Abstract
When magnesium alloys are tested using ultrasonic techniques, their oxide coating will affect the transmitted ultrasonic energy and the accuracy of the flaw sizing. In this work, the effects of the coating thickness on the flaw sizing are investigated. An ultrasonic measurement model is employed to predict the flaw response signal, and the reflected and transmitted ultrasonic energy in the coated surface are corrected by modifying the reflection and transmission coefficients related to the effects of the coating thickness. The effectiveness of these coefficients and the ultrasonic measurement model are verified through experiments. With the correction of the coating thickness effects, the flaw-sizing curves predicted using the ultrasonic measurement model are provided. The flaws in magnesium alloy specimens with different coating thicknesses are tested, and the determined flaw sizes from these curves agree well with the actual sizes, which reveals the effectiveness of the proposed work. This work provides an effective tool to improve the flaw sizing performance using ultrasonic techniques in practical applications.
Highlights
The AZ80 magnesium alloys have been widely used in aerospace, ship infrastructure, military, and automotive because they have high strength and stiffness and low density and can bear a large impact load [1]
AZ80 magnesium alloys, thethe oxide coating thickness is is usually ultrasonic nondestructive tests are conducted in a low frequency, i.e., less than
On the basis of the ultrasonic measurement model and the correction method for the coating thickness, the flaw-sizing curve is provided for coated specimens
Summary
The AZ80 magnesium alloys have been widely used in aerospace, ship infrastructure, military, and automotive because they have high strength and stiffness and low density and can bear a large impact load [1]. The conventional method for obtaining these curves is based on an empirical formula which may lose its accuracy in the near sound-field distance of the transducer, or based on the experimental results which need many test blocks and a heavy workload [8]. When these curves are obtained, the reference signals reflected from the front or bottom surfaces are needed. More work is needed to accurately size the small flaws in coated materials and make these curves more suitable for practical applications using ultrasonic techniques. A flaw-sizing method suitable for coated materials is provided, and its effectiveness is verified by evaluating the flaw sizes in coated AZ80 magnesium alloys
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