INVESTIGATION OF FRACTURE IN PURE ALUMINIUM AFTER ECAP BY MEANS OF SMALL PUNCH TEST

Abstract

The properties of pure 99.99% aluminium after severe plastic deformation by equal channel angular pressing (ECAP) with low (1, 2) and high (4, 6, 12) number of passes were investigated. The constant-deflection mode of the small punch test was used to compare the mechanical behaviour. The advantages of the test are that smaller amount of material is needed and the sample preparation is easier. Characteristic points as yield force and maximum force were evaluated from the recorded dependence of force vs. deflection. A possibility of their conversion into variables of conventional tensile test is discussed. Fracture energy was calculated from this dependence. The tests were performed at both room temperature and elevated temperatures up to 300 °C. The appearance of fracture surfaces was observed by scanning electron microscopy. The tendency for increased strength of ECAPed Al in comparison with virgin Al was notable at room as well at elevated temperatures. The number of ECAP passes that gave Al with the greatest strength were however not the highest number of passes (12) but 1 or 2 passes depending on testing temperature. Higher numbers of ECAP passes showed stagnation and slight decrease of the strength of ECAPed Al.