The continuous CO2 laser beam welding of two aluminum metal matrix composites (6061 and 2618 reinforced with 20% of Al2O3) has been investigated with special attention to the influence of the base alloys, the filler material and the process parameters on the microstructure of the welding bead. In this work square butt welding has been obtained with different CO2 laser power, feed rate and shielding gases. The microstructure of the welding beads has been examined by optical and electronic microscopy. A migration of the Al2O3 reinforcement particles from the fusion zone (FZ) towards the heat affected zone (HAZ) has been detected and the particles agglomerate near the interface FZ-HAZ. An increase in both porosity and agglomerate sizes inside the welding bead has been observed as the feed rate has been reduced. The hardness of welding beads has been higher than the unaffected composites. A reduction of both the beads hardness and the Al2O3 migration and agglomeration has been obtained by the use of magnesium-rich filler material in the welding process, probably because magnesium is able to increase the reinforcement wettability, and to reduce the rate of formation of spinel phase MgAl2O4. The use of Ar as shielding gas was the most effective, both in order to avoid the development of porosity and to reduce the Al2O3 agglomeration.
Influence of CO2 Laser Beam Welding on Microstructure of Aluminum Metal Matrix Composites Reinforced with Al2O3 Particles
DABALA', MANUELE;MAGRINI, MAURIZIO
2001
Abstract
The continuous CO2 laser beam welding of two aluminum metal matrix composites (6061 and 2618 reinforced with 20% of Al2O3) has been investigated with special attention to the influence of the base alloys, the filler material and the process parameters on the microstructure of the welding bead. In this work square butt welding has been obtained with different CO2 laser power, feed rate and shielding gases. The microstructure of the welding beads has been examined by optical and electronic microscopy. A migration of the Al2O3 reinforcement particles from the fusion zone (FZ) towards the heat affected zone (HAZ) has been detected and the particles agglomerate near the interface FZ-HAZ. An increase in both porosity and agglomerate sizes inside the welding bead has been observed as the feed rate has been reduced. The hardness of welding beads has been higher than the unaffected composites. A reduction of both the beads hardness and the Al2O3 migration and agglomeration has been obtained by the use of magnesium-rich filler material in the welding process, probably because magnesium is able to increase the reinforcement wettability, and to reduce the rate of formation of spinel phase MgAl2O4. The use of Ar as shielding gas was the most effective, both in order to avoid the development of porosity and to reduce the Al2O3 agglomeration.
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