THE EFFECT OF SOAKING TEMPERATURE AND QUENCHING MEDIA ON THE MICROSTRUCTURE AND MECHANICAL PROPERTIES OF AL-SI EUTECTIC ALLOY

AUTHOR: IYEBEYE KELVIN OGOCHUKWU

DEPARTMENT: METALLURGICAL AND MATERIALS ENGINEERING

AFFILIATION: NNAMDI AZIKIWE UNIVERSITY, AWKA

Aluminium – Silicon eutectic alloy is one of the most popular alloys for shaped casting of automobile components because of its excellent mechanical properties. The alloy has Si as the principal alloying element and it imparts high fluidity and low shrinkage, which result in good castability and weldability. Al-Si alloys are designated 4xxx alloys according to the Aluminium Association Wrought Alloy Designation System. Different methods have been applied to improve on its mechanical properties and microstructure. Heat treatment is one of these methods. The alloy was heat treated by T4 treatment, which consists in two different steps: solution heat treatment and quenching. In the study, the specimens of Aluminium silicon (Al-Si) eutectic alloy were prepared and solutionized at temperatures of 4000C, 4500C and 5000C for 0hr, 1hr, 2hrs and 3hrs at each temperature before quench in water, oil and air. This was done to determine the effect of soaking temperature and quenching media on the microstructure and mechanical properties of Al – Si eutectic alloy. Standard specimens from the rapidly quenched alloys were subjected to various tests to determine their ultimate tensile strength, hardness and impact strength. Their micro – graph was equally taken using metallurgical microscope. The results showed that the specimen heat-treated at 5000C for 3hrs and quenched in water had the highest tensile strength, hardness and impact strength. The toughness property of the alloy, as indicated by Charpy impact values, is better at 5000C for specimen quenched in water and least impact strength was observed in specimen cooled in air for 4000C. Study of the microstructures showed that higher cooling rate results in formation of finer microstructure of aluminum–silicon eutectic alloy and solution heat treatment spheroidies silicon particles and fragments long silicon fibres. This led to the increase in the mechanical properties. The analysis of variance was used to identify the interactions between the significant variables affecting the process.

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