Plastic deformation and fracture mechanisms of a novel Al/Mg bimetal composite at cryogenic temperatures

Examining the cryogenic-temperature characteristics of composites is imperative for ensuring the sustained functionality of their components in environments with cryogenic temperatures. The plastic deformation and fracture mechanisms of a novel Al/Mg bimetal composite (5052/AZ31B alloys bimetal composite) fabricated by the corrugated and flat rolling were investigated at cryogenic temperatures in this study. A mixture-law constitutive model was established to describe the flow behaviour of each constitute alloy of bimetal composite based on the stress-strain relationships obtained from cryogenic tensile tests, which were performed on a universal testing machine equipped with a liquid nitrogen in the temperatures of −180 °C, −80 °C and room temperature (RT) at the strain rate of 0.001 s−1. It is found that the elastic modulus of the 5052/AZ31B bimetal composite experiences minimal impact at lower temperatures, whereas the flow stress shows an increase with decreasing temperature. The AZ31B layer exhibits a quasi-disintegrated brittle fracture and reduced elongation to failure, leading to premature fracture, while the 5052 layer demonstrates a mixed tough-brittle fracture and increased plasticity, resulting in a two-stage fracture process with AZ31B fracturing earlier at the temperature of −180 °C. These findings align with finite element simulations, validating the intricate interplay between bimetal composite properties and cryogenic temperature in influencing fracture behaviour.