Fig. 1. Schematic of the keyhole monitoring system.

Fig. 2. Experimental setup of the keyhole monitoring system.

Fig. 3. Keyhole morphology on (a)–(d) 304 stainless steel and (e)–(h) 6061 Al alloy. The welding speeds are (a), (e) 10, (b), (f) 25, (c), (g) 50, and (d), (h) 100 mm/s, respectively.

Fig. 4. Seam surface macrograph and weld cross-section micrograph of (a) 304 stainless steel and (b) 6061 Al alloy.

Fig. 5. Surface views of keyhole morphology on 304 stainless steel at (a) 10 and (b) 100 mm/s; 6061 Al alloy at (c) 10 and (d) 100 mm/s. The processing beam center is marked by the crosshairs, and the processing beam diameter is represented by the red circle. The white regions represent no signal.

Fig. 6. Longitudinal views of keyhole morphology on (a)–(d) 304 stainless steel and (e)–(h) 6061 Al alloy. The welding speeds are (a), (e) 10, (b), (f) 25, (c), (g) 50, and (d), (h) 100 mm/s, respectively. The processing beam center is marked by the black lines, and the processing beam diameter is represented by the red dotted lines. The welding direction is from left to right.

Fig. 7. Keyhole lag for 304 stainless steel and 6061 Al alloy with different welding speeds.