CO₂ laser weldability of aluminium alloys (2nd Report): Defect formation conditions and causes

Summary

This paper describes the results of a systematic study to clarify the effects of CO₂ laser welding conditions on porosity formation in commercial A5052, A5083, A5182, A6061, and A7N01 aluminium alloys. The causes and mechanism of porosity are examined through observations and evaluations of weld beads based on radiographic inspection and analysis of the gas content in pores by Q-mass spectroscopy in a vacuum, and on the amount of hydrogen in base and weld metals. The effects of the welding conditions on the high-temperature (solidification) cracking susceptibility of aluminium alloys are also investigated. The results show that porosity is reduced under the following conditions:

1. a fairly long preflow time of argon shielding gas;

2. polishing of the plate surface to decrease or remove sources of hydrogen and oxygen;

3. a lower welding speed to help gas bubbles float to the surface or a higher welding speed to produce smaller pores;

4. defocusing conditions of moderate power densities;

5. use of nitrogen or helium instead of argon. Solidification cracks are present in laser-welded fusion zones of A6061 and A7N01 alloys produced at higher welding speeds. The solidification cracking susceptibility of the alloys is evaluated to be higher in the following sequence: A5182, A5083 A5052 A7N01 A6061. The high sensitivity of the latter to cracking is attributable to a wide brittle temperature range (BTR) and low ductility.