Vicker’s hardness and impact strength tests). Their micrographs were equally taken using metallurgical microscope. The results showed that the specimen aged at 350oC for 2hrs gave optimum mix of tested mechanical properties with UTS of 610MPa, %Elongation of 17.5%, yield strength of 480 MPa, Vicker’s hardness value of 350Hv and impact energy of 26J. This makes the alloy suitable as alternative material to steel in low/medium strength structural applications. Response Surface Methodology (RSM) was used to determine the optimum operating conditions at which the best mechanical properties are achieved. RSM shows the optimum process conditions (ageing temperature of 337oC and soaking time of 167mins) as the best condition for production of aluminum bronze alloy and the optimum values obtained as UTS of 587.062MPa, yield strength of 491.921MPa, %E of 15.23%, hardness of 363.672Hv and impact strength of 26.498J respectively. The result from the optimization met ASTM requirement for aluminum bronze alloy. Study of the micro structures showed that as ageing temperature and soaking time increased, finer agglomerates of α+γ2 phase were precipitated from the martensitic β’ phase which caused the improved mechanical properties of the heat treated specimens.

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