Effect of process parameters on seam weld quality of ZM21 tubes

The increasing attention to magnesium alloys in extruded profiles, especially in the
transportation industry, is related to their low density associated with good mechanical properties
and complete recyclability. This allows to push towards both increasing efficiency and pollution
restrictions. However, these advantages are negatively balanced by the production rates drop in
relation to dangerous profile temperatures increasing that force to keep low velocities. In this
context, a novel porthole die has been purposely designed for magnesium alloys allowing an
increasing of the process velocity up to four times with respect to past solutions. The mandrel
consisted of three ports made by 120° bridges that created an equal number of seam welds. The
extruded tubes, made in ZM21, were 50 mm in diameter and 2 mm in thickness and were tested
under different process conditions. In the present work, the quality of the seam welds has been
investigated in relation to each process condition by means of the rubber plug testing method that
allowed to apply an hydrostatic tensile state.