Effect of interfacial layer on bond strength of friction-welded interface of Al-Mg5083 alloy to mild steel

Abstract

The metallographic factor controlling the strength of friction-welded interface of mild steel to Al-Mg alloy A5083 has been investigated by TEM observations. The bond strength, estimated from the tensile strength of a specimen with a circumferential notch at the interface, rose rapidly with an increase in friction time, and then reduced. A maximum strength of 311 MPa was obtained at a friction time t 1 of 2 s (rotation speed = 20 s -11, friction pressure = 40 MPa, and forge pressure = 230 MPa). At a friction time of 1 s, an interfacial layer about 100 nm wide that consisted of (Fe,Mn)Al 6 and Mg 2Si was formed at the interface, and an Al oxide layer of width less than 10 nm was observed between the (Fe,Mn)Al 6 layer and mild steel substrate. The joint bonded at t 1=1 s was fractured mainly along the Al oxide layer. In a joint showing the highest bond strength (t 1 = 2 s), no Al oxide layer could be detected between the mild steel substrate and interfacial layer, which consisted of (Fe,Mn)Al 6, Fe 4Al 13, Fe 2Al 5, and Mg 2Si. The width of the interfacial layer was increased to about 300 nm at t 1=2 s. The fracture occurred along the IMC layer of (Fe,Mn)Al 6, Fe 4Al 13 and Fe 2Al 5. At t 1 of 4 s, a layer of MgAl 2O 4 about 100 nm in width was observed in addition to the intermetallic compounds observed at t 1=2-3 s. The crack on the tensile test was propagated mainly along the MgAl 2O 4 layer. Thus the controlling phase of the bond strength was altered from the Al oxide film, intermetallic compound layer, and MgAl 2O 4 layer, depending on friction time. The formation mechanisms of the observed interfacial phases are discussed from a metallographic point of view.