In-Situ, Laser-Ultrasonic Monitoring of the Recrystallization of Aluminum Alloys

One of the most critical manufacturing defects of cast metal-matrix composites is a non-uniform porosity distribution over the composite volume. Unevenness of the distribution leads not only to local softening, but also plays a key role in the evolution of the damage process under the external loads. The goal of the study is to apply a new laser-ultrasonic method to in-situ study of a local porosity in reactive cast aluminum-matrix composites. The proposed method is based on statistical analysis of the amplitude distribution of backscattered broadband pulses of longitudinal ultrasonic waves in the studied materials. Laser excitation and piezoelectric detection of ultrasound were carried out using a laser-ultrasonic transducer. Two series of reactive cast aluminum-matrix composites were analyzed: reinforced by in situ synthesized Al3Ti intermetallic particles in different volume concentrations and by Al3Ti added with synthetic diamond nanoparticles. It is shown that for both series of the composites, the amplitude distribution of backscattered ultrasonic pulses is approximated by the Gaussian probability distribution applicable for statistics of large number of independent random variables. The empirical dependence of the half-width of this distribution on the local porosity in composites of two series is approximated by the same nearly linear function regardless of the size and fraction of reinforcing particles. This function was used to derive the formula for calculation of the local porosity in the studied composites. The developed technique seems to be promising in revealing potentially dangerous domains with high porosity in reactive-cast metal-matrix composites.

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Monitoring of Thermal Aging of Aluminum Alloy via Nonlinear Propagation of Acoustic Pulses Generated and Detected by Lasers

Applied Sciences ◽

10.3390/app9061191 ◽

2019 ◽

Vol 9 (6) ◽

pp. 1191 ◽

Cited By ~ 10

Author(s):

Mengmeng Li ◽

Alexey Lomonosov ◽

Zhonghua Shen ◽

Hogeon Seo ◽

Kyung-Young Jhang ◽

...

Keyword(s):

Heat Treatment ◽

Aluminum Alloy ◽

Aluminum Alloys ◽

Yield Strength ◽

Thermal Aging ◽

Finite Amplitude ◽

Quadratic Nonlinearity ◽

Laser Ultrasonic ◽

Ultrasonic Techniques ◽

Non Destructive

Nonlinear acoustic techniques are established tools for the characterization of micro-inhomogeneous materials with higher sensitivity, compared to linear ultrasonic techniques. In particular, the evaluation of material elastic quadratic nonlinearity via the detection of the second harmonic generation by acoustic waves is known to provide an assessment of the state variation of heat treated micro-structured materials. We report on the first application for non-destructive diagnostics of material thermal aging of finite-amplitude longitudinal acoustic pulses generated and detected by lasers. Finite-amplitude longitudinal pulses were launched in aluminum alloy samples by deposited liquid-suspended carbon particles layer irradiated by a nanosecond laser source. An out-of-plane displacement at the epicenter of the opposite sample surface was measured by an interferometer. This laser ultrasonic technique provided an opportunity to study the propagation in aluminum alloys of finite-amplitude acoustic pulses with a strain up to 5 × 10−3. The experiments revealed a signature of the hysteretic quadratic nonlinearity of micro-structured material manifested in an increase of the duration of detected acoustic pulses with an increase of their amplitude. The parameter of the hysteretic quadratic nonlinearity of the aluminum alloy (Al6061) was found to be of the order of 100 and to exhibit more than 50% variations in the process of the alloy thermal aging. By comparing the measured parameter of the hysteretic quadratic nonlinearity in aluminum alloys that were subjected to heat-treatment at 220 °C for different times (0 min, 20 min, 40 min, 1 h, 2 h, 10 h, 100 h, and 1000 h), with measurements of yield strength in same samples, it was established that the extrema in the dependence of the hysteretic nonlinearity and of the yield strength of this alloy on heat treatment time are correlated. This experimental observation provides the background for future research with the application goal of suggested nonlinear laser ultrasonic techniques for non-destructive evaluation of alloys’ strength and rigidity in the process of their heat treatment.

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