on the formation of onion ring structure in friction stir butt welds of copper plates produced by non -threaded tool pin

onion -ring structure is a probinent feature of the many friction stir welds the aim of this investigation is to understand the formation of onion -ring structure in the welded joint produced by a non-threaded tool pin in copper plates. It is shown that the phenomenonof onion - ring structure formation is the consequence of dimple in middle area o feach layer of material which deposited to back of the tool in one rotation and cutting through the section of the material moreover onion-ring structure can be created by non-threaded tool pin in transverse cross -section and the space and depth of semi-circular surface features are equal to welding pitch displacemnet /revolution and plunge depth respectively. a micrl -structural study shows that the weld has lamellar structure and the bonding force in friction stir welds is caused by the mixing of materials from the sides of layer interfaces.

کلیدواژه ها:

friction stir welding ، onion -ring ، copper ، non- threaded pin