Analysis of a weld failure of a rolled Zn-alloy strip – A case study

Rolled alloys of the system Zn–Cu–Ti are mainly used in the construction industry for the fabrication of various building components: roof sheets, gutters, pipes and other relevant accessories. Downpipes or tubes are formed usually by TIG or MIG welding of the slit zinc coils in conventional seamed-tube making machines. In order to perform the installation and assembly of the Zn tube system, radial expansion of the upper part of the tube should be done using appropriate tooling. Successful expansion leads to the fabrication of sound components ready for installation. Cracked welded tubes were delivered with a request of a failure analysis investigation. In this work, the steps of the weld evaluation and the following failure investigation are presented. Weld defects such as extensive gas porosity and linear discontinuities are detected and are considered significant contributors of the failure.