Nanoindentation measurement of interfacial reaction layers in 6000 series aluminum alloys and steel dissimilar metal joints with alloying elements

Abstract

Nanoindentation measurements were successfully applied to the interfacial reaction layers in dissimilar metal joints of 6000 series aluminum alloys containing alloying elements to steel in order to characterize their mechanical properties. The nanoindentation hardness of the reaction layer formed at the aluminum side was lower than that formed at the low carbon steel (SPCE) side of the investigated joints. At the aluminum side, the nanoindentation hardness changed by the addition of alloying elements. The hardness of the resulting Al12Fe3Si intermetallic compound (IMC) (and the same IMC containing Cu) was lower than that of Al3Fe. In comparison with the hardness values obtained from bulk Al-Fe binary series IMCs, it is considered that hardness changes of interfacial reaction layers are derived from the crystal structural changes produced by the alloying elements. The result of micro-testing of Al-Fe series IMCs indicates that the modification of the interfacial reaction layer by alloying elements contributes to higher ductility and the improvement of joint strength through crystal structural change.