uted along the interfaces. According to Fig. 2A–D, the number of voids decrease with increasing vibration amplitude and increasing normal force and is also lower in bottom layers compared to top layers in thicker samples processed from the SL7200 machine. However, it is worth mentioning that these process parameters were not designated as the best parameters for Al3003-H18 and do not represent the maximum capacity of the SL7200 machine, which can produce 100% linear weld density or no voids in Al3003- H18 builds. It was also noted as more layers were deposited and the build got higher (Fig. 2B–D), the number of voids increased in the upper interfaces near the top surface as compared to interfaces between layers below despite using the same processing parameters (samples TB-10-28-5340 and SL-66-28-5340). This result suggested that in order to achieve better metallic bonding in the higher layers, larger vibration amplitude and larger normal force was necessary, especially when higher welding speed is used. Table 2 lists the average reduction in thickness of Al3003-H18 foils after being processed by VHP-UAM compared to the original foil thickness of 150 μm in the as-received condition. The largest reduction in thickness of 10% was found in sample TB-10-38- 8000 (where both vibration amplitude and normal force are larger) as compared to only 2% in sample TB-10-38- 4000 (where only vibration amplitude was larger but normal force was lower). Also, the samples processed by the SL7200 machine tend to undergo larger reduction in thickness compared to samples processed by the TB machine except for sample TB-10-38-8000. It is also noted that increasing vibration amplitude had a greater effect in introducing plastic deformation on the foil layer than increasing normal force, as the average reduction in thickness of sample SL-80-34-5340 was higher than sample SL-80-34-5340 and sample SL-66-28-5340, respectively. Figure 3 displays the average bulk Vicker hardness of Al3003-H18 foils in VHP-UAM samples fabricated from the TB machine. In order to determine the change in hardness after VHPUAM and heat treatment, microhardness measurement was also performed on the original Al3003-H18 foil with the average hardness of 70.5 VHN. Hardness data of the original foil and each layer in VHP-UAM samples were plotted before and after heat treatment at 343ºC for 2 h. It is noted that the first layer or Layer Number 1 in the figure represents the average hardness from the 20 indentations measured at the central region of the first foil layer deposited on the substrate, while Layer Number 10 is the last layer or the top-most layer of the VHPUAM samples. The result showed a slight decrease in foil hardness in sample TB-10-28- 5340, where hardness in Layer Number 1 was equivalent to the original foil hardness and hardness decreased gradually in the upper layers. This implies that using vibration amplitude of 28 μm and normal force of 5340 N rarely affected the hardness of the original foil. In contrast, the bulk hardness of the deposited foil increased from bottom layers to top layers in sample TB-10-38-8000, although the overall hardness of 55-60 VHN was 10-15 VHN lower than hardness of the original foil. Unlike samples TB-10-28-5340 and TB-10-38- 8000, sample TB-10-38-4000 showed neither an increasing trend nor a decreasing trend in hardness from bottom layers to top layers. It is also worth mentioning that increasing vibration amplitude from 28 to 38 μm greatly affected the bulk hardness in the deposited foil, whereas increasing in normal force from 4000 to 8000 N had much less effect on the change in hardness. Increasing vibra- WELDING RESEARCH 188-s WELDING JOURNAL / JUNE 2016, VOL. 95 Fig. 6 — Plot of ultrasonic power vs. time during VHPUAM processing of Al3003H18 samples using the TestBed machine. Fig. 5 — Plot of the average Vicker hardness measured at the middle of the bulk region of each deposited layer in three Al3003H18 VHPUAM samples fabricated from the SonicLayer 7200 machine.
Welding Journal | June 2016
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