Investigation of Distribution Inhomogeneity for Longitudinal Ultrasonic Wave Velocity in Cast Aluminum-Matrix Composite Reinforced with Hollow Ceramic Microspheres

Abstract

The article deals with the development of technique for ultrasonic inspection of cast aluminum matrix composites reinforced with hollow ceramic microspheres. The aim of the study was to evaluate the possibility of using ultrasonic scanning by a small-sized piezoelectric transducer to evaluate the distribution heterogeneity of longitudinal wave velocity and structure. Six plane-parallel circular cross-section specimens were studied, differing in the total volume fraction of micropores and reinforcing hollow microspheres. The propagation velocity of longitudinal waves was determined by the ultrasonic echo method. Scanning was performed along two mutually perpendicular directions. It is shown that the velocity of longitudinal waves reaches maximum values in the peripheral zones and decreases monotonously at the approach to the center for all studied specimens, which is due to the peculiarities of melt crystallization during casting with mechanical mixing. It is found that the standard deviation of the velocity of longitudinal waves over the specimen cross-section and the average amplitude of the first echo depend linearly on the total volume fraction of micropores and reinforcing microspheres. It is concluded that during nondestructive testing of cast aluminum-matrix composites, joint analysis of average velocity, its standard deviation and first echo amplitude makes it possible to estimate the total volume fraction of micropores and reinforcing microspheres and characterize the heterogeneity of their distribution over the section of product. In general, the conducted studies have shown the prospects of using ultrasonic cross-sectional scanning for rapid quality assessment of cast aluminum-matrix composites reinforced with hollow ceramic microspheres.