Laser ablation of aluminium before welding : Effect of weld preparation on number and sizes of pores

Sammanfattning: Welding aluminium often results in porosity in the weld. One way to reduce porosity is by carful weld preparation and cleaning. In this master thesis report laser ablation was done on aluminium plates before welding to remove dirt and the surface oxide layer. Different hold times from finish of laser ablation to start of welding was also used and evaluated. Cleaning with only ethanol or brushing and cleaning with ethanol was also used for comparison. In addition, two filler wires of the same material were used for the welding, one new unopened and one old that had been opened and kept in open packaging for two years. For one weld on laser ablated plates the old filler wire was also laser ablated before use. The results showed that new filler wire gave the least number of pores, and the results were nearly the same with laser ablated plates welded directly as with ethanol cleaned plates. Welds with old filler wire had a bigger range in the results and the cleaning methods of the plates had a bigger impact. The results from the welds with old filler wire showed less porosity in the welds on laser ablated plates with hold times of six minutes, one hour and one day compared to ethanol cleaned plates and brushed plates. In common for both filler wires were that the weld of the laser ablated plates with a hold time of a week had the most pores. The conclusions are that it is good to use the filler wire as close in time to the opening of the packaging as possible and not store it a long time to then use it later. Laser ablation is a valid option for cleaning, but the machine is expensive and therefore most suitable for weld preparation of welds in high demand applications or on plates with very much dirt or thick oxides.