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Effects of Cu and Ag additions on age-hardening behavior during multi-step aging in AlMgSi alloys
Ist Teil von
Materials science & engineering. A, Structural materials : properties, microstructure and processing, 2013-01, Vol.560, p.154-162
Erscheinungsjahr
2013
Link zum Volltext
Quelle
ScienceDirect Journals (5 years ago - present)
Beschreibungen/Notizen
Low Cu and Ag additions ( less than or equal to 0.10at%) were found to strongly affect the age-hardening behavior in AlMgSi alloys with Mg+Si>1.5at%. The hardness increased during aging at 170 degree C and the formation of beta double prime precipitates was kinetically accelerated. The activation energy of the formation of the beta double prime phase was calculated to 127, 105, 108 and 99KJmol-1 in the base, Cu-added, Ag-added and CuAg-added alloys, respectively using the Kissinger method. The negative effect of two-step aging caused by the formation of Cluster (1) during natural aging was not overcome by the addition of microalloying elements. However, it was suppressed by the formation of Cluster (2) through a pre-aging at 100 degree C. Quantitative analysis of the precipitate microstructure was performed using a transmission electron microscope equipped with a parallel electron energy loss spectrometer for the determination of specimen thickness. The formation of Cluster (2) was found to increase the number density of beta double prime precipitates, whereas the formation of Cluster (1) decreased the number density and increased the needle length. The effects of low Cu and Ag additions in combination with multi-step aging are discussed based on microstructure observations and hardness and resistivity measurements.