Investigation on laser coaxially assisted friction stir welding of aluminum alloys

The laser coaxially assisted friction stir welding process of aluminum alloys of different series (5A06, 6061, 2219) was investigated, concentrating on the effects of friction stir heat and laser heat distribution on weld appearance, mechanical properties and microstructure characteristics of the joints. The optimized heat distribution conditions for alloys of different series were obtained. The results show that assisted laser heat can effectively enlarge the process window, especially for 5A06 and 2219 which have low fluidity, can increase the welding speed by 30%. Assisted laser heat has no obvious influence on microstructure of 5A06 FSW nugget zone, but decreases the amount of second phase Mg₂Si in 6601 FSW nugget zone and makes them dispersed, the assisted laser also decreases the amount of strengthening phase CuAl₂(θ) and increases their sizes. For 5A06 and 6061, assisted laser heat has no obvious influence on the joint mechanical properties. However, for the heat treated alloy 2219, assisted laser heat decreases the joint strength, but can obtain high joint strength by welding under low friction stir heat input.