Effect of friction stir welding parameters on the surface features and onion rings formation in 1080 aluminum

Friction stir welding (FSW) is a solid-state welding process for joining of similar and dissimilar metals. The joint soundness is under the control of material flow in welding zone. Onion rings appearing on the welded surfaces as the main surface feature are a helpful criterion to evaluate the materials flow in welding zone. For this purpose, 10 mm thickness, 1080 aluminum plates were welded with FSW process under the various welding conditions. Joints were produced by employing rotation speeds ranging from 450 to 1120 rpm, welding speed from 100 to 160 mm/min, tilt angle from 1 to 3 degrees and 3 different tool shapes.The onion rings’ distance was evaluated by metallographic techniques and the resultant flow lines from vertical-horizontal materials transfers were studied by metallographic techniques and SEM. The results of onion rings’ distance and flash weight variations have been used as an indirect criterion to study the effectiveness of extrusion and forging as materials transfer mechanisms. The results showed that in a constant welding speed, the distance between two onion rings decreases as the rotational speed increases. At high welding speeds, the pin with more corners is more effective which is due to the predominant effect of materials shearing by tools corners. However, at low welding speeds the main material transfer mechanism is forging and pin with less corner is more effective.

Keywords:

Friction stir welding , Onion rings , welding speed , Tilt angle , forging.