The effects of microstructure on the response of aluminum E-127 calibration standards

The reproducibility of the ultrasonic response of aluminum calibration blocks, as defined in ASTM standard E-127 is of considerable interest because of the use of these blocks as calibration and reference standards. However, there is a general perception that the ultrasonic attenuation in the materials from which these blocks are produced has changed with time, a consequence of the evolution of the metallurgical processing procedures used to produce the rolled rod from which the standards are fabricated. Among the issues that this raises are questions concerning the influence of E-127 block attenuation on the sizing of flaws in materials produced by other processes, e.g., rolled plate, and whether standards should be alloy specific. As the first phase in a program to address these issues, a series of specimens has been obtained, representative of the material used in both standards and rolled plates. Measurements were made of the grain morphology and ultrasonic attenuation in each of three orthogonal directions in each sample. To further characterize the samples and gain insight into some unexpected relationships between the attenuation and microstructure, additional measurements of velocity and backscattering were performed.