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 6082aluminium alloy with the application of direct electrical current. An experimental setupwas designed and built to conduct experiments on aging treatments with current applied.The precipitation kinetics were monitored through measurements of Vickers hardness andelectrical conductivity. Moreover, a collection of heat treated samples were investigated bytransmission electron microscopy(TEM) to carry out quantitative estimates of precipitatedimensions, number density and volume fraction.
Natural aging with a direct current applied showed accelerated precipitation kinetics forcurrent densities above 12.5A/mm^2. In addition, a direct current was applied as aninitial natural pre-aging treatment prior to storage and final artificial aging. After twoweeks of storage, the hardness on artificial aging increased with increasing current densityapplied during the initial natural aging for current densities above 12.5A/mm^2. Thehardness of samples stored for two-three months after a 60 minutes long initial currenttreatment, 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 twomonths storage suggest that the precipitates coarsened with the higher current density.However, when artificial aging followed directly after 90 minutes of current application atroom temperature, the precipitates formed were smaller in size and of higher number density.This microstructure was accompanied by a slightly higher hardness in comparisonto the samples treated without current. Application of a current of 2.5A/mm^2 duringartificial aging was observed to accelerate the aging process. The TEM investigations performed at the underaged state showed that the current had resulted in increased numberdensity and precipitate refinement.