Influence of mechanical working on properties of aluminium base short steel fiber reinforced composites

In the present investigation aluminium base short plain steel fiber, copper and nickel coated steel fiber reinforced composites were prepared by vortex method. These were subsequently given deformation upto 40% by hot rolling. Microstructure of deformed sample showed random orientation of fibers. Breakdown of fibers due to the hot rolling was also predominant. Density of composites increased with increase in % of deformation due to reduced porosity. The hardness and strength improvement observed is attributed to decrease in porosity and increase in the number of fibers due to fiber breakage. In case of copper-coated fiber reinforced composite some additional mechanism is observed to operate. After 40% rolling, porosity level of 5-wt% copper coated fiber composites was decreased from 3.9% to 0.7%. Hardness of as cast Al-5FeCu composite was 38.2 BHN, which increased to 45.8 BHN on 40% reduction. UTS (Ultimate tensile strength) of 5-wt% copper coated steel fiber composites increased from 124 MPa to 145 MPa on 40% deformation along with an improvement of percentage of elongation from 9.2 to 11.6. The simultaneous increase in UTS and percentage of elongation indicate that reduction in porosity is the main factor-giving rise to improvement of the properties. Fracture surface investigation showed that cracks are initiated at the fiber matrix interface, propagated through the interface and linked up with other cracks or fiber/matrix interface leading to failure. In case of as cast composites micro-porosity played a vital role in failure which is noted from SEM fractographs.