Relationship between Al-Ni intermetallic Phases and Bond Strength in Roll Bonded Steel-Aluminum Composites with Nickel Interlayers

• Main Authors: Siri Marthe Arbo, Tina Bergh, Bjørn Holmedal, Per Erik Vullum, Ida Westermann
• Format: Article
• Language: English
• Published: MDPI AG 2019-07-01
• Series: Metals
• Subjects: roll bonding; steel-aluminum joining; nickel interlayer; intermetallic phases; the kirkendall effect; bond strength
• Online Access: https://www.mdpi.com/2075-4701/9/8/827

In this work, the interface characteristics and resulting bond strength were investigated for roll bonded steel-aluminum composites with nickel interlayers, both after rolling and after post-rolling heat treatments at 400 °C−550 °C. After rolling, only mechanical interlocking was achieved between the steel and nickel layers, which resulted in delamination. Post-rolling heat treatments resulted in sufficient metallurgical bonding between the steel and nickel layers, and a significant increase in the bond strength. An intermetallic phase layer formed during the heat treatments, which below 500 °C consisted of Al₃Ni and above, Al₃Ni and Al₃Ni₂. With increasing temperature and time, the Al₃Ni₂ phase consumed the Al₃Ni layer, voids developed along the Al₃Ni₂-aluminum interface, and a duplex morphology developed inside the Al₃Ni₂ layer, in accordance with the Kirkendall effect. The highest bond strength was obtained for the composites that only had an Al₃Ni layer along the interface, and the optimal thickness was found to be 3−5 µm. The bond strength decreased with increasing temperature and time, due to increasing Al-Ni layer thickness, an increase in the fraction of Al₃Ni₂ relative to Al₃Ni, and the development of voids. The results show that nickel can be used as an interlayer in steel-aluminum joints, and a high bond strength can be obtained through post-rolling heat treatments.