In situ SEM study on tensile fractured behavior of Al/steel laser welding- brazing interface

Microcracks initiated and propagated behaviors in Al/steel interface determined interfacial bonding strength and this was observed by in situ scanning electron microscopy (SEM) technology. Interface with-out or with discontinuous intermetallic compound (IMC) had low bonding strength owing to insufficient metallurgical bonding. When interface was joined with 2-3 lm serration-shaped s5-Fe1.8Al7.2Si, largest bonding strength of 205 MPa was obtained. Microcracks initiated at protrusion of s5-Fe1.8Al7.2Si and then propagated to s5-Fe1.8Al7.2Si layer and s5-Fe1.8Al7.2Si/Al interface. When interface was joined with 3- 5 lm h-Fe(Al,Si)3 + s5-Fe1.8Al7.2Si, microcracks initiated at root of IMC layers and the interfacial bonding strength was 150 MPa. When interface was joined with 5-10 lm h-Fe(Al,Si)3 + s5-Fe1.8Al7.2Si, microc-racks initiated and propagated along IMC layer. Lower interfacial bonding strength (106 MPa) was pro-duced owing to large lattice mismatch between h-Fe(Al,Si)3 and s5-Fe1.8Al7.2Si, microdefects and higher residual stress. When interface was joined with 10 lm g-Fe2(Al,Si)5 + h-Fe(Al,Si)3 + s5- Fe1.8Al7.2Si, microcracks initiated and propagated along g-Fe2(Al,Si)5 layer or steel/g-Fe2(Al,Si)5 inter-face. Lowest bonding strength (64 MPa) was obtained resulted from pre-generated microcracks in g- Fe2(Al,Si)5 layer, largest residual stress, crystal defects and abnormal aggregation of Si. (c) 2022 Harbin Institute of Technology. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

The study investigates the effect of microcrack behavior on the bonding strength of Al/steel interfaces. It is observed that interfaces without or with discontinuous intermetallic compounds have low bonding strength. However, the addition of specific compounds can significantly improve the bonding strength.