Combined Effects of Optimized Heat Treatment and Nickel Coating for the Improvement of Interfacial Bonding in Aluminum–Iron Alloys Hybrid Structures

Abstract

The effects of nickel coating and heat treatment on the interfacial bonds of aluminum–iron (Al/Fe) alloys hybrid structures were investigated using microstructural analysis. The application of a nickel coating successfully suppressed the formation of defects such as gaps and oxide scale, improving the physical bonding of the interface. Optimizing the heat treatment conditions generated superior chemical bonding at the interface and facilitated the formation of a nickel-bearing phase in the Al matrix. Also, the types of nickel-bearing phase were influenced by solution treatment and proximity to the interface. By analyzing the isopleth phase diagram of the aluminum system for the ranges of nickel present in the Al, it was confirmed that the Ni:Cu ratio affected the precipitation characteristics of the system. However, when heated under conditions that were optimized for chemical bonding, the Al matrix decreased by approximately 40% (from 100 HV to 60 HV), due to grain growth. The effect of artificial aging increased the hardness of the Al matrix away from the interface by 35% (from 63 HV to 90 HV). On the other hand, this did not occur in the Al matrix near the interface. These results indicate that the nickel that diffused into the Al matrix interfered with the precipitation hardening effect.