Application of Cu-Al-Mn Superelastic Alloys to Building Components

To mitigate the damage to structures such as buildings and bridges caused by large earthquakes, research on the use of superelastic alloys in seismic applications have been intensively conducted worldwide for a couple of decades. Among many types of superelastic alloys, Ti-Ni, a representative superelastic alloys, is known to exhibit excellent shape recovery properties when produced under specific manufacturing conditions, which involve a combination of cold working and heat treatment at around 773 K. However, due to significant work hardening during cold working, it is difficult to manufacture bars with a diameter of 10 mm or more, which are often required to be used in seismic applications. Significant temperature dependence of the transformation critical stress poses another challenge because it leads to large variations in strength with seasonal temperature changes. On the other hand, the Cu-Al-Mn alloys with high workability developed under phase diagram study allows us to easily produce larger diameter bars. The temperature dependence of transformation critical stress is significantly lower than that of Ti-Ni alloys. This presentation introduces examples of how various technical challenges have been resolved associated with commercializing Cu-Al-Mn superelastic alloys in seismic applications. The challenges include single crystallization by cyclic heat treatment, understanding the dependence of plasticity and fracture response on crystal orientations, techniques for splicing Cu-Al-Mn alloys with steel bars, assessing and increasing corrosion resistance, etc.