Research On The Ultrasonical Brazing Of 55VOL.%SiC_p/A356 Composites

Mechanisms for the ultrasonic aided interaction between Zn-Al solder and 55vol.%SiCp/A356 metal composites in air were investigated by light microscopy (Olympus-PMG3), scanning electron microscopy (SEM, S-4700) equipped with an energy dispersive X-ray spectrometer (EDS), electron probe X-ray microanalysis (EPMA, JEOL-733) and transmission electron microscopy.The experimental results show that there are many differences between the surface of 55vol.%SiCp/A356 and 20vol.%SiCp/A356. In the 55vol.%SiCp/A356 the SiCp size is big and the SiCp shape is irregular. There are many bared SiC particles in the rough surface of the 55vol.%SiCp/A356,which become an important factor influencing the wettability of the surface. There are two kinds of interface between the Zn-Al alloy and 55vol.%SiCp/A356.One is the interface between the SiCp and the Zn-Al alloy, the other is the interface between the A356 alloys and the Zn-Al alloy. Thereby, there are two wetting processes between the Zn-Al alloy and the 55vol%SiCp/A356: the wetting of Zn-Al alloys with SiC particle and the wetting of the Zn-Al alloys with the A356 alloys.The experiments prove that as the amplitude of ultrasonic increases, the time of the wetting of the alloys with the 55vol.%SiCp/A356 reduces. When the Zn-Al alloys wet the A356 alloys, the oxide layer is broken up with the aid of the ultrasonic vibration. When the Zn-Al alloys wet SiC particle, the ultrasonic vibration plays an important and assistant role.Due to the element content difference between the Zn-Al alloys and the A356, a diffusion zone forms in the base metal near the interaction interface by the element diffusion and dissolution. Along with the ultrasonic vibration time increases, more Zn element enters the base metal. The content of Al element reduces from the diffusion zone to the solder area. By the ultrasonic vibration, the SiC particles get into the Zn-Al filler metal.As the ultrasonic vibration time increases, the shear strength of brazed joints of SiCp/A356 composites also increases. With the ultrasonic vibration time changing from 0.5s, 1s, 2s, 5s to 10s, he shear strength increases from 51MPa to 165.5MPa. But the shear strength of brazed joints with 10s ultrasonic vibration drop slightly compared to the joints with 5s. The increase of shear strength with the ultrasonical acting time is mainly because the filler metal can wet more reinforcement particles and matrix metals on the surface of composites.