Effect of nickel as interlayer in laminated roll bonded 355 MC E steel and AA1080 aluminumThursday (07.11.2019) 11:45 - 12:05 Part of:
In this work, a nickel interlayer was added between the 355 MC E steel and AA1080 aluminum layers in a laminated roll bonded composite, in an attempt to avoid the formation of the brittle and unwanted Fe-Al intermetallic phases. Composites with and without a nickel interlayer were roll bonded at 150°C and post-rolling heat treatments were performed at 450°C for one and two hours before measuring the bond strength by peel-testing. In order to compare the formation and growth rate of intermetallic phases in composites with and without a nickel interlayer, additional post-rolling heat treatments were also performed in the temperature range 450-550°C for one hour. The addition of a nickel interlayer reduced the bond strength in the composites in the as-rolled condition. It was found that the fracture in these composites occurred between the steel and nickel layers, and the fracture surfaces revealed no signs of metallurgical bonding, only mechanical interlocking. No fracture was observed between the aluminum and nickel layers in the as-rolled composites, making the steel-nickel bonding the limiting factor in the composites with respect to bond strength. After post-rolling heat treatments, metallurgical bonding between nickel and steel was obtained and the nickel interlayer was found to successfully prohibit the formation of the brittle Fe-Al intermetallic phases. An Al-Ni intermetallic phase layer was observed to grow along the aluminum-nickel interface and no intermetallic phases were observed along the steel-nickel interface. The growth rate of the Al-Ni intermetallic phase layer was observed to be similar as for the Fe-Al intermetallic phase layer. However, the growth of the Al-Ni intermetallic phase layer, resulted in a substantial increase in the bond strength. It was found that the bond strength was mainly dependent on the thickness of the Al-Ni intermetallic phase layer, and the optimal layer thickness was found to be between 3-5 µm.