Ultrasonic characterization of shrinkage microporosity in aluminum castings

Role of Pore Size Distribution in Ultrasonic Characterization of Microporosity in Aluminum Castings

“…The starting material was base 319-type alloy, to which Sr and/or TiBor were added to produce a large range of porosity. Five plates, spanning the range of porevolume fraction from 0 to 0.025, were studied [1]. Metallographic samples of the castings were analyzed to observe the grain structure.…”

“…To aid in advancement and improvement of casting processes, we have devised a simple and accurate technique for laboratory characterization of porosity in cast aluminum plates [1]. In this technique, porosity is characterized based on the frequency dependence of ultrasonic attenuation caused by scattering from pores ( Figure 1).…”

“…Therefore we represent the actual distribution of shrinkage pores with an equivalent distribution of spherical pores. Although it is not obvious a priori, this approach has been shown to be valuable for inferring the porosity volume fraction [1].…”

Numerical and analytical investigation of the influence of porosity on the frequency response of GLARE composite

“…Calculated attenuation coefficients for cavities with radius R = 10 µm, volume fraction φ = 5%, and longitudinal (c l ) and shear (c s ) wave velocities of c l = 3330 ms −1 and c s = 1870 ms Cavities of unequal radii, i.e. with a distribution of radii, can be evaluated by using an effective attenuation α ef f [5]. For the corresponding average void volume fraction of φ the effective attenuation is the sum of the imaginary parts of the effective wave numbers for each of the ith pore sizes within a discretised distribution:…”

“…Measurement of this attenuation allows the evaluation of the bulk-averaged porosity. The measurement principle is in general independent of the investigated material and has been successfully applied in composites [2] and in aluminum castings [3], [4], [5] but does not provide any information about the depth distribution of the porosity. For this, a pulseecho method is required but the reflected waveform is complex for GLARE due to the high reflection coefficients at each interface.…”