Interfacial Microstructure and Mechanical Properties of Fluxless Arc Brazing of Aluminum Alloy to Steel with the Aid of Milling

Abstract

Fluxless arc brazing technique using Zn15%Al filler wire with the aid of an additional milling procedure was developed to join aluminum alloy to low-carbon steel. It was found that the addition of a milling procedure during arc brazing could significantly change morphology and distribution of interfacial reaction products of the joint. By adjusting the radial cutting depth (a_e), the original continuous layer-wised Fe–Al intermetallic compounds (IMC) was broken into discrete IMC layer. The IMC layer was identified to be θ-FeAl₃ with thickness ranging from 2.5 µm to 14.4 µm under optimized a_e of 0.10 mm. Upon shear loading, the maximum average interfacial shear strength reaches 182 MPa and the crack propagated through both the steel/braze interface and remaining Zn–Al filler alloy, which is highly favorable in crack deflection and in turn, improving bonding strength. It is thus concluded that milling assisted arc brazing is of great potential to achieve strong bonding between dissimilar Al alloy and steel.

Fig. 1 Schematic of milling treatment at steel surface during ABM joining process.