MECHANICAL, CORROSION AND WEAR BEHAVIOUR OF STEEL CHIPS AND GRAPHITE REINFORCED Zn-27Al ALLOY BASED COMPOSITES

Abstract

The prospect of enhancing mechanical, corrosion and wear properties of Zn27Al alloy based composites reinforced with steel machining chips by graphite addition was the focus of this investigation. Double stir casting was used to produce Zn27Al alloy based composites with 7 wt.% reinforcement but with varied compositions containing 1, 2, and 3 wt.% graphite, steel chips making up the balance. Microstructural analysis, mechanical, corrosion and wear tests were used to characterise the composites. The results show that the hardness of the composites decreases slightly with an increase in graphite content in the reinforced composites. The tensile strength and fracture toughness of the composite only showed improvement with the addition of 3 wt.% graphite in the hybrid mix (steel chips and graphite) compared with the use of lower graphite content in the mix and steel chips only. The percent elongation did not show dependency on the composition of the reinforcement phase and was basically within the range 6.0 - 6.8 %. The fracture surfaces of all the composites were essentially rough, a preponderant feature of ductile fracture mode. The wear index of the composites was generally low indicating good wear resistance. However, despite the seeming self-lubricating advantage of graphite, the wear resistance of the composite reinforced with only steel chips was relatively better than that of the hybrid graphite, and steel chips reinforced composite compositions. Finally, the steel chips and graphite reinforced Zn-27Al alloy based composites were generally more corrosion resistant in 3.5% NaCl solution compared with the unreinforced Zn-27Al alloy.