Effect of Local Melting on the HAZ Toughness of GMA Welded AA6082 and AA6005 Extrusions Containing Cu

摘要

In the present investigation the conditions for local melting during GMA-welding of AA6082 and AA6005 extrusions using a AA5183 filler wire, have been examined with the view of evaluating how this incident affects the resulting heat-affected zone (HAZ) impact toughness. Local melting within the so-called subsolidus region has been observed using optical microscopy, and three low-melting point phases (i.e. a-AlFeMnSi, Mg_2Si, Al_5Cu_2Mg_8Si_6) have been identified by means of scanning electron microscopy (SEM). In general, Cu additions in the range from 0.18 to 0.30 wt% are seen to increase the tendency to local melting in the HAZ of both weldments. In particular, the Q-phase (Al_5Cu_2Mg_8Si_6) has been observed to melt as far as 1mm from the fusion boundary and an analytical heat flow model has been used to rationalise this observation. The subsequent Charpy-V notch testing shows that Cu has an adverse effect on the HAZ impact toughness in AA6005, whereas the AA6082 extrusion revealed no such toughness deterioration.