Abstract
In the powder immersion method, ultrasonic testing is carried out on test pieces while immersed in pressurized powder. However the drawback to this method is the necessary use of high pressure. To solve this problem two methods using high density coupling powder have been developed. They have an effect in reducing the pressure required. One is a mixture of two or more different sized powders and the other is excitation of powder in a pressure vessel. Powder with a mean grain size 5.6 μm and 27 μm were mixed for testing Magnesium Alloy. The density of the powder mixture increased several percent in comparison with the density just of the 27 μm powder. To measure the effectiveness of the excitation process 27 μm mean grain size powder was excited in a pressure vessel measuring 30 mm outside and 20 mm inside. Twelve ceramic actuators excited the pressure vessel and the amplitude of the vessel in the radius direction was 0.1 mm and the frequency was 3.0 kHz which was the resonant frequency of the vessel. The density of the coupling powder increased 20 percent by using this method. Moreover, it was found that these two high-density methods improved the ultrasonic characteristics of the coupling powder in lower pressure. When using the multi sized powder only, the pressure was reduced from 51 MPa to 14 MPa in the case of testing Magnesium Alloy.
