Mechanisms For Ultrasonic Assisted Wetting Of Liquid Sn To Zr-based Amorphous Alloy And Bonding Strength Examination

Amorphous alloy, also known as the metallic glass, is a special metal. Its atomic structure arrangement state is disordered, which makes it have many different prppertie from the traditional crystalline materials, so it has raised widespread concern of scholars since discovered on the middle of last century. For half a century, although researchers have been gradually enlarging the size of amorphous alloys by increasing the cooling rate and complexing alloy elements, they failed to make a breakthrough in it. Since the 21 st century, researchers have been endeavoring to increase the size of the amorphous alloy by welding in order to improve its application. However, amorphous alloy is metastable, indicating that it will turn to its glass transition or crystallization when heated to a certain temperature, which will severely affect its performance. Thus, it is particularly important to find a proper welding method.Ultrasonic soldering can be achieved on difficult wetting base metal at lower temperatures, thus is a highly-potential amorphous welding methods.Ultrasonic is applied to help liquid Sn with wetting on Zr_50.7Cu₂₈Ni₉Al_12.3. After that, it is found that ultrasonic can dissolve elements diffusion of the base metal and solder which will trigger the amorphous structure transformation at the interface, so that the binding mode of Sn crystalline and Zr_50.7Cu₂₈Ni₉Al_12.3 amorphous alloy transfer physical adsorption to the binding between atoms, which will affect the bonding strength of the jointAccording to the studies, the longer the function time of ultrasonic is, the greater the thickness of the diffusion binding layer is and the higher the joint strength is. From the fracture morphology of the interface, it is found that there were pits of remnant solder inside cavities. This is because the remant solder is so tightly combined to its base metal that it tends to be torn apart from the solder matrix. Thus, the cavitation effect at the interface directly affects the inter-facial strength of the joint.The mechanism of ultrasonic-assisted liquid Sn wetting on amorphous alloy is based on ultrasonic cavitation. Periodic ultrasonic vibration leads to the generation of randomly distributed cavitation bubbles inside the material and these bubbles can be divided into two types: one is a steady-state cavitation bubble, which tends to collapse within a few cycles of ultrasonic; the other is a transient cavitation bubble, which collapses within one cycle of ultrasonic. Microjet bubbles collapse and energy produced by transient cavitation on amorphous alloy surface will produce cavitation effects. Studies have shown that the intensity of cavitation effect is significantly correlated to the absolute value of the sound pressure. The larger the absolute value of the ultrasonic pressure is, the stronger the cavitation is. Through analog computation, it can be found that in a cycle, the intrnal ultrasonic pressure of solder changes alternatively from positive to negative. In the vertical direction of the solder pot, the absolute value of sultrsonic pressure decreases from the bottom of the solder to the top. Moreover, the ultrasonic amplitude, frequency, the depth of the insert plate and other facots will also affect the size or distribution of the ultrasonic pressure in the system.