The effects of Zn-based alloys coating (Zn, Al-Zn and Al-Mg-Zn) on the bondability of steel/aluminum alloy dissimilar metals joints were evaluated, in order to achieve strength in lower welding current. In the joint with Zn-based alloys insert, the oxide film on the aluminum alloy was sufficiently removed through eutectic reaction of Zn-based alloys and aluminum. In the joint with Zn-coated steel (GI), higher welding current is necessary to discharge the zinc coating and the oxide film from the bonding interface sufficiently. The thinner aluminum plate after welding and the thick reaction layer cause the decrease of cross tensile strength in the joints with no coating steel (SPCC) and Al-Zn-coated steel. Using Al-Mg-Zn-coated steel, higher strength was achieved in a lower welding current. This is because Al-Mg-Zn-coating melted at lower temperature than Zn and Al-Zn-coating, and the removal of the coating material and the oxide film on the aluminum alloy were sufficiently performed in the lower welding current.

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 Al 12 Fe 3 Si intermetallic compound (IMC) (and the same IMC containing Cu) was lower than that of Al 3 Fe. 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.

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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 Al 12 Fe 3 Si intermetallic compound IMC and the same IMC containing Cu was lower than that of Al 3 Fe. 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.