Precipitation hardening of a 6082 aluminium alloy upon application of direct electrical current

Abstract

The research deals with the investigation of the precipitation hardening response of a 6082 aluminium alloy with the application of direct electrical current. An experimental setup was designed and built to conduct experiments on aging treatments with current applied. The precipitation kinetics were monitored through measurements of Vickers hardness and electrical conductivity. Moreover, a collection of heat treated samples were investigated by transmission electron microscopy(TEM) to carry out quantitative estimates of precipitate dimensions, number density and volume fraction.

Natural aging with a direct current applied showed accelerated precipitation kinetics for current densities above 12.5A/mm^2. In addition, a direct current was applied as an initial natural pre-aging treatment prior to storage and final artificial aging. After two weeks of storage, the hardness on artificial aging increased with increasing current density applied during the initial natural aging for current densities above 12.5A/mm^2. The hardness of samples stored for two-three months after a 60 minutes long initial current treatment, also exhibited a current density dependency. The effect was negative for middle-range densities (5-12.5A/mm^2) and increased with current densities above 20A/mm^2. TEM micrographs taken of samples initially aged with 2.5 and 25A/mm^2 before two months storage suggest that the precipitates coarsened with the higher current density. However, when artificial aging followed directly after 90 minutes of current application at room temperature, the precipitates formed were smaller in size and of higher number density. This microstructure was accompanied by a slightly higher hardness in comparison to the samples treated without current. Application of a current of 2.5A/mm^2 during artificial aging was observed to accelerate the aging process. The TEM investigations performed at the underaged state showed that the current had resulted in increased number density and precipitate refinement.