WELDING RESEARCH Fig. 2 — Acoustic pressure test in the ultrasonicactivated water rise. Fig. 4 — Variation in the vertical filling height with ultrasonic exposure time. JULY 2016 / WELDING JOURNAL 265-s Fig. 1 — Schematic of the ultrasonicassisted capillary filling. Fig. 3 — Capillary rise of the filler metal without exposure to ultrasonic vibration. the surface oxide films of the clearance. This process allows the solder to wet and protrude progressively toward the bath surface. However, rising of the solder to the bath level causes the hydrostatic pressure to disappear and leads to the lack of a prefilled solder to support oxide removal (cavitation). Therefore, further wetting and capillary rise could not occur. Vianco (Ref. 15) also suggested that the substrate should be immersed into the solder bath for ultrasonic soldering to produce a joint. By contrast, Antonevich (Ref. 13) reported that ultrasonic-agitated zinc solder fills the vertical aluminum capillary to a maximum height of 2 mm above the normal liquid level at a specific immersion depth. However, no alloying or metallurgical bonding occurs between the solder and the inside tube diameter above the immersion depth. We recently examined solder capillary in the the level joint clearance under ultrasonic activation (Refs. 16– 18). The use of a solder droplet instead of a solder pool eliminated the effect of hydrostatic pressure created after sample immersion on the capillary filling. The solder droplet located at one end of the clearance readily filled an oxide-covered joint clearance under ultrasonic activation. Thus, either in vertical or horizontal joints (Refs. 13, 16–18), the solder filled the capillary before wetting or alloying the capillary wall, suggesting that forces other than surface tension act during ultrasonication. This phenomenon is different from that in flux soldering, in which solder filling depends on wetting (Ref. 19). However, the possible mechanisms underlying ultrasonic-induced capillary rise remain ambiguous. Accordingly, the present study investigated the capillary rise of liquid solder in a vertical joint under ultrasonic activation and identified the influencing factors of this process to acquire indepth information about the ultrasonicinduced capillary filling of liquid solder. Considering the difficulty of observing Table 1 — Chemical Compositions (wt%) of 2024 Al Alloy Element Mg Cu Si Fe Mn Ag Cr Ni Al Zn 2024 Al 1.2–1.8 3.8–4.9 <0.5 <0.5 0.3–0.9 － <0.1 － Bal. －
Welding Journal | July 2016
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