Effect of annealing method and applied stress on aging behavior of copper-aluminum bimetals

Abstract

The purpose of this study was to investigate the effect of aging method and the presence or absence of external stress on the aging behavior of Cu/Al diffusion couples. For this purpose, three processes including constant temperature furnace annealing (CTFA), constant temperature electrical annealing (CTEA) and variable temperature electrical annealing (VTEA) were performed as aging cycles.The samples were subjected to tensile stresses of 0, 65, 325 and 650 kPa during aging. After the aging, the microstructure of the samples interfaces was examined by optical and scanning electron microscopy. After identifying the intermetallic phases, the thickness of individual phases and the total thickness of the interfacial intermetallics were measured.The results showed that after 250 h of aging without applying external stress, the thickness of the intermetallic phases for VTEA samples was about 3–4 times the thickness of the layers formed in the CTFA samples and about 2 times the thickness of the intermetallic layers in CTEA samples. The results also showed that if external tensile stresses were applied during the aging besides the use of a constant electric current, the increase in the thickness of the intermetallic phases would be much more significant. Applying the stress increases the thickness of the intermetallic layers as well as their numbers.The results of this study show that the investigation of the aging behavior of bimetals and diffusion couples used in the electrical, electronics or other industries that their aging occurs due to the flow of electric current by conventional methods does not have the desired accuracy. Therefore, a fundamental review of these methods, which are established and utilized by most researchers and scientific institutions based on the assumption of constant temperature of the components during the aging, is proposed.