Interfacial microstructures and properties of aluminum alloys/galvanized low-carbon steel under high-pressure torsion

• We develop a new composite processing technology.
• A sound metallurgical bond between aluminum alloy and galvanized steel is achieved.
• The formation and evolution of microstructure of the Al/steel interface are studied.
• The effect of high pressure on the Al/steel interface zone is studied by HPT.
• The Al/galvanized steel interface zone with a good plastic property is achieved.

A new composite processing technology characterized by hot-dip Zn–Al alloy process was developed to achieve a sound metallurgical bonding between Al–7 wt% Si alloy (or pure Al) castings and low-carbon steel inserts, and the variations of microstructure and property of the bonding zone were investigated under high-pressure torsion (HPT). During hot-dipping in a Zn–2.2 wt% Al alloy bath, a thick Al5Fe2Znx phase layer was formed on the steel surface and retarded the formation of Fe–Zn compound layers, resulting in the formation of a dispersed Al3FeZnx phase in zinc coating. During the composite casting process, complex interface reactions were observed for the Al–Fe–Si–Zn (or Al–Fe–Zn) phases formation in the interfacial bonding zone of Al–Si alloy (or Al)/galvanized steel reaction couple. In addition, the results show that the HPT process generates a number of cracks in the Al–Fe phase layers (consisting of Al5Fe2 and Al3Fe phases) of the Al/aluminized steel interface. Unexpectedly, the Al/galvanized steel interface zone shows a good plastic property. Beside the Al/galvanized steel interface zone, the microhardnesses of both the interface zone and substrates increased after the HPT process.