Investigation on electrical conductivity and hardness of 6xxx aluminum conductor alloys with different Si levels

Abstract

The impact of Si levels on electrical conductivity (EC) and hardness in Al-Mg-Si 6xxx aluminum conductor alloys was studied at different aging times. Three experimental alloys with the Si levels of 0.4, 0.66, 0.89 wt.% containing a constant Mg content of 0.65 wt.%, designated as Si4, Si6, and Si9, were selected. It is found that the average peak hardness of Si4, Si6, and Si9 alloys were 114, 127 and 140 HV, respectively. The Si9 alloy with the highest Si level exhibited the highest peak hardness, which was consistent with the number density of strengthening precipitates. However, the EC of all studied alloys at peak aging was lower than the minimum required one (52.5 %IACS). The higher Si level in the alloy, the longer aging time required to enhance EC. The Si4, Si6, and Si9 alloys reached the minimum required EC after 3, 5 and 34 h aging time, of which the corresponding hardness was 103, 119 and 111 HV, respectively. Consequently, the Si6 alloy represented a better trade-off between EC and hardness among three studied alloys. The quantitative analyses of precipitates at peak aging and overaging states were carried out by a transmission electron microscope (TEM) investigation.