The effects of power density, concentration of volatile alloying element (magnesium, Mg), and welding speed on the mechanisms of fusion-zone defects, i.e., spiking and humping (and coarse rippling) during keyhole mode electron-beam welding of Al 6061, Al 5083, and SS 304 are investigated experimentally. Spiking represents a sudden increase in penetration beyond the average penetration line. Rippling exhibits rather regular, arcshaped topographic features on a solidified surface, whereas humping shows an irregular surface contour consisting of a series of swelled protuberance. These defects seriously reduce the properties and strength of the joint. The quantitative variations of humping, coarse rippling, and spiking defects with the beamfocusing characteristics, volatile element, and scanning speed are quite limited in the literature. The experiments in this paper confirm that average pitch of the humps or coarse ripples is approximately identical to that of the spikes. Thus, the frequency of spiking can be determined from the observation of the weld surface. The results show that the average pitches and amplitudes of humping or coarse rippling and spiking increase with decreasing welding speed and increasing content of volatile element Mg from Al 5083. The frequency and amplitude of spiking, however, are increased by lowering the focal-spot location. The measured amplitude and frequency of spiking and humping and fusionzone depth are confirmed from good agreement with available scaled analysis. This paper provides quantitative results useful for understanding mechanisms of these defects, so that preventing spiking and humping during keyhole mode welding becomes possible.
Spiking, rippling and humping seriously reduce the strength of welds. The effects of beam focusing, volatile alloying element concentration and welding velocity on spiking, coarse rippling and humping in keyhole mode electron-beam welding are examined through scale analysis. Although these defects have been studied in the past, the mechanisms for their formation are not fully understood. This work relates the average amplitudes of spikes to fusion zone depth for the welding of Al 6061, SS 304 and carbon steel, and Al 5083. The scale analysis introduces welding and melting efficiencies and an appropriate power distribution to account for the focusing effects, and the energy which is reflected and escapes through the keyhole opening to the surroundings. The frequency of humping and spiking can also be predicted from the scale analysis. The analysis also reveals the interrelation between coarse rippling and humping. The data and the mechanistic findings reported in this study are useful for understanding and preventing spiking and humping during keyhole mode electron and laser beam welding.
Pitches of surface humps or coarse ripples and spikes affected by the focusing characteristics and scanning speed in high-intensity electron-beam welding or melting are quantitatively measured. Humping and coarse rippling are referred to surface roughness, which often accompanies with undercut, segregation, porosity and other defects. Spiking represents a sudden increase in penetration beyond the average penetration line. In this work, acceleration voltage and welding current of the electron beam welder used are 55 kV and 20 mA, whereas scanning speed is between 15–30 mm/s. Specimens are Al 6061, 1050, 1100 and 5083, and SS 304. This study found that humping and coarse rippling are enhanced by lowering the focal spot location. The measured amplitudes of humping are confirmed by successfully comparing with scale analysis.
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