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

Abstract

The origin of the onion ring structure is an important issue in friction stir welding process but has not been firmly established yet. This paper peresents optical macro- and micrographs of friction stir welds on a copper alloy produced by a non-threaded tool pin. It is shown that onion ring structure can be created by non-threaded tool pin in transverse cross-section of friction stir weld of copper plate. The macrographs of transverse cross-sections exhibit contrasting bands. A microstructural study shows that the weld has lamellar structure, and the bands are sections of weld layers.