*4.1. Appearance and Measurement of the Weld Beads*

First, the macroscopic appearances, and cross-sections of weld beads of L1–L9 are shown in Table 4. In the table, the photos of the cross-sections of the weld beads, which were obtained using a microscopy with 20 times magnification, were provided. It can be observed that the overall appearance of the weld bead of L1 was unsatisfied, the grains of the fish scale ripples were rough, and there were some unfused parts appearing in the edge of the bead. The appearance of weld bead of L2 was still unsatisfied, the widths and heights of the ripples were non-uniform, as well as the weld bead was not straight and some curved bead existed. The bead of 2–5 cm was so thick, but the thickness in 7 cm was suddenly decreased, which meant that some sudden transitions occurred during the process. In addition, arc pits appeared in terminate of the bead. The quality of weld bead of L3 was very low and the appearance was irregular. Sudden transitions appeared in 10–15 cm, and serious splashes occurred in 13 cm, also, the shape located in the terminate was seriously irregular. The weld bead of L4 was regular and successive without any arc interruption or short-circuit occurring, however,

the grain of the fish scale ripples was a bit rough and some unfused ripples appeared. The weld bead of L5 has high quality, the bead was straight and regular, and both of the penetration and height were reasonable. Moreover, compacted fish scale ripples are shown in the bead, and no obvious splash appeared during the process. The weld bead of L6 was very thin and high, and fish scale ripples were so obvious. However, the edge of the bead was irregular, and a few splashes occurred during the process. The weld bead of L7 was successive, but some irregular humps in the bead can seriously affect the mechanical performances. Both of the weld beads of L8 and L9 were regular, the overall shape of the bead was thin and high, though some splashes occurred during the process. According to the cross-sections of all the weld beads, the penetration of the weld beads in L1–L3 was so large that full penetrations appeared, while the widths of bead were irregular with a bit large. The penetration of weld bead of L4 was small, while the penetration of weld bead of L5 was 60% of the whole thickness of the base plate, which showed the penetration was proper. In addition, the penetrations of weld beads of L6, L8 and L9 were a bit small, while the penetration of weld bead of L7 can reach half of the whole thickness of the base plate.

Furthermore, to further understand the morphology of the weld bead, detailed measurements for the shape of the weld bead were also conducted. Relative key measurement parameters of the shape can be seen in Figure 3.

**Figure 3.** Schematic of shape parameter measurement for a weld bead.

Where the key shape parameters included bead width *B*, bead height *h*, penetration *H*. Then for the above nine weld beads, corresponding measurements were also conducted; the results are shown in Table 5.

**Table 5.** Measurement of the weld bead (mm).


Combined with Tables 4 and 5, it can be noticed that the bead height *h* of L1 was proper, while the same item of L3 was relatively larger. However, the bead height of L3 was irregular with some heaves appearing on the surface; in addition, the transition was also not smooth. Under this circumstance, the stress may concentrate, which may deteriorate the load bearing capacity of the joints, and the cracks may appear when special loads were applied, which can affect the appearance of the weld bead. In addition, the penetration of weld beads of L1–L3 were so large, even full penetrations appeared, and the values of the bead width were also large enough. According to the observation of the cross-sections of these three beads, the forming situation was also not satisfactory. The bead height and bead width of L4 and L5 were proper, however, the penetration *H* of weld bead of L4 was small. The value of bead height *h* of weld bead of L6 was a bit larger, this was because both of the penetration and the bead width were relatively small, which showed the thin and high weld bead as shown in Table 4. The reason for this phenomenon was that the heat delivery was not sufficient during the process. The weld bead of L7 was hump type bead, which had irregular bead height *h*, and the stress may concentrate under this situation. The bead heights of L8 and L9 were proper, but the values of penetrations were small. Especially for the weld bead of L9, the bead width *B* was very small, so the overall bead appeared high and thin, therefore the forming situation was not well enough.

#### *4.2. Materials Characteristic Performance Analyses of the Weld Beads*
